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Computer Control of a Horn Antenna and Measuring the Sun at 11

1. 49 32 57 62 65 68 71 1 Introduction A Short History of Radio Astronomy Electromagnetic radiation can exist at any frequency We are able to see signals coming from high energy gamma or X ray radiation all the way down to low energy radiation from radio waves Over time radio astronomy has come a long way and underwent a lot of changes The first astronomical radio observation was made by Karl Jansky He used a rotating array of antennas that was sensitive in the horizontal direction By rotating the array he was able to measure the intensity of the signal as well as the horizontal component of the direction that the signal came from Nothing could be said about the vertical direction however Janksy made his measurements at a wavelength of 14 6 meters Jansky 1982 This translates to a frequency of 20 5 MHz He concluded that the radiation came from a region of the Milky Way 11982 His observation was made in 1933 Figure 1 Left Karl G Jansky 1905 1950 Right Jansky s antenna array Images credit en wikipedia org wiki Karl_Guthe_Jansky and http www nrao edu whatisra hist_jansky shtml Interested by Jansky s discovery Grote Reber also started working in the field of radio as tronomy Reber built a much more advanced telescope to make his observations with He built a 9 5 meter parabolic dish telescope 11944 Reber s telescope had three receivers oper ating at 3300 MHz 900 MHz and 160 MHz With t
2. T university of faculty of mathematics kapteyn astronomical Ja y g ro ni n g en F and natural sciences ff institute Computer Control of a Horn Antenna and Measuring the Sun at 11 GHz UNIVERSITY OF GRONINGEN KAPTEYN ASTRONOMICAL INSTITUTE NETHERLANDS INSTITUTE FOR SPACE RESEARCH Supervisors Author Dr J P MCKEAN Mind Pnor DR A M BARYCHEV FRITS SWEIJEN 52364883 Dr R HESPER Second Reader Pnor Dr M C SPAANS Abstract This thesis presents the work I have done as part of a project to build a radio telescope to observe the CMB at 11 GHz It covers some basic radio astronomy theory and the weather conditions in Groningen After this it focusses on controlling the telescope and its measur ing equipment through a Raspberry Pi It will conclude with observations of the Sun and a satellite to verify the beam size This was found to be 12 07 0 13 using the Sun and 12 61 0 19 using a satellite in agreement with expectations SRON Netherlands Institute for Space Research Contents 1 Introduction 2 Radio Astronomy Theory 2 1 Antenna Temperature 2 2 Noise and System Temperature 0 0 00 00 eee ee ee CRaG eG eee eee tare eee eae ee ee ee 2 2 2 Propagation of Noise 2 3 Sensitivity and Integration Time 2 00000008 2 4 Applying the Theory to the Kapteyn Radio Telescope 3 Weather Conditions in Groningen mE EM 3 4 Situation in Groninge
3. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 Day Figure 32 Temperatures of June 2007 separated by part of the day Average Cloud Cover by Part of Day for June 2008 Night r2 e d Cloud Coverage octants m ON FO O O ON O O O O N O O O O N O O O 1 2 3 4 5 6 7 8 9 1011 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 Day Figure 33 Cloud coverage of June 2008 separated by part of the day 58 Average Cloud Cover by Part of Day for June 2009 Night Ep e Cloud Coverage octants I ON FOO O O N O O O O N F amp F O O O O N O O O OFX Px 10 11 13 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 Day Figure 34 Cloud coverage of June 2009 separated by part of the day Average Cloud Cover by Part of Day for June 2010 Night gt e d Cloud Coverage octants m ON FO WO O ON FOO O O N O O O O N O O O 123 45 67 8 w 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 Day Figure 35 Cloud coverage of June 2010 separated by part of the day 59 Average Cloud Cover by Part of Day for June 2011 Night E Pp Cloud Coverage octants m O N AOOO ONAR OOO ONAR OOO ONAR OOO 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 Day Figure 36 Cloud coverage of June 2011 separated by part of the day Average Cloud Cover by Part of Day for June 2012 Night r2 e d Cloud Cove
4. self set_direction False Calculate the number teps needed steps abs ang 360 self STEP_DISK istep 0 while istep lt steps self step istep 1 self _rotating False set_direction self direction Set the movement forwards or backwards Args bool direction True backwards False forwards Return None 3 GPIO output self PIN DIR direction set turbo self x Change the delay between switching pin states If turbo is on the torque produced by the motor will be lower Args 69 int x 0 or 1 for turbo on or off Return None iT X self TURBO True self SLEEP_TIME 0 0013 else self TURBO False self SLEEP_TIME 0 002 def step self Make the stepper motor do one step Sleep occurs _after_ state change This means the following cycle high sleep low sleep This means movement is slower by a factor of two w r t to the sleep time Args None Return None GPIO output self PIN STEP True time sleep self SLEEP TIME GPIO output self PIN STEP False time sleep self SLEEP TIME def quit self Properly exit the motor controls Args None Return None I GPIO cleanup if __name__ __main__ mot StepperMotor 38 40 200 72 while True cmd raw_input gt gt gt lower com cmd split if len com command com 0 lower arg com 1 if command rot deg ne evaluate arg mot rot deg if comman
5. 19d oge1oAoo pno o oSeJoAe aug 0T AMSA 38g AON VO das ny nf unf Aej dy sew qay uef 229 AON 20 das ny nf unf Ae dy se qay uef 2239 AON VO desbny nf unf Ae dy se qay uef ban ban Ban L L rou rou L L unu L a Uut unu unu L Bao S3ue320 9561240 pno E T T E x x T UL T PUT uau x umiy umiy ZTOZ TTOZ ds OrOc a 22 AON VO das ny In unf ely ady sew qay uef 229 AON VO das ny jnf unf Ae idy se qay uef 229 AON VO desbny n unf Aewidy se qay uef Ban L Tu L urut L 800z y3u0N Jed 3621340 pnoj Bei AV 21 umuirurul on q 98geJoA MO 9X umuixeui poy Aep oy jo red Aq pajexedas FOZ un Jo 9SPIDA09 pno oO II 31N3IH Aeg OE 6c 8Z Lc 9c Gc vc EZ 22 TZ OC 61 81 I 9I GL vL EL CL II OL 6 8 Z 9 G v CT X X s1ue320 8be12A025 pnoJ 9 3U IN bTOZ eunf 104 Aeg jo Weg Ag 1350 pnoj abe1any 22 3 4 Situation in Groningen The two most important factors of the weather are atmospheric temperature and cloud cov erage It turns out we have limited control over the first one We can make a rough estimate of when the temperatures will be lowest and hence best for observing This is in the winter months January February and March Further breaking it down and looking at the time of day we also saw that night time has the lowest temperatures The best observing date and time would therefore be sometime in the winter during the night i e 00 00 0
6. If amplification in the first stage is high enough we can even consider the noise of the second amplifier to be negligibly small because of this only the noise of the first amplifier is important 2 3 Sensitivity and Integration Time In the previous section we saw that a radio telescope measures a total temperature Tsys at its output given by Eqn 3 This temperature has a RMS uncertainty oT associated with it given by Toys 6 VAY t The quantity o7 is called the sensitivity of the telescope Av is the receiver bandwidth and t the integration time i e how long signals are collected for a measurement The smallest signal that can be detected is a signal that is or higher than these RMS fluctuations Sources of interest are often weaker than the noise sources so good sensitivity is a major plus for an observation Looking at Eqn 6 we see that we can increase the sensitivity in three ways OT e Decrease System Temperature Creating a system that has a low noise level will lower 1 and make the system more precise Increased Bandwidth With a large bandwidth the telescope will receive power from a wider spectrum and therefore sensitivity is increased e Longer Integration Time By observing the source for a longer time more signal is collected increasing precision To get an understanding of how Eqn 16 comes to be we look at what or actually is The system temperature T can be seen as a noise temperature with al
7. active regions Space Science Reviews 133 1 4 73 102 Mulder W 2015 Calibration ofa 11 GHz Pickett Potter Horn and Measurements of the Cosmic Microwave Background Orientalmotor 2015 Stepper motor basics Platania P Bensadoun M Bersanelli M Amici G D Kogut A Levin S Maino D and Smoot G F 1998 A determination of the spectral index of galactic synchrotron emission in the 1 10 ghz range The Astrophysical Journal 505 2 473 50 Prologix 2013 GPIB Ethernet Controller User Manual Readhead A C S and Lawrence C R 1992 Observations of the isotropy of the cosmic microwave background radiation Annual Review of Astronomy and Astrophysics 30 1 653 703 Reber G 1944 Cosmic Static Astrophysical Journal 100 279 van Schooneveld C 1990 Ruis Wilson Kristen Rohlfs S H et al 2013 Tools of Radio Astronomy Springer Zandvliet M 2015 The back end and mechanics of a pickett potter horn at 11 ghz 51 A Average Temperatures for June 52 Average Temperatures by Part of Day for June 2007 Night Morning Temperature K 1 2 3 4 5 6 7 8 9 1011 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 Day Figure 25 Temperatures of June 2007 separated by part of the day Average Temperatures by Part of Day for June 2008 Night Temperature K 1 2 3 4 5 6 7 8 9 1011 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 Day Figure 26 Temperat
8. is negligible Here we show this is not the case The noise temperature of the second amplifier ALMA2 has an average value of 127 35 K Zandvliet 2015 Using Eqn b its final contribution would then be 4 25 K The noise temperature of the first amplifier MITEO is 110 90 K Since the CMB has a temperature of 2 7 K a noise of 4 K on 110 K is in this case not negligible This is all taken in however in the measurement of the receiver temperature The noise temperature of the back end will thus lie close to the noise of the two amplifiers combined The noise temperature of the back end is measured by 2015 11 Sensitivity and Integration Time The noise temperature of the system allows us to make a prediction of our sensitivity If we want to be able to measure the temperature of the CMB to 10 accuracy the upper limit on the sensitivity will be as follows Thus the limit is set on 0 2 K Eqn 6 depends linearly on T ys As the receiver temperature fluctuates so will the sensitivity We measured the receiver temperatures ranging from around 180 K to around 200 K Looking at Fig 4 and Fig 5 we see that for a sensitivity of 0 2 K the integration time will be of the order of milliseconds Even in bad conditions with high optical depths this is still the case The low integration times tell us that our measurements will not be limited by the system noise Instead the limiting factors will be how well we can determine the other quantities li
9. might damage the sensor due to material stresses To connect the sensor to the temperature monitor another cable was made which can be seen in Fig The temperature is determined by measuring the resistance of the sensor This introduces a problem wires have resistance If we were to construct a circuit as in the left of Fig 30 gt m EN n 4 m LU YAT MANDA P Hi Figure 17 The Pt1000 temperature sensors with the cable to connect it to the Lakeshore tem perature monitor we would not only measure the resistance of the sensor but that of the wires as well This is a direct error in the measurement The solution to this problem is to separate the current and voltage measurements The current will be the same since it is a series circuit The voltage however drops by Ohm slaw V IR To eliminate the wire resistance one should only measure the voltage drop over the sensor as in the right picture of Fig 18 This is known as four wire sensing or Kelvin sensing The wires to the voltmeter only carry a tiny current The voltage drop caused by them can therefore be neglected The measured voltage is now only the voltage drop caused by the sensor wire wire Ca Pt1000 v Pt1000 wire wire Figure 18 Measuring the resistance of the sensor left vs measuring the voltage drop over the sensor right 31 Figure 19 The GPIB controller to allow communication with the power meter Image credit Prologix 4 3 3 Communi
10. this would not be ideal It has too many downsides Having many peripherals would mean one would need to access the Pi frequently for connecting and disconnecting and we would need a way to handle all the cable work It also meant carrying many things alongside the telescope This would compromise portability a lot Furthermore the whole setup would become just too bulky All these situations make the setup less user friendly so we discarded this idea Thinking about the portability led us to consider the operator controlling the telescope from his or her own laptop The only problem was then how the communication between the Pi and the laptop would work The only ethernet port was taken by the GPIB controller and there are no other connections Connecting everything by ethernet does solve the problem of not knowing what device has what name since everything gets an IP address We thought of setting up a small LAN network depicted in Fig 20 The network would consist of the following components e Raspberry Pi e GPIB Ethernet controller 33 Laptop Switch TM Figure 20 The LAN network connecting all devices in the telescope with each other 34 e User laptop e Network switch or router The switch or router will provide the ethernet ports to connect everything together The Pi will take care of communication between the user s laptop and the system 4 4 1 Connecting to the Telescope To operate the telescope the user will con
11. to make one revolution We operate the motor in half step mode With each step it will move by 1 8 To mount the telescope the motor is connected to a larger rotatable disk Our supervisor told us that in this setup it takes 72 revolutions of the stepper motor for the disk to make one We verified this by marking the disk and then sending 200 72 pulses to the motor This means with each step our telescope will move 0 025 or 90 arcsec on the sky In between the pulses there is a small delay of 2 ms or 1 3 ms depending on the speed setting If the pulses 26 arrive too fast the motor will not have time to respond and it will hang It takes the horn 80 seconds to do a measurement with a 1 degree step and 32 seconds with a 13 degree step both at the fastest mode 4 2 2 Communicating with the Motor To control the motor we use the General Purpose Input Output GPIO pins on the Raspberry Pi The stepper motor controller we use has a 15 pin connector but we only need three pins ground step and direction These pins are connected to a ground pin and two GPIO pins on the Pi respectively We cannot however directly connect the motor controller to the Pi as the GPIO pins run at 3 3 V while the controller needs 5 V If the 5 V would flow into these pins the Pi could possibly get damaged To prevent this from happening we made a special connector with Zener diodes connecting the step and direction pins to ground A Zener diode allows current to flow b
12. uef ban L Tu L urut L 6007 E 800 xd LOooc ud yjuoy Jed sa njeJadua Bei AV 17 2007 2008 2009 2010 2011 2012 2013 2014 Minimum 9 43 27 27 40 Jas 68 42 Average 1448 15 59 Maximum 26 6 Table 1 Minimum average and maximum temperatures in June per year in C ature per month This is shown in Fig 7 From these plots we can see that the coldest months are January February and March We will be doing our observations in June however Table 1 shows the minimum average and maximum temperatures of June for the past years The average temperature is around 15 16 C but the minimum and maximum are far apart For a better view of how the temperature is spread across the day we will look at different parts of the day separately We define night 00 00 06 00 morning 06 00 12 00 afternoon 12 00 18 00 and evening 18 00 00 00 Figurel8 shows this for June 2014 For the other years see App A Hourly the temperatures can fluctuate strongly and this varies on a daily basis however from these figures we do see that in general the night time is the coolest part of the day Tem perature wise observing conditions are best during the night 3 3 Cloud Coverage Even more important than the atmospheric temperature is the cloud coverage When there is a cloud in the field of view of the telescope the opacity of that area can increase dramatically For larger optical depth the facto
13. with 0 octants meaning clear skies and 8 octants meaning a sky completely covered in clouds In some situations the sky may not be visible at all such as with dense fog In this case the cloud coverage gets a 9 3 2 Atmospheric Temperature Equation 8 for the antenna temperature shows that the atmosphere increases the signal with unwanted noise and does so inverse exponentially With e 0 95 for t 0 05 the contri bution from the atmosphere may seem small but because the atmospheric temperature is high relative to the CMB and other sources the T 1 e term still contributes significantly typically ranging from 3 10 K 2015 We therefore aim for an atmospheric tempera ture that is as low as possible In Fig 6 we have plotted the minimum average and maximum temperature for every day of the year The distribution looks roughly the same every year We can see that the highest and lowest temperatures are during the summer and winter months respectively For a more clear view we calculated the minimum average and maximum temper http www knmi nl klimatologie uurgegevens selectie cgi hourly or http www knmi nl klimatologie daggegevens download daily 15 UOTJBITPUI poos e sars mq YJUOU Aq sjurod eyep y o1e1edos Appoexo jou op s eqe YJUOU au STOZ H L007 Woy ep eg 1e p rnse ur se onje1oduro VUNVITXPUL pue 9SPIIAR umururu DY 9 9IN3TY 229 AON po des ny n unf Aew dy Jen qay uef 22 AON 12
14. 0 des ny n unf Aew Jdy sew qej uef oz oT 0 OT ds x x v p 2 mp o o q E Y S unu unu 0 X x x OV OV STOZ vTOZ 229 AON pO des ny n unf Aew Jdy jew q 4 uef 229 AON pO des ny n unf Aew Jdy sew qej uef fav Lee unu urut x ZToz TTOZ 229 AON pO des ny n unf Aew Jdy jew qa um 3eq NN po des ny jnf unf Aew Jdy sew qa us oT OT rout L RO a x lox s AS 0c pee SOR M Lee re oE urut unu X X x 6007 E 800z kd Aeg sed ainjesodway 29g AON po des ny n unf Aew sdy sew q j uef oz oT 0 OT 0c oE Ov 3eq MN po des ny jnf unf Aew sdy sew q3 E Whbocu s Aen 0c Sr e 0 o unu 3 aunjesadua X oroc 3eg AON pO des ny n unf Aew Jdy sew qa oT OT 0c oE urut x 00z m 16 ogeI9A DY JO uorerAop prepuejs IY VAIS SIPQIOJIO ou IBI Aq poyeredas ujuoui qo 10 sam3e19dula sosso15 pax umuirxeui pue sjop Ao 9 9JPIDAR SISSOLI INTA wnunury oN 229 AON 20 das ny nf unf Ae dy se qay uef 229 AON VO desbny nf unf Ae dy se qay uef 38g AON VO das ny nf unf e ady se qay uef 0c oz oz ban ban L T Uut l a Uut L urut unu L ban fav Bao L 99 d I T Uut T Uut TU L x X L L unu unu unu LL X L L Z2Toz TTOZ dd OTOZ de 22 AON VO das 6ny In unf ely ady sew qay uef 2239 AON VO das ny jnf unf Ae dy sey qay uef 229 AON VO desbny n unf Ae dy se qay
15. 16 32 64 128 256 512 1024 Return None rp 20 40 200 av 2x i for i in range 11 rps int rps avg int avg if rps not in rp or avg not in av print Invalid value in measure speed return else self send SENS AVER COUN d avg self send SENS SPE d rps def get_measurespeed self p True Requests the averaging rate and readings per second Args bool p print the values to the terminal or not Returns int read readings per second int aver the number of averages taken for a measurement P POP self send SENS SPE 66 def def aver self read prnt p self send SENS AVER COUN read self read prnt p return read aver units self un Set the units of measurement Possible units are W or dBm Args str un unit to return Return None u un lower if u w self send UNIT POW W self read prnt False elif u dbm self send UNIT POW DBM self read prnt False else print Invalid unit quit self Correctly close the connection to the controller Args None Return None 1 self sock close if name __main__ YELLOW BOX IP 192 168 0 142 PORT 1234 GPIB Controller YELLOW BOX IP PORT send ver send read while 1 C C c read C C idn cm raw_input gt gt gt if cm quit c quit break else c send cm c read
16. 19 52 11 91 0 087 42 5 4 Measuring the Brightness Temperature of the Sun If we have calibrated data we can relate the power from the Sun to a brightness temperature This can be determined by calculating the antenna temperature of the Sun This is most easily done with the system temperature Toys Tompe Ius e T Ine 13 To determine the brightness temperature we thus need to know the gain of the telescope to convert the incoming power to a temperature and the optical depth of the atmosphere such that we can invert the above relation to obtain lpo Tsys lowpe edad e les 14 Due to unforeseen complications with the cold load that emerged at the final stages we un fortunately were not able to correctly calibrate the measurements Hence it is not possible to determine the brightness temperature of the sun at this moment 43 6 Measurements of other Sources 6 1 Galactic Synchrotron Radiation Electrons in the Milky Way and cosmic ray electrons are accelerated in the magnetic field thus producing synchrotron radiation To see if the galaxy s synchrotron radiation will affect our measurements we need to know how strong it is with respect to the CMB at 11 GHz Since this radiation is frequency dependent we need to know how it scales with v which in turn depends on how the energy is distributed among the electrons The energy spectrum of cosmic ray electrons follows a power law relation giving the energy distribution give
17. 22 0 2 25 22 5 z E 5 2 30 c 23 0 amp amp 2 35 23 5 2 40 24 0 2 45 24 5 2 50 25 0 20 40 60 80 100 120 140 160 180 O 20 40 60 80 100 120 140 160 180 Angle deg Angle deg Figure 22 Data from the unofficial first light Top data from 13 08 with no clouds The little peak around 20 degrees is our supervisor John McKean standing in the beam Bottom data from 13 12 39 5 3 Verifying the Beam Pattern As mentioned before we can determine the main beam size through observations of the Sun This is possible due to the fact that we are able to consider the Sun as a bright and isolated point source In the middle of the main beam the point source would give the highest power peak and when the source is moving out of the main beam the signal will decrease Therefore moving the beam of the antenna over the point source the Sun will map out the main beam Determining the beam size requires a few steps 1 Starting with the whole sky observation of 13 08 which is the data set where there were no clouds present We only need the data where the radiation from the Sun is measured The Sun is represented by the second peak in Fig Therefore from now on we only consider the data in the range of 100 lt angle lt 150 2 The data representing the Sun also involves a moving baseline and background radiation To remove all the data except for the peak caused by the Sun a function can be fitted on t
18. 6 00 We will be observing in June but the night time will still have the lowest temperatures Cloud coverage on the other hand is beyond our control Due to its changing nature we cannot make an estimate of a best observing moment The best moment for this would need to be decided by the observer by checking the weather conditions Although this analysis has given some insight in the weather conditions it still remains difficult to find reliable correlations between observing time and cloud coverage For the best observing time it comes down to checking the weather forecast or the weather outside directly to see if conditions are and will stay suitable 23 Arduino Uno Raspberry Pi B ATMega328 Broadcom BCM2835 SoC SVIT 12V CPU Speed CPU Speed Table 2 Arduino Uno and Raspberry Pi B specifications 4 Controlling the Telescope 4 1 Computer Control Our measurements will involve moving the telescope over a strip in the sky in elevation To make a reliable measurement we decided to mount the horn on a frame and control the tele scope with a computer The telescope moves with a motor and power is read digitally from a powermeter This gives us a couple of advantages First of all the mount will ensure that we start and end in the same strip of the sky This way we only have to worry about the received power as function of elevation easing the data reduction later on Secondly we will control the speed factor Using a motor controlle
19. 6 seconds we should be able 030245 12 83 to detect Cassiopeia A with a sensitivity of 0 0049 K To de 030443 12 73 tect Cygnus A we need to use the 12 8 second integration 030706 12 57 time to obtain a sensitivity of 0 0017 K To detect Virgo A 030908 12 66 we need a much longer integration time The longest in 73 439 12 77 tegration time possible is 51 2 seconds This gives a sensi tivity of 8 6 107 K This is larger than the signal of Virgo Table 9 Measurements containing A and fluctuations of this order are in the regime of fluc the satellite and the corresponding tuations caused by the Allan time Therefore we are not HPBW from that dataset able to detect this source with our telescope As for the other sources any measurement of the brightness temperature will most likely not possible Theoretically it should be possible to make a detection of these sources by making a lot of mea surements and then stacking them This way the noise will be reduced compared to the signal of the source However this is based on the radiometer equation which in our case does not give the limiting sensitivity Detection of other sources is therefore most likely not possible 6 3 Non Astrophysical Sources The sky is also home to man made objects such as sattellites We discovered a sattellite by accident when trying to find a clear piece of sky When viewing the data we saw a large peak that was approximately 3 5 dBm higher than the background Th
20. 67 E Stepper Motor Control usr bin env python from __future__ import division import numexpr as ne import readline import time cry import RPi GPIO as GPIO except RuntimeError print Error importing GPi GPIO Try running as root class StepperMotor object Stepper motor F P P def __init__ self pdir pstep stprev revdisk PARAR AA a KASU Raspberry Pi GPIO pin setup THBGEIBIGHHIPIHETH DIG HIBIBIHEHIBHHBIBIEHBIHER self PIN DIR pdir self PIN STEP pstep Set pin numbering as on the pi GPIO setmode GPIO BOARD Set pins as output pins GPIO setup pdir GPIO OUT GPIO setup pstep GPIO OUT THHHHHHHHHHHHHHBHHHHHH Motor constants THHHHHHHHHHHHHHHHHHBI self REV DISK revdisk disk revolution self STEP STPM stprev self STEP DISK self STEP STPM self REV DISK self SLEEP TIME 0 002 self TURBO False self PARK POS O self ANGLE 0 self CALIBRATED False self _rotating False def calibrate self override False dk dk dk dk dk Calibrate the telescope to the parking posistion Args Number Number Number Number of of of of stepper revolutions required for one steps per stepper motor revolution steps per disk revolution seconds to sleep between steps Shorter sleep time hence faster movement Parking position Tracks telescope position Check for calibration float cal_ang set the current angle to the parking angle bool overri
21. Hz and 18 GHz and powers between 70 dBm and 20 dBm The power meter is a key component in the sensitivity of our system as given by Eqn 6 The power meter is set to take a certain number of readings and average them together to produce a measurement The measurement speed amount of readings per taken per second and the number or readings to average are separately adjustable These quantities now determine what our integration time will be according to Eqn 9 readings averaged DESI LS m 9 measurement speed The available options are limited however Table 4 lists the possible integration times as func tion ofthe measurement speed and the number of readings averaged for a measurement Averaging more samples will give lower noise levels improving the precision For an absolute measure ment it is 0 02 dB when measuring in dBm or 0 596 when measuring in W igies 2013a This error can be brought down by taking multiple measurements i e changing the number of readings that are averaged The error will go down as the square root of the number of readings 4 3 2 Temperature Monitor To measure the atmospheric temperature and the temperature of the hotload we use a Pt1000 sensor It operates between 50 C and 150 C with tolerance class 2B This means the sensor has an accuracy given by 0 6 0 005 t 2013 10 Note that t should be in C Outside this range the sensor still functions but the uncertainty becomes larger and it
22. Interrupt pass finally GPIO cleanup 64 D GPIB Communication usr bin env python import readline import socket class GPIB_Controller object pre III def def def def def GPIB_Ethernet Controller __init__ self ip port Initialize a new connection to a GPIB Ethernet Controller Sets up a TCP connection to the controller at the specified ip address and port self ip ip self port port self sock socket socket socket AF_INET socket SOCK_STREAM socket IPPROTO_TCP self sock connect ip port self sock settimeout 1 Initalize to the power meter self addr 14 address self addr Change the address to the specified value The address can range from 0 to 30 Args int addr address of the device to communicate with Returns None self addr addr self send addr d n addr self read prnt False measure self Query the power meter to return a measurement Assumes the address is set to the power meter Args None Return str res the answer of the power meter OR None if the address is wrong self send FETC n res self read prnt False return res measure_temp self sens Query the temperature monitor to return a measurement Assumes the address is set to the temperature monitor Args str sens the sensor to read out Returns str res the answer of the temperature monitor OR None if the address is wrong 1 senso
23. ackwards once a certain breakdown voltage is exceeded The connector has two 3 3 V Zener diodes If the voltage over the Zener diode now exceeds 3 3 V the current will flow towards ground The schematic for the socket is shown in Fig 13 These three wires are then connected to the following pins on the Pi 29 31 and 30 for direction step and ground respectively The pins on the Pi can be set either high 3 3 V or low 0 V For movement we set the direction pin either high or low to move forwards or backwards Next the step pin is continuously switched between high and low Every time the step pin is powered the motor will move one step After testing with a prototype of loose wires a custom cable was made which can be seen in Fig 3 3V Step Direction Figure 13 Schematic for the connector connecting the motor controller to the Pi The connector is a 15 pin female D Sub connector 27 sutd OIAO 94 10 1o 99uuoo pue sed umrurume YIM o qeo o1e duroo DY 448TA SIPOTP 19UIZ Iy pue s rrA Y SuLMOUS 10122uuoo DY JO prsur oY 1J9T Id 11eqdsew y 0 xoq 19 01 JU09 JOJOUI y Suno uuo2o I ALI au pT MSI 28 4 3 Measurement Hardware and Control To measure the power received by our telescope we use an Agilent E4412A power sensor con nected to a Agilent E4418B power meter These devices are shown in Fig To measure temperatures we use a Lakeshore 218S Temperature Monitor for reading out the sensor see Fig To save
24. an almost certainly be im proved is the code itself Certain routines can be optimized or special libraries designed for speed could be used For even better performance we could switch to a compiled language such as C instead of Python an interpreted language This will however require a complete rewrite of the control code and it will reduce the flexibility of possible measurements The per formance gain from this switch will not be of great importance either as the other components in the system become the limiting factors The code can still be optimized but it will not give a significant improvement 7 2 Reading Results from the Power Meter The major bottleneck as of now is reading the power from the power meter Due to the way it is done now this can take up to a second This interrupt causes the telescope to wait after each step instead of moving continuously Attempts have been made to get around this interrupt problem by running movement and measurement in parallel It turned out however that the CPU on the Pi is not fast enough to handle this The only way to change this is to use a different method of reading from the device There is a specific setup for the GPIB controller and the power meter that makes it respond as soon as it has something to respond when asked for it With this response times should drop to nearly instantaneously 7 3 Motor Power and Control A stepper motor like any motor has a maximum load it can drive Steppe
25. ature to the measured power it is insightful to look at the origin of the receiver noise in particular that of the amplifiers 2 2 1 Johnson Nyquist Noise The noise of the amplifiers in the back end comes from random thermal motions of electrons inside the components The random nature of this motion means that the average displacement is zero but the mean square displacement is not Moving charges will create currents so the motion of the electrons causes a small current I with 1 0 but I V 0 to start flowing Higher temperatures will make the electrons move faster and thus the noise goes up Cooling the amplifiers properly can therefore reduce the produced noise Because of its nature this noise is called thermal noise or Johnson Nyquist noise after the two people that played an important role in discovering and explaining this type of noise To find a relation between the measured power and the corresponding noise temperature lets look at a resistor Theoretically we can replace the noisy resistor with a noise source fol lowed by a noiseless resistor The noise power can be determined by loading a resistor R with another resistor Rr The power that R puts into Ry is then given by P R 4kT 3 van Schooneveld 1950 This power is maximum when the loads are matched i e R Rr Now all factors except for kT cancel out We have now found a relation between power and temperature P kT 4 Here T is the effective tempera
26. because each device has its own address for communication Two limitations should be considered however Each device can have an address between 0 and 30 but a driver can only drive 14 devices at a time Second the cable length should not exceed 20 m in total or 2 m between devices for maximum data transfer rates For this project it turned out that GPIB connection would be the easiest to work with The Pi does not have a GPIB connector either so to communicate with the equipment we use a GPIB Ethernet controller shown in Fig This acts as a bridge converting signals received over ethernet to GPIB and vice versa To read out results one connects to the controller via an 32 ethernet cable Before commands can be sent we need to set up a connection with the controller This is done by setting up a TCP connection at port 1234 at the controllers IP address Prologix 2013 In Python this is easily done using sockets in the socket module The details can be seen in Appendix C The equipment can now be read out by sending the appropriate commands over the socket When talking to a device two things should be accounted for Commands should always be terminated by the newline character Nn This indicates you are done sending the command and that it can start processing it The second is the way sockets work In the Python documentation they warn the user that when sending or receiving a message you may not send or receive the entire message in one call It
27. brightness temperature of the Sun NASA Sun Fact Sheet http nssdc gsfc nasa gov planetary factsheet sunfact html 37 WAVELENGTH 10m im 10 a FL DOE umum Sy E 107 108 L 105 _ oe 104 L kP EL 10 E Hauk 1 dr c MN i L am 10 H J 4 10 MHz 100 MHz 1 GHz 10GHz 100 GHz v FREQUENCY Figure 21 Spectral distributions of various radio sources Image credit Tools of Radio Astron omy 5 2 Observing the Sun We had an unofficial first light at June 8 2015 to see if everything worked During this obser vation we tried to measure the Sun This was in a phase where the hot and cold load were still under construction so the full range of 0 to 180 degrees was measured It also means that the system is uncalibrated Therefore we cannot draw conclusions from the received power itself The beam size however is independent of calibration Two data sets of this observation can be seen in Fig 38 Power measurement of the sky FirstLight 06 08 15 13 08 Power per angle in mW 2 10 181 Power per angle in dBm 21 0 2 15 21 5 2 20 22 0 2 25 _ 722 5 5 2 30 v 23 0 amp amp 2 35 23 5 2 40 24 0 2 45 24 5 2 50 25 0 0 20 40 60 80 100 120 140 160 180 O 20 40 60 80 100 120 140 160 180 Angle deg Angle deg Power measurement of the sky FirstLight 06 08 15 13 12 2 10 lel Power per angle in mW 21 0 Power per angle in dBm 2 15 21 5 2 20
28. cating with the Devices To communicate with the power meter and temperature monitor we had two options RS232 or GPIB The Pi does not have an RS232 interface but there are USB converters so that would be no problem Our supervisors advised against RS232 for two main reasons First of all RS232 would be a difficult protocol to work with One would have to account for e g start stop bits the number of data bits sent or the number of bits transmitted per second A second problem would arise when using an RS232 to USB converter The name by which the computer addresses the USB device depends on the order in which all devices are plugged in The names are not persistent so if multiple devices will be used we cannot be sure that the next time devices are plugged they will have the same names again GPIB or IEEE 488 was developed in 1974 by HP for devices that can automatically test other devices or perform measurements automatically It was an attempt to standardize communi cation between computers and instruments With the General Purpose Interface Bus GPIB all instruments would have the same connector Later with the introduction of the Standard Com mands for Programmable Instruments SCPI all devices obtained a common basic programming command set along with a set of guidelines for manufacturers should they wish to include new commands Using GPIB multiple measuring devices can easily be used and is as simple as daisy chaining them together This is
29. comes a straight line The plot is in log scale so a straight line means a power law relation In the Rayleigh Jeans limit hv lt kT the Planck function reduces to a power law resulting in a line with slope 2 B 2kT y BT 11 The radiation we measure with our telescope is thus mostly that of the quiet Sun Based on its temperature we can estimate the brightness of the Sun and the power that we will receive To find the power we receive from an object we multiply the brightness B with the solid angle of the object AQ the effective area of the telescope A and the bandwidth Av giving P B AQA Av 12 The estimated brightness is B 2 15 10716 W Hz m sr The solid angle of the sun can vary slightly so we use its size at a distance of 1 AU 1919 arcsec This gives a solid angle of AQ 6 8 10 sr The effective area of our telescope is 0 023516 m and our bandwidth is 1 05 GHz This gives an expected power of P 3 61 10 W or P gt 94 42 dBm Combined with the CMB and the atmosphere mentioned earlier in Chapter 2 we expect a total power of P 84 55 dBm arriving at the antenna when pointing at the Sun with an optical depht of t 0 05 The gain of the telescope is around 60 dBm so this will be well within the observable range and we are able to measure the Sun By measuring the Sun we can do two interesting experiments We can try to measure properties ofthe main beam and we can try to determine the
30. d rot deg ne evaluate arg mot rot deg override True elif cmd calib mot calibrate elif cmd calib mot calibrate override True elif cmd park mot park elif cmd quit break else print Invalid command GPIO cleanup 70 F DNS Configuration Set up for the ethernet port of the Pi interface eth0 Give out IP addresses betweeon 0 and 100 with 1 hour lease time dhcp range 192 168 0 20 192 168 0 100 255 255 255 0 1h Logs log facility var log dnsmasq log log async log dhcp 71
31. d by a computer ensures that each measurement will be taken in the same amount of time This way data collection is consistent for every mea surement Lastly it makes determining the received power at a certain angle easier and more reliable A full computer would be too large to fit into our build so we opted to go for something smaller This gives us the choice between an Arduino and a Raspberry Pi 4 1 1 Arduino vs Raspberry Pi The telescope will be rotated by a stepper motor Controlling the motor is a simple task and can be done by a simple system but maybe expansions are desired in the future needing a more advanced system To make a decision we compared the two devices with each other Table lists the specifications of the Arduino Uno and Raspberry Pi B respectively It immediately shows that a Raspberry Pi from here on Pi is much more powerful than an Arduino This is because there is a key difference in how they operate The Arduino has a microcontroller It has no OS it just runs its code when told to do so The Pi however is a full computer complete with OS Programming the Arduino would in principle require programs in C and the programming would be indirect One would write the code and upload it to the microcontroller It would then be able to do the one thing the program was written for Programming the Pi can be done in Python on the machine itself This has multiple advantages For one Python is a flexible and easy to use p
32. de override the existing calibration Returns None i a d if not self CALIBRATED or self CALIBRATED and override Set the current angle to this position self ANGLE O self CALIBRATED True else print System already calibrated property def is_rotating self Returns wether the motor is rotating or not E i return self _rotating 68 def def def def def park self Return the telescope to park position Args None Returns None LEN 1 self rot self ANGLE prep self Prepare the telescope for calibration starting from zero point This points the horn to the cold load at 15 degrees from the horizontal Args None Returns None a d self rot 15 override True rot self ang override False Rotate the disk by a given amount of degrees There are built in safety limits so that the telescope will not move below 0 or over 180 degrees This protection should not be overridden unless you know what you are doing In general it should not be necesarry to do this Args float ang rotation angle in degrees bool override override the safety limits Use carefully Return None self _rotating True Update the telescope position if self ANGLE ang gt 180 or self ANGLE ang lt 0 and not override print Going too far Aborting return self ANGLE ang Set forwards or backwards if ang lt 0 self set_direction True else
33. e Pi to coordinate everything but the load would be spread over multiple devices allowing for smoother operation 7 5 Conclusion During this project I was responsible for control of and acquiring data from the telescope While there is still room for improvement it is in a well usable state for observations The observations that I carried out had varying results The brightness temperature of the Sun could not be determined due to unforeseen complications however verifying the beam size was successful with both the Sun and the satellite The Sun yields a beam size of 12 07 and the satellite one of 12 61 The latter is closest to the beam size determined in the lab This is not surprising since the satellite was a much stronger source than the Sun 48 8 Acknowledgements I would like to thank John McKean for providing this project It was a great opportunity to actually apply some of the theory learned in the Radio Astronomy course to a real life problem of building a radio telescope My share in this project would not have been possible without all the help from the electronics department of SRON and the help of other people I would like to thank Andrey Barychev Andrey Kudchenko Ronald Hesper Henk Ode and Duc Nguyen for their help in constructing the electronics acquiring measurement devices trouble shooting and overall help 49 References 2012 AstroBaki Referenced on May 10th 2015 Agilent Technologies 2013a Agilen
34. ell known supernova remnants In it s center is a pulsar emitting radio waves Lastly Virgo A or M87 is an elliptical galaxy with an radio emitting AGN at its center Table I8 lists the flux density and the resulting contribution to the antenna temperature of these sources The flux densities are calculated according to 1977 who use log 5 Jy a blog y v MHz clog v MHz 18 for calculating the flux density of these sources The parameters for this equation of each source are listed in Table 44 Source a b e Cassiopeia A 5 745 0 770 0 Cygnus A 7 161 1 244 0 Taurus A 3 915 0 299 0 Virgo A 5 023 0 856 0 Table 7 Selected sources with their parameters for the flux density equation Source Flux Density Jy Antenna Temperature K Cassiopeia A 322 29 0 0054 Cygnus A 135 99 0 0023 Taurus A 508 89 0 0086 Virgo A 36 61 0 00062 Table 8 Flux density of the selected sources at 11 GHz and antenna temperature for t 0 01 To be able to measure these sources the fluctuationsin Data Set HPBW deg Ty need to be smaller than their respective contribution 021432 12 27 This means that we need a sensitivity of 0 0086 K or lower 021643 12 48 to detect Taurus A the brightest of the sources From the 022009 12 31 available power meter settings we need to use an integra 025854 12 69 tion time of 0 8 seconds giving a sensitivity of 0 0069 K 030052 12 78 With an integration time of 1
35. erature this becomes 1 por QA Jan T 9 9 P 0 dO K which follows from the fact that P kT see next section and the Rayleigh Jeans approxima tion of the Planck function B Here T4 is now the antenna temperature 24 the beam solid angle T the brightness temperature in some direction 0 b and P the normalized power pat tern in that direction Finally using the definition for the beam solid angle we get the following expression for the antenna temperature Wilson et al 2013 nu fan To 0 p P 0 9 dO Ja P 0 p dC The antenna temperature can be interpreted as the weighted average of the power received from all over the sky The sky brightness distribution is contained in Tj the brightness temperature The power received from a certain position on the sky is now multiplied by the value of the 1 normalized power pattern P at that position The normalized power pattern is 1 at its maximum and decreases for the sidelobes Sidelobes are positions outside of the main beam where the response of the antenna is non zero The maximum is usually located in the center of the beam Therefore most of the power will come from the main beam It is not possible to know from what direction what power was received unless the observer knows there is a source at a certain position Therefore ideally we would want all of the power to come in through the main beam so that we know exactly where the power is coming from Hence reducin
36. es The FWHM was then calculated the same way as above for each measurement The results are listed in Table 6 Averaging these values yields a beam size of 12 07 0 13 The error is calculated according to This is still off from the measured value in the lab Most likely this is because pointing the tele scope such that the sun passes exactly through the middle of the beam is difficult to do causing us to measure a smaller FWHM This may also explain the spread in the values themselves 40 Power measurement of the sun FirstLight 06 08 15 13 08 3 60 le 3 Power per angle in mw 3 55 3 50 Power mW w w w w UJ UJ B Un o Un w N Un 3 20 100 110 120 130 140 150 Angle deg a The signal of the Sun enlarged In green is the fit for the background Power of the sun filtered FirstLight 06 08 15 13 08 3 0 le 4 Power per angle in mw Power mW 100 110 120 130 140 150 Angle deg b The Gaussian fit for the main beam in green Gaussian determining HPBW FirstLight 06 08 15 13 08 3 0 le 4 Power per angle in mW 2 5 2 0 1 5 Power mW 1 0 0 5 100 110 120 130 140 150 Angle deg c Indication of the FWHM of the main beam The value comes down to 11 99 41 Table 6 Sun observations June 30 Time hh mm ss HPBW deg Error deg 12 01 32 12 09 0 071 12 03 18 12 23 0 073 12 04 58 12 08 0 073 12 07 01 12 25 0 085 12 15 58 11 99 0 082 12 17 53 11 92 0 087 12
37. fective temperature now is a combination of the antenna temperature and the receiver temperature P k Ta ES Try AV If we assume a receiver temperature fo Tg 200 K this gives an incoming power of P 3 13 10712 W or P 85 03 dBm using k 1 3807 107 K and Av 1 05 GHz The measuring range of the power meter extends from 70 dBm to 20 dBm Agilent Technologies 20132 Our system uses two amplifiers of around 30 dB each Zandvliet 2015 If we assume the system gain comes only from the amplifiers and is 60 dB this results in a signal of approximately 25 03 dBm If the optical depth decreases to t 0 01 the antenna temperature drops to 5 5 K Using the same value for the receiver temperature and gain the power becomes P 25 26 dBm The 10 4 0 1e 18 CMB with Observed Range Hz sr N Un B T MB W n 2 0 100 200 300 400 500 600 700 800 v GHz 1e 19 Zoom of Red Line Hz B T MB W m 2 v GHz Figure 3 Top the brightness B of the CMB as given by the Planck function for Tcp 2 72584 K Bottom a zoom of the available frequency range showing the expected B v property of the Rayleigh Jeans law final signal will be somewhat different because of effects of the other components cables the horn and changes in both atmospheric and receiver temperature but it will be around these values Noise and System Temperature We assumed before that the noise produced by the second amplifier
38. g the sidelobes as much as possible is a major part of designing a radio telescope to ensure the antenna temperature incorporates only the signal of the source we want to measure and nothing else For measuring the CMB we will consider three components for the antenna temperature the CMB itself the atmosphere and possible ground pickup This results in a total antenna temperature of TA ES Tempe Iam m e T leround Mulder 2015 2 2 2 Noise and System Temperature We consider all measured sources as noise sources The telescope will thus measure a total noise power P with associated noise temperature T Not all of the noise however comes from external sources Besides the power received by the antenna there is also noise power generated in the receiver itself with noise temperature Tp The total noise temperature will then be the receiver Tp temperature plus the antenna temperature T Sys TA Trx 3 Here T4 can include contributions from any noise source one can think of Toys TcmB atm source leround T T galaxy Tags Ly As we will see later on for our observations we will only consider the CMB and the atmosphere contribution of Eqn 2 To eliminate the ground contribution the horn was designed with min imal sidelobes Even if we were to pick up some ground its contribution is negligibly small in our case Mulder 2015 In Chapter 6 we will see that the galaxy is also negligible To relate this system temper
39. he 160 MHz receiver he detected radiation coming from the center of the galaxy Reber 1944 Nowadays we are still building new radio telescopes to further improve our observations by collecting more signal or by having even higher angular resolution for more detailed images Both signal strength and angular resolution depend on the size of the telescope Inventions range from large parabolic reflector dishes like the 100 meter Effelsberg Radio Telescope or the Using c 299792458 m s Figure 2 Left Grote Reber 1911 2002 Right Reber s parabolic reflector Image credit www nrao edu whatisra hist_reber shtml 300 meter Arecibo telescope to large arrays of antennas like the Low Frequency Array LOFAR or the upcoming Square Kilometer Array SKA The Cosmic Microwave Background After the Big Bang the Universe was hot and dense Matter and photons were strongly coupled and light could not escape Minutes after the Big Bang atomic nuclei formed but it was still too hot for the electrons to recombine with the nuclei The Universe was a hot plasma of charged particles and photons and would remain so for approximately 380000 years After this the temperature dropped sufficiently for the electrons to recombine with the nuclei and atoms to form the Epoch of Recombination Before this photons could not escape because of Thomson scattering but now that the free electrons were captured the photons were less likely to be scattered and they co
40. he background data This is done by using the SciPy function scipy optimize curve_fit The peak extends over the region from 115 to 145 Fitting a polynomial to the data on the angles 100 to 115 and 145 to 150 will induce the green plot in Fig 23a 3 Subtracting the fit for the background from the original data will leave the data repre senting only the Sun The main beam has got a Gaussian shape Therefore to correct for possible side lobes and interferences a Gaussian model is fitted for the data This model will represent the main beam of the antenna Figure 23b shows this fit again in green 4 To say something about the resolution of the antenna we need to determine the Full Width Half Maximum FWHM of the main beam also known as the Half Power Beam Width HPBW The FWHM is specified to be the limit of the antenna beam width and therefore equals the resolution It can be determined by plotting a line at half of power of the maximum power in the Gaussian model and intersect with the model itself The dif ference in angles at these intersection points represent the FWHM The relation between the FWHM and the standard deviation o of a Gaussian function is FWHM 2vV21n2o Looking at Fig 23c we can state that the FWHM of the antenna equals 11 99 0 094 This is somewhat off from the FWHM of 12 78 measured by Lap 2015 For a better estimate we need to take more measurements We observed the Sun again at June 30 multiple tim
41. ired devices are there If you see a None response it means a command did not receive a response and the connection should be checked Once the identifiation finishes you will see a prompt starting with gt gt gt From here the user can either control the telescope directly or run a script The commands for direct control are listed in Table 5 When making a sweep of the sky it is not ideal to simultaneously measure the power and the atmospheric temperature Measuring simultaneously will interrupt often the sweep and therefore cause the motor to stop or even miss a step When the motor misses a step the angle of the horn will be off and the data becomes unusable Instead it should be measured at one of the loads or set the temperature monitor to log the data and retrieve it later on 35 Table 5 A list of commands available to the observer for manual control Command Description Icalib Forces recalibration of the zero position park Returns the telescope to its zero position prep Points the telescope to the cold load rot tang Rotates the telescope by the given amount of degrees Will give an error when attempting to move out of bounds i e below 0 or above 180 degrees Irot can The same as rot but it ignores the limits Use this with caution 8 8 run script Executes the script Name should be given without the py extension p p 8 speed rps avgs Changes the setting of the power meter rps sets the readings per second avgs
42. is rules out the Sun as it is much 45 weaker It is also unlikely to be an astronomical source The peak is located at 150 meaning it is 30 above the horizon Checking the sky for possible sources at this location revealed that there are geostationary satellites at this location These satellites are used for communications and emit high power radio signals As the satellite is an even stronger point source than the The Sun and Geostationary Satellite 20 21 22 23 Power dBm 24 25 90 100 110 120 130 140 150 160 170 180 Angle deg Figure 24 The mysterious signal The left peak is the signal from the Sun and the right peak is from the satellite Sun it is an ideal object to check the size of the beam We use the measurements from June 30 to do this The results are listed in Table B From these measurements we obtain an average HPBW of 12 61 0 19 46 7 Future Improvements and Conclusion Performance of the telescope is not yet optimal on the software and measuring side Possible points of improvement are Improve the overall speed and efficiency of the code e Change the way results are read from the power meter and temperature monitor e Use a more powerful motor or implement more advanced motor control e Use a more powerful version of the Pi or split the system into multiple components 7 1 Code Efficiency and Speed The code to control the telescope is self written Something that c
43. is the users responsibility to make sure everything is sent or received Sending the entire message can be done with the socket module itself by using the socket sendall method Commands are then sent to the controller which processes them and queries the power meter for a response However there is no such method for receiving To make sure we receive everything the power meter sends us we keep querying it for more data until it returns None indicating there is nothing more to send The code governing communications with the GPIB controller and the powermeter can be found in GPIBComm py in Appendix ID The fact that we can use ethernet influenced the decision on how to operate the telescope This is discussed in the next section 4 4 Operating the Telescope There are many question as to how the telescope can be operated Should the measurements be automatic to eliminate user error Should the operator have input If so to what extent How will the user interface look like What preliminary knowledge does the user need to have These are all questions to consider when thinking about the interface to the telescope The telescope will possibly be used for the astronomy bachelor course Radio Astronomy in the third year Thus it will mainly be students operating the telescope The Pi has four USB ports and an HDMI port so the first idea was to simply have a monitor keyboard and mouse During the frame design however see Zandvliet 2015 it became clear
44. ke the atmospheric temperature the opacity and the receiver temperature 12 19311 x 002 pue 19 M OST JO 2un3e1eoduro IOATIIAI IOJ IWT uored89jur Jo UOTJOUN se JLATIISUOS au p IMSI s aw uoneuba1ul s au uone681ul 0 0 570 ozo STO OT O so o 00 0 0 0 570 ozo STO OT O so o 00 0 00 0 00 0 10 0 10 0 Z0 0 Z0 0 un un D D 2 2 00 00 lt Q lt Q v0 0 v0 0 so o G0 O TY wigo 0 90 0 90 0 00z r pue x esc r pue g0 0 Jo A 08T 7r pue y esc r pue q0 0 10 au uone1ba3u jo UOIWDUNY se AAnisues au uoneju693u jo UOIWDUNY se AiAnisues 13 JUST A 002 PUR GFT A OST JO rn1ez dur 1 19419991 Y 103 su1dop eorido 1u z jrp 103 SUIT uoneiS tur DY S AMSTA Hap z Hap z 06 08 OL 09 0G Ot oE 0c OT 0 06 08 OL 09 0G Ot oE 0c 01 0 50000 00000 50000 01000 01000 SI1000 T SI0070 0000 02000 GC00 0 GC000 0 00 0 0 000 0 yualayup pue c 0 o A3IAISU S 104 z 9 Buv YNU3Z JO uomnoung se 7 SUI uonej6931ul z 9 Buv uiiuez JO UOI DUNY se 7 uuil uonej693ul 0 qu8JayJlp pue c 0 to A3AIsuss 10J s 3 14 3 Weather Conditions in Groningen Despite being able to reach our requirements even in relatively bad circumstances we still want the observing conditions to be as good as possible In Groningen we have two main concerns the atmospheric temperature and the cloudiness In this chapter an estimate of what is approximately the best observing moment in Groninge
45. l signals to be coming from noise sources The random nature of this signal results that we are in fact measuring the vari ance of a random signal with noise Measuring the variance o of random samples has an uncertainty of V20 This gives the first part of the equation OT Vos For the denominator we need the Shannon sampling theorem and the Central Limit Theo rem The sampling theorem provides the minimum frequency one needs to sample a signal at in order to completely reconstruct it It states that if a signal has a frequency f then one can reconstruct this signal completely by sampling it at a rate 2f 1977 Suppose an incom ing signal with a bandwidth Av The theorem then implies this signal needs to be sampled at 2Av After a time t we will have collected a number of samples N 2A vt Finally the Central Limit Theorem tells us that the uncertainty in T drops as VN with N being the number of measurements This will give PL OT V2Avt thus yielding Eqn 6 2 4 Applying the Theory to the Kapteyn Radio Telescope The horn is a Pickett Potter horn design about 30 cm in length The receiver is built to receive signals at 11 GHz with a bandwidth of 1 05 GHz going from 10 45 to 11 5 GHz This means we are looking at signals with a wavelength of 2 7 cm 2015 This section will apply the theory discussed above to the telescope to get a feeling for the quantities we will be dealing with Antenna Temperature and CMB Brightnes
46. n 4 Controlling the Telescope 6 41 Computer Control 4 1 1 Arduino vs RaspberryPil eee eee 4 2 Controlling the Motor 4 2 1 Stepper Motors 4 2 2 Communicating with the Motor 2004 43 Measurement Hardware and Control 43 1 Power Meter 4 3 2 Temperature Monitor ee e e es s os eee 4 3 3 Communicating with theDevices 4 4 Operating the Telescope 44 1 Connecting to the Telescope o r e 44 2 Observing with the Telescopel lll 5 Measurements of the Sun 51 Solar Emission 5 2 Observing the Sun 5 3 Verifying the Beam Pattern 5 4 Measuring the Brightness Temperature of the Sun Measurements of other Sources 6 1 Galactic Synchrotron Radiation len 6 2 Astrophysical Radio Sources ee ln 6 3 Non Astrophysical Sources 15 15 15 18 23 24 24 24 25 25 27 29 30 30 32 33 35 35 37 37 38 40 43 x Future Improvements and Conclusion 7 1 Code Efficiency and Speed 7 2 Reading Results from the Power Meter 7 3 Motor Power and Control 7 4 More Powerful Hardware 7 5 Conclusion Acknowledgements Average Temperatures for June Average Cloud Coverage for June C Telescope Server D GPIB Communication Stepper Motor Contro DNS Configuration 47 47 47 47 48 48
47. n by N E dE lt E dE 15 This means the brightness temperature will follow the power law given by T v av 16 with p 6 3 2 being the spectral index for synchrotron radiation In the range of 1 42 14 9 GHz this spectral index is B 3 0 Platania et al 1998 The relative intensity of the galactic synchrotron radiation with respect to the intensity of the CMB is given by Lsync oc yB 3 eltv kTcms 1 Readhead and Lawrence 1992 17 ICMB For a spectral index of 3 0 only the exponential part remains This results in p 0 21 This relation is proportional to but we can calculate an approximate contribution to the antenna temperature assuming this ratio and a gain of 60 dB The power from just the CMB would be Pemg 85 03 dBm as seen in chapter 2 If the synchrotron radiation contributes 20 of this power this changes to Pemgs 84 19 dBm This will result in a change of antenna temperature of AT 0 046 K Contribution of synhrotron radiation is therefore most likely negligible in our case 6 2 Astrophysical Radio Sources Besides the Sun the sky houses many other radio sources I have chosen four sources to in vestigate Cassiopeia A Cygnus A Taurus A and Virgo A Cas A is a well known supernova remnant and is one of the brightest radio sources in the sky Cygnus A is also a strong radio source Itis a radio galaxy with two large lobes on either side Taurus A or the Crab Nebula is one of the most w
48. n will be made It is not insightful to pinpoint an exact date so we will limit the investigation to find an approximate best time of the year and time of day to observe 3 1 Data Aquisition To be able to get a good overview of the weather in Groningen we need data that spans over multiple years To do this we use data from the KNMI the institute that monitors the weather throughout the Netherlands These data are publicly available on the website It is also possible to request the data through a script which is the way it was done here With the available data it is possible to go all the way back to the previous century In this case we will use the data from 2007 till 2015 Since there is no weather station in Groningen we will use the data from the nearby station in Eelde KNMI The data from the KNMI is available in either daily measurements or hourly measurements We used the hourly measurements to have the greatest flexibility The KNMI tracks all sorts of data such as windspeed sunshine precipitation cloud coverage and temperatures For us only the cloud coverage and temperature data are important When reading data from their database 1t should be taken into account that all the temperatures are presented in units of 0 1 C and hence needs to be converted to units of 1 C first Cloud coverage is expressed in special units of oktas or octants This unit indicates how many eights of the sky are covered in clouds It ranges from 0 to 8
49. nect a laptop to the router or switch To deal with the IP addresses we have two choices configure the Pi to handle them or use a router While the router might save us some work we chose to configure the Pi to act as a DHCP server and hand out the IP addresses To do this we used the dnsmasq tool a free DNS forwarder and DHCP server The configuration file is in Appendix F The network was set up in such a way that the Pi and the GPIB controller have a static IP so that we know for sure they are at those addresses The address of the laptop is not important as we do not need to address it The user should now establish an SSH connection to the Pi The IP addresses are set as 192 168 0 15 for the Pi and 192 168 0 142 for the GPIB controller The Pi now automatically assigns addresses between 192 168 0 20 and 192 168 0 100 to other connecting devices All scripts are executed on the Pi They should therefore either be written on the Pi or be transferred to it beforehand Normal observers should connect to the Pi with the observer account with password observer 4 4 2 Observing with the Telescope Once logged in the user should change directories to the Desktop folder where the main script for controlling the telescope is located ScopeServer This script should be run with the sudo command otherwise control through the GPIO pins is not possible When run the script will try to have all GPIB connected devices identify themselves to make sure all the requ
50. ny times It had not missed any steps during the tests so the error is negligible A stepper motor consists of two parts a stator and a rotor Figure 12 shows this basic structure The stator is the outer ring consisting of electromagnets with teeth Each pair of opposing poles of electromagnets is called a phase Most common is the 2 phase stepper motor Adding more phases will give a higher resolution 1 e a smaller angle per step Recently 5 phase stepper motors have achieved higher resolutions and more steps per revolution A 2 phase motor has four poles per phase while a 5 phase motor for example has two poles per phase In Fig 12 we see a 2 phase and a 5 phase motor with the phases labeled It might seem that the 2 phase motor actually has four phases but this is because it are actually two motors together For 2 phase motors the coils usually have a center tap which allows for easy reversing of the magnetic poles without switching the current direction This is called a unipolar motor The rotor is the inner disk This disk has magnetized teeth all coming in north south pairs Once a phase is turned on some of these teeth on the rotor will be out of alignment with those on the stator Magnetic forces will now pull the rotor in alignment with the stator the step To move the motor the phases are turned on and off in a certain sequence Orientalmotor 2015 These sequences are determined by so called drive methods There are three main dri
51. r e becomes increasingly smaller This reduces the signal from the CMB and increases that of the atmosphere For comparison the contribution of the atmosphere is 2 97 K for t 0 01 while it is 14 53 K for t 0 05 assuming T 298 K Besides increasing the opacity clouds will also make it non uniform over the area of the beam This adds another complication in accounting for the contribution from the atmosphere In Fig 9 we see the cloud coverage as measured by the station in Eelde We see that the data is spread out through the plot filling the entire 0 to 9 scale It does however seem to tend to the higher cloud coverage values on average To get a better view of the data we took the average per month The results of this are shown in Fig This confirms the earlier statement of higher overall cloud coverage Even in the months that were good in terms of atmospheric temperature the sky is still covered in clouds for the most part This is not completely unexpected Even if there would be days of little to no cloud coverage these are averaged out by days of high cloud coverage It would be quite rare for an entire month to have a low cloud coverage Finally we split the data by part of the day like for the temperature to see if it changes significantly Figure 11 demonstrates this but the results are inconclusive Appendix B has the plots for the other years but they do not give usable information either 18 SUIUDAD PUL uoouiojje Su
52. r motors in particular are limited by the amount of torque they can produce The highest torque is gotten from the lowest rotation speeds The faster it spins the less torque it can generate This means it might not be able to start at full speed More advanced control schemes with for example acceleration towards maximum speed can solve this A more powerful motor can generate more torque and would therefore be able to drive the horn at higher speeds right from the start Another option would be to implement more advanced control of the motor The motor has a recommended operating voltage but it can endure much higher voltages when moving 47 Applying a higher voltage gives the motor an increased torque allowing it to start faster The downside to this is that higher voltages also induce higher currents and hence increase heat output If the motor becomes too hot it can potentially damage or kill it This can be circum vented by having the voltage gradually increase as the motor gains speed and decrease as it slows down 7 4 More Powerful Hardware The last and most profound changes can be made at hardware level The Pi is now the main unit that both controls all devices and processes all signals To reduce the load on the system the control could be split up across multiple units An example would be to use separate units for moving the motor and for reading the power meter and temperature sensors These would then still be controlled from th
53. rage octants m ON FO O O ON O O O O N Z O O O O N O O O 1 2 3 4 5 6 7 8 9 1011 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 Day Figure 37 Cloud coverage of June 2012 separated by part of the day 60 Average Cloud Cover by Part of Day for June 2013 Night Ep d Cloud Coverage octants I O N FO WO O O N O O O O N FOO O O N O O O 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 Day 1 2 3 4 5 6 7 8 9 1011 12 Figure 38 Cloud coverage of June 2013 separated by part of the day 61 C Telescope Server usr bin env python THHEHIEIHHHHBIEHHBHHHBEHHHHHHHE Regular Python modules THBHEHIEIHHHHPIEHHBHHHBEHHHHHHHE from future _ import division import numexpr as ne import datetime as dt import errno import os import readline import sys try import RPi GPIO as GPIO except RuntimeError print Error importing GPi GPIO Try running as root THAI AAA Radio telescope modules THIBETHIBIBERHIDIBEIHIBIHEHHDIHHHIBIHERHIDI E import StepperMotor as sm import GPIBComm as gc THHHBHHHHHHHHHBHHHHHHHHHBHHHHBHHHBHHBHHBI Server constants and functions THHEHBHHHHHHHHHBHHHHHHHBHHBHHHHBHHHBHHBHBI YELLOW BOX IP 192 168 0 142 PORT 1234 label m calib rot park prep turbo funct_m m calibrate m rot m park m prep m set_turbo label c measure speed speed send unit funct_c c measure c set_meas
54. rogramming language making developing with it much more convenient Being able to program on the device itself is also a plus for quickly making small changes later on Arduino specifications are taken from http www arduino cc en Products Compare Raspberry Pi spec ifications are taken from https www adafruit com datasheets pi specs pdf 24 Finally the Pi is the most future proof should upgrades e g more sensors be desired in the future It is for these reasons that the telescope will be controlled by a Raspberry Pi B 4 2 Controlling the Motor 4 2 1 Stepper Motors To control the elevation of the horn we used a stepper motor A stepper motor divides a full rotation into a number of steps of equal size Applying an electrical pulse moves the motor one step This allows for the precise control of the position of the motor Since it moves in discrete steps we can determine its position simply by counting the number of pulses we sent to it This eliminates the need of external tools for measuring the position There will be an error associated with the angle moved due to the possibility of missed steps A great property of stepper motors is that this error is non cumulative One step will therefore have the same error as a million steps Ericsson We will not account for this error in the position The reason for this is that we tested the motor multiple times by letting it move to various angles and then return to the park position ma
55. rs hot 1 cold 2 atm 4 self send KRDG d n sensors sens res self read prnt False return res read self prnt True maxiter 2 Read responses from the buffer Keep looping until we receive None to make sure we have the response Args 65 bool prnt print the output to the console default is True int maxiter number of secondary attempts to make when response is None default is 2 Returns str data or None response of the GPIB controller data None itr 0 Keep reading until we have everything while data is None and itr lt maxiter try Query the yellow box to speak to us self sock send read r n Read from the socket strip all whitespace spaces LF CR etc on the right end data self sock recv 4096 rstrip except socket timeout No response or empty Lines pass finally itr 1 if prnt print data return data def send self cmd Send a command to the GPIB controller Args str cmd command to send Returns bool True False success or failure of sending the command try self sock sendall cmd Nn return True except return False def set_measurespeed self rps 20 avg 1 Sets the integration time of the telescope by specifiying the readings per second and the number of averages taken for a measurement Args int rps readings per second Available 20 40 or 200 int avg number of averages for a measurement Available 1 2 4 8
56. ru1oui qustru ui0310q 03 doy Wor Aep oy jo wed Aq pajexedas prog un jo senje1oduro 9 a3m314 Aeg DE ec 8c LC 92 GZ vc El 22 TZ OC GT 81 LT 9L ST PI EL ZIT TTOT 6 8 9 G v E C T DE DuiusS 3 uoouJs9j Jv y sunqesedway DE JUBIN yTOZ eunf 104 Aeg jo Hed Ag seinjessdwe abeJlany 19 UNVUIUTU n g D PIDAR MO 9 UImulrxeur Poy uomneorpur poos Y AIS Mq PEX JOU I s oqe YJUOU oY IBI y Jo sKep 103 sjuej9o ut 98eJ9A02 pno O 6 9INSIH 220 AON po das ny n unf Aew udy sew qay uef 229 AON YO das ny n unf Aew Adv sew qej uef 22 AON po das ny n unf Aew dy sew qe4 uef Tout soe ae oye T X X o o yet i o o fwy o ol a x x pe HIRT TE w 3 E AT x x ST0z us vTOZ iu 229 AON po des ny n unf Aew ady sew qej uef 229 AN YO des ny n unf Aew Jdy sew qe4 uef OMS gt a 506 o IX X gt O Bac rg 8 OO X XQ x xxx Xx tuu d X ban pee aut i x lt X Ban L unu L x x rout L x x Bao Lee unu LEAR unu T x x S1ue320 abe1an0 pno 5 croce 229 AON po des ny n unf Aew ady sew qay uef OR X OXX G Coe gi i q x ox x x80 x e 999009 x x e xe e e e O o X ego a Uut L x x p fav Lee unu Jj X X urnu s L X X xo unu L x x 8002 Aeq 1ed Bei Ao2 pnoj 20 Umnuirurui on q DSBIDAR MO 9 umulIXeui PIY ISPIDAL IY Jo uorerAop prepuejs DU SAL SIPQIONIO ou ujuoui
57. s The main purpose of this telescope was to be able to measure the temperature of the CMB The CMB is a near perfect black body radiating at a temperature of Temp 2 72548 0 00057 K 2009 For designing the back end it is important to know what order of power we are receiving Black body radiation is characterized by the Planck spectrum 2hy 1 Bug c exp hv kT 1 7 where h is Planck s constant v is the observing frequency c is the speed of light k is the Boltzmann constant and T is the temperature of the black body Figure 3 shows the spectrum of the CMB The peak of the signal lies at a frequency of v 160 GHz At this frequency the CMB has a brightness of B 3 88 10 16 W Hz m sr The available hardware however will limit us to a range of frequencies between 4 and 11 GHz In Fig 3 we see that this range is at the faint end of the CMB spectrum Therefore we chose the highest possible frequency of 11 GHz This gives a brightness of B 9 29 10 1 W Hz m sr The atmosphere will both attenuate the CMB signal and add to the signal 2015 This will result in an antenna temperature of Ta Teme Tatm 1 8 Assuming Temp 2 72584 K T 283 K and t 0 05 see Mulder 2015 when looking at zenith we can make an estimate of the antenna temperature and the received power Using Eqn 8 the antenna temperature is T 16 4 K The incoming power follows from multiplying Eqn 4 with the bandwidth The ef
58. sets the number of readings averaged for a measurement speed Queries the current speed setting turbo 0 1 Switches speed settings for rotation 36 5 Measurements of the Sun The ultimate goal of this telescope is to measure the temperature of the CMB It is nice to check though if we could observe more sources with it The Sun for example is a near bright source so it would be nice to see if we are able to measure it with our telescope We also look into the possibility of detecting some of the brightest radio sources in the sky besides the Sun 5 1 Solar Emission Emission from the Sun has multiple origins Charged particles accelerated in the Sun s magnetic field will emit radiation via mechanisms such as synchrotron radiation free free emission or a form of gyro radiation This is mainly important for sunspots however The conditions in these areas allow for gyro resonant emission which is an efficient emission mechanism coming from electrons rotating around the magnetic field lines 2007 Another part of the emission comes from thermal radiation If we consider the Sun to be a black body with a temperature equal to its surface temperature it will radiate according to Planck s law Eqn 7 with T 5778 KE Sunspots are part of the active Sun while the thermal emission comes from the quiet Sun Fig 21 shows spectra of different sources We see that at 11 GHz the contribution of the active Sun and quiet Sun are nearly equal and be
59. ssary to both move the telescope and provide a means to collect the data and I carried out observations of the Sun Finally Willeke Mulder focussed on calibration of the telescope to look into the stability of the system and receiver temperature which is crucial to know if we are going to measure the CMB for which she also did the observations Summary This thesis will present my contribution to the project The first two chapters will cover material that is not directly related to controlling the telescope since during this time it was still under construction The material presented here is general information that is useful to know In Chapter 2 I will first look into some basic theory behind radio astronomy to see what kind of signal we are actually receiving when doing observations and how the error in this signal comes to be Chapter 3 will next look into the weather conditions in Groningen and the effect observing conditions have on the measurements The fourth chapter will be a more practical section about the electronics and the software for operating the telescope Chapters 5 and 6 will present observations of the Sun and discuss the possibility of detecting other sources respectively at 11 GHz Lastly Chapter 7 will have a discussion about possible improvements for the control of the telescope and about the results of the observations 2 Radio Astronomy Theory This chapter will give an explanation of what signal the telescope will recei
60. t E4418B Power Meter User s Guide Agilent Technologies 2013b Programming Guide E4418B E4419B Power Meters Baars J W M Genzel R Pauliny Toth I I K and Witzel A 1977 The absolute spectrum of CAS A an accurate flux density scale and a set of secondary calibrators AAP 61 99 106 Bernard F Burke F G S 2010 An Introduction to Radio Astronomy Cambridge Committee on Radio Astronomy Frequencies 2005 CRAF Handbook for Radio Astronomy European Science Foundation 3 edition Ericsson Industrial circuits application note Stepper motor basics Last referenced 10 06 2015 Fixsen D J 2009 The Temperature of the Cosmic Microwave Background The Astrophysical journal 707 2 916 Heraeus 2013 Housed Platinum Resistance Temperature Detector SOT223 ICS Electronics 2009 IEEE 488 Application Bulletin GPIB 101 A Tutorial about the GPIB Bus Jansky K G 1982 1933 Electrical Disturbances Apparently of Extraterrestrial Origin page 23 Article in the book Classics in Radio Astronomy Jerri A 1977 The shannon sampling theorem 8212 its various extensions and applications A tutorial review Proceedings of the IEEE 65 11 1565 1596 J J Condon S R Essenstial radio astronomy Last referenced on 17 05 2015 KNMI Data aquisition from a script Last referenced 06 06 2015 Lap B 2015 Design of a pickett potter horn to measure the cmb at 11 ghz Lee J 2007 Radio emissions from solar
61. the measurements we have to set up a connection between the Pi and the devices so we can read out values and store them i HEWLETT EAA12A ee E Jj O PACKARD E SERIES CW POWER SENSOR A 100pW 100 mw 70 to 20 dBm 10 MHz 18 GHz 1 j Use with HP EPM Series Power Meter only Maximum power 200 mW peak or average 20VDC must be ed a urn connector nut only to tighten 135 N cm 12 Ib in Figure 15 The equipment used for measuring the power Left power meter Right power sensor Image credit http www sglabs it and http www us instrument com T l g I I 4 BI akeShore F gt E au AUR EOR A we a t z BR lt y i 86 2 3 uwa 718 Temperature kieres a w Figure 16 The Lakeshore 2185 Temperature Monitor used for reading out the sensor Im age credit http www Lakeshore com products cryogenic temperature monitors model 218 pages Overview aspx 29 Table 4 The integration time in seconds as for all combinations of speed and number of averages per measurement Readings Averaged A ESE AE SEE ao 005 oa 02 04 08 16 32 4 3 1 Power Meter The used power meter has a wide detection range capable of detecting signals with frequencies between 100 kHz up to 110 GHz and powers between 70 dBm and 44 dBm Agilent Technolo gies 2013a The power sensor falls nicely within this range being able to measure frequencies between 10 M
62. to the switch and are the devices turned on sys exit 1 Initate a motor and calibrate it to zero m sm StepperMotor 31 29 200 72 m calibrate Set up a directory on the users desktop to store measurements in try os makedirs os path expanduser home os environ SUDO_USER Desktop dt datetime now isoformat 10 replace except OSError as e if e errno errno EEXIST raise try Enter the main Loop while 1 Ready the input inp raw_input gt gt gt cm inp split if len cm gt 1 cmd cm 0 args cm 1 elif len cm 1 cmd cm 0 args else cmd inp lower Process input if cmd quit c quit m quit break elif cmd run User wants to run his her own script f args 0 try execfile f py except Exception as e print e print Failed to execute script elif cmd in CMD_CTRL 63 if len args gt 0 call cmd controller args else call cmd controller elif cmd in CMD_MOTR if len args gt 0 call cmd motor float a for a in args call cmd motor float a if a strip isdigit else a for a in args else call cmd motor Special commands starting with elif cmd startswith rot m rot float cm 1 override True elif cmd startswith calib m calibrate override True else c send inp c read except Keyboard
63. ture of the component This can be equal to its physical temper ature but generally is not It is important to note that this relation only holds for the spectral power P The power that the telescope will measure will be changed by both the bandwidth and the gain To convert this into a temperature we will need to correct for these before using the above relation 2 2 2 Propagation of Noise Our telescope uses two amplifiers Zandvliet 2015 Adding more amplifiers naturally adds more noise which can get hard account for as the number of amplifiers increases However we only have to consider the noise coming from the first amplifier This has to do with where in the chain the amplification happens Consider a chain of n amplifiers with effective temperatures Te n and gains G The output of an amplifier is Tout G T Te van Schooneveld 1990 The total noise temperature for n amplifiers is given by Friis formula Wilson et al 2013 La 1 3 dos I edo oq eS d ae Ge UI 5 For a system consisting of two amplifiers this gives an effective temperature of Iz ids que 6 55 e l c Physically this means the following The noise added by later amplifiers is with respect to an already amplified signal This implies that the true noise added by this amplifier is its noise temperature divided by the gain of the previous amplifiers From Eqn lit becomes clear that this rapidly makes the noise added by later amplifiers negligible
64. uld escape It is these first photons that we see when we look at the Cosmic Microwave Background CMB Antennas When charged particles are accelerated they emit electro magnetic EM radiation This is the way radio signals are broadcasted A current in the emitting antenna causes the electrons to be accelerated and emit radiation with a power proportional to the acceleration squared The reverse can also happen EM radiation can accelerate particles This is what happens in a receiving antenna The EM wave causes electrons in the antenna to start moving and create a current This current can then be recorded and is a measure of the power received by the antenna With high angular resolution a source could be resolved and the radiation at various positions could be measured to create e g an image of the source in radio emission The Project The ultimate goal of this bachelor project is to measure the temperature of the CMB To do this we built a computer controlled horn antenna Measurements will involve making sweeps of the sky to measure the power as a function of elevation The project was done by four students each of them focussing on some aspect of the telescope The design of the horn was done by Bram Lap Lap 2015 Next Maik Zandvliet was in charge of constructing the mount and mechanics of the telescope and for designing the back end where the electronics are I am responsible for the control of the telescope I wrote the software nece
65. ures of June 2008 separated by part of the day 53 Average Temperatures by Part of Day for June 2009 Night Temperature K 1 2 3 4 5 6 7 8 9 1011 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 Day Figure 27 Temperatures of June 2009 separated by part of the day Average Temperatures by Part of Day for June 2010 Night Temperature K Evening m TEE 1 2 3 4 5 6 7 8 9 1011 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 Day Figure 28 Temperatures of June 2010 separated by part of the day 54 Average Temperatures by Part of Day for June 2011 Night Temperature K 1 2 3 4 5 6 7 8 9 1011 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 Day Figure 29 Temperatures of June 2011 separated by part of the day Average Temperatures by Part of Day for June 2012 Night Temperature K 1 2 3 4 5 6 7 8 9 1011 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 Day Figure 30 Temperatures of June 2012 separated by part of the day 55 Average Temperatures by Part of Day for June 2013 Night Temperature K 1 2 3 4 5 6 7 8 9 1011 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 Day Figure 31 Temperatures of June 2013 separated by part of the day 56 B Average Cloud Coverage for June 57 Average Cloud Cover by Part of Day for June 2007 Night E Pp Cloud Coverage octants p O N AOOO ONAR OOO ONAR OOO ONAR OOO
66. urespeed c get_measurespeed c send c units CMD_CTRL dict zip label_c funct_c CMD_MOTR dict zip label_m funct_m def call func device args Processes the commands given to the server prompt Call functions specific to a certain device Currently available devices are controller motor Args function func the function to execute str device name string of which type of device to address misc args additional arguments to the function Returns None if device controller if args is not None CMD CTRL func args else CMD CTRL func elif device motor if args is not None CMD_MOTR func xargs else CMD_MOTR func else print Unknown device THHHHHHHHHHHHBHHBHHEE Telescope server 62 FAA AAA AAA AAA AA Server startup Clear the terminal and check if everything is ok os system clear print Kapteyn Radio Telescope Server try See if the yellow box is alive c gc GPIB_Controller YELLOW_BOX_IP PORT c send ver c read Ask the power meter to identify itself c send addr 14 c read prnt False c send xidn c read c send SENS AVER COUN AUTO OFF c read prnt False Aks the temperature monitor to identify itself it responds by itself c send addr 10 c read Default to powermeter c send addr 14 c read prnt False c units dbm except print An error occured Is the Raspberry Pi connected
67. ve methods wave drive or 1 phase full step 2 phase full step and half step Ericsson e Wave Drive Wave drive has one phase on at a time It is the simplest way to drive a stepper motor and the coil activation scheme would be A B gt A gt B The downside is that for a unipolar motor this way does not give maximum torque because only a quarter of the coils is used at any time e 2 phase Full Step For maximum torque the 2 phase full step scheme is better This way two phases are on at all times using half of the available coils The coil activation scheme for this drive method is AB BA AB BA 25 Phase B a e Phase C 2 Phase 5 Phase Figure 12 Schematic drawing of the stepper motor structure Image credit http www orientalmotor com technology articles 2phase v 5phase html e Half Step Half stepping combines wave drive and 2 phase driving This way the motor can rotate half the angle it would with the other two methods The coil activation scheme for half stepping is A gt AB BA gt A AB B BA Stepper Motor Properties Type Unipolar Phases 2 Step Angle 1 8 Holding Torque 9Ncm Operating Voltage 12 V Steps per Rev 200 Table 3 General properties of the Astrosyn Y129 stepper motor The motor driving the telescope is an Astrosyn Y129 2 phase stepper motor Table 3 lists some general information about this motor The most important is that it takes 200 steps for the motor
68. ve and how it will propagate through the system The signal that comes in will be changed both due to atmo spheric effects and noise effects within the receiver For the best detection we want to minimize these effects as much as possible 2 1 Antenna Temperature Measuring a received power is quickly done however the data is unusable until 1t is calibrated to a standard scale In radio astronomy the signals are often calibrated against a temperature From a body with a known physical temperature we can measure the power it emits and use it to set a scale for other measurements The power received can now be related to a temperature the so called antenna temperature The antenna temperature is thus not the physical temperature of the antenna The received power comes from all over the sky including other sources and even ground emission To get the total power we need to account for all of these contributions by taking into account the power pattern of the antenna and the observed brightness of the sky The power pattern is a measure of how sensitive the antenna is to power from a certain direction To get the total power that is received we should thus convolve the observed brightness with the power pattern Ae P 2 B 9 p P 8 p dC Here P is the received spectral power A the effective area of the telescope B the Planck function P the normalized power pattern and the solid angle The integration is over the whole sky As a temp

Computer Control of a Horn Antenna and Measuring the Sun at 11

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