Medicina User Manual THE RADIOTELESCOPE
Contents
1. 8 080 OL range GHz 0 0 Single USB Single USB Conversion GHz 0 18 0 34 0 10 9 Standard parameters of the 2 3 8 3 GHz coaxial receiver It is possible to use the receivers both together coaxial 2 IF outputs one per each freguency and separately 2 IF outputs For the VLBI coaxial observation one channel only for each receiver is used typically the right polarization one this because the Mark IV can handle only 2 IF inputs fo HS Fhe ED r Mai SH Sri gt 2 3 GHz receiver scheme green lines 24 of gt 5 EH ES gt Fay o gt gt vis gt EH gt Eh ds T ei NM 8 3 GHz receiver scheme green lines At 2 3 GHz available bandwidths may be considered less then what reported because of interferences 25 5 GHz Type Cooled Channels 2 Polarization LHC RHC Central frequency GHz 4 875 Noise temperature 44 Useful RF band GHz 4 65 5 15 RF filter width MHz 500 IF filter width MHz 350 Istantaneous RF band GHz 4 700 5 050 OL frequency GHz 1 150x4 OL range GHz 1 138 1 175 ingl B Conversion GHz 22 Standard parameters of the 5 GHz receiver To shift the IF standard band inside the RF band of Av the OL freguency must be changed within the range listed in the table according to the following 4 600 Av Ya EE This receiver will be soon updated the band will become wider2. GHz cm Ne N S w GHz GHz weno tink L 1 4 21 Ihp 31 0 31 3 1 35 1 45 2x80 50 LH L 16 18 27 5 27 6 1 595 1 715 2x80 60 5 2 3 13 ssp sxp 18 6 17 3 2 20 2 36 2 160 40 Coxial 8 3 GHz SS 5 7 50 7 40 4 65 5 15 2x350 44 6 5 7 00 6 50 5 90 7 10 2 400 57 GE x 8 3 3 6 xxp sxp 4 80 5 00 8 18 8 98 2x800 25 Coaxial 2 3 GHz XX K 22 1 3 2 00 2 00 21 86 24 14 2 800 80 KK Tab 4 2 Receivers parameters Name related to the coaxial use Primary Focus Cassegrain Focus Visky receiver maximum bandwidth The receivers label has been assigned only for identification purpose the p and c letters for primary and Cassegrain focus respectively HOW TO READ THE CALIBRATION TEXT FILES See Appendix At 1 4 1 6 2 3 GHz available bandwidths may be considered less then what reported because of interferences Multifrequencies observations can be conducted by quick receiver changes frequency agility LL LH SX SS XX LL LH 46 sec 3 min 20 sec 3 min 20 sec 22 sec SX SS XX 46 sec 3 min 25 sec 3 min 25 sec 26 sec 3 20 sec 3 min 25 sec 3 3 21 sec 3 20 sec 3 min 25 sec 3 sec 3 min 21 sec KK 22 sec 26 sec 3 min 21 sec 3 min 21 sec Tab 4 3 Switching times between receivers COLORI DIVERSI 21 1 4 1 6 GHz Type Hot Channels 2 Polarization LHC RHC Central frequency GHz
3. Kinematics Linear travel x axis mm 160 Linear travel y axis mm 160 Linear travel y axis out of focus mm 2240 Linear travel z axis mm 250 Angular travel x axis 9 4 2 Angular travel y axis 9 4 2 Linear velocity x axis mm sec 55 5 Linear velocity y axis mm sec 17 1 Linear velocity z axis mm sec 48 3 Angular velocity 5 1 9 Tab 3 5 Sub reflector kinematics 17 18 19 4 Front End The Medicina antenna covers the range 1 35 24 1 GHz As shown in the following scheme the receivers installed in the primary focus 1 4 1 6 2 3 8 3 22 GHz share some electronic parts the single sections dedicated to the receivers show the connection lines for each freguency RICEVITORE SXKL fuoco primario Fig 4 1 Primary focus receivers scheme The Cassegrain focus receivers are currently being updating and will soon be substituted with the wider band system developed for the Sardinia Radio Telescope the 6 GHz receiver will be included the new 7 GHz system The taper levels are the following Frequency Taper GHz dB 1 4 1 6 17 2 3 16 5 10 6 14 83 16 22 1 15 Tab 4 1 Taper levels 20 4 1 Feeds and Receivers The following receivers are available click on freguencies for detalis Ban 7 Receiver Beam 7 Receivers Noise __ Calibration Name
4. The following conversion scheme is related to the new receiving system 5GHz CONVERTER 5GHz CONVERTER Cryogenic parts 5 receiver scheme 26 Receiver mounted 5 GHz on the left and 6 GHz on the right CONVERTITORE 5 7GHz em HERRIHDC Ath vita Les ol 164 me Wo eh cu SEE Lork LIESS Me kein 150 Tak 2 HITO citecimento per eventuale OL diccoica 0 1 7 8 9 2 7CHz O L 6 5 7 3 5CHz Conversions scheme 5 7 GHz converter 27 28 6 GHz Hot Channels 2 Polarization LHC RHC Central frequency GHz 6 1 6 7 Noise temperature 57 Useful RF band GHz 5 90 7 10 RF filter width MHz 1200 IF filter width MHz 400 Istantaneous RF band GHz 5 90 6 30 6 50 6 90 OL1 frequency GHz 8 10 8 70 OL2 frequency GHz 2 30 2 30 OL1 range GHz 8 10 9 30 Double LSB Conversion GHz 1 80 2 20 0 1 0 5 Standard parameters of the 6 GHz receiver To shift the IF standard band inside the RF band of Av the OL freguency must be changed within the range listed in the table according to the following Vo 8 10 Av This receiver will be soon updated the band will become wider and the central frequency will be 7 GHz The following conversion s scheme is related to the new receiving system Miog Amplifier AMFW 45 056078 08 L0P 33 dB NF 0 8 dB 33 dB cM Conv
5. 1 406 1 665 Noise temperature 50 K 60 K Useful RF band GHz 1 35 1 45 1 595 1 715 RF filter width MHz 100 120 IF filter width MHz 80 80 Istantaneous RF band GHz 1 366 1 446 1 625 1 705 OL frequency GHz 1 036 1 295 OL range GHz 1 020 1 040 1 265 1 305 Single USB Conversion GHz 0 33 0 41 Standard parameters of the 1 5 GHz parameters The maximum bandwidth is 80 MHz tunable only within the two RF ranges listed in the above table To shift the IF standard band inside the RF band of the OL frequency must be changed within the range listed in the table according to the following RF 1 350 1 450 gt v 1 036 Av 1 595 1 715 gt v 1 295 Av gt 6 22H gt He gt gt gt L EE Hl 242 gt Gx 1 4 GHz receiver scheme green lines 22 gt 99 Een gt Mm 9 9 Vi ut 1 6 GHz receiver scheme green lines At 1 4 1 6 GHz available bandwidths may be considered less then what reported because of interferences 23 2 3 8 3 GHz Type _ Cooled Coaxial Canali 2 Polarization LHC RHC LHC RHC Central frequency GHz 228 V as Noise temperature 40 25 Useful RF band GHz 2 20 2 36 8 18 8 98 RF filter width MHz 160 800 IF filter width MHz 160 800 Istantaneous RF band GHz 2 20 2 36 8 18 8 98 OL freguency GHz 2 020
6. 4 LI Li LI 4 4 8 t u 100 900 100 500 43 443043 b 4 4 1 i Li 4 L 4 b 4 bo 4 t 4 4 I LI 4 4 4 TOTAL POWER DETECTOR 79 A D 16 bit Fig 8 4 Maximum total bandwidths MHz example at 22 GHz At 1 4 1 6 2 3 GHz available bandwidths may be considered less then what reported because of interferences 48 8 3 Polarimeter polarimeter be connected to and receives directly 2 analog inputs from the Front End corresponding to the circular polarizations It supplies 4 outputs on 2x400 MHz sub bands Total power measurement on the two channels Stokes Ij I Linear polarizations measurements Stokes Q U INPUT 2 INPUT 1 Moltiplicatore 2 Umis out monitor out monitor out monitor out monitor TP1mis Omis Umis TP2mis 100m converter controllo Fig 8 5 Polarimeter sketch At 1 4 1 6 2 3 GHz available bandwidths may be considered less then what reported because of interferences 49 8 4 Pulsar 8 4 1 5 The pulsar system has been developed as part of the SRT radiotelescope research Srt Pulsar EXperiment SPEX SPEX is connected with he Mark IV IF distributor and with a further interface MARk IV Interface for Single dish Antenna MARISA these are the ma
7. 8 6 SPEX scheme example at 1 4 GHz band in MHz 50 8 5 VLBI 8 5 1 VLBI observations are handled with the Mark IV base conversion bands splitting A D conversion and the Mark V data storage terminals The Mark V is made of 2 blocks of 8x400 Gbyte hard disks Once the VLBI session is terminated the hard disks are sent to the EVN JIVE correlator Dwingeloo Holland IF DISTRIBUTOR 3 500 900 100 500 IF DISTRIBUTOR 1 amp 2 14 VIDEOCONVERTER Attenuators 100900 100 220 100 500 100 900 100 220 100 500 220 500 28x16 MHz 1 Gbit s HARD DISK A D lt lt 2x8x 400 Gbyte 1 2bit Fig 8 7 Mark IV V scheme example at 22 GHz bands in MHz 8 5 2 e VLBl In order to optimize the data collection time at the correlator it is important to develop a solution for a real time data transfer The telephone network used for internet is not able to handle the huge amount of data resulting from a VLBI session and now is used only during the initial check phase Recently it is wide spread in Europe the installation of fiber optic networks for commercial uses and this new technology has all the characteristics to be used for a real time connection to the JIVE correlator Recently the connection between the Medicina station and the GARR network has been completed It s still not the final solution on the shorter section 40 km by now the backup ring 120 km via Faenza city is used
8. 1 Gbit s Hard Disk 2 x 8 x 400 Gbyte Tab 8 6 At 1 4 1 6 2 3 GHz available bandwidths may be considered less then what reported because of interferences 8 1 Spectrometers 8 1 1 Arcos Arcos ARcetri COrrelation Spectrometer is digital spectrometer developed by the Osservatorio di Arcetri It is connected to the Mark IV and receives 2x16 MHz input from the videoconverters of the terminal The system could handle 2x20 MHz bands anyway the Mark IV imposes 2x0 125 16 MHz bands 2 steps The main constituents are 2 correlation boards 2048 channels in total 2 A D sampler 4 channel sampler boards 2 bit 4 levels 45 IF DISTRIBUTOR 3 500 900 100 500 IFDISTRIBUTOR 1 amp 2 14 VIDEOCONVERTER Attenuators 100900 100 220 dd 220 500 100 900 100 220 100 500 220 500 28x16 MHz TOTAL POWER DETECTOR A D 16 bit Fig 8 1 ARCOS correlator scheme example at 22 GHz bands in MHz 8 1 2 Mspec0 MspecO WEB SITE Italian only This high resolution digital spectrometer installed in 1994 offers from 512 to 131072 channels 2 steps on a maximum bandwidth from 125 kHz to 16 MHz Inside those ranges the resolution is user defined In the following table there are some examples Band Channels Resolution 0 125 kHz 512 0 24 Hz 1 MHz 4096 244 Hz 16 MHz 131072 122Hz Tab 8 7 Resolutions that can be obtained with MspecO The spectrometer receives 1 a
9. 56035 10 1 7229174 10 4 4017117 107 5 5 3473118 10 6 0312044 10 8 2993592 10 6 5 8197959 10 9 4270958 10 6 1824204 107 8 3 7 2457279 10 1 0623634 10 6 1059261 107 22 2 4658337 10 2 0935913 10 4 4252013 107 Tab 5 1 Normalized gain curves coefficients FROM THIS PAGE IT IS POSSIBLE THE DOWNLOAD OF THE UPDATED CALIBRATION FILES 36 The sensitivity can be estimated as follows aT ys AS GyAvt NN a receiver constant 1 Tsys system temperature G gain K Jy Av bandwidth T integration time n integration number Nr available channels 1 2 In the following table the system temperatures and the sensitivities of the Medicina antenna are listed Vo T receiver Tsys na G SEFD Band AS GHz K K Jy Oy MHz mzy 4s Erz 50 58 41 0 120 483 2x80 38 2 16 60 64 36 0 106 604 2x80 478 2 3 40 58 43 0 125 464 2x160 26 0 5 44 50 58 0 169 296 2x350 11 2 57 65 50 0 145 676 2x400 23 9 8 3 25 40 48 0 141 284 2 800 7 1 22 80 145 38 0 110 1318 2 800 33 0 Tab 5 2 Sensitivity of the antenna assuming 1 sec n 1 2 Primary Focus Cassegrain Focus Usually at this freguencies the band used is narrower than the maximum allowed by the receivers beacuse of the interferences 37 6 VLBI Regarding the VLBI observations the Medicina antenna is part of the EVN European VLBI Network since 1984 Some observ
10. Medicina User Manual 32 m Antenna Version 1 Elena Cenacchi Alessandro Orfei Karl Heinz Mack Giuseppe Maccaferri e cenacchi ira inaf it THE RADIOTELESCOPE Last update 20 April 2006 Index 1 INTRODUCTION nini ee ehr 5 2 ANTENNA STRUCTURE 7 2 Azim th rall vid 7 2 2 Primary reflector noie dw GY a 7 2 3 Quadrupod and secondary reflector 000 8 2 3 1 Wobbling see aw ck RON 10 pac sehn 10 2 5 Specification summary 1 1 11 nenn nennen nennen 11 2 5 1 Observation C E 11 25 2 Surface ha a Para Re HYO 11 2 5 3 POE O REP 12 E a FFY 13 31 Primary fOCUS ir een 13 3 2 Cassegrain focus ei ce RYN ERA SARA Ai 14 3 3 Servosystem 6 66 EA RED UDD 16 4 FRONT END e ee 19 4 1 Feeds and receivers 6 6 enean nnn aene nnns 20 1 4 GHZ A 21 GHZ DET 23 5 GHZ aia te
11. O 1 5 29 lt 2 9 22 2 s 0 2 Tab 2 4 Beam and pointing errors The systematic errors are usually quite high Some arcminute Anyway they have been determined according to the antenna position Az El after apposite astronomical observations reference radio sources and a correction model has been derived Once the model has been applied the residual error is 0 13 both in azimuth and elevation exactly as required 2 5 Specification Summary 2 5 1 Observation conditions Precision Normal Survival Parameters Wind continuous Wind gusts Sun Precipitation Temperature Humidity Wind continuous Wind gusts Precipitation Temperature Humidity Wind Precipitation Seismic 11 Specifications lt 25 km h 20 30 km h Absent Absent 25 30 9C lt 90 96 lt 65 km h 50 80 km h Absent 30 50 9C lt 100 200 km h lt 5 cm h snow 0 3 g horizontal Tab 2 5 Observation conditions In survival conditions and when not in use the antenna must be settled at 909 elevation and 1809 azimuth stow position 2 5 2 Surface Accuracy Structural Elements Primary reflector panels Secondary reflector panels Gravitational deformation Total surface accuracy RSS mm RSS mm 90 El 60 EI 0 4 0 35 0 35 0 58 0 19 0 6 Tab 2 6 Surface accuracy at 90 and 60 elevation To estimate the phase error from the surface accuracy the following can be used surf
12. OFF ON OFF 7 2 Mapping Technigues If the radio emission is extended over an area larger than the antenna beam several pointings might be necessary in order to cover the entire area of interest The Nyguist theorem states that the correct source sampling along a direction reguires an angular distance between the pointings of 20 The Nyquist sampling is commonly expressed as 5 fraction ag 0 43HPBW 2D 40 The Medicina antenna mainly offers two mapping techniques Raster Scan The map is obtained through discrete adjacent pointings point and shoot mode At every step the antenna stops and acquires data for the exposure time required The time necessary to cover an area A considering the on source time only with a monofeed system can be roughly estimated with the following tw esp N HPBW N number of pointings single exposure time depending on the sensitivity required The Nyquist sampling is approximated with a 2 beam shift in both directions vertical and horizontal Usually this mapping technigue is associated with an ON OFF technigue therefore the total time necessary to complete a survey is given by tor Coy tto Lor N Cg t sh ON antenna shifting time Position Swiching or secondary mirror shifting time Wobbling The scan can be conducted in several user defined ways the most common is along two perpendic
13. ace accuracy A observation wavelength _ 410 2 rad 12 Usually a maximum tolerable phase error is assumed as 369 0 63 rad so that the minimum observable wavelength is Amin 206 For the Medicina antenna An 16 12mm gt v 1925GHz 2 5 3 Pointing accuracy E IN ITALIANO Precisione di puntamento m pena di van rms arcmin Normale Precisione 0 13 Tab 2 6 Precisione di puntamento 13 3 Optics The Medicina antenna has 2 focal positions e Primary focus F1 e Cassegrain focus F2 6240 Fig 3 1 Optics of Medicina antenna dimensions mm 3 1 Primary Focus With the Cassegrain optic the primary reflector focus is usable only if the secondary reflector is completely retracted Behind the mirror a movable positioner is installed equipped with 3 receiver bays Fig 3 2 Primary focus feed positioner 14 primary mirrror focal length is nearly 10 3 m therefore the focal ratio is F D 0 32 Fig 3 3 Primary focus dimensions mm 3 2 Cassegrain Focus The secondary mirror 9 m from the primary mirror allows the usage of the Cassegrain focus at nearly 20 cm above the reflector s vertex This focus has been studied to offer more adjacent focal positions which can be obtained through the angular movement of the secondary mirror see fig 3 4 Fig 3 4 Cassegrain focal plane At this focus 9 receivers
14. anyway the available transfer rate is already of 1 Gbit sec and it allows to join completely the e VLBI observing sessions By now the antenna has been involved in two experiments one on Janaury 23rd 2006 and one on March 9th 2006 in this second occasion for the first time we obtained the fringes in real time To view a picture of the results obtained from the correlation click HERE 51 The test phase will be made on 16 MHz band than an interface will be developed which will send to the electro optical transducer the whole 28x16 MHz bands IF DISTRIBUTOR 3 500 900 100 500 IFDISTRIBUTOR 1 amp 2 14 VIDEOCONVERTER Attenuators 100 220 100 500 ee 100 900 100 900 100 220 100 500 220 500 Fig 8 8 Mark IV scheme fiber optic link 52 53 9 Remote Control The Medicina antenna can be used remotely at the following locations Istituto di Radioastronomia Bologna section Osservatorio Astronomico di Arretri Istituto di Radioastronomia Noto section Osservatorio Astronomico di Cagliari It is possible to ask for the remote use of the antenna and to do astronomical campaigns even from one of the above mentioned institutes The personnel who already have experience with the Observatory devices can ask the authorization to access the internal net also from other locations through a static IP addressed pc Anyway the availability of this observing mode must be d
15. ations are conducted using only the two Italian antennas Noto and Medicina and the Bonn correlator Once SRT will be operating there will be the possibility of using an all Italian VLBI network I VLBI 38 39 7 Observing Modes 7 1 ON OFF Technigues In order to reduce as much as possible the atmospheric contribution during an observation it is possible to apply some technigues based on at least a couple of exposures one on source and one on an adjacent area OFF source reference position sufficiently free from emission At high freguencies short scale and strong atmospheric fluctuations affect the observation hence the need of guick antenna shifts between the two positions which have to be reasonably next to each other or the usage of other technigues which do not involve the movement of the entire structure The Medicina antenna offers the following ON OFF technigues Position Switching The antenna shifts between two different positions The time needed to cover some beams is nearly 5 seconds at all freguencies Wobbling The shifting of the beam is obtained moving the secondary mirror only This technigue reguires always a shorter time than the Position Switching but it can be used only with the external circumference receivers As the maximum angular travel of the secondary reflector is limited a single OFF position inside the circumference can be setted In both cases the algorithm used is of the type ON
16. can be mounted a central one plus eight around 15 Fig 3 5 Cassegrain receiver bays NORD Fig 3 6 Cassegrain focus dimensions mm The secondary hyperbolic reflector operates a magnification ip which depends on the ratio between the focal length and the distance from the prime focus nearly 20 m and 3 m respectively The total focal length can be estimated as follows i 9 074 0 956 F i F 97 36 m 9 49 The focal ratio is therefore F gt D 3 04 By now at this focus the 5 GHz and 6 GHz receivers are installed 16 3 3 Servosystems Specifications Azimuth drive Unity Value Angular travel 9 540 Kinematics Angular velocity sec 0 8 Angular acceleration 5 0 82 Number of wheels 4 Configuration Driving wheels 2 Drives per wheel 1 Track Diameter m 18 3 Tab 3 1 Azimuth drive Elevation drive Unity Value Angular travel 9 90 Kinematics Angular velocity sec 0 5 Angular acceleration sec 0 31 Tab 3 2 Elevation Drive Primary focus feed positioner Unity Value Linear travel mm 420 Kinematics Linear velocity mm sec 7 2 Linear acceleration mm sec 24 Tab 3 3 Primary focus feed positioner transverse axis Primary focus feed positioner z axis Unity Value Linear travel mm 350 Kinematics Linear velocity mm sec 7 2 Linear acceleration mm sec 24 Tab 3 4 Primary focus feed positioner z axis Sub reflector Unity Value
17. elay which is also function of the frequency If the total delay is comparable to the pulses period the impulsive peculiarity of the signal can be cancelled Hence the need of many narrow adjacent channels that must be revealed and summed with the right respective delay This technique is named coherent dedispersion 42 43 8 The Medicina antenna is equipped with the following processing systems ARCOS Autocorrelator Input 2 Maximum bandwidth per input 16 MHz Minimum bandwidth per input 0 125 MHz Channels 2048 A D Conversion 2 bit Available software ADLB4 Tab 8 1 Can be further reduced on reguest MspecO Spectrometer Total Power Polarimeter Input 1 Maximum bandwidth per input 16 MHz Minimum bandwidth per input 0 5 MHz Channels by choice 512 131000 A D Conversion 10 bit Available software SPETT Tab 8 2 Input 3 Maximum bandwidth per input 400 MHz A D Conversion 16 bit Available software ON OFF Tab 8 3 Input 2 LHC RHC Maximum bandwidth per input 400 MHz Stokes output Digital Q U POLSCHED Available software POLMED Tab 8 4 44 e Pulsar SPEX Input 2 Maximum bandwidth per input 64 MHz Filters 4 x 32 x 1 MHz A D 16 x 8chx 1 bit Data acquisition 3 15 us Timing precision lt 1 us Tab 8 5 e VLBI Mark IV Mark V Input 2 Maximum bandwidth per input 400 MHz Output by chance 28 x 0 125 16 MHz A D Conversion by chance 1 2 bit Data transfer
18. erter 7 GHz OMT gt Noise COM NC3205A Mini Hybrid Narda 4032C Directional Coupler Flann 14270 30 33 7 GHz receiver scheme nex RE 3 A nate OU FST SHT Ud 120 T4 time stout pov TIS RLC PF 254 1 Lon al 164 ho Len of Conversion scheme HITO cifeci ento pec eventuale OL diccoico O L 7 8 9 2 7CHz 8 2 6 5 7 3 29 30 5 7 GHz converter 31 22 GHz Cooled Channels 2 Polarization LHC RHC Central frequency GHz 22 464 Noise temperature K 80 Useful RF band GHz 21 86 24 14 RF filter width MHz 2300 IF filter width MHz 800 Istantaneous RF band GHz 22 064 22 864 OL1 freguency GHz 1 7355 x8 OL2 freguency GHz 8 080 OL1 range GHz 1 710 1 945 Double USB Conversion GHz 8 18 8 98 0 1 0 9 Standard parameters of the 22 GHz receiver To shift the IF standard band inside the RF band of Av the OL frequency must be changed within the range listed in the table according to the following _ 21 964 8 080 Vor 8 al 2 4 II Schema del ricevitore a 22 GHz evidenziato in verde E IN ITALIANO 32 4 2 Distribution connections between the radiotelescope s foci involve three different kinds of signal Local Oscillator in order to cut down the expenses related t
19. g 2 1 First solution Then a more efficient solution in terms of endurance was proposed and metal plate was interposed between the rail and the grout basement Fig 2 2 Installation of the metal plate antenna lifted and finished work the plate and the basement are both white painted 2 2 Primary Reflector The primary reflector diameter 32 is made of 240 aluminium panels RMS 0 4 mm substained by a backup reticular truss The housing of the Cassegrain focus feeds is at the mirror vertex Fig 2 3 Primary reflector front D2 Di gt C1 D1 D2 mm mm mm Raw B 2617 8 437 62 1113 96 RawC 2604 15 1113 96 1770 4 RawD 2617 24 887 1 1206 06 Raw E 2648 38 1206 1515 Raw F 2659 33 1515 04 1810 74 Raw G 2718 1810 74 2098 14 Tab 2 1 Geometry of the panels 2 3 Quadrupod and Secondary Reflector The primary reflector backup structure substains the secondary mirror placed at a distance of 9 m through 4x45 inclined beams guadrupod The secondary mirror is hyperbolic reflector 3 2 diameter made of single aluminium panel rms 0 35 mm On the backup structure 3 mechanical actuators installed and allow the mirror to tilt around the 3 axis Besides the whole system can translate along the x and y axis 2 1 2 conto 3 4 5 Amor Z Fig 2 4 Hyperbolic mirror The mirror must co
20. hown in the following red line and green line are fiber optic links PRIMARY FOCUS ROSSO F O PUNTO PUNTO BLU DOPPINO TWISTED PAIR VERDE LAN FO ACU Drive Cab Metrology CONTROL ROOM Fig 4 3 Control links From the control room it is possible to act on receivers antenna s movement and sub reflector s movement Besides it will be possible to interact with the new metrology system temperature sensors and a little optical telescope installed at the Cassegrain focus projected for SRT and that will be tested on the Medicina s antenna The control room is part of the Observatory LAN at nearly 500 meters from the antenna 34 35 5 Efficiency and System Temperature The antenna gain is defined as G 1075 14 B k Jy B m 0 5 non polarized radiation Ag geometric area Boltzmann s constant antenna efficiency B For the Medicina antenna the constants are 1075 s 0 292 2 k B nais the overall efficiency estimated assembling all the signal degradation factors The antenna gain varies according to the elevation and it reaches a maximum at 45 A good interpolation is obtained with a second degree curve such as bx c The coefficients of the normalized polynomials at each frequency are listed in the following Frequency GHz a b C 1 4 6 8310687 10 7 285044 10 8 0577027 10 1 6 2 6828893 10 3 4836402 10 8 869153 10 2 3 1 32
21. in characteristics of the whole system 4x32 MHz inputs divided in 1 MHz channels through 2 filterbanks 64 channels for each polareization realized by the Jodrell Bank Observatory 1x128 channels filterbank with 2 poles active filters central freguency programmable 0 9 kHz 1 kHz 5 kHz 10 kHz and anti aliasing function Interference monitoring system 128 channels 0 4 Hz anti aliasing filters 12 bit acguisition converter 128 channels 1 bit per channel Reference time signal generator for the programmable sampling synchronized with the hydrogen maser and the 1 PPS signal inside the observatory The time allocation of the signal with respect of UTC has a precision of less than 1 microsecond Interface board FEMB between the A D and the link Slink CERN to the user s pc Link Slink trasmitter and receiver trasfer s rate 133 Mb s User s pc Pentium III 500 MHz with RAM 128 Mb system Linux Red Hat 6 1 with the necessary software for the data processing coherent dedispersion Tape recorder DLT single tape storage 20 Gb GPS receiver Motorola Oncore UT for the synchronization of the user s pc internal clock MARK IV IF DISTRIBUTOR 1 IDEOCONVERTER Att t 330 410 ad dc H MASER 330 410 5 330 410 330 410 A D 16 x 8 ch 1 bit FILTERS 4 x 32 x 1 MHz FEMB MARISA ANTIALIASING FILTERS 4 x 32 330 394 330 394 PC LINUX 20 GB M Fig
22. iscussed on a case by case basis The ARCOS autocorrelator is still on updating and by now doesn t offer the remote control mode 54 55 Appendix How to read the calibration files The calibration files are text file with the rxg extension and are computer generated after the calibration operations For each receiver they contains mainly the FWHM the gain curves and the calbrations temperature as function of the freguency The calibrations temperature are given for fixed freguency values in order to cover the whole receiver s band The calibrations values for not listed freguencies must be interpolated from the nearest values The following table shows how to read the data Line Label Description 1 Receiver name 2 Fixed values MHz Range LO range of values MHz 3 Creation s date yyyy mm dd 4 Constant FWHM rad Freguency FWHM constant FWHM 1 22 value A D rad Available polarizations 6 Maximum gain DPFU for each polarization as listed above K Jy Elev Poly G el Normalized gain curve s polynomial coefficient increasing 7 powers Altaz G z Normalized gain curve s polynomial coefficient increasing powers 8 Polarization Freguency MHz Calibration temperature following D diameter of the antenna DPFU Degrees Per Flux Unit el elevation 7 zenith distance
23. mpletely be retracted along the y axis when the primary focus is used Fig 2 5 Configuration for Cassegrain focus usage plain line and primary focus usage dotted line The mirror and the guadrupod induces an obstruction on the primary reflector of nearly 4 Cause Obstruction Sub reflector 2 Quadrupod 2 Total 4 Tab 2 2 Primary reflector obstruction 10 2 3 1 Wobbling The system that rotates the secondary mirror has been optimized in order to enhance the number of receivers that can be installed at the Cassegrain focus Anyway for the receivers installed in the external circumference the same movement can be used for the Wobbling technigue Typical shifting times guite more advantageous if compared with the Position Switching technigue are listed in the following table Freguency HPBW nro eeu Required time Required time ES 2 5 beam 5 beam GHz C 9 sec 9 sec 5 450 2 56 1 16 5 12 2 12 6 390 2 22 1 03 4 44 1 86 22 120 0 68 0 45 1 37 0 71 Tab 2 3 Wobbling time for 2 5 beam and 5 beam 2 4 Pointing Errors The accuracy of the pointing correction increases with the observing frequency i e as the antenna beam width decreases It is commonly assumed the following HPBW 10 Op pointing accuracy HPBW 3 dB beam width main lobe For the Medicina antenna the values are listed in the following Frequency HPBW Error GHz O
24. nalog band from the Mark IV digitizes it and applies an high efficiency FFT algorithm The main components are 1 Ultra ADC A D board 1 VT 524 board 2 UltraDSP 1128 board equipped with 2 LH9124 processors VME environment The processors run in parallel and operate the 24 bit 256000 spectral points Fourier transforms The resulting spectra are integrated on the VT 524 board 46 DSP boards completely programmable through the VME bus VT 524 board also allows the results to be shown in real time as they are processed the time reguired for the processing of a single spectrum is nearly 1 ms The spectrometer is TCP IP connected to an external PC equipped with the Spett software which supplies the user interface in order to set the control system channels number sampling freguency number of spectra to be averaged number of On Off cycles and which is integrated in the Field System software for the antenna set up pointing observing freguencies etc The same PC is used to see the results during the observation IF DISTRIBUTOR 3 500 900 100 500 IF DISTRIBUTOR 1 2 14 VIDEOCONVERTER Attenuators 100 900 100 220 100 500 lt 220 600 1002 900 100 220 100 500 d 220 500 MSPECO 1x16 MHz Ultra DSP 1128 i i Ultra DSP 1128 Fig 8 2 Mspec0 scheme example at 22 GHz bands in MHz 0 125 MHz and 1 MHz band are available
25. nse ea svi tois etin DAD wanes 25 ECL IDEE 28 22 Sc 31 4 2 Ree Pee eade x rac e ERN RE MR oe ete PA UR 32 4 3 Control OOM ve ka va even ene TAL OVER AY V VR a EA 33 5 EFFICIENCY AND SYSTEM TEMPERATURE 35 VLBI ia 37 7 OBSERVING MODES eiii ai a Baba ERE ND LER RAS 39 7 1 ON OFF techniques ci Fake Rx a XXX HERR ERR EAR OA ER UE Sie an 39 7 2 Mapping techniques 0 1 1 messes semen messen seen nenne 39 7 3 Pulsar en ea 41 8 BACK END rrr A UK n RAO OFYN A KEEN RD 43 8 1 Spectrometers au A ana 44 8 1 1Ar608 an ne a Rene 44 2 A DS M MEL 45 8 2 CONTINUUM eek 46 82 2 IV 46 9 3 ROME ind pa E 48 8 4 Pulsar iii ad FAR 49 SPEX d TP 49 Oo eet 50 8 5 1 Mark IV aan a a a neh 50 30 20 VEB EFE rasen a a Dr FF FOR ia 50 9 REMOTE CONTROL ee en Pe 53 APPENDIX HOW TO READ THE CALIBRATION TEXT 55 1 Introduction The Medicina 32 m antenna is a Cassegrain radiotelescope operating since 1983 managed by the Istituto di Radioastronomia until 2004 part of the CNR Consiglio Nazionale delle Ricerche and no
26. o the construction of an high number of independent superheterodyne recevers a very common solution is to share some local oscillators at least for one conversion A single local oscillator therefore can serve more receivers through a signal distribution system IF the RF signals once received and converted by the Front End are sent to the Back End installed in the Control Room at the antenna s base Reference 5 MHz H maser signal necessary for the local oscillator stability the signals are distributed via coaxial cable The distribution scheme is simplified by the fact that there are only two double conversion receivers 6 GHz at the Cassegrain focus and 22 GHz at the primary focus and both use the same local oscillator for the second conversion Besides the two receivers channels can t be placed in different position inside the RF bandwidth The OL signal is distributed by and OL distributor OLD The reference distributor REFD and the IF distributor IFD are also installed at the Cassegrain focus From the control room it is possible to choose the receiver through the selector PRIMARY FOCUS CONTROL ROOM Fig 4 2 Signal distribution between the foci 33 Fig 4 3 Distributors reference signal on the left and local oscillator on the right 4 3 Control Room The backend systems are installed in the control room located at the antenna s base It is connected to the foci through the links s
27. only with external filter please ask if available at the site 8 2 Continuum 8 2 1 Mark IV The Total Power observations use the Mark IV terminal and the Field System software The terminal is made of two parts IF distributor receives the input from the Front End and splits them in sub bands Videoconverters 14 unities that operate the base band conversion and the integration It is possible to choose between two outputs 28 narrow bands minimum width 0 125 MHz maximum 16 MHZz central frequency user defined maximum total bandwidth 400 MHz 47 DISTRIBUTOR 3 500 900 100 500 IFDISTRIBUTOR 1 amp 2 14 VIDEOCONVERTER Attenuators 100900 100 220 100 900 100 220 100 500 220 500 28x16 MHz TOTAL POWER DETECTOR A D 16 bit Fig 8 3 Maximum bandwidths MHz processed by the Mark IV example at 22 GHz 0 125 MHz and 1 MHz band are available only with external filter please ask if available at the site B Processing of the whole inputs 2 400 MHz centered at 300 MHz and 1x400 MHz centered at 700 MHz IF DISTRIBUTOR 3 500 900 100 500 IF DISTRIBUTOR 1 amp 2 14 VIDE OCONVERTER gomme O qn m qq em mmm quan open em 4 b 4 1 4 b 4 b 4 b 4 i b 4 b 1 4 b 4 b 4 4 4 Attenuators ae 3 4 4 IA 9 bs 4 4 1 b 4 Li 4 100 500
28. ular directions cross scan On The Fly In the On The Fly mode the antenna is moved along one direction usually with a raws and columns path at constant speed The data are continously acquired and downloaded by the backend every few seconds OTF dumps corresponding to angular excursions of few arcseconds depending on the antenna speed To reach the required sensitivity it is necessary to scan the same area several times preferably along different directions The ON source time is t acquisition time Na number of dumps depending on the required sensitivity The Nyquist sampling is obtained if the acquisition time for each dump corresponds to an angular antenna shift equal or shorter than the ideal Nyquist distance Also the distance between raws and columns must be coherent with the Nyquist sampling 41 On The Fly technique is characterized by very short scanning times so it is the best one in order to reduce the atmospheric contribution anyway it is necessary to use an ON OFF technigue For a sguared spectroscopic map the total observing time is estimable with the following Eon Coy Core Lor yN Eon The Medicina antenna offers the On The Fly Mapping on a user defined RA Dec map with a maximum scan s speed of 200 s this technique has been tested and used only for polarimetric observations 7 3 Pulsar The radio pulses observed from pulsar sources meet with a d
29. w part the INAF Istituto Nazionale di AstroFisica Fig 1 1 The Medicina antenna The main features of this instrument are the following e Frequency agility the observing frequency can be changed ve uickly tmax 4 min e Secondary reflector wobbling shifting time lt 1 sec Gi STUD e Complete automation and remote control of the observing settings Position Medicina BO Italy Coordinates Lat 44931115 N Long 11938 49 E Alt 25 m f s l Optics Cassegrain Freguency coverage 1 4 22 GHz Primary reflector diameter 32 m Secondary reflector diameter 3 2m Primario f D 0 32 Available foci Cassegrain f D 3 04 Elevation range 0 90 Azimut range 270 Slew rates wind speed lt 60 km h ot 2 Surface accuracy rms specified 0 6 mm Pointing accuracy rms specified 8 arcsec FWHM Beamwidth 38 7 arcmin f GHz Gain 0 10 0 16 K Jy First secondary lobes 20 dB under the main lobe Primary focus movable positioner 3 receiver bays Cassegrain focus fixed 9 receiver bays Receivers mounts Tab 1 1 Characteristics of Medicina s antenna 60 Elevation TOP of poot yn x Fig 1 2 Medicina s antenna side 2 Antenna Structure 2 1 Azimuth Rail The whole antenna leans upon the azimuth rail which has a 18 3 m diameter and has recently 2001 been renewed Until 2000 the rail was directly substained by the grout basement see 2 1 Fi
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