Tuning the T4 Science hydrogen maser
Contents
1. Freq Synth 14 9 2009 Initial monitor 1420420877 00495 810 Before OK 1420420877 00495 1420405750 301044 After OK 1420420877 00495 1420420877 004959 After closing window 1420420877 00495 1420405750 299908 Freq Synth and reopening it After closing window 1420405750 29990 Freq Synth Table 2 Windows appplication behaviour 4 FREQUENCY CORRECTION 8 The windows application was used for the last time on September 14th 2009 After that date the Linux code was used 4 Frequency Correction The 5 MHz master oscillator OCXO is controlled by the hydrogen cabin signal 1420 MHz using a loop in which the latter signal is transformed to 405 KHz and compared to 405 KHz derived from the OCXO after multiplications see Maser manual i c avity Varactor voltage J ik ji WE 14204 MEs 100 Bm Ae us v gt A N 20M BW f ve U onii LA VS bom sw NA E 900M Hz SRD 1400 MHz meg diker 120 ut xy VW TF 20405 MES 0 Bue A i lt 00 MHz gonz F 14204 MBs 80 dBm IF 4 59 MHs 40 Bu lt I IF 405 3Hs 10V lt k j OCXO Vor f Phase Vaan lui Le 105 KHz 5 MHZ un AN 8 Figure 4 PLL iMaser scheme The OCXO frequency adjustment is done tuning the frequency of the 405 KHz synthesizer This procedure differs from that used with the KH 75 maser from Kvarz in which the cavity was tuned using an electronic varactor Let f be the hydrogen2. Hz New Frequency Synthesiser freq to apply 632264BB hex Do you want to apply this correction 8 4e 13 y n y Applying the correction Frequency Synthesiser freg after the correction 632264BB hex Maser frequency after the correction 1420405750 298716 Hz The applied correction should have the same sign as the measured drift When the measured drift is positive the maser frequency is higher than the GPS synthesized frequency This should be checked after the correction has been applied In the previous example a positive drift was measured and applied The maser frequency before the tuning was 1420405750 2999072 Hz and after the tuning 1420405750 298716 Hz This means that if the last value were closer to the optimal one the maser frequency before the change was slightly higher than the correct one L Barbas has created a database to store information on the maser status a python script to fill it by using the previous Python class and a web page to plot any parameter stored in the database The maser status is requested once per hour and stored in the database The database contains the whole list of parameters in table 3 plus the maser frequency The web page is located in http hera oan es graficas interactivas and can be reached only from inside the private OAN LAN Figure 5 shows a snapshot of the web page that allows to plot any of the previous maser parameters as a function of time The web form is programmed in PHP and
3. byte followed by CRLF This command is used to read the synthesizer values on RAM addresses OE OF 10 and 11 WXXYY CRLF Used for writing data Y Y at address XX in the RAM This command is used to modify the synthesizer values and hence the hydrogen output frequency RAM addresses written are OE OE 10 and 11 The monitor parameters are read and transformed from hexadecimal to integer and multi plied by value in column 4 of table 3 to obtain the physical unit from the hexadecimal byte readout The following high level functions have been implemented in the maser python class to monitor the status and modify some of its parameters readRAM addr Function which read RAM registers and returns a two byte hexadeci mal value writeRAM addr value Function which writes a two byte hexadecimal value on the RAM register swVersion Returns a string with the software version activatesynth Activates the synthesizer with new values readAnalogChannelsAndLockStatus Returns a python list with the monitor val ues in meaningful physical units readSynthFregAndACTRegisters Returns a list with the frequency synthesizer and ACT registers Used mainly to get the maser frequency and the current synthesizer frequency as an hexadecimal value computeFrequencyCorrection d Computes the new synthesizer frequency from the current status and a supplied relative error frequency 5 CODE IN LINUX AND DATABASE Channel Descri
4. frequency at the cavity output fo the OCXO frequency and f the 405 KHz synthesizer frequency Then if the system is locked fs fo 5 fo fu 280 fo 1 where 280 and 5 are the multiplying factors to get the mixing frequencies at 1400 MHz and 25 MHz from fo Symplyfing the above equation we get fs fu 284 fo 2 4 FREQUENCY CORRECTION 9 fs is obtained from f applying linear operations So let us write de ks fo 3 where k is a factor which can be changed to modify the 405 KHz signal then 284 S Therefore the frequency at the cavity output can be considered proportional to the frequency from the frequency synthesizer and also to the OCXO frequency From a practical point of view and according to the iMaser manual the hydrogen frequency at the cavity output is fx is fu fuo FM FMO 9 09496 10 5 where FM and F MO are the frequency synthesizer values for the desired frequency and the reference maser frequency fao 1420405751 0000 Hz respectively FM value can be modified by modifying four bytes of the register at a given address 9 09496 1079 corresponds to the frequency synthesizer resolution 5106 6 530 7 9 09496 10 6 Equation 5 relates the frequency synthesizer resolution with the frequency at the cavity output Let us suppose we wish to modify the frequency to correct for a relative error frequency The new frequency should be fy Af fa fa H 7 and hence
5. starts a Python script that uses Matplotlib and MySql and is integrated in the Apache server via the mod python module The web form allows to select the parameter from a combo box the date time interval from a calendar widget the plot title axis labels and the X axis resolution The plot will be shown on a separate tab in 5 CODE IN LINUX AND DATABASE 13 D Centro Astron mico C fi x httpij hera oan es graficas_interactivas Generaci n de gr ficas 40m Radiotelescopio de 40m Maser Generaci n de Gr ficas Selecciona los par metros de los que quieres generar la gr fica batteryVoltageA Maser batteryCurrentA Maser batteryVoltageB Maser batteryCurrentB Maser hydrogenPressureSet Maser hydrogenPressureMeas Maser Rangos Tipo Diaria v Fechas Fecha Inicio yyyymmdd a las 20100307 00 00 horas Fecha Final yyyymmdd a las 20100311 23 59 horas Formato gr fica Titulo fritulo Eje x Tiempo h O dataGraph 2 dat D dataGraph 1 dat ia Mostrar todas las descargas Figure 5 Web page at http hera oan es graficas_interactivas which allows to plot maser parameters as a function of time Hydrogen Pressure Storage 452 450 4 48 4 46 4 44 Hyd Press bar e 0 ETTOL TT eee ee eee 01 0ct09 01Nov09 01Dec09 01 an10 Ol Feb 10 01 Mar 10 Date Figure 6 Hydrogen storage pressure bar as a function of time This graph is a snapshot obtained from th
6. A fuo FM F MO 9 09496 1076 fu fuo FM FMO 9 09496 109 8 and reordering terms Af fu FM FM04 FM FMO 9 f 9 09496 10 6 0 and the new register should be Af fu FM FM4 1 f 9 09496 1076 do 11 where fr is the frequency at the cavity output before modifying the frequency synthesizer Hence FM can be computed from the current FM and fy values provided by reading the current status maser 5 CODE IN LINUX AND DATABASE 10 5 Code in Linux and Database R Bola o has written a Python class which connects via sockets to the Lantronix device and requests the maser its status This class allows to write on some memory registers and modify the synthesizer frequency and hence the output maser frequency 5 MHz The serial commu nication between the Lantronix and the maser is achieved using a baud rate of 9600 bit s No parity 8 data bits 1 start bit and 1 stop bit Table 3 summarizes the monitored parameters The list has been taken from the Maser manual A total of eight commands may be used to obtain the maser status and modify its frequency Here we include the 3 most used ones M CRLF Used for reading the 40 analog channels and lock status The string read has a length of 113 bytes and is composed of 3 bytes per channel channels 1 to 32 2 bytes per channel channels 33 to 40 and 1 bit for the lock status 1 or 0 followed by a CRLF RXX CRLF Used for reading RAM at address XX XX is 1
7. E INSTALLATION Date Time Meas Af f Appl Af f Soft used 03 09 2009 09 20 4 5010 4 510 Windows 07 09 2009 07 15 8 86 10 8 9107 Windows 09 09 2009 07 30 8 86 10 910 2 Windows 14 09 2009 10 15 8 52 10713 8107 Windows 08 03 2010 17 40 2 80 10 13 8 41071 Linux Table 1 Date and time of the tuning The measured drift is the drift up to the tuning date The correction was applied in that date and time There was an error in last correction and a different value from the measured relative error was applied 2e 96 Yebes iMaser SN 37 Drift since installation 1e 96 f 1e 06 2e 06 3e 86 f GPS Haser 4e 06 5e 06 6e 86 7e 06 T iMaser Drift 1 9 2009 to 24 3 2018 8e 06 55050 L 55100 L 55158 HJD 1 1 55268 55258 55368 Figure 3 Maser drift since installation to March 2010 The time units are Modified Julian Days The discontinuities in the line indicate the tuning moments On day 55100 MJD there was no tuning The observed jump is only due to a synchronization but not to a change of drift 3 TUNING AND DRIFT SINCE INSTALLATION 7 3 3 Windows Tuning Application The windows application when opened displays a window frame called Monitoring Param eters which always remains opened and updates the value of some parameters It is possi ble to correct the maser frequency by opening a new window called Frequency Synthesizer The Windo
8. Tuning the T4 Science hydrogen maser P de Vicente S Garc a Espada A Barcia R Bola o L Barbas Informe T cnico IT OAN 2010 1 Revision history Version Date Author Updates 1 0 10 03 2010 P de Vicente First version CONTENTS 2 Contents 1 Introduction 3 2 An overview on the installation 3 3 Tuning and drift since installation 4 3 1 A review on PPS Pulse Per Second comparison 4 32 a toe pirati derde gh yoke An Hee ree ga NT Ne 5 3 3 Windows Tuning Application e 7 4 Frequency Correction 8 5 Code in Linux and Database 10 1 INTRODUCTION 3 1 Introduction A new hydrogen maser was rented from T4 Science and installed in Yebes on August 28th 2009 The model is iMaser EFOS C Serial Number 37 This clock will stay in Yebes until a definitive maser from that same company is built and installed 2 An overview on the installation The hydrogen maser was installed in the maser room located in the basement of the 40 m tower building The maser can be monitored and remotely tuned through a serial port T4 Science provided a DOS program which runs in Windows and allows to monitor a number of parameters and change the output frequency by tuning an internal synthesizer That application was installed on a laptop from the OAN Observatorio Astron mico Nacional The laptop was placed on top of the maser connected to the maser serial port via a serial cable The laptop is only
9. VLBI data acquisition Time Box Both pulses are compared by an HP 53131 A counter with 1 ps accuracy 3 1 A review on PPS Pulse Per Second comparison The 1 PPS from the GPS is received in connector 1 at the HP 51313A counter the 1 PPS from the maser on connector 2 The counter measures the time ellapsed between the pulse on connector 1 and the pulse on connector 2 This value is displayed on the counter screen The VLBI data acquisition time box generates 1 PPS by counting 5 10 cycles from the 5 MHz signal The count starts when the amplitude signal is zero There are two possibilities for this event within a cycle when the ramp is positive or when the ramp is negative The alternative used depends upon the connection of an external synchronizing signal The timing box has got two connectors for an external 1 PPS sync signal which are labelled Input and Input If the sync signal is connected to Input the count will start when the ramp is positive and the signal crosses zero On the contrary if the sync signal is connected to Input the count will start when the ramp is negative and the signal crosses zero Currenlty only Input 1s connected The sync signal is 1 PPS from the GPS receiver Synchronization is achieved by pressing the black button in the Timing Box for more than a second Once the button has been released the timing box will start counting immediately after it has received 1 PPS from the GPS and the 5 MHz amplitude signal i
10. e web form available at http hera oan es REFERENCES 14 the browser If another parameter should be plotted the web form needs to be reloaded and the new parameter and options selected Data can also be extracted and stored in an ASCII local file with two columns date and value Figure 6 shows the Hydrogen storage pressure as a function of time as shown by the web page interface References 1 P de Vicente A Garrigues Monitorizaci n del maser de hidr geno del CAY IT OAN 2005 5 2 P de Vicente J D Gallego R Bolano C Almendros Monitorizaci n del maser de hidr geno antes y despu s del traslado al radiotelescopio de 40m IT OAN 2007 3 3 T4 Science SA Installation Operation and Maintenance User Manual 2008
11. equency error between the maser and the GPS synthesized frequency If the time interval is larger a parabolic behaviour will be seen This means that the maser frequency is not stable and drifts slowly with time probably due to cavity deformations See figure 2 for an example Here the behaviour of the drift for the iMaser since November 2009 to March 2010 is depicted Yebes iMaser SN 37 Drift between Nov 11th and March 8th 1 8e 96 T T T T T novi1ToMarch8 log 1 6e 86 4 1 4e 96 4 1 2e 96 f 4 le 06 7 8e 07 7 GPS Haser 6e 07 4 4e 07 4 2e 07 4 a aw 4 2e 67 L L L L L L 55148 55168 55180 55200 55220 55248 55268 55280 HJD Figure 2 Maser drift between November 11 2009 and March 8 2010 The time units are Modi fied Julian Days The vertical line is due to an electrical power disruption which left the GPS antenna unavailable for 1 day and a half The PPS comparison was trustless during that period 3 2 Tuning history 5 tunings were performed since installation up to March 24t 2010 Table 1 summarizes the date and time each tuning was performed the measured drifts the applied corrections and the application used for the correction The measured drift is obtained from the slope of the graph The maser frequency was corrected using a Windows application running in the laptop up to March 8 2010 Since then this is achieved via a Linux Program as described below 3 TUNING AND DRIFT SINC
12. itude U 405 kHz V 3 662E 03 32 OCXO varicap voltage U ocxo V 2 441E 03 33 24 V supply voltage 24Vde V 9 766E 02 34 15 V supply voltage 15Vdc V 7 813E 02 35 15 V supply voltage 15Vdc V 7 813E 02 36 5 V supply voltage 5Vdc V 3 906E 02 37 5 V supply voltage 5Vdc V 3 906E 02 38 8 V supply voltage 8Vdc V 3 906E 02 39 18 V supply voltage 18Vdc V 7 813E 02 40 Unused Unused 0 000E 00 Table 3 List of iMaser monitor parameters Taken from the imaser manual 11 5 CODE IN LINUX AND DATABASE 12 e applyFrequencyCorrection df Modifies the frequency synthesiser value apply ing a correction to compensate the relative error frequency P de Vicente wrote a small script which calls the previous Python class and interacts with the user It basically uses functions e readAnalogChannelsAndLockStatus e readSynthFregAndACTRegisters e computeFrequencyCorrection df and e applyFrequencyCorrection df The user runs the script followed by a parameter which contains the relative frequency This script allows to modify the maser frequency The host account and directory where this script can be run is known by the authors and is not included here for security reasons Below we include an usage example correctMaser py 8 4e 13 Connecting to the maser Do you want to see all current parameters y n n Current Frequency Synthesiser freg 63226438 hex Current Maser frequency 1420405750 2999072
13. powered up when needed Image 1 shows a photograph of the clock in the room with the laptop on top Figure 1 EFOS Maser in its room This configuration was changed by a more flexible one Currently the serial port is con nected to a Lantronix Serial to Ethernet converter A Python class which connects via sock ets to the Lantronix device was developed by R Bola o and can be used from computer meteomaser P de Vicente wrote a simple script to be used by users which uses the pre vious class It asks for the relative frequency error shows the current maser status computes 3 TUNING AND DRIFT SINCE INSTALLATION 4 the new synthesizer value and corrects it taking into account the supplied relative frequency error This maser provides several signals of which only 3 are being used now 2 signals at 5 MHz and 1 signal at 100 MHz The three are sent via RG 58 cables to the backends room One 5 MHz signal and the 100 MHz signal are sent to a Quartzlock AS distribution amplifier The second 5 MHz signal is sent to the VLBI data acquisition terminal In order to measure the maser frequency the same setup as described in report ITOAN 2005 5 was used This setup has been used since the Kvarz CH1 75 maser was installed in the 40 m building see report IT OAN 2007 3 3 Tuning and drift since installation Figure 3 shows the maser drift obtained by comparing 1 PPS from the maser and 1 PPS from the GPS The 1 PPS from the maser is generated at the
14. ption Name physical unit LSB 1 Battery voltage A U batt A V 2 441E 02 2 Battery current A I batt A A 1 221E 03 3 Battery voltage B U batt B V 2 441E 02 4 Battery current B I batt B A 1 221E 03 5 Hydrogen pressure setting Set H V 3 662E 03 6 Hydrogen pressure measurement Meas H V 1 221E 03 7 Purifier current I purifier A 1 221E 03 8 Dissociator current I dissociator A 1 221E 03 9 Dissociator light H light V 1 221E 03 10 Internal top heater IT heater V 4 883E 03 11 Internal bottom heater IB heater V 4 883E 03 12 Internal side heater IS heater V 4 883E 03 13 Thermal control unit heater UTC heater V 4 883E 03 14 External side heater ES heater V 4 883E 03 15 External bottom heater EB heater V 4 883E 03 16 Isolator heater I heater V 4 883E 03 17 Tube heater T heater V 4 883E 03 18 Boxes temperature Boxes temp C 2 441E 02 19 Boxes current I Boxes A 1 221E 03 20 Ambient temperature Amb Temp C 1 221E 02 21 C field voltage C field V 2 441E 03 22 Varactor voltage U varactor V 2 441E 03 23 external high voltage value U HT ext Kv 1 221E 03 24 external high voltage current I HT ext uA 1 221E 01 25 internal high voltage value U HT int kV 1 221E 03 26 internal high voltage current I HT int uA 1 221E 01 27 Hydrogen storage pressure Sto press bar 4 883E 03 28 Hydrogen storage heater Sto heater V 6 104E 03 29 Pirani heater Pir heater V 6 104E 03 30 Unused Unused 0 000E 00 31 405 kHz Ampl
15. s zero when the ramp is up Hence the generated 1 PPS may differ from the sync signal at most one cycle period 1 5 MHz 0 2 us However the 1 PPS signal from the maser still delays in the Time Box and in cables to the counter and this difference may increase up to 350 ns in the counter That is the usual value seen on the HP51313A screen immediately after a synchronization If the GPS ticks before the maser the counter will display a small positive value If the maser ticks faster than the GPS and hence its frequency is higher than the GPS synthesized frequency there will be a moment in which the maser will tick before the GPS When this happens the counter will display a number close to 0 99999 The counter is read via GPIB by a computer which stores this information on a database The recorded value is however the smallest difference between Time GPS Time Maser Hence when the GPS ticks before the 3 TUNING AND DRIFT SINCE INSTALLATION 5 maser Time GPS lt Time maser and the value will be negative and close to zero If the maser ticks before the GPS Time GPS gt Time Maser and the value will be positive and close to zero since only the smallest distance between pulses is recorded The difference between the GPS and maser pulses is recorded on a database as a function of time When these values are represented on a graph a straight line is seen for time intervals smaller than a month The slope of the line will be the relative fr
16. ws application shows a strange behaviour before and after correcting the maser fre quency The monitored maser frequency was read in different moments before and after the tuning and from the main window and the Frequency Synthesizer window These tests are summarized in table 2 The conclusion is that the final cavity maser frequency after the correc tion is displayed in the Actual Freq Synth window correctly once this window is closed and reopened again The correct value is also displayed in the main window after the Freq Synth window is closed for the second time but it has less resolution than in the former window These values have been highlighted in bold face in table 2 The sign of the frequency correction was discovered by trial and error The correct sign to be used is the opposite of the measured drift Date Moment DDS readout Actual Freq Synth Applied readout Correction 7 9 2009 Before OK 1420420877 00495 1420405750 287257 8 9 107 After OK 1420420877 00495 1420420877 004959 After closing window 1420420877 00495 1420405750 287257 Freq Synth and reopening it After closing window 1420405750 28825 Freq Synth 9 9 2009 Initial monitor 1420420877 00495 Before OK 1420420877 00495 1420405750 287257 910 After OK 1420420877 00495 1420420877 004959 After closing window 1420420877 00495 1420405750 301044 Freq Synth and reopening it After closing window 1420405750 30104
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