DFB Delay Calibration
Instrumental delays in the DFB systems can be calibrated using a modulated bandpass signal. The modulation is provided by the Agilent pulse generator in Rack 5, O/P 1 of which is fed to a pin modulator (HP 8731A for 20cm, 256 MHz bw; HP 8732B for 10cm, 1024 MHz bw). The pin modulator is placed in the downconverter input FC1 line (rear of Rack 6). The modulated A poln signal can be fed to both PDFB3 or PDFB4 inputs by a small modification to the Engineering Test Rack cables.
The function generator O/P 1 can be monitored on the CRO, triggered by the 1ms pulse.
Settings for the function generator are given in the file DelayList.txt; a copy exists in ~pulsar/ on the Parkes linux system. The entries are: instrument, config, min period (ms), nbin, bw, nchan, cal freq, pulse period (microsec), nr of cycles per 1ms group, duty cycle.
The pulse generator is set up as follows:
- Connect trigger (Ext In) to 1ms output of Parkes Clock (pkclk00, rear of Rack 5). Select External Trigger.
- Select "Pulse" function
- Set Period (from Delaylist.txt according to config), Phase = 0.0, Leading Edge Delay = 2.5ns, Duty cycle (normally 40%), (Page 2) P-P Amplitude 2.0V, Offset -220 mV, Load Impedance 50 ohm, (Page 3) Output impedance 50 ohm, Polarity normal, Freq. Coupling Off, Freq Mult 1, Freq Div 1.
- Select "Burst" function
- Set # of cycles according to DelayList.txt
To make the observations, use TCS next, ensure that the relevant receiver is switched on, that the corresponding losetup has been run and that the cal is switched OFF. Use the appropriate schedule file ~/tcs/sched/P456_MB_CalDly_DFB*.sch, setting the pulse generator appropriately for each configuration.
Timing templates are (currently) made using /u/kho018/dr/software/caldelay/delay_template. This program reads in DelayList.txt (or a file with similar structure) and an impulse response, normally 6db_filter.txt and computes templates for a selected instrument.
A modified version of pat, pat2, is used to analyse the data. Options are:
- -r: list phase of the reference point, the delay in microsec and its uncertainty
- -t -K 1/xs: plot the observation, template and difference profiles. The observation is rotated by the reference point phase and normalised to the same area as the template before differencing.
- -u: a list of equivalent TOAs in Tempo2 format.