430 dome PolB Jennings relay APR19

23APR19

Links:

resolution : 30apr19 the polB jennings relay was replaced. Tsys for both channels are now the same.

The problem.

The tsys measurements for gr 430 polB has been jumping around day to day.

The plots show tsys polA,B and their difference for jan19->APR19 (.ps) (.pdf)

Top tsys polA (black), polB (red) from the daily measurements (jan19->APR19)
bottom: Tsys polA - polB.

occasionally Tsys polB jumps over 30 K higher than polA.

Switching the load/sky jennings relay.

On 23APR19 around 14:30 i did multiple gr430 tsys measurements. Between the measurements i switched the jenning switch sky->load -> sky (staying in the lrr side of the switch. The results were:
hh:mm:ss TsysA TsysB 02:09:57 72.9 73.6 .. early miring 14:33:59 67.5 196.9 .. start of test.. switch sky->load->sky between measurements 14:37:01 67.9 194.6 14:38:53 67.7 196.1 14:41:53 68.2 84.6 14:43:48 68.7 85.2 14:45:25 71.7 88.9 14:48:19 67.6 77.5 14:49:53 66.9 77.5 .. endtest
The first few switches made no difference, tsysPolb remained at 195 K.
The switch prior to 14:41:53 brought the tsys polB down to 88.9. The switch prior to 14:48:19 lowered it to 77.5K

winking cal data while going sky->load->sky.

Setup:

blank sky was tracked using the 430gr receiver
the 25 Hz hardware winking cal was used (lcorcal)
the mock spectrometer setup: 2048 channels, 2ms dumps,160MHz clock. 22.504 MHz bw, centered at 432 MHz.

at 2ms sampling, there are 10 spectra for each calon, 10 spectra for each cal off.

data was taken continuously for about 200 seconds.
The sky load switch:

start on sky (lrr).. for 70 secs
switch to load for 3 secs, then back to sky..
repeat the above about every 20 seconds.

processing the data:

use masgethwcal to separate the calon, caloff spectra.
using the first 40 seconds on data (no load switching), compute the rms/mean for each channel
to a robust linear fit the rms, excluding points above 3 sigma.
use the rms points within 3 sigma to compute the total power for all of the calon,caloff spectra (this is to remove rfi).
compute the cal deflection in device units: tpOn - tpOff
the the lcorcal value in kelvins (there is only one measured value for each pol ( at 430 MHz)
Scale the tpOff from device to kelvins (calValK/median(tpOff)

plots of Tsys vs time while moving the sky,load switch (.ps) (.pdf)

The daily tsys measurements use 1 MHz about 431MHz to measure tsys.
these measurements used about 18 MHz about 432 MHz to measure tsys.
The cal value used was the same for each (since we only have a single value). If the cal output changes over the band, this could cause some differences in the measured tsys values.
Top: tsys vs time.. full scale.

While on load, polA is about 300K, while polb is only 240 K.

It may be that polB is not making a good contact with the load.

Bottom:

blowup of tsys values about the sky values
After the first and 3rd sky->load-> sky switches,

tsys polB did not come back to the previous sky value.
after the 3 rd switch , it continued to rise till the next switch.

SUMMARY:

The polB jennings relay (or maybe the switch driver) is bad.
moving from sky to load and back to sky can cause Tsys to dump up by up to 130 K.
Sometimes the tsys will continue to drift for 10's of seconds after the switch.
If tsysPolB is high, going sky->load-> sky may fix it..

processing: x101/190423/430mock.pro

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