Intro
The xband receiver on the p12m telescope
was monitored for 4 hours on 02jun21. The setup was:
- we used the cal noise diode rather than the sky as the
input signal
- we disconnected the cables that connect to the lna amp
(up at the horn).
- the 30enr noise diode -> 6db splitter -> cables
disconnected above.
- So we were driving polA,polB with a 30-6= 24enr noise
source
- We need to measure the noise diode setup more
accurately.
- This will tell us if the wandering around of the signal
is from the if/lo or the lna's.
- take data 14:58 to 18:47 AST on 02jun21
- The telescope was tracking the position ra 12:41:32,
dec 16:00:00
- The input signal was the cal diode so we were not
looking at the sky.
- We went from elevation 10 to 67 degrees.
- We wanted to see if tracking motion would cause anything
to vibrate and affect the signal strength.
- xband receiver using 8050 to 9200 MHz
- Mock spectrometer used to record the data.
- 7 172 MHz bands centered at:
- 8132,8296,8460,8624,8788,8952,9116
- Each band spaced by 164 MHz
- 2 pols, 4096 channels/pol, 42 KHz channel width
- spectra dumped once a second
- We used the same processing as when on the sky (even
though there wasn't any rfi).
- When computing the total power, frequency channels with
rfi were rejected:
- compute rms/mean for each freq channels.
- do a linear fit to the rms vs freq and reject any
channels with fit residuals > 3 sigma.
- the rfi rejection was not very helpful. We had 19
hours of data with the mean value varying with temp. The
rms/chan was large so clipping at 3 sigma left a lot of
rfi.
- the total power for each 1 second spectra was then
computed over the good channels (scaling by the channels
used).
- The first and last bands were only partially filled with
rf power. They were cutoff by the p12m rf bandpass filter.
In these cases only the part of the band with power was
used for the computation.
- The total power vs time for each frequency band was
normalized to the average of the first 1000 points
taken (so the units become Tsys).
Mock bandpasses used
The plot shows the mock bandpassed used (.ps)
(.pdf)
- These bandpasses were used for the may,jun21 total power
measurements on the 12meter.
- The bands are 172.032 Mhz wide.
- They are spaced by 164 Mhz
- The first and last bands are only 1/2 filled with signal
(when computing total power, only the part with signal was
used).
Total power vs time, temp, and ra
The total power vs time for the
4 hour session was plotted:
The
total power vs hour of day with temp (.ps)
(.pdf)
- The x axis is hours since the start of 02jun21
- Top
- over plot total power vs hour of day for the 7
polA bands
- there were no jumps in the total power.
- Middle:
- over plot total power vs hour of day for the 7
polB bands.
- Bottom: pedestal temperature
- The pedestal temperature (behind the postamp chassis)
was recorded once a minute.
Total
power vs temperature (.ps) (.pdf)
- Top: median (over the 7 freq bands) total power vs
hour of day.
- The green curve is the temperature over plotted on the
curve (scaled to fit)
- Bottom: linear fit total power vs temp.
- solid lines: total power vs temp
- dashed lines: linear fit
- black polA, red polB
- The coef:
- tpA=5.38 - .0475*tempF
- tpB=5.32 - .0470*TempF
- The total power units are Tsys.
- The shows the electronic gain changing by 4.7%/degF
- This should probably be ignored since the delta T
was only about 2degF.
blowup total power vs time
total power vs time blowup
(.pdf)
- The total power vs time is plotted in 1 hour blocks.
- polA 1st and 3rd frames
- polB 2nd and 4th frames.
- The 7 bands for each pol are over plotted.
- Each 1 hour plot is normalized to unity.
- There are no total power jumps.
- There is no frequency dependent wandering of total power.
Summary:
- Moving the telescope did not cause any jumps or drifts.
- We had results similar to the 01jun21 data when we took
cal data with the telescope sitting still.
- The gain vs temp fit was limited because the temperature
only changed by about 2deg F
processing: x101/210602/xbmontp.pro