Intro
The polB 20db xband hub amplifier had a
problem with the power connection. Both of the 20db xband hub
amplifiers were replaced on
29jun21 with 2 11.5 db amplifiers. The short rf cables were
added to the input so the input cables were no longer
stretched.
On 01jul21 the xband receiver was monitored
for 17hours. The setup was:
- data taken: 16:28 01jul21 to 09:21 02jul21 AST
- telescope sitting at Az=1 el=75.
- 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
- The temperature sensor in the pedestal was offline during
these measurements.
- 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).
Total power vs time, and ra
The total power vs time for the
entire 17 hour session was plotted:
The
total power vs hour of day (.ps) (.pdf)
- The x axis is hours since the start of 01july21 (so hr 30
is 6am 02jul21)
- Top
- over plot total power vs hour of day for the 7
polA bands
- there were several jumps up and then back down. The
amplitude of the jumps looks like a function of the
frequency band.
- Middle:
- over plot total power vs hour of day for the 7
polB bands.
- polB looks pretty stable.
Total
power vs Right Ascension (.ps) (.pdf)
- Top: PolA total power vs ra
- Bottom: polB total power vs ra
- the dashed red line is the galactic plane.
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.
- some jumps
- there were 2 polA jumps.
- 19hrs and 25 hours
- there were a number of times when the power drifted
(usually being a function of freq).
- polB was relatively stable.
Summary:
- PolA
- had 2 sharp jumps where the amplitude was a function of
freq band.
- There were periods where it drifted by up to 10% within
1 hour
- we saw something similar to this on 21may21
- Pol B
- was relatively stable. We no longer see the drifts in
polb that was present with the 20db amps.
processing: x101/210701/xbmontp.pro