Dome 430 MHz calibration
Sep 2004
There is a 430 MHz reciever on the gregorian
dome.
It can be used for transmitting and receiving. It has native circular
polarization.
Sections:
History
Recent
system performance measurements
Daily
monitoring of Tsys
Dewar
temperatures
Calibration measurements
Miscellaneous
Cal values
rfi measurements
History:
19jul06: tsys polB increased. Stayed high till about 10aug06. The
jennings
relay for polB was bad.
18jul06: new turnstile installed. Better isolation. Still needs to
be tuned a bit.
25may06: power supply for cal driver circuitry was bad. replaced it.
23may06: tsys starting to go infinite.. turns out power supply for
cal driver went bad.
27jan05: filters (both pols) installed before dewar to get rid of tv
station intermods.
oct04: filter placed in front of dome polA dewar removes
tv station intermods.
Calibration
measurements:
Miscellaneous:
10aug09: 430 polA unstable
Project
a2415 reported that 430 dome polA was unstable with a 15 second
periodicity. Data was taken on 10aug09 AM with the mock spectrometers.
The setup was:
- az,za=270,1.09 sitting.
- mock spectrometer: 8k channels, 34 MHz Bw, and .1 second sampling.
- Data taken for 300 seconds.
The total power for the 300 seconds of data was
computed for each
.1 second sample after throwing out rfi (compute rms/mean by channel
and throw out channels with large rms). The total power was then
normalized to the median value over the 300 seconds
The plots show the total power and spectrum of
the total power (.ps) (.pdf)
:
- Black is polA, red is polB
- Top: total power vs time
- Middle: The spectrum of the total power was computed and plotted.
The 1.2 hz and harmonics come from the dewar refrigerator cycle.
- Bottom: blowup of the spectrum of the total power (0-1 hz). There
is no obvious 15 second periodicity (.066 hz). Maybe what people saw is
not very stable in time.
Summary:
- Pol A has a large 1.2 hz periodicity in its total power. This is
coming from the refrigerator. We should probably bang on the can to see
if something is loose inside...
processing: x101/090810/430.pro
mar03 thru oct03 GAIN
CURVE.
Calibration data taken mar03 thru oct03 was used to
compute a gain curves. The fits were done versus za. The plot
shows the data, fits, and the residuals. This needs to be redone
once
the filters are installed on the frontend (to cut out the tv
stations).
11jan05:
TsysPolA - TsysPolB drift for 2003 and 2004
The system temperature for the dome 430 receiver is
measured
regularly during the normal maintenance
procedure. I've plotted Tsys
for the years 2003 and 2004 (.ps). (.pdf)
Fig1- Top: Tsys for 2003. Black is
polA,
red is polB, Bottom: TsyspolA-tsysPolB
Fig2:- Top: Tsys for 2004. Bottom:
TsysPolA-TsysPolB
From the plots you can see that the difference
TsysPolA-TsysPolb
has been changing. In july 2003 the difference started to increase
(TsysA
larger then TsysB). Around 17nov03 the difference jumped by 10 degK so
that TsysB was larger then tsysA by about 10 degK. It
stayed
at this level until august 2004 when it started to increase gradually.
The tsys measurements tend to be taken
at 16:30 AST so the RA of the measurement will move during the year. It
seems unlikely that the gradual drift in TsysPolA - TsysPolB is
coming
from the sky since the receiver is circularly polarized (and there are
no extended sources of circular polarization that i know
of).
Looking at the src deflections over this time period the polA,polB
ratio
remained fairly constant, so my guess is that Tsys was changing (and
not
the cal size).
processing: x101/430/tsysByYr.pro
home_~phil
