resonances in the cband receiver
jul02
The cband receiver was searched for resonances in
the
omt by doing 1 minute on/off position switching on VirgoA. See resonances
in the lbw receiver for a description of the technique. The
resonance
signature of cband will be different than lbw and sbw. The omt of
lbw,sbw
is at 70 K while the cband omt is at 20K. The Off positions will not
have
a bump at the resonance since the omt 20K temperature is close to
that of the scattered radiation coming in through the horn. There
should
still be a dip in the on position if the source is stronger than 20
Kelvins.
Virgo A was chosen because it was the only strong
source available during the test time. It is actually too strong and
extended.
It did not give very good band passes. The correlator was run with 4 by
25 Mhz bandwidths overlapping each sbc by 2.5 Mhz. The band was
measured
in 80 MHz junks from 3920 Mhz to 5675 Mhz. It took 22
measurements
to cover the range. The frequency scans needs to be continued to 6 Ghz
when time becomes available The plots
show the results:
Fig 1 PolA and Fig 2 PolB show on/off -1 normalized to the
median
value in each sbc. The 22 different measurements are over plotted. The
4 frames are the 4 sbc. The band passes look similar except for:
the top plot blue line at -10 Mhz. This is 4160.5 Mhz.
The 3rd frame from the top with the light blue line dipping at -6 Mhz.
This is 5246.5 Mhz.
The bottom frame has the red line dipping at 6 MHz (5676.5Mhz) and the
green line at +10 Mhz (4160.5Mhz).
The 3rd figure plots the individual band passes with the resonances.
The
black line is polA and the red line is polB. The two blue lines are the
polA band passes +/- 80 MHz from the resonance bandpass.
Resonances found
|
4160.5 Mhz
|
|
5246.5 Mhz
|
|
5676.5 Mhz
|
The resonances probably extend farther in
frequency
when doing polarized measurements (stokes q,u,v). The
observations
should be repeated on a strong point source.
processing: x101/020729/doitsbh.pro
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