resonances in the cband receiver
The cband receiver was searched for resonances in
omt by doing 1 minute on/off position switching on VirgoA. See resonances
in the lbw receiver for a description of the technique. The
signature of cband will be different than lbw and sbw. The omt of
is at 70 K while the cband omt is at 20K. The Off positions will not
a bump at the resonance since the omt 20K temperature is close to
that of the scattered radiation coming in through the horn. There
still be a dip in the on position if the source is stronger than 20
Virgo A was chosen because it was the only strong
source available during the test time. It is actually too strong and
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
in 80 MHz junks from 3920 Mhz to 5675 Mhz. It took 22
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
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.
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.
The resonances probably extend farther in
when doing polarized measurements (stokes q,u,v). The
should be repeated on a strong point source.