sband RFI measurements.
last updated 16oct05
20sep01.Measuring the power
levels at the output of the sband wide dewar. (rfimtop)
parked at az=309. and the gregorian was at 3.35 degrees.
The measurement was from 1000 Mhz to 2950 Mhz. The dewar response goes
beyond 3 Ghz but the spectrum analyzer didn't want to switch to the next
band. The data was taken during close to noon with the sun about 15 degrees
away (dec=01 deg). The
plots show:
-
Figure 1 top plots the spectrum 1000 Mhz to 2950 Mhz for polarization A.
The resolution bandwidth was set to 3 Mhz. The system temperature is about
40 K. The red line averages 100 sweeps of the spectrum analyzer. The black
line is a peak hold for greater than 30 seconds (I don't believe that the
black line is a peak hold, it looks like it was left on averaging mode).
Integrating the spectra gave -23.5 dbm.
-
Figure 1 bottom plots the spectrum 1000 Mhz to 2950 Mhz for polarization
B. The red line averages 100 sweeps of the spectrum analyzer. The
black line is a peak hold for greater than 30 seconds Integrating
the spectra gave -11dbm (peak hold) and -24.3 dbm (100 sweeps). The peak
hold values where there is no interference should be about 3 db larger
than the averaged version (not 13 db). So something went wrong in the measurement.
Doing a consistency check on the power levels:
-198 dbm/hz/K + alog10(3Mhz rbw)*10 + alog10(40K)*10 + 40 db gain=
-77 dbm.
The spectrum analyzer value in the middle of the band where there is
no interference is about 17 db higher than this. These measurements need
to be redone.
The large interference at 1940 Mhz are from cellular phones. The large
birdie at 1350 Mhz is the san juan airport radar. I don't think that there
is any filter between the dewar and the post amps. This needs to be corrected.
We also need to decide what to do about the birdies at 1940 Mhz. Do we
cut them out with a bandpass filter or try and use a notched filter?
Our spectral line list does not have any lines between 1720 (OH) and 2661
(HC5N).
processing: x101/010920/sbwdewar.pro
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