430 az swings with polA filter removed


The plots:
   PolA intermod (spectra) for azimuths 123-128 (.ps) (.pdf)
    the average and peak spectra for each azswing (.ps) (.pdf):
   the rfi power at a particular freq vs azimuth for the 4 az swings (.ps) (.pdf):
   showing the time variation of these signals (.ps) (.pdf)
azswings: setup, processing
Az swing dynamic spectra
PolA intermods from tv stations.
Average, Peak hold power for each swing.
Plotting the az dependence of individual birdies
Birdies that are also time dependent.


     There is a cavity filter in front of the 430 dome lna. This was installed back in 2005? to remove intermods in the lna from some analog tv stations (it has 2 notches for channel 14 and 22). The switch to digital tv  moved some of the strongest tv stations to adjacent frequencies (that are no longer covered by the notch).

    This  polA filter has one of the 4 bolts holding the input rf cable stripped (a c clamp is used instead). It was thought that this might be contributing to the 430 dome polA ripples that have intermittently plagued 430 dome for the last two years (more info).
    On 30nov12 the polA cavity filter with notches  was removed. We made the following measurements:

Setup and processing

    4 azimuth swings were done with the polA cavity filter (with notches) removed from in front of  the dewar.

 The setup was:

Processing the data:

Dynamic spectra were then made for each az swing.

CW 1
.gif .gif 11am
CW 3
.gif .gif 2pm
.gif .gif 2pm

Notes on the images:

Tv station intermods in polA.

    PolA had the filter in front of the dewar removed. In the dynamic spectra you can see >5MHz interference between 120 and 130degs az (swings 1-3). Swing 4 had the interference at az=110. This rfi was seen (but much weaker in polB).
       PolA intermod (spectra) for azimuths 123-128 (.ps) (.pdf)

The Analog tv stations used to give intermods at 2*VideoN - AudioM where M,N were different channels. These tended to be narrow in freq (since there was lots of power in the carriers). The digital tv stations are  spread out over the enter 6 MHz band. Any intermods should probably cover at least  6 MHz.
    The hilltop monitor shows the strongest tv Stations here at AO.

Average, peak hold spectra for swings:

The first set of plots shows the average and peak spectra for each azswing (.ps) (.pdf):

Plotting the azimuth dependence of individual birdies

The 2nd set of plots show the rfi power at a particular freq vs azimuth for the 4 az swings (.ps) (.pdf):

Over plotting birdies with similar az dependence (.ps) (.pdf)

Birdies with time dependence:

    Data was taken with 50 millisecond integrations to get higher time resolution.
The setup was:
Dynamic spectra  showing 418-442 Mhzth 50 millisec integrations (.gif)
Dynamic spectra  blowup showing 432.3-435 MHz (.gif)The bandpass filter in the IF falls off at 422 and 442 MHz. Plots were made showing the time variation of these signals (.ps) (.pdf)


processing: x101/061201/rfi430_periodic.pro, 430azswing.pro

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