[evlatests] Characteristics from L-band, using 30 hour run

[Todd R. Hunter]

On Thu, 2 Feb 2011, Michael Rupen wrote:

> I was wondering about RFI, though it seems hard to believe it would move
> the whole band up and down by 3db!

       Michael

Having followed this thread loosely, I was curious about what the W8 RFI 
monitor would show in terms of total power vs time of day.  So, I quickly 
added a feature to my script that generates movies of the W8 monitor data. 
It now also integrates the spectrum recorded each minute and generates a 
plot of the total power vs local time.  Here are the results for Jan 1 and 
Feb 1, 2011.  As usual, the system is currently set up for L-band, with 
spectra recorded from 1.0-2.0 GHz:

https://staff.nrao.edu/wiki/pub/Main/ToddsEVLATools/20110101.1500.tpvstime.png
https://staff.nrao.edu/wiki/pub/Main/ToddsEVLATools/20110201.1500.tpvstime.png

While there is a lot of short-term variation as one would expect, there is 
a diurnal change from the middle of the night to daytime of ~10 dB.  I 
suppose there are many effects that could explain this observation besides 
a change in the total power entering the receiver (especially since there 
is 500 feet of buried coax cable involved in the signal path to the 
spectrum analyzer!).  But I post this result for what it's worth.

Todd