[evlatests] Curious P-band RFI

[Dan Mertely]

"2" is probably, as you say, the ABQ Sunport ILS signal, ... but
we will verify.

The occasional, short amplitude dropouts *might* be due to the
VLA 410.55 & 419.55 MHz site radios overloading of the Front Ends.
That may cause curious amplitudes elsewhere in the bandpass.
-Mert


On 9/13/2013 4:38 PM, Rick Perley wrote:
>      Adding to my last note:
>
>      The test used only two spectral windows (to reduce the data load),
>
>      SP1:  312 -- 328 MHz
>      SP2:  328 -- 344 MHz
>
>      Very curious RFI was found at:
>
>      1) 324 MHz in 'LCP' ( = vertical dipole).  This was absolutely
> constant in both amplitude and phase, and nearly completely absent in
> the opposite polarization.  Also seen on all antennas. I suspect
> something internal, due to the constant nature.
>
>      2) 333 MHz in 'RCP' (= horizontal dipole).   This one rotates in
> phase, and is I think due to the Abq. airport ILS signal.  (We saw this
> back in the 'old days').  Nearly invisible in vertical polarization.  I
> would be good for Dan to confirm the origin, and the polarization ...
>
>      In every one of the tests I've done so far, I have seen short
> 'amplitude dropouts' -- lasting a few seconds, probably on all spectral
> windows, in both polarizations, and on all antennas.  The frequency of
> occurence is a few minutes to a few tens of minutes.  In this current
> short (15 minute) test, there were four occurrences.  I ran SPFLG on
> these data, and the effect is easy to see.  What is notable is that in
> the two spectral windows, a single channel in each of the two IFs had a
> huge (hundreds or thousands of Jy) spike.  The frequencies of these two
> 'spikes' are 323 and 330 MHz.   It seems that these impulses are
> saturating the receivers sufficiently to reduce the gain.  I can't tell
> from these data if the real origin lies outside the two small frequency
> windows (that is, the 'spikes' aren't the primary cause).
>
>      Does anybody have a speculation on the origin of these 'dips'?
>
>
>
>
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