[evlatests] A bit more on VOIP RFI.

[Peter Napier]

Viveck,
After thinking about this a little more I wonder if we really need to 
attenuate the RFI from the phone so that the "self-RFI", that is the 
signal picked up by the antenna on which the phone is located, is below 
ITU limits. By definition the only time that "self-RFI" occurs is when 
there is someone on the antenna so the antenna is not observing. Isn't 
it sufficient to ensure that the signals on adjacent antennas are below 
the ITU limits? In which case don't your numbers show that the phone is 
already close to acceptable? Perhaps not quite good enough for E-array?
Peter

vdhawan at aoc.nrao.edu wrote:
> More on the VOIP RFI test:
> 
> The cross correlation data (much more sensitive than the total-power)
> show that the phone signals leak into almost every other antenna.
> 
> Anten 22, the closest south of 6, shows the strongest signal, 50-70 dB
> down from antenna 6 at different frequencies, (e.g. -190dBm at
> 1300MHz.)
> 
> Antenna 11, just north of 6, shows little, over 100 dB down.  The
> leakage appears almost random with distance from ant 6.  Many antennas
> are about 80-90 dB down from 6, at 1300MHz. A few, not the farthest,
> show nothing. The array was tracking Santa at the north pole, so
> fringe winding should not be affecting the RFI. My guess is that the
> leakage is very frequency and direction dependent.
> 
> In any case, shielding that cleans up the autocorrelations
> (i.e. suppresses leakage from an antenna's equipment into its own
> receivers) is more than adequate for the cross-power spectra.
> 
> V.
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-- 
Peter Napier
NRAO, PO Box 0, Socorro NM 87801
Ph 505 8357218, Fax 505 8357027