[evlatests] More on 128 MHz comb

[Jim Jackson]

Thanks to Rick, Claire and Ken for taking a closer look at 
this.  From all of this, it looks like we probably just have a bad 
RFI leak on one antenna, probably 10.

Dan, can you please go take a look at Antenna 10 for a strong 128 MHz 
comb leakage mainly in S-band (followed by Antennas 8 and 6 if you 
don't find it in 10).

Thanks,
Jim




At 03:00 PM 3/14/2011, Rick Perley wrote:
>     The limited spectral sweep done by Ken this morning has already
>given us a lot of information on this 128 MHz comb.
>
>     As noted earlier, it is limited to the antennas towards the end of
>the north arm, and appears strongest on 8 * 10.
>
>     It is in both polarizations, and is seen in both cross-power and
>autocorrelations.
>
>     It is seen at L, S, and C bands.  The reason that most of the
>earlier reports have singled out S-band is that the strength of the comb
>is *much, much* stronger in S-band than in any other.
>
>     The odd harmonics are much stronger than the even.  Most even
>harmonics are not visible -- the strongest is the 32nd harmonic -- at
>4096 MHz.  (But I imagine this one could have a different origin).
>
>     The lowest frequency I could find the line was at 1408 MHz (11th
>harmonic).  The highest was at 4992 MHz.  Both of these are weak
>compared to the Sband harmnics.
>
>     The strongest harmonic is the 25th, which is at 3200 MHz.  To a
>reasonable approximation, the harmonics weaken uniformly for both higher
>and lower harmonics.
>
>     There are many other narrow responses seen, not multiples of 128
>MHz.  A complete tabulation will be made when all the data are available.
>
>
>
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