[evlatests] A curious new birdie at X-band

[Bryan Butler]

from an email from keith morris on may 10th of this year on this topic:

"Rick:

The first LO for the API (both old and new) is 10750MHz.  Do you notice
the birdie stronger towards the center of the array, or on the east arm?

Shielded chamber tests of the new API LNBs didn't show any emissions at
the LO frequency, though there was radiation at certain subharmonics,
which we have found a way to suppress."



Rick Perley wrote, On 7/23/13 9:50 :
>      As part of the 'receiver rotation' experiment, I've taken wideband
> data covering all of L, S, C, and X bands.
>
>      Looking at the higher half of X-band (10 to 12 GHz), one, and only
> one, piece of RFI is seen.  It's a pure tone, at
>
>      10750 MHz
>
>      This is not a harmonic of 128 MHz (but is close -- the 84th harmonic
> is 10752 MHz).  No other birdies are seen, so this tone is definitely
> special.
>
>      And it's only seen on antennas near the center of the array --
> strongly arguing for a local origin.
>
>      The autocorrelations are useful for diagnosis -- unfortunately, only
> half the antennas provide this (what do we have to do to get them all?)
>
>      Antennas with strong 10750 MHz tone are:
>
>      ea13 at W02
>      ea15 at E02
>      ea22 at N02
>
>      Antennas with detectable tone (but weaker than above list) are:
>
>      ea05 at W08
>      ea09 at W10
>      ea11 at W06
>      ea24 at W04
>      ea 26 at W12
>
>      Antennas with no visible tone (in autocorrrelations) are:
>
>      ea01 at N14
>      ea03 at E10
>      ea07 at E12
>      ea17 at E14
>      ea19 at W16
>      ea28 at E16
>
>      All other antennas provided no autocorrelations.
>      The cross-correlation data are consistent with a local origin, near
> the array center.
>
>
>
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