[evlatests] Issues at X-band

[Bob Hayward]

Rick,

Antenna 13 has one of two X-Band receivers (S/N 29) that we had 
modified with EVLA-style LNA's some years back (CDL couldn't fix the old 
GasFET amps anymore). The old narrowband LNAs were replaced with wider 
3-13 GHz InP amps. While the receiver still has the old narrow 8.0-8.8 
GHz septum polarizers, some (randomly polarized) out-of-band photons 
must be making it through, just like we saw with the Interim C-Band 
receivers.

-Bob


Rick Perley wrote:
>     Examination of the X-band data from last night shows a few 
> interesting issues:
> 
>     Antenna 16 has cross-power low by a factor of 10 to 100.  The system 
> temperature about 600K -- explaining most of the low cross-power. 
> 
>     Antenna 20 has the same characteristics as antenna 16, but not as 
> extreme -- Tsys about 300K. 
> 
>     Antenna 22 is also low in cross power, with high Tsys (about 90). 
> 
>     Antenna 27 has low cross power (by 12 dB) on IFs A and C only, but a 
> normal system temperature.  Attenuators mis-set? 
> 
>     Antenna 21 claims to have a system temperature of 200K, but it is 
> certainly not that high, as I can see normal sky variations.  Bad Tcal 
> for sure. 
> 
>     By looking at the bandpass solutions only, the following antennas 
> *appear* to be wideband (meaning, there is no high-frequency roll-off):
> 
>     7, 13, 14. 
> 
>     I don't understand how 13 can have such a nice flat bandpass -- it 
> is not supposed to get a new receiver until March, next year ...
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