[evlatests] S band fringes

[Bob Hayward]

We should first establish whether there is a mix up in the heliax cables 
between the receiver and the LO/IF Rack. If not, then the problem may be 
in the connections to the hybrid coupler inside the receiver.

There is a simple test we can do in the lab to confirm whether future 
S-Band receivers are polarized correctly. Someone on the S-Band 
technical team should come and talk to me if they are unaware of it. 
This step may have been missed on one (or both) of the 1st two receivers 
sent into the field.

Just a reminder that merely swapping the output cables at the receiver 
on the antenna is not a perfect fix. The Tcal values given to Ops will 
be imposed on the wrong polarization unless they are swapped in the 
database as well. Also, there will likely be an opportunity for 
confusion in the future. For example, if there is a maintenance write-up 
for a dead LCP amp we could easily open up the receiver and waste time 
working on the wrong channel as it will actually be the LNA in the 
physical "RCP" location within the Dewar that is buggered.

-Bob


Ken Sowinski wrote:
> Antennas ea09 and ea28 now have S band receivers installed.
> Fringes were obtained but the two systems have opposite
> polarization sense.  I will leave it to others to decide
> which one to swap.
> 
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