[evlatests] S band fringes

[Charles Kutz]

Yesterday, 

I took a look at the two receivers and turned off their biases to the 
RCP channel. On antenna 9 the RCP went dead as viewed at the output of 
the T5. Turning off the RCP bias in antenna 28 resulted in the LCP going 
dead as viewed at the the T5. I had John go out and swap the heliax at 
the receiver output and hang a tag on the receiver so we know what happened.

I think that this points to either crossed output coaxes inside the 
receiver or crossed heliax at the output of the receiver. Haven't yet 
had a chance to talk to John about what he actually was able to 
ascertain in antenna 28.

For now...


Chuck


Bob Hayward wrote:
> 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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