[evlatests] C-Band Switched DAta

[Keith Morris]

I currently have the cal switching outputs of both an F14 and an F317 
connected to a scope in the lab -- they are in phase within about 400ns 
(the F14 leads), including all cabling and filtered connectors.  I 
wanted to be sure that there was no "designed-in" polarity reversal 
between the two modules.



Ken Sowinski wrote:
> On Wed, 22 Jun 2011, Rick Perley wrote:
> 
>>    Same experiment as described earlier.  Cygnus A at 6cm doubles the
>> system temperature.
>>
>>    About half the antennas show neither a zero offset (when switched
>> power is turned off), nor PDif compression when observing Cygnus A.  The
>> other half show varying degrees of the following:
>>
>>    A) Most show PDif compression, typically a few percent, but as large
>> as 30% for antenna 24 in RCP.
> 
> I reported long ago that a 10 Hz signal is seen in total power
> measured in the downconverter for 24 RCP at C band when the noise
> tubes are turned off.
> 
> I looked for a source for this this morning.  Turning off the noise
> tubes for each receiver controlled by an F317 one at a time made no
> difference at all to the 10 Hz signal.  Turning off the all noise tubes
> at the F320 cleaned up the C band signal.  I tested each one in turn
> and no single band was the culprit; rather the more bands with noise
> tubes on the greater the amplitude of the 10 Hz seen in the RCP signal.
> 
> At ea24 only the K and Q band receivers are controlled by the F320,
> but turning on noise tubes for the four possible receivers produced
> a larger amplitude signal than when turning on just the noise tubes
> for the receivers that are in fact present.
> 
> the leakage mechanism proposed to explain this must explain why the
> 10 Hz seen in the C band RCP output is in antiphase with the noise tube
> switching pattern.
> 
> An experiment not yet done is to verify that the C band signal is
> clean with the F320 noise tubes off and the other F17 noise tubes on.
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-- 
Keith Morris
National Radio Astronomy Observatory
1003 Lopezville Rd.
Socorro, NM 87801
575-835-7060 (phone)
575-835-7027 (fax)