[evlatests] Mystery Moon Test

[Rick Perley]

     Very doubtful.  I've done setups on cygnus A before (notably at 
P-band and L-band), with very good results.

     The off-sky power was about 5 'counts'.  Hardly extreme, and 
nowhere near low enough to cause a depression by a factor of 5 to 10 ...



On 12/17/2015 08:56 AM, Ken Sowinski wrote:
> On Thu, 17 Dec 2015, Rick Perley wrote:
>
>>    Rob ran the 'Moon compression test' last month at X-band.  The 
>> results are bizarre:
>>
>>    1) We expect a power increment of about a factor of 5 to 8. This 
>> is what was observed in the 'PSum' digital power.  So far, so good.
>>
>>    2) The 'set and remember' regimen was applied when the source was 
>> on the moon.  The digital power level should be about 15, when on the 
>> moon.  This was also the case.  Still good....
>>
>>    3) We then expect a 'PDif' compression (PDif on moon)/(PDif off 
>> moon) of about 0.9.  In fact, this ratio was about between 0.1 and 
>> 0.4 (!!!!!)  That is, for every antenna and every IF channel, the 
>> PDif when on the moon was only 10 to 40% of the value when on cold sky.
>>
>>    This is a level of compressin that I have never seen before.
>>
>>    It may be worth noting that the PDif values, which are normally 
>> hundreds of millicounts, where only 10 -- 50 millicounts.
>>
>>    Something is wrong.  Any ideas?
>>
>>    Rob reports that the TPD values (recorded in parallel) were also 
>> weird.
>
> This was X band, so the T301 attenuators are irrelevant.
>
> I've looked at the script and compared it with the one I had prepared
> for previous tests.  There is a difference in the protocol.  In
> the past we did set and remember on "cold" sky" and used that for
> the moon; here we did just the opposite, set and remember on the moon,
> and use that for the "cold" sky.  That under drives the sampler when
> looking at cold sky so much that it is close to being used as a 1-bit 
> device.
>
> Might this have something to do with it?