[evlatests] Birdie at 30.976 GHz

[Ken Sowinski]

On Thu, 15 Feb 2018, Wes Grammer wrote:

> Jim, it does seem possible, since this birdie is the second harmonic of one 
> of the L301 tuning frequencies (15.488 GHz). I did a bench test of harmonic 
> output from the downconverter back in 2015, when a similar birdie at 29.44 
> GHz was found; a PDF is attached. It shows the LO-IF leakage for a wide range 
> of the possible LO drive frequencies, but the ones applicable to the VLA are 
> between 14.720 and 16.256 GHz, as they are within the passband of the output 
> filter after the LO tripler.
>
> Interestingly, this new one is right in the center of that band, but my 
> earlier measurement showed no detectable IF output at 15.488 GHz (which would 
> correspond to a sky frequency of 30.976 GHz). There was a substantial spike 
> at 15.744 GHz, however.
>
> I'll double check this result in the lab today - I happen to have a good 
> downconverter in the test set and the equipment set up. Rick, in your 
> observation with this detection, was the L301 set to 15.488 GHz?

L301-1 was 15488
L301-2 was 13184

Ken