[evlatests] Slow Wobbles -- back with a vengeance!

[Ken Sowinski]

On Thu, 17 Jan 2013, Brent Carlson wrote:

> Rick,
>
> On 17/01/2013 12:06 PM, Rick Perley wrote:
>>    Brent:
>>
>>    The amplification of the effect at the bottom edge of subband #1 is
>> likely from the bandpass correction.  The  attenuation is caused by an
>> anti-aliasing filter within the T304.  This suggests that the effect
>> is added in after this filter.  But then this would seem to contradict
>> the indication that the effect is proportional to the correlated
>> power, which (I think) would cause the wobble amplitudes to decrease
>> after that filter.  On the other hand, if the effect is related to
>> some complicated aliasing from some non-linear process, then the
>> filter effect would be avoided.
>>    We do see, very faintly, wobbles at other IFs.  However, in nearly
>> all cases, these are only seen in the two or three channels on each
>> side of the subband filter 'notches'.
> This would indicate that it is a correlator effect since, presumably,
> the sub-band band-pass correction would amplify the effect in a similar
> manner as you indicated for the T304.  Curious, though, why it doesn't
> show up or is much weaker in some sub-bands and is weaker in ~1/2 of
> sub-band 2...
>
> Setting up non-beating corr chip integration times would be the first
> test I'd run...

Rick reports that this is seen only in IF C.  I would expect things
like CC dump interval and the like to affect all IFs or none.  IFs
A and C have identical sky frequency, fringe frequency and LO offset.
They differ only by, perhaps, a few nanoseconds of delay.

Ken