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

[Brent Carlson]

That would seem to rule out correlator beating effects alright.
Brent

On 17/01/2013 12:27 PM, Ken Sowinski wrote:
> 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
>

-- 
Brent R. Carlson
Brent.Carlson at nrc-cnrc.gc.ca
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