[evlatests] RFI birdie in Ka-band

[Ken Sowinski]

On Fri, 18 Aug 2023, Evangelia Tremou wrote:
> Thanks, Ken. Indeed, it makes sense.
>
> Rick and I were just looking at the yesterday's data and there is no birdie 
> at 28808 MHz.

The power in the second harmonic is not the same for all tunings.
I seem to remember that Wes once had this measured and created
a list of how strong each harmonic was.  I will see if I can find
that again.

If simple continuum is desired this birdie can be "avoided" by
tuning each baseband pair to a multiple of 128 MHz.  This will
put any birdies in the "crack" between the subbands.

Ken


> Lilia
>
>
> On 8/18/23 15:21, Ken Sowinski wrote:
>>  On Fri, 18 Aug 2023, Evangelia Tremou wrote:
>>
>>>  Looking at some test data taken yesterday (Ka_3bit_23A256*), the
>>>  30.976GHz birdie is not present.
>>>
>>>  The scripts was using:
>>>
>>>  LoIfSetup(True,"33GHz",35900,37900,28500,30500,1)
>>
>>  This sets L301-1 to 14404 MHz, so if there were a birdie I would expect
>>  to see it at 28808 MHz in this case.
>>
>>  Ken
>> 
>>
>>>  Lilia
>>> 
>>>
>>>  On 8/18/23 09:59, Ken Sowinski via evlatests wrote:
>>>>   On Thu, 17 Aug 2023, Rick Perley via evlatests wrote:
>>>>
>>>>>   I find a fairly strong 'birdie' in Ka-band -- at 30.976 GHz. This is
>>>>>  the
>>>>>   242nd multiple of 128 MHz.  Don't know if this is relevant ...
>>>>
>>>>   This was in 23A-317 observed on July 17, 2023 using
>>>>
>>>>        LoIfSetup(True,"33GHz",37500,35500,33500,31500,1)
>>>>
>>>>   Which resulted in an L301-1 setting of 15498 MHz, the second harmonic
>>>>   of which is 30976 MHz.
>>>>
>>>>   We have previously seen such birtdies in Ka band with a variety
>>>>   of tunings; some of them much stronger than this one.  I don't
>>>>   know if anyone was able to show whether it was really the second
>>>>   harmonic getting into the RF, or some other path with the same
>>>>   outcome.
>>>>
>>>>   Ken
>>>>
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>>> 
>
>