[evlatests] Internal Birdie at 1408.25 MHz

[Rob Long]

Unfortunately, the L301 does not have the ability to slightly move (in 
frequency).  Can this birdie be seen on a single dish or only after 
correlation?  Is it seen in all 4 IFs of the bad antenna(s)?  Does 
antenna position make any difference?

Rob

Dan Mertely wrote:
> Hi Ken.  One way to test it would be to:
> 
> 1) Re-run the test as is, and verify the continued existence
> of the 1408 MHz signal, then
> 2) If it is still there, *slightly* move the frequency of the
> L301 & see if the signal is now @ 14336 - (the new L301 frequency).
> 
> If so, it makes the API more suspect, & we could arrange for a
> API on/off test.  As Bryan observed, however, it seems odd that
> east arm antennas didn't show stronger RFI than other antennas
> if it was API sourced.
> 
> -Mert
> 
> 
> 
> 
> Ken Sowinski wrote:
>> On Mon, 13 Jul 2009, Rick Perley wrote:
>>
>>>    We are seeing in recent tests the presence of a strong birdie,
>>> centered at 1408.25 MHz.    The characteristics of this RFI strongly
>>> indicate is is *NOT* of external origin:
>> Here is some numerology.
>>
>> The first LO was set to 12928 MHz for this observation.
>> The API generates a comb with 298.611 MHz spacing.
>> Its 48th harmonic is 14336 MHz, and 14336-12928
>> is 1408 MHz.
>>
>> Should we try this again with the API turned off?
>> If this were the source, I might expect to see other
>> teeth of the comb as well.
>>
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