[evlatests] Internal Birdie at 1408.25 MHz

[Jim Jackson]

The L301 can only tune in 256 MHz steps.

Has this birdie been seen before?  Is it still seen if the input or 
output attenuator settings are increased? This would if it is an 
internal birdie in the T304 or DTS module.  The DTS module 
particularly worries me since the 128 MHz is used as a clock 
throughout that module.  If that is the source, it should be present 
even with the T304 output attenuator set to a high value.

Terry also pointed out that we could be seeing the 11th harmonic (or 
comb line) of the 128 MHz leaking out of the L300 or a cable and 
being picked up by the receiver.

Jim
At 04:25 PM 7/13/2009, 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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