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<p>All:</p>
<p>I've been dealing with some interesting issues, subsequently
resolved, but have questions.</p>
<p>My HPSDR setup is locked to a GPS-stabilized 10 MHz reference.
(Excalibur, Mercury, Penelope, Metis, PennyWhistle)<br>
</p>
<p>Yet, I received reports of being 150 Hz or so low and slowly
drifting on 10 meters. I was able to confirm with a GPS-locked
frequency counter (EIP 545A)<br>
</p>
<p>AFter a lot of measuring and digging, I resolved the frequency
issue -- the 10 MHz reference was not getting to the radio. Fixed
that and I'm now on frequency, verified on-air and with the
frequency counter.</p>
<p>Here's the question: I don't know how it worked at all without
the reference.</p>
<p>I have Excalibur jumpers set to use the external reference.
Unless there's a LOT of leakage, there should have been NO 10 MHz
on the Atlas bus. Mercury jumpers are set to get 10 MHz from the
Atlas bus. I couldn't find any similar jumper on the Penelope
board. In SETUP, the Excalibur Present flag is set. Mercury is
set to be the source for the 122.88 MHz signal.</p>
<p>Looking at the schematic, I see that Penelope has an on-board 10
MHz reference which goes to the FPGA. It appears that the PLL for
the 122.88 MHz is within the FPGA, with a discrete loop filter
outside of the FPGA. I see that the Atlas bus 10 MHz signal also
goes to the FPGA.</p>
<p>SO, it would APPEAR that the FPGA senses the presence of the 10
MHz signal from the Atlas bus, and if there, uses it, if not, it
uses the onboard 10 MHz and uses it for the PLL reference, AND
puts it on the Atlas bus for Mercury. <b><u><i>Is this correct?</i></u></b>
I can see nothing about this behavior in any of the
documentation. Absent that behavior (which looks like a nice
fallback, if intentional), I would expect the radio to not work at
all, without the external reference. A friend with a similar
setup (Hercules amp) has noticed the same behavior, so I don't
think there is something else wrong.</p>
<p>I would really like to understand what is going on, and would be
most grateful if anyone could explain what I am seeing.</p>
<p>Thanks & 73,</p>
<p>Jim</p>
<p><a class="moz-txt-link-abbreviated" href="mailto:wb4gcs@amsat.org">wb4gcs@amsat.org</a></p>
<p><br>
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