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On the other hand, while acknowledging the problem with receiving
WWV specifically, I hope provision can be made to lock to 10 MHz and
perhaps other frequencies. It is more likely that 10 MHz is
available to lock various instruments together than 1 PPS in
people's shack or lab.<br>
<br>
Good coax is key for distribution. I have thrown out a lot of cheap
RG-58 jumpers as they have poor shield coverage (sometimes as low as
35%). Genuine Belden or equivalent can be OK (95% coverage) though
double-shielded (2 braids or braid + foil) is better.<br>
<br>
73,<br>
<br>
David N1HAC<br>
<br>
<div class="moz-cite-prefix">On 6/2/20 11:47 AM, Phil Erickson via
TangerineSDR wrote:<br>
</div>
<blockquote type="cite" cite="mid:CAAZaqEvZTSqqpyd02A01jtDaZzjzFUtiyExs07nQGrP9cDC3jQ@mail.gmail.com">
<div dir="ltr">Hi all,
<div><br>
</div>
<div> John has the right approach.</div>
<div> </div>
<div> Bill: I guess I don't understand how a 10 MHz clock can
generate a 15 MHz harmonic, unless some kind of a divide-by-2
happens in the radio to get to 5 MHz and then you are seeing
the 3rd harmonic. Others can add.</div>
<div><br>
</div>
<div>73</div>
<div>Phil</div>
</div>
<br>
<div class="gmail_quote">
<div dir="ltr" class="gmail_attr">On Tue, Jun 2, 2020 at 11:19
AM John Ackermann N8UR via TangerineSDR <<a href="mailto:tangerinesdr@lists.tapr.org" moz-do-not-send="true">tangerinesdr@lists.tapr.org</a>>
wrote:<br>
</div>
<blockquote class="gmail_quote" style="margin:0px 0px 0px
0.8ex;border-left-width:1px;border-left-style:solid;border-left-color:rgb(204,204,204);padding-left:1ex">10
MHz leakage is a real problem. cf my lab/ham shack. :-)<br>
<br>
But I'm pleased to say that the current design for the
Tangerine CKM<br>
module will avoid, or at least won't add to, this problem.
We're going<br>
to directly slave the 122.88 MHz ADC/DAC clock to GPS PPS,
with no 10<br>
MHz oscillator in the mix. So with good practices applied to
the<br>
digital layout, we shouldn't create any HF spurs in the clock
system.<br>
<br>
We will have a 10 MHz output available (synthesized in the
FPGA) but it<br>
will be for optional uses and we can make it switchable.<br>
<br>
BTW, I don't recall for sure but on the original Hermes board
which had<br>
a 10 MHz TXCO to which the 122.88 MHz was locked, I don't
think there<br>
was any bleed-through noticeable in the receiver. So it's
possible to<br>
avoid the problem with good design.<br>
<br>
The real problem is when the 10 MHz is running around on leaky
coax<br>
cables. Then it gets into the air and is pretty difficult to
suppress.<br>
(I found that cheap RG-58 jumper cables running in parallel
in my lab<br>
were porous enough to allow two OCXOs to injection lock -- I
ended up<br>
replacing all the jumpers with double-shielded cables and that
problem<br>
has gone away.)<br>
<br>
73,<br>
John<br>
----<br>
On 6/2/20 11:04 AM, Engelke, Bill via TangerineSDR wrote:<br>
> A little discovery that might have a bearing on something
in the<br>
> TangerineSDR…. Or maybe this is just my ignorance at
work.<br>
> <br>
> <br>
> <br>
> We’re putting a lot of emphasis on being able to observe
the doppler<br>
> shift of WWV, often focusing on 10MHz. I have been
looking at this using<br>
> FlexRadio 6600 and Spectrum Lab. In observing the
frequency moving<br>
> around quite a bit (by this I mean 20 to 40 millihertz),
I thought,<br>
> maybe that is the Flex’s TXCO doing its thing. So I got a
Leo Bodnar<br>
> GPSDO and started using this as the Flex’s clock.<br>
> <br>
> <br>
> <br>
> What I noticed is that even with the antenna grounded and
the rig<br>
> connected to a dummy load, there is a pretty significant
(and totally<br>
> stable) 10 MHz signal shown in Spectrum Lab. I speculate
that this is<br>
> the clock signal finding its way into the front end of
the receiver. So,<br>
> when watching for WWV doppler shift, I see a 10 MHz
signal (which is<br>
> comparable in strength to WWV) superimposed on it. The
same signal can<br>
> be seen on 15 MHz and 20 MHz – not surprising, since the
Leo Bodnar<br>
> GPSDO provides a square wave output (i.e., rich in
harmonics). I<br>
> recognize that the Flex is not a lab instrument, so I
have no grounds on<br>
> which to complain, but still…<br>
> <br>
> <br>
> <br>
> I wonder if this will play into the Tangerine SDR? Are
we able to keep<br>
> RF from the clock from leaking into the front end and
overlaying the WWV<br>
> we’re trying to observe? Do we need to?<br>
> <br>
> <br>
> <br>
> Any thoughts? -73- Bill AB4EJ<br>
> <br>
> <br>
<br>
<br>
-- <br>
TangerineSDR mailing list<br>
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</blockquote>
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-- <br>
<div dir="ltr" class="gmail_signature">----<br>
Phil Erickson<br>
<a href="mailto:phil.erickson@gmail.com" target="_blank" moz-do-not-send="true">phil.erickson@gmail.com</a><br>
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