[TangerineSDR] 10 Mhz leakage

[David G. McGaw]

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.

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.

73,

David N1HAC

On 6/2/20 11:47 AM, Phil Erickson via TangerineSDR wrote:
> Hi all,
>
>   John has the right approach.
>   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.
>
> 73
> Phil
>
> On Tue, Jun 2, 2020 at 11:19 AM John Ackermann N8UR via TangerineSDR 
> <tangerinesdr at lists.tapr.org <mailto:tangerinesdr at lists.tapr.org>> wrote:
>
>     10 MHz leakage is a real problem.  cf my lab/ham shack. :-)
>
>     But I'm pleased to say that the current design for the Tangerine CKM
>     module will avoid, or at least won't add to, this problem. We're going
>     to directly slave the 122.88 MHz ADC/DAC clock to GPS PPS, with no 10
>     MHz oscillator in the mix.  So with good practices applied to the
>     digital layout, we shouldn't create any HF spurs in the clock system.
>
>     We will have a 10 MHz output available (synthesized in the FPGA)
>     but it
>     will be for optional uses and we can make it switchable.
>
>     BTW, I don't recall for sure but on the original Hermes board
>     which had
>     a 10 MHz TXCO to which the 122.88 MHz was locked, I don't think there
>     was any bleed-through noticeable in the receiver.  So it's possible to
>     avoid the problem with good design.
>
>     The real problem is when the 10 MHz is running around on leaky coax
>     cables.  Then it gets into the air and is pretty difficult to
>     suppress.
>      (I found that cheap RG-58 jumper cables running in parallel in my lab
>     were porous enough to allow two OCXOs to injection lock -- I ended up
>     replacing all the jumpers with double-shielded cables and that problem
>     has gone away.)
>
>     73,
>     John
>     ----
>     On 6/2/20 11:04 AM, Engelke, Bill via TangerineSDR wrote:
>     > A little discovery that might have a bearing on something in the
>     > TangerineSDR…. Or maybe this is just my ignorance at work.
>     >
>     >
>     >
>     > We’re putting a lot of emphasis on being able to observe the doppler
>     > shift of WWV, often focusing on 10MHz. I have been looking at
>     this using
>     > FlexRadio 6600 and Spectrum Lab. In observing the frequency moving
>     > around quite a bit (by this I mean 20 to 40 millihertz), I thought,
>     > maybe that is the Flex’s TXCO doing its thing. So I got a Leo Bodnar
>     > GPSDO and started using this as the Flex’s clock.
>     >
>     >
>     >
>     > What I noticed is that even with the antenna grounded and the rig
>     > connected to a dummy load, there is a pretty significant (and
>     totally
>     > stable) 10 MHz signal shown in Spectrum Lab. I speculate that
>     this is
>     > the clock signal finding its way into the front end of the
>     receiver. So,
>     > when watching for WWV doppler shift, I see a 10 MHz signal (which is
>     > comparable in strength to WWV) superimposed on it.  The same
>     signal can
>     > be seen on 15 MHz and 20 MHz – not surprising, since the Leo Bodnar
>     > GPSDO provides a square wave output (i.e., rich in harmonics). I
>     > recognize that the Flex is not a lab instrument, so I have no
>     grounds on
>     > which to complain, but still…
>     >
>     >
>     >
>     > I wonder if this will play into the Tangerine SDR?  Are we able
>     to keep
>     > RF from the clock from leaking into the front end and overlaying
>     the WWV
>     > we’re trying to observe? Do we need to?
>     >
>     >
>     >
>     > Any thoughts?     -73- Bill AB4EJ
>     >
>     >
>
>
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>
>
> -- 
> ----
> Phil Erickson
> phil.erickson at gmail.com <mailto:phil.erickson at gmail.com>
>

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