[TangerineSDR] 10 Mhz leakage

Tue Jun 2 12:43:26 EDT 2020

Yes, there'll be at least 10 MHz available for other uses.

73,
John

On Jun 2, 2020, 12:26 PM, at 12:26 PM, "David G. McGaw via TangerineSDR" <tangerinesdr at lists.tapr.org> wrote:
>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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>>     TangerineSDR at lists.tapr.org <mailto:TangerineSDR at lists.tapr.org>
>>    
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>>
>>
>> -- 
>> ----
>> Phil Erickson
>> phil.erickson at gmail.com <mailto:phil.erickson at gmail.com>
>>
>
>
>
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