[TangerineSDR] 10 Mhz leakage

Tue Jun 2 12:47:51 EDT 2020

Have same 10 Mhz local contamination so just use 15 Mhz WWV

Lester B Veenstra  K1YCM  MØYCM  W8YCM   6Y6Y

lester at veenstras.com

452 Stable Ln (HC84 RFD USPS Mail)

Keyser WV 26726

GPS: 39.336826 N  78.982287 W (Google)

GPS: 39.33682 N  78.9823741 W (GPSDO)

Telephones:

Home:                     +1-304-289-6057

US cell                    +1-304-790-9192 

Jamaica cell:           +1-876-456-8898 

From: TangerineSDR [mailto:tangerinesdr-bounces at lists.tapr.org] On Behalf Of John Ackermann via TangerineSDR
Sent: Tuesday, June 02, 2020 12:43 PM
To: David McGaw; Engelke, Bill via TangerineSDR
Cc: John Ackermann
Subject: Re: [TangerineSDR] 10 Mhz leakage

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

73,

John

On Jun 2, 2020, 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> 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 

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