[TangerineSDR] 10 Mhz leakage

Tue Jun 2 13:01:01 EDT 2020

Hi Lester,

  Your comment is exactly the reason why I was puzzled that Bill was
reporting LO leakage at 15 MHz - this seems strange to me.

73
Phil W1PJE

On Tue, Jun 2, 2020 at 12:48 PM Lester Veenstra via TangerineSDR <
tangerinesdr at lists.tapr.org> wrote:

> 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
> >
> >
>
>
> --
> TangerineSDR mailing list
> TangerineSDR at lists.tapr.org
> http://lists.tapr.org/mailman/listinfo/tangerinesdr_lists.tapr.org
> <https://nam12.safelinks.protection.outlook.com/?url=http%3A%2F%2Flists.tapr.org%2Fmailman%2Flistinfo%2Ftangerinesdr_lists.tapr.org&data=02%7C01%7CDavid.G.McGaw%40dartmouth.edu%7C02b7a4743765433aaddc08d8070c5441%7C995b093648d640e5a31ebf689ec9446f%7C0%7C0%7C637267096824743913&sdata=aXd%2BtOj5Rs0tgfGXrWi1T402cGUqgXcbtof5Akn7hU0%3D&reserved=0>
>
>
>
>
> --
>
> ----
> Phil Erickson
> phil.erickson at gmail.com
>
>
>
>
>
> --
> TangerineSDR mailing list
> TangerineSDR at lists.tapr.org
> http://lists.tapr.org/mailman/listinfo/tangerinesdr_lists.tapr.org
>
> --
> TangerineSDR mailing list
> TangerineSDR at lists.tapr.org
> http://lists.tapr.org/mailman/listinfo/tangerinesdr_lists.tapr.org
>

-- 
----
Phil Erickson
phil.erickson at gmail.com
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.tapr.org/pipermail/tangerinesdr_lists.tapr.org/attachments/20200602/e473ec63/attachment-0001.html>