[TangerineSDR] 10 Mhz leakage

[Engelke, Bill]

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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