[time-nuts] WWV Doppler Shift

[Attila Kinali]

On Tue, 20 Nov 2018 15:30:54 -0800
"Tom Van Baak" <tvb at LeapSecond.com> wrote:

> How hard would it be to use a hands-off SDR to produce a 5 MHz WWV phase 
> data point every second?

Fairly easy. If you go for one of the RTLSDR dongles, you will
have to do the direct-sampling-mod[1], as the tuner chips do not
go this low, and provide an external filter. Using the right
sampling rate (ie something odd) and both 60kHz and 5MHz will
end up somewhere nice. For additional goodness, I would either
lock the 28.8MHz crystal to a stable source, or use a third
RTLSDR dongle to provide the 28.8MHz clock for the other two,
and sample with that a convenient stable signal (eg. the harmonics
of an 10MHz signal).

Alternatively, and much simpler, bu5 more expensive, you can go
for an airspy[2] which already has an external reference input
and two ADC inputs. All you need are some pigtails with U-FL
connectors for the ADC inputs, and an MCX one for the reference
clock source.

			Attila Kinali


[1] https://www.rtl-sdr.com/rtl-sdr-direct-sampling-mode/

[2] https://www.itead.cc/airspy.html?acc=cfcd208495d565ef66e7dff9f98764da

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