[time-nuts] GPSDO project (SDR)

Alberto di Bene dibene at usa.net
Mon Jun 29 22:20:50 UTC 2009

Dave Baxter wrote:
> Personally, I wouldn't bother with any high accuracy clock/oscillator
> for the SDR, unless you can also synch the AD sampling clock in the
> soundcard.

The SDR-IQ,  SDR-14, Qs1r, Perseus and the HPSDR project do not rely on a sound card ADC to sample any signals.....
The RF signal is directly sampled at RF, with sampling rates up to 122.88 MHz (depending on the model), then it
is frequency-shifted, then downsampled by the firmware in the accompanying FPGA. Then the downsampled stream
is sent to the PC via the USB 2.0 port.  The software on the PC receives directly digital data, no pesky
sound card is needed to digitize it.

So the _only_ factor affecting the frequency calibration is the clock of the RF ADC.

73  Alberto  I2PHD

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