can we do Quadrature pairs?

Sylvain Munaut 246tnt at gmail.com
Thu Apr 26 05:44:35 UTC 2018


> can the USB to VGA adapter output quadrature I and Q pairs via the red and
> blue channels? with maybe using green as a configurable local oscillator.

Sure, we thought about that. But :

 - IQ modulator chips are not cheap and you'd need to low pass I/Q
before injecting them there.
 - The LO range would be quite restricted because for a LO you want a
clean signal (no hamonics, or as litte as possible, and as little
jitter as possible) so you'd have to use a freq way lower than the
sampling rate and filter it. But then you have like ... 0 - 35M LO,
not super useful.
   Using an IQ mod with built in LO and control it via I2C is much
more viable ... but more expensive (several times the price of the vga
dongle in the first place)


Cheers,

   Sylvain


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