[hpsdr] Closing the loop.....

[Dan Mills]

Just wondering if anyone else out there is playing with cartesian
feedback for PA linearisation (And/Or drain supply envelope tracking),
with DUC/DDC radios?

Doing it really right really wants a few things Hermes does not have
(Several fairly fast AD & DA converters, switched attenuator somewhere
further down the TX chain for lower overall noise when power is backed
down, switched inputs to the ADC), but hermes would make an acceptable
platform for some experiments.   

I have it working in matlab, and some bits of it in VHDL, but if there
is existing work out there, that would be useful to know about?

I started off building a cartesian loop TX in the analogue domain, which
worked, but DC stability and component matching became a nightmare,
DUC/DDC looks much easier.

Regards, Dan M0HCN.