[hpsdr] predistortion

[Warren C. Pratt]

Hi Frank,

I already have pre-distortion up and running in prototype form--using
full-duplex to collect the information to calculate the correction.  Samples
are continually collected during transmissions and correction is
re-calculated at intervals as desired.  There are still a few rough edges to
work out; however, testers with 50V LDMOS amplifiers are seeing typical
reductions of IMD from about -30dB (without pre-distortion) to about -60dB
(with pre-distortion).  12V FET and bipolar amplifiers are considerably more
difficult to correct as they typically have a much higher level of thermal
and supply-related memory effects.  There is a special configuration
required in firmware to facilitate collection of the samples; however, I've
implemented all the core algorithms in software--I can do the job much more
simply and precisely there than in firmware.

This is still prototype--not sure yet about a release plan.

73,
Warren  NR0V



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