Topband: Rig Comparisons

[Paul Christensen]

> "I read the technical report on "Pure Signal" and it
sounds like what we used to call a "hero experiment"
in the research lab where I worked, consisting of a
few impressive results, but with many disclaimers,
and nothing you could productize.  What is supposed
to be new is the adaptive part, but it depends
on the amplifier being "well behaved".

Rick N6RK"

Rick,

Their implementation of adaptive pre-distortion (APD) works very well even 
without "well behaved" amps and substantial IMD improvement is easily 
attained with existing bipolar transistor, FET, and vacuum tube amps.  I 
have personally witnessed 3rd-order IMD improve from -30 dBc to -55 dBc 
using tube and solid-state amps.  In fact, the algorithm works so well, you 
can take a Class B amp and typically improve IMD from -18 dBc to -40dBc with 
*no other alterations to the amp*.  This is not just some lab tinkering that 
looks good to impress on paper.  It's real and the effect is huge.   The 
improvement is easily seen (via panadapter) and heard on the bands.

Moreover, what I've seen is not just two-tone improvement.  These numbers 
are attained with dynamic speech.  Go ahead, deliberately mistune an amp 
into non-linearity.  Within reasonable limits, the adaptive algorithm 
immediately re-establishes the IMD improvement.   If we want, we could 
forget all about "50V finals" in our solid state transceivers and amps.   We 
don't need 50V with APD.   Based on what I've seen from AC2IQ and WA1OXT, 
one could take an RM Italy solid-state amp and make it perform as well as 
any 50V final amplifier running class A.   It's that good.

Paul, W9AC