On 03/05/2014 07:48 PM, Mel Whitten wrote:
> The HPSDR has now implemented predistortion and soon I think Walter K5WH, who
> is very active on FreeDV will have it for his TX. Perhaps, he'll share his
> experience with predistortion with us in the near future.
>
From what I've read, predistortion linearization does two things:
1. Model the inherent phase error of the amplifier and correct it by
applying an inverse phase change to the input signal.
2. Model the amplitude compression caused by "soft" saturation of the
amplifier, and increase the amplitude by the amount necessary to negate
this compression.
Obviously the amplifier reaches a point of "hard" clipping beyond which
no further correction is possible. But it's said that you can recover 3
to 6 dB of additional headroom for transient peaks this way, and reduce
the backoff accordingly. Thus, the efficiency of a linear amplifier can
be increased substantially when the input signal is known to have a high
PAPR.
Another alternative for us is to build amplifiers with more headroom. We
can provide power supplies that are capable of transient peaks of 12 dB
but not continuous operation. And the same for the heat sinks. An AB
amplifier might operate efficiently enough this way. I have the 300 Watt
power amplifier card for Angelia here (from the Russian designer) and
will try this if I ever get time.
Thanks
Bruce
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