On Wed, 11 Mar 2009 23:36:57 -0500, Tim Wescott
wrote:

On Wed, 11 Mar 2009 21:11:18 -0500, Bart Rowlett wrote:

PSK31 uses a raised cosine amplitude weighted amplitude function in
order to contain the occupied bandwidth. Use of a class C amplifier
disrupts the weighting and causes the bandwidth to spread considerably.
The demodulator will still work fairly well but the spectral spreading
is considered un-neighborly!

bart
wb6hqk

So, PSK-31 is out.

(Unless you want to get fancy and amplitude modulate to preserve the
envelope at the same time that you phase modulate the VFO input to
preserve the phase. There's almost no sane reason to try this, but it'd
be fun if it worked. Kind of a "Look how well my old iron works! (pay no
attention to the DSP behind the curtain).")

A plate modulated AM transmitter is basically a class C amplifier with
variable supply voltage, unfortunately it is hard to get 100 %
modulation with such simple systems, i.e. it is hard to get the power
down to 0. However, much of the PSK-31 envelope can still be
simulated.

Plate modulated AM transmitters for voice communication might have a
modulation transformer with a quite limited bandwidth, which might not
work well the slow PSK31 envelope.

Paul OH3LWR