Sigi as you are using VST plugins have
you tried the Waves L3 Multimaximizer? It is hard to make it
sound bad and it certainly increases talk power with minimal
distortion, it never overshoots.
the nice thing when using all in software (sdr) you can do
things with compression, limiter, etc etc ... that you can
NOT do with analogue circuits
your "rf clipper" may produce a more boosted signal ... but
i guess when all is made in software you can be a bit better
the sdr has the audio in a chain (buffer) and you can have
a look forward agc ... limit every word to the maximum
without overshooting or harmonics produced
and with a monitor receiver on the output of your amp you
can add predistortion ... result is an even cleaner (but
more punchy) signal
you could try to combine your rf clipper with the processor
in sdrc (but do not crank it up tooo much) ... i do a simlar
thingy with my mixing software (voicemeeter potatoe) with
some vst plugins added in the chain ... first the plugins do
a tiny bit of compression and limits the peaks not to
overdrive the sdrc input ... and a bit of processing of the
sdrc is added afterwards ... the result is a well boosted
signal with no splatter (pay also attention not to produce
intermod distortion on the final amp or driving stages!!)
simon you have the equalizer ... what if each filter in the
eq would have its own processor and limiter?? is that what
you mean with half octave filters (and boosting those) ?!?!?
Interesting article. I did experiment
further with the processor settings and compared the
result with an analogue speech processor that was part of
a ssb rig I designed about 20 years ago. This processor
uses variable rf log clipping of an ssb signal (at
10.7MHz) followed by another ssb filter. The audio is
pre-processed by a syllabic compressor (a vogad). The
clipping is done with two stages of log amplifiers. In the
original design the resulting ssb was converted to the
required frequency but I had already added a demodulator
back down to audio for something else so here the output
is audio. As the article points outs, non dc baseband
clipping avoids the serious harmonic distortion that
baseband clipping induces at all but very light clipping
because the harmonics multiply outside the passband. There
are still intermodulation products that eventually limit
Of course this processor is very
component hungry by today’s standards and I happened to
have it on the shelf. As the article also points out, the
the same result can be achieved in dsp by other means that
could not be realised in practice by analogue circuits.
I feed the audio output at line level
into the pc and have the SDRC processor turned off. The
audio processor bandwidth is from about 200Hz to 2.4kHz,
determined almost entirely by the analogue ssb filters.
I think that overshoot is a slightly
different, but related problem. Interestingly though I had
a look at this processor’s performance by putting test
sine and square-waves frequencies into it and looking at
the audio output on a scope. Probably by more luck than
judgement, the overshoot is a few percent unless the
processing is set ridiculously high. I suspect that a
fortuitous combination of filters and time constants, plus
the relatively narrow bandwidth requirement helps.
I have not checked for overshoot on the
rf output from the Limesdr that eventually generates the
signal for transmission.
My metering indicates that the average
to peak power ratio has increased significantly and,
although this is pretty unscientific, the “hf pileup
breaking index” is markedly improved.
Nothing can be all things to all men
(or women). Everything is a compromise of requirements,
performance, complexity, time and cost.
Sent from Mail for Windows
I use a single band RMS compressor
followed by a very-well designed limiter which avoids
overshoot. I’ve tried multi-band compressors but not
achieved much benefit. When I get into my main winter
project I may look at this again, having a compressor
instance for each octave or half-octave.
For winter I want to finally play with
my Hermes-Lite 2, with my main amplifier I’ll have ~350
watts so will want to boost the audio.
Simon Brown, G4ELI
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