Hi Peter,
> >Look at the TS-2000 as an example. It is almost class C quality, yet
> >reviews all ignore that fact.
>
> Not quite Class C - it would be about 7 or 8 dB worse in that case! Tom is
> correct though - it is really unacceptably poor.
I've measured solid state zero-bias transistor amps at about the
same IMD level as the TS-2000. I wonder what they did wrong? It
would be interesting to look at one on a three-tone test, and to see
how IMD varies with power.
> >Keyclicks are designed in by manufacturers using excessively fast rise
> >and fall times
>
> I believe there are two parts to this:
>
> 1. A demand (or a belief that there's a demand) for rigs to be regularly
> operated at 50 or 60wpm.
I can operate 60 WPM and have bandwidth below a few hundred Hz.
> 2. A failure to look on a spectrum analyser at the design stage with the
> transmitter keyed with a square wave at 30wpm or so.
Keying speed is relatively unimportant as to bandwidth, and every
key is a square wave output. Sideband bandwidth is controlled by
the shape of the waveform, and level is a function of delta voltage at
the slope.
The problem is everyone, including the ARRL, has this fixation
about a single-pole R/C filter (or the shape produced by such a
poor filter) being adequate for waveshaping. The waveform in the
ARRL Handbook is a pathetic single-pole filter slope (3dB per
octave).
The ideal shape is a raised sine wave shape, not the "perfect"
shape they show.
If you filter the keying signal in a multi-section filter and apply it to
a linear modulator scheme you can cut off the sidebands at 150 Hz
and have very good sounding CW at more than 60 WPM with
sidebands suppressed 50 dB or more.
A single LM358 op-amp and a single PIN diode modulator would
make a virtually clickless AM modulator for CW. It would cost less
than $1 to make click-free radios. In some cases it is adding only a
few resistors and capacitors!
>
> This latter may well be because there aren't that many designers of
> transceivers who actually are operators, especially CW operators.
>
> If transmitters met the old marine specs, it would be an improvement.
> Incidentally, in my recently built 'classic' 807 tx, I found that it was
> impossible to get down to 99% power bandwidth of 250Hz (as per ITU
> recommendations) at 30 wpm dots without excessive rounding of the
> characters. I could get it within 400Hz, though. The 'break' seems usually
> to be the problem, but not in this case.
>
> And I still don't go a bundle on ALC!
>
> 73
>
> Peter G3RZP
>
>
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>
73, Tom W8JI
W8JI@contesting.com
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