[AMPS] 3/2 power law and Rich's very wide signal

[Peter Chadwick]

Steve says:

>What is a reasonable value for the source impedance of the rectifier. 

I looked this up and posted it a while back. The rectifier resistance is of
the order of 8 to 15 ohms (it varies with current) so the total source
resistnace isn't going to exceed about 350 to 400 ohms. The original G2DAF
used a total of .007 microfarads screen bypassing/ reservoir capacity, so
the the tc is a bit under 3 microseconds. So if it takes 5 tc's to charge, I
make it that 99.33% of the voltage will be reached in under 15 microseconds.
So the bandwidth of the system (from rise time multiplied by bandwidth =
.35) is about 23kHz. As this is about 10 times the signal bandwidth, prima
facie, there shouldn't be a problem.

And I still don't like the G2DAF! Don't forget that at the time, there was a
lot of argument in the RSGB Technical Committee circles about it; G6JP (who
worked in the design, manufacture and applications of valves for the M-O
Valve company all his working life and served on some of the International
Electrotechnical Committees as a UK delegate) openly criticised the design
in the letters page of the RSGB Bulletin, as it then was, on grounds of
linearity.

Technicalities apart, there was a definite attitude in some parts of RSGB at
that time that anything G2DAF did or said was right, and those disagreeing
were cast beyond the pale into the outer darkness with much wailing and
gnashing of teeth..........a number of professional engineers working in SSB
design were 'sidelined' out of the way of RSGB position for disagreeing, as
I heard it. One of the guys who told me a lot of this has just gone SK,
unfortunately.

73

Peter G3RZP


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