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SV: [AMPS] Re: SV: G2DAF

To: <amps@contesting.com>
Subject: SV: [AMPS] Re: SV: G2DAF
From: G3SEK@ifwtech.demon.co.uk (Ian White, G3SEK)
Date: Sun, 1 Nov 1998 10:31:05 +0000
Lars Harlin wrote:

>
>-This is a plot from HP Spectrumanalyser taken about a year ago, and using 
>speech - not
>-two tone. Lower curve is for exciter alone....
>
>-Sorry for the bandwith, but guess a picture says more than a thousand 
>words....
>
>-73 de Lars/SM3BDZ
>
>Well, this did not seem to work - fileattachment. After another thought,  it 
>might be just as good, especially
>here on the reflector.
>
>So, anyone of you guys who find interest in seeing these plots, drop me a mail 
>and I will mail you directly!

Yes, please send me a copy, Lars.

Can you also say what tube, what anode voltage, and how the screen
voltage was generated (voltage doubler/tripler? solid-state rectifiers
or vacuum tubes? Value of DC smoothing capacitor?)

Something tells me that all of these details could be important...

One risk with the G2DAF configuration is that a screen rectifier with
poor efficiency would tempt the user to overdrive the whole amplifier in
order to generate sufficient output. Thus there could be a lot of
variation between a good G2DAF linear and a bad 'un. 

The choice of tube could also make a big difference between good and
bad. As far as I know, all the original published work was done with
813s and 4-125s.

In the late 1960s I had my education about SSB from listening to G2DAF's
80m net, whose members were bitingly critical of poor-quality signals -
so much so that like many other listeners I didn't even dare to check in
for a report! Certainly there were several G2DAF amplifiers in use on
that net, and if they hadn't generated a clean SSB signal the owners
would have been flamed to a crisp after the first transmission.

Later I met Dick Thornley a few times, heard him talk to clubs, and saw
his construction work. He was a perfectionist in every detail; and he
owned his own spectrum analyser which was a real rarity in those days.
Certainly he was the first to ask for criticism about his own signal
quality. He also wrote a regular magazine column on SSB techniques when
this was all new, experimental stuff. 

So I am in two minds about his amplifier. Part of me says "This should
not work." But having been around at that time, and known some of the
people involved, I also feel that G2DAF would not have given his name to
anything that put out a poor-quality signal.

There's much more to learn about this.

73 from Ian G3SEK          Editor, 'The VHF/UHF DX Book'
                          'In Practice' columnist for RadCom (RSGB)
                           http://www.ifwtech.demon.co.uk/g3sek

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