Quote: The measurement of this improvement, however, would be
difficult, because the tuned input would improve the IMD of the
transmitter driving the amp (or, to be more specific, the lack of a
tuned input could decrease the IMD of the transmitter).
Herzog insists that The above is not true.
I have two points;
1. Using a tuned circuit, or deleting it and saving a million dollars,
left me lots of time to study it's effects.
IMD was the same, and the AN/FRT 84 transmitters, and it'
successors prove something, 600 Ten Kw transmitters driven by standard
1 KW transmitter, through 15 feet of coax.
2. Driving a tube, (I only used cathode driven stuff) with transistor
drivers gives MAGIC IMD performance. a 25 db IMD transistor driver,
driven to same power as used by the tube, but into a 50 ohm load.
Then a pair of paralleled tubes which gave also 25 db IMD distortion
when driven by a really clean lab transmitter.
But when these were coupled, the 45 db IMD distortion spec was met
consistently. They were Eimac triodes, Beryllium block cooled, and gave
100 watts out. We had to get Eimac to promise NOT to change anything
about the tube, for fear it wouldn't correct the transistors distortion
so well. There was no tuned circuits between. This was a AM???? Marine
transmitter, with over 600 units produced.
Similar lab test using a stock 500 watt transistorized transmitter to
drive the AN/FRT 84 final yielded IMD that was below 50 or 60 db,
couldn't be seen. Unfortunately The management said there was no market
for it, as this only held true up to 24 MHz. Then the driver distortion
changed.
This all dropped when I was retired in 1986, as Collins won the next
Military transmitter round.
K 2 L B Wil Herzog, professional engineer.
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