>
> Hmmm.
> That was a related but different subject - how to load push pull 807
> finals
> for maximum RF into transmission line, if not perhaps into load.
> Counts on mental fingers. Hmm. Perhaps just under 50 years ago. How time
> flies when you're having fun.

I remember doing stuff like that. First amateur transmitter used a 6146.
First broadcast transmitter I worked on used 833s for the finals and 807s
as the drivers (this was a Gates BC250T). Later AM transmitter used 4-400
tubes (Bauer 707). Then FM with a 4CX3000. My current amateur HF
transmitter (converted maritime mobile) has an external antenna tuner with
an interesting design. It has a pi network. The input C is a string of
capacitors with relay contacts to ground. The C values are powers of 2 so
a binary code selects the capacitor value. Similarly, a bunch of inductors
(again, binary weighted) are in series with a shorting relay across each.
Finally, at the output is another C network with relays. A MC68705
monitors the input SWR (actually, voltage, current, and phase samples),
and adjusts the L and C values to present 50 ohms to the input.

For VHF and above, I've largely relied on the antenna presenting the
proper load to the transmitter and not done any tuning. Maybe some day
I'll dig into that some more with stripline networks, Smith charts, etc.

Harold
WA6FDN



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