Fred,
Dirt was young when I was first licensed too.
I do remember those days of link coils that you slowly advanced into the
PA inductor and re-dipped the plate until the current draw was correct
for the power level that you wanted to operate. Those were the days of
plug-in coils for each band. Yes, I do have some of those plug-in coils
and swinging link coils in my stash of "old stuff" in the attic.
Then came the Johnson Matchbox with its band switching capability (I
have one of those too), and multi-band PA stages with a Pi-Network.
Those days are past. Many new hams do not know how to 'dip the plate'
and then increase the "loading " and re-dip the plate until the plate
current was as desired.
I now do not recommend a transceiver to a new ham if it has 'tuning' and
'loading' knobs - the information about how to do that properly is just
not abundant today as it was in years past.
Add to that fact that the re-tuning had to be repeated for each band
change or significant QSY in the band.
We have come a long way with the advent of solid state PA stages and
broadband tuning with only a Low Pass Filter at the PA output - but the
penalty of that is we now have to operate the PA stage into a 50 ohm
load. That is where the ATU comes into play. The variability in the
antenna feedpoint impedance has been moved from the PA output stage to
the "tuning unit" to allow us to feed antennas that present an impedance
of other than 50 ohms to the PA stage.
73,
Don W3FPR
On 8/4/2016 8:41 PM, Fred Jensen wrote:
All this "matching bafflegab" was unheard of when I was a young ham.
You fed your dipole with 75 ohm twin-lead, coupled it to the PA with a
2 or 3 turn link coil, and as the reactance of the link changed the
resonance, you compensated by "re-dipping the plate."
Of course, when I was a young ham, dirt was pretty young too. :-)
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