Chuck is correct that trying to hit 160 through 6 meters with
a single output transformer at T501 has to be a compromise.
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Another compromise may be in having each LPF hit multiple bands.
There's 6 LPF's covering 12 bands, two of those LPF's cover 3 bands each.
They will obviously have much different characteristics across such a wide passband,
and there may be some fairly wild deviations in complex impedance.
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The QCX has a Class E LPF optimized for a much narrower band of frequencies.
Not surprising the QCX final is so much more robust.
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For some of us, 12 bands are more than we need.
Might be worth worth modifying the torroid turn count and cap values
so we have one LPF for each of 80,40,20,15,10 meters, plus one bonus WARC band.
Perhaps the WARC band could be made a plug-in LPF, I'd probably just settle on 30m.
Do away with attempting to also hit 160 and 6 meters, allowing T501 to be optimized.
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Jerry, KE7ER
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On Sat, Jan 18, 2025 at 09:39 PM, Chuck Harris wrote:
There is more to a final stage than just the output transistors.
A big part is the turns ratio of the output transformer, core
permeability, vs. the frequency range the transformer has to
handle.
If you have a radio that only covers 80m to 20m, it is going to
have an easier, more conservative time of it, than a radio that
covers 160m - 6m.
It is all about compromise:
Enough turns to provide sufficient reactance at the lowest frequency,
vs having too many turns, and too much reactance at the highest
frequency...
All the while providing a turns ratio that gives a safe impedance
match between the safe operating current of the finals at the
supply voltage and the 50ohm antenna.
And, a safe operating voltage at the maximum vswr that you reasonably
wish to survive.
So, if you want to know more about the problem, compare the output
transformers, and the bandwidth of the radios you think are rugged,
and the QMX+.
-Chuck Harris, WA3UQV
