Re: ATUs, Delta and Losses (QQ, Jan 96)


Date: Sun Dec 31 1995 - 05:47:02 EST


Many thanks for the kinds words on the article. I wanted to introduce
the readers to the overlooked but very useful concept of delta and
worried about already overusing the pages of QQ. However, anyone
interested can verify your observations about the limitations of any of
the ATU networks by running a few low impedances through the program and
seeing the pattern of what I call root network efficiency (which does not
account for losses from component deficiencies, connectors, wiring, case
proximity, etc.). HAMCALC 12 is the current version available from
VE3ERP and has an updated version of ZL1LE's program on board.

Back in the final days of tube amplifiers, PI networks were discouraged
for ATU use due, apparently, to the difficulty of obtaining capacitors
with the requisite capacitance and power ratings. However,
well-constructed capacitors suitable for QRP power levels are more or
less easily available, and that strike against PIs is now only a pass ball.

I can only reaffirm your remarks about sustaining component Q throughout
tuner construction and minimizing strays, especially to the metal walls
of tight cases.

I hope you will be sure Ron Stark gets a copy of your observations, as is
or extended. Many readers of QQ are not on this list and deserve to read
your remarks. Perhaps I am a little less critical of the C-L-C Tee,
since I believe in advance filtration to suppress harmonics without
relying on the ATU. However, although not compact, an L-C-L Tee is a low
pass network ATU. High Q variable inductors permit hitting the low-delta
tuning combinations, and a plexiglass case eliminates case strays. See
the next issue of <72> for some ideas on this design. In any ATU
network, a variable inductor is as important as a variable capacitor for
hitting the most desirable matching values. Switched inductor values, in
this regard, are always compromises, although circumstances may dictate
their use.

Thanks again for the observations and the kind words.


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