[TowerTalk] Mismatch Loss and Tuners

[Jim Reid]

-----Original Message-----
From: sbest@cushcraft.com <sbest@cushcraft.com>
To: towertalk@contesting.com <towertalk@contesting.com>; w2du@journey.com
<w2du@journey.com>
Date: Monday, August 24, 1998 7:14 AM
Subject: [TowerTalk] Mismatch Loss and Tuners


Steve Best writes,  in part:

--snip--
>
>     In order to arrive at the steady state condition,

--snip--

>     SUMMARY -  A matched antenna will significantly outperform a
>     mismatched antenna with a tuner.  A tuner cannot introduce "reflection
>     gain" to change this fact.

That summary is not correct!!  Other wise most broadcast stations,  most
of which use antenna tuners would be wasting a lot of money!!  Their
vertical radiating towers are not 1/4 wave tall,  in most cases,  for
example.


In this overly wordy argument put forth by Steve,  he omits one tiny
detail:  the tiny amount of time that these reflections within the
transmission line between the antenna and the tuning network exist,
both initial and  following about which he belabors!

These reflections  are over and done with in  nanoseconds,  in even the
lowest propagation velocity coax where  the speed of the signal is
only 60 some % of the speed of light in space!

How long does a 30 wpm CW dit last;  that is,  the shortest "pulse"
of RF energy from a typical HF amateur transmitter?  About
40 milliseconds;  or around 40,000 times longer than the reflection
phenomena over which he labors!!!  Can either the transmitting rig
or the rcvg rig react to the nanosecond reflection phenomena,  as
far as perceived radiated power is concerned??  Of course not,
in  fact,  the only signals such reflection could become noticeable
would be certain types of digital modulated signals,  and even then
ONLY at UHF frequencies when the bandwidths of the circuits
of both rcvg and xmitng rigs were a few MHz wide;  not the case
at HF at all.

Even with a 20:1 vswr low loss line,   99+  watts of power of a 40 msec,
30 wpm "dit"  will be radiated,  and none of the nanosecond reflection power
will
be missed,  nor will  the coax or twin line heat up in those nanoseconds,
so resistance due to heating will not occur,  and attenuation will not
increase!!

No field strength meter will detect a dB's difference between a 1:1
antenna/line match and a 20:1 line match in the above example with
the tuner between solid state rig and the transmission line properly
adjusted,
or the tube output plate circuit properly adjusted in a tube transmitter's
final output stage.

73,  Jim,  KH7M
On the Garden Island of Kauai





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