[TowerTalk] Reflection Gain

[Guy Olinger, K2AV]

Hi,

I believe the confusion lies in the use of "gain" in an esoteric term,
rather than to describe something which makes us louder than the other guy
in a pileup.

Reflection Gain is apparent gain (makes the Bird meter in the transmission
line read higher) with respect to power delivered to the tuner/transmission
line/antenna system. Try a mechanical equivalent:

Consider a go-cart with a one horsepower engine hooked up to a huge flywheel
geared way down to the drive wheels. You hit the gas, but the engine revs up
very slowly because it is investing energy in the flywheel. When you let out
the clutch the effect is much larger than the one horsepower engine because
of the energy that has been stored in the flywheel. If you measured the
force from the flywheel at the time, it would be larger than you could
possibly get out of the engine. Further, if you kill the engine out on the
track at top speed, the energy from the flywheel will keep you going for a
while longer, even though the engine is off.

BUT, the total energy, if you added it up over the time of the drive, is
still no more than you can get out of the little engine over that time. If
we used parallel terminology, the apparent increase in force when one lets
out the clutch and does a wheelie with the flywheel could be called flywheel
gain. It's real in the short term, a mirage in the long term.

In the mismatch system discussed to oblivion here recently, assuming small
losses in the feedline & tuner, the reflections just add up in the system,
flywheeling back and forth in the transmission line system until it finally
can be dissipated in the antenna load. The Bird in the transmission line is
measuring the power moment (the flywheel energy), the transmitter is still
only putting out rated output (the engine output) and we are still putting
something less than the rated output on the antenna (power on the rubber on
the road). The power moment vs... the transmitter output is the reflection
gain.

As you can see, reflection gain is gain you don't get to keep. (A cynical
mind would say that they invented reflection loss just to cancel it out.)

Ain't this junk wunnerful?

73, Guy.



-----Original Message-----
From: Charles R Constantine <kr6c@juno.com>
To: towertalk@contesting.com <towertalk@contesting.com>
Date: Wednesday, September 09, 1998 10:31 PM
Subject: [TowerTalk] Reflection Gain


>
>I have read several articles and books including Walters W2DU Reflections
>and ARRL Antenna book and they all basically say the same thing.  The
>enlargement of the forward power or the re-reflection of the power in the
> Transmatch is called "REFLECTION GAIN".
>"REFLECTION GAIN" cancels "REFLECTION LOSS".
>
>Once again im confused. (or dont understand). If its not gain what is it?
>
>Chuck KR6C
>
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