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[TowerTalk] Force12

To: <>
Subject: [TowerTalk] Force12
From: (Paul Christensen)
Date: Thu, 4 Oct 2001 13:44:31 -0400
> > resistive with a purely reactive content.  The bottom line is it
> > doesn't matter.  In a 2:1 environment, 88.9% of your power is still
> > radiated by the antenna.
> The worse thing anyone ever did to understanding how RF systems
> work was present SWR as "match efficiency" or "percent reflected
> power".

I'll certainly agree with that Tom.  The quoted statement above is still 
correct if we modify it to indicate that "In a 2:1
environment, 88.9% of the generated power is the *minimum* power radiated by 
the antenna with loss-less line."  With a purely
resistive generator such as today's genre of solid-state transmitter blocks and 
no built-in ATU or Pi network (e.g., Ten-Tec Omni
Six), the best "match efficiency" we could expect to see under a 2:1 
environment is 88.9% with loss-less line.

If a network is placed anywhere between the generated source and the antenna 
feed point (e.g., transmatch, ATU, VT Pi-network, or
strategically-placed L/C components) and if that network is adjusted to provide 
a system conjugate, then the best match efficiency
will be greater than 88.9%, and likely approach 100% with a loss-less 
transmission line. (100% match efficiency being equal to a 1:1
VSWR antenna input match).  If we begin to introduce line loss, transmitted 
power at the antenna terminals becomes less as the
aforesaid network is placed further away from the antenna terminals and back to 
the generator.

I suppose the moral of the story is that "match efficiency" is a function of 1) 
the presence of a system conjugate, 2) if used, the
location of the corrective conjugate network, and 3) the complex, collective 
combination of line VSWR and line loss.  Any discussion
of match efficiency without knowledge of all three parameters is pointless.

-Paul, W9AC

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