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[AMPS] reflections

To: <amps@contesting.com>
Subject: [AMPS] reflections
From: cshinn@connect.net (Charles D. Shinn)
Date: Wed, 5 Mar 1997 19:40:01 -0600
If SWR is such a major concern, why do satellite antenna designs typically have 
SWR's of (pick a value-usually large)? They design for maximum radiation 
efficiency and be damned with the SWR. ERP and efficiency are the name of the 
game and apparently SWR has little or nothing to do with that circumstance.
de W7MAP Chuck.......

----------
From:   Tom Rauch (W8JI)
Sent:   Wednesday, March 05, 1997 2:32 PM
To:     amps@contesting.com
Subject:        [AMPS] reflections

Doug Hall wrote:

> seems totally incorrect to me. What happens to the 1000 watts of
reflected
> power? Does it come back into the amp and just sit there? Of course not!
> It's reflected back up the feedline to the load, right? 

Doug,

A complete discussion of reflected power would make a good textbook.
There are two ways to look at it, as voltage and current changes in the
line (the line as a circuit), or as wave theory.

Either method works perfectly in an analysis of the system. 

No matter HOW you look at the problem, the answer is the same. The
reflected power is subtracted from the forward power, and the result is
the actual power. Only a poorly designed meter or a non-directional
meter would give a false reading.

NONE of the reflected power "makes it back" to the tube, unless the
pi-network is improperly tuned. When the network is adjusted for maximum
power transfer, the tube still sees a perfect load. Reflected power does
not even  increase RFI or TVI, unless the line has common mode
(parallel) current problems. 

Walt Maxwell's book "Reflections" handles the discussion nicely from the
wave theory angle.

73 Tom



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