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[TowerTalk] ++ High SWR and Modern Transceivers

To: <towertalk@contesting.com>
Subject: [TowerTalk] ++ High SWR and Modern Transceivers
From: K3BU@aol.com (K3BU@aol.com)
Date: Wed, 12 Dec 2001 08:36:29 EST
In a message dated 12/12/01 7:01:41 AM Eastern Standard Time, w8ji@akorn.net 
writes:

> 
>  > Guys, all I asked was whether I could do any harm to my transceiver by
>  > operating it into a high-SWR load, or at least one high enough to
>  > cause the output power to be folded back by the protective circuitry.
>  
>  I wasn't answering your question, because no one can answer it. 
>  The only answer is if it didn't blow up, it is probably OK. 

I can answer it :-)

You most likely will be stressing the circuitry in the transmitter. Depending 
on the SWR cut back protection circuit and its time constant, there could be 
glitches of overload on final transistors before the circuit cuts back and 
you would be operating the finals on the borderline where protection circuits 
take on. Let's say that protection kicks in at SWR 1.999, you would be 
"allowing" finals to run with percentage of loss even if protection cuts back 
the power.
 
I like to operate my power circuits without unnecessary hurdles. Antenna 
impedance designed to match feedline, PA matched to feedline, exciter output 
matched to PA input. Takes little effort, avoids potential problems 
especially in the contests.

So the final answer? 
It is better to let the protection circuits do their job - protect the finals 
in case of failure (of matching circuits) rather than using it as "power 
control".
Now the $10,000 question please?

Yuri

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