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[AMPS] High-SWR protection

To: <amps@contesting.com>
Subject: [AMPS] High-SWR protection
From: rakefet@rakefet.com (Vic Rosenthal)
Date: Mon, 30 Oct 2000 07:29:22 -0800
Tom Rauch wrote:
> 
> > 2. use the SWR alarm relay to apply cutoff ALC voltage to the exciter;
> > this method protects the amplifier's relays, so it's better than just
> > de-keying the amp.
> 
> If the relays in the amp are properly sequenced, dropping the relay
> line won't hurt a thing.

By 'properly sequenced' I presume you mean that the output relay closes before
the input relay and opens after it.  But even in this case, dropping the amp
relay line hot-switches the input relay.  I am afraid the 50-100 watts from the
exciter could damage the small input relay.

The exciter PTT line is another story and might be OK.  In my case, I operate
full break-in CW with the internal keyer in my exciter, so there isn't an easily
accessible 'ptt' connection.  I intend to find a more foolproof way of quickly
shutting off the output of my exciter.

Interestingly, the other day I was testing a 160-meter antenna with a remote
tuning device in which I had underestimated the required spacing for a
capacitor.  It arced, causing the swr protection circuit to actuate.  The arc
lasted much longer than I liked!  I think the problem is that the VFD uses a PIC
(or something) to compute the SWR, and that this circuit takes a long time to
actuate.  So I'm not sure any more that this is the ideal type of protection
device -- a simple directional coupler with a DC-amplifier would be a lot
quicker.

73,
Vic, K2VCO
Fresno CA

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