At 01:12 PM 10/29/00 -0500, Chuck Counselman wrote:
>
>A few days ago in one of my all-too-frequent mental lapses, I tried to put
>200 W of CW RF power into a coax switch while it was set to short the line.
>There was a nasty, rich, fat, juicy sounding arc somewhere inside my Icom
>IC-775DSP that stopped only when I shut the transmitter off -- which took
>me a very long second to do. I was relieved and impressed that the Icom
>still worked afterward. OTOH, I was disappointed that its protective
>circuitry had allowed the arc to happen. (I wonder whether there's a
>deliberate spark gap in there somewhere, or whether I burned some expensive
>component to within a micron of the end of its life.)
>
>Naturally I worry about what will happen when I pull the same stunt with my
>even-more-expensive high-power amp. What do AMPS members suggest about
>protective circuits? I hear almost nothing about them, which is
>surprising. It'd be easy to connect a fast relay or solid-state switch to
>the exciter/amplifier keying line. The question is what / how to actuate
>that relay. Wouldn't a simple reflected-power detector do the job? If
>such protection is as simple as I imagine, why isn't it standard in every
>hamshack?
The RF Applications VFD wattmeter, though not inexpensive itself, has an
inexpensive option for unkeying the amplifier as soon as it senses SWR
above an adjustable limit. The company also makes (or at least, did make)
a sensor unit to do the same job by itself (without the VFD). It's not
cheap, though.
Just a satisfied customer...
73, Pete Smith N4ZR
Contesting is ... Extreme Radio
The World Contest Station Database
is back up and running at
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