[AMRadio] WARNING: Overload protection is not 100% reliable even when relays are functioning properly

Donald Chester k4kyv at charter.net
Mon Oct 26 14:38:24 EDT 2015

-----Original Message-----
 Steve WA1QIX wrote:

This is a definite overload scenario, and there really should be a detection
element for this condition.

In the overload protection system I use for the solid state transmitters,
one of the inputs is SWR.  This is very easy to detect
- I modified an existing SWR meter and fed the forward and reflected power
outputs back to the overload shutdown system.  A comparator compares the
reflected power to the forward power, and if the reflected power is too
high, that's an overload and the system shuts down.

SWR shutdown is part of virtually every "rice box", and it's not too hard to


I have pondered the idea of something like that, but the problem is I don't
have a  sprig of 50-ohm coax anywhere in my entire antenna system, so I
can't conveniently monitor SWR; everything in the system is inter-connected
with open wire line, some of it running as a tuned feeder and some as a flat
line.  I did cobble together a balanced MicroMatch several years ago, based
on the one described in the April, 1947 QST, but it is too cumbersome to
permanently insert in my feeder section where the line runs flat. Maybe some
variation of the "twin lamp" indicator could work. In the meantime, I  just
make it a point to keep an eye on the scope and the final tubes.  I made
that a little easier with my Gates BC1-T/Raytheon RA-1000 hybrid I use on
160,  by cutting out the missing corner from that goofy little triangular
peep-hole on the door, converting it fully to a  rectangular window.


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