[NLRS] Protecting a transverter from an IC-746

[David Palm]

My main rig in the shack is an Icom IC-746.  I'm extremely fond of it--I
bought it from a ham who had tried to "fix" it, by replacing the surface
mount connector for the control head ribbon.  Well, he fixed it alright,
hosed it up good and proper.  I got it at a good price, rebuilt the area on
the surface mount rework station at work, mounted a new connector, and
Voila! I have a working 746!  On account of that rig's respectable 100 watts
and decent receiver on 2 meters, I'm now into VHF stuff.

I love the rig, but it's not at all transverter friendly.  There isn't any
low power output port.  You can turn down the main power to about 5 watts,
but even then it's a manual operation that can easily be forgotten.  Sure as
heck, if I hook that dude up to an unprotected transverter I'll be toasting
it in a hurry.

It seems to me that all I need is a circuit that will detect that the 746 is
in transmit mode, then look at the current on the IF.  If the current is
above, say, 100 mA (200 mW into a 50 ohm load) then it leaves a relay open,
dumps the RF into a dummy load, and turns on a warning LED.  If the current
from the IF is below 100 mA then it goes ahead and closes the relay and that
flows to the transverter.

I've looked a bit on the 'net and strangely, haven't come up with a circuit
for that purpose.  Am I on the right track?  I can design it myself, but
does anybody know of an existing design out there?  Anything else I'm
missing?

Thanks and 73,

David  W9HQ