[NLRS] Protecting a transverter from an IC-746

[Chris Elmquist]

I was able to set the MAX power out of the 2m port on my IC-746 with an
internal pot...  so that when the front panel power control was at max,
at most 1W was produced by the rig.

If you study the schematic, you will find a pot inside that sets the max
power to which the front panel pot can go...

My '746 then drives into a DEM 902 transverter at a 1W level.

Chris N0JCF

On Wednesday (09/16/2009 at 02:52PM -0500), David Palm wrote:
> 
> 
> 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
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-- 
Chris Elmquist