Topband: TX/ RX Antenna Switching

Rick Karlquist richard at
Wed Nov 14 20:21:19 EST 2012

Tom W8JI wrote:
>> Getting away from what we are discussing now (limiters) and back to the
>> original question... it really is just a few bucks for a relay for a rig
>> (without separate T and R jacks) at the 100W level, to add separate T
>> and
>> R based on the amp key line.
> ........but the line has to be sequenced properly. That can be a problem
> in
> many systems. To work safely and properly....
> 1.) The switch has to be wire controlled from the radio (it cannot use RF
> keying). Some radios actually output RF after the relay send line goes

Lots of good points, Tom.  The problem is basically the same as
a QSK linear.  Most modern rigs have a pin on the back that goes
low about 10 ms before any RF comes out of the rig.  Common reed relays
like Panasonic switch in only a couple of ms, so it is quite easy to
make a RX antenna switch box.  I made one for my TS-570 using a subset
of the circuitry that I used for the QSK box for my converted marine
amplifier.  That box also needed a Gigavac relay for the amplifier
output.  When running high power, both switch boxes work simultaneously.

If something goes wrong in the RX antenna switch, you don't have to
worry about the rig transmitting into its own receiver.  That can't
happen.  The only thing that can happen is that you could damage the
antenna or its preamp.  The reed relay is just like the one in your
radio, so it shouldn't be unreliable.  I've never heard of one of
those failing.

Rick N6RK

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