Electronic T/R switch

Dennis Brady dbrady at US.IBM.COM
Wed Mar 7 17:59:24 EST 2001

I've been using the EF Johnson T-R switch for several years now.

The 6SL7 does provide some receiver gain, but it's still possible for
the transmitter (when connected to the coax connector) to "suck
out" as they used to call it, some of the received signal.  Since I
don't do much weak signal/DX work, it's never been a problem for

As to the TVI, yes, the EFJ T-R switch can make it worse if you already
have some TVI. For example, in my 'winter' shack, the ground system
is very close (4') to the  transmitters and antenna tuner, so TVI isn't a
big problem.  In the 'summer' shack, where the wire to earth ground is
22' long, TVI is a much bigger problem and I can cut it down a bit by
using a relay instead of the EFJ T-R switch.

I keep a muffin fan in top of the EFJ unit, sucking the heat out the top
and it stays nice and cool that way.  Of all the things that should have
a rectifier tube replaced with S-S diodes, the EFJ T-R switch is one
for sure. I just haven't gotten around to do that yet, since the fan is
a good job. Without the fan, it gets really hot and it has no fuses (unless
you add one like I did) so I think it's not terribly safe in stock form.

The T-R functional aspects are good and it allows QSK if you want it.

73 de W5FRS

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