I just use a footswitch to switch two relays. One is a coax relay
that selects the transmit antenna or the RX antenna. The other is a
3PDT relay that allows me to do a few things:
1) Lock out transmit on the rig when the RX antenna is selected
(enabled by a microswitch on my antenna switch). My radio has a "TX
Inhibit" pin that precludes RF output when it's held in some state...
either 5V or GND, don't remember which. Anyway, I still seem to need
a diode limiter and resistor on my preamp output but this keeps me
from cooking the limiter.
2) Detune my transmit antenna
3) Light up a little "RX" light to remind me that the RX interlock is on ;-)
- - - - - -
That said, if your preamp doesn't have a diode clamp like mine (and
maybe it shouldn't for distortion reasons), you shouldn't trust
anything but a time-delay sequencer to protect it.
I thought I could do it with careful foot timing but I had to replace
the transistor in mine twice before I put the diode protection on.
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