Coaxial relays

[PrivatelyJeff]

I just discovered coaxial relays and I was wondering if there was any way to use some sort of current sensing relay to trigger the coaxial relays as to disconnect other radios antennas when I key up a radio. For example, if I have 2 scanners, a ham radio and a CB radio and the antennas are mounted near each other on the trunk, I want to disconnect the scanner antenna and CB when I key up the ham, or disconnect the ham and scanner when I key up the CB.


Also, did someone already do this and am I just reinventing the wheel?

 

[zz0468]

It's been done, and there is some merit to doing that sort of thing. I'd use a sequencer to switch things on and iff, depending on the requirement.

 

[PrivatelyJeff]

Do you know of any premade kits or will I have to build it myself? And what’s a sequencer!

 

[AK9R]

VHF/UHF weak signal operators sometimes use sequencers to make sure things happen in the right order.

Let's say you are using a mast-mounted pre-amp that is triggered with a DC voltage riding on the coax. You want the pre-amp enabled when you are in receive mode, but it has to be disabled in transmit mode so that high levels of RF don't go through the pre-amp. Let's say you are also using a power amp to step up the output of a transmitter (exciter) from, let's say, 5 watts to 100 watts.

Your sequencer would do the following: When you key up to transmit, the DC voltage is sent to the pre-amp to disable it, then the PA is keyed so that its ready, then the exciter is keyed to start transmitting. When you un-key, the exciter is turned off, the PA is turned off, then the pre-amp is turned on. Do these things in the wrong order and you'll zap some expensive electronics.

Here's a link to a product description of a sequencer from Down East Microwave: http://01895fa.netsolhost.com/PDF/trs.PDF

 

[PrivatelyJeff]

That’s cool but a little over my head. I’m just now getting into electronics at this level. I was just hoping to install some sort of current sensor on the power line to the radio, and when it gets above the monitoring level, engage the coaxial relay to open the other antenna circuits.