Auto Mute a Second Radio

[VK2HRX]

Dear VK Logger Brainstrust,

I'm looking for ideas on the ways that I can do the following:

2 single band VHF and UHF roadios running with external speakers. They receive the same signal, the VHF one direct and the UHF through a cross band repeater from a simplex VHF signal.
I want to Tx on either one of my chosing but dont want to turn down volume, change channel etc and dont want to hear my signal ( thus feedback) on the one I am not Txing on. So I need the Tx of one radio to automatically mute the audio of the other.

Idea to date is to use the PTT of the one doing the Tx to switch a relay that breaks (or sends it to a resister) the speaker line on the Rx one.

Suggestions??

Compton
VK2HRX

[VK3ALB]

Your idea will work just fine.

[VK3ZTE]

Sounds pretty straight forward: couple of muting relays with some simple diode logic to route each of the tx logic signals to the relays. You could go more exotic and more flexibly with microprocessor / software driven logic, but I'm doing something similar here with simple old-style relay logic controlling 2x 2m receivers both of which have to be muted when I transmit (either manually via tx/rx switch for voice comms or automatically via computer driven tx/rx switching for digital comms) - works fine. 73 Grant

[VK3YE]

Dear VK Logger Brainstrust,

I'm looking for ideas on the ways that I can do the following:

2 single band VHF and UHF roadios running with external speakers. They receive the same signal, the VHF one direct and the UHF through a cross band repeater from a simplex VHF signal.
I want to Tx on either one of my chosing but dont want to turn down volume, change channel etc and dont want to hear my signal ( thus feedback) on the one I am not Txing on. So I need the Tx of one radio to automatically mute the audio of the other.

Idea to date is to use the PTT of the one doing the Tx to switch a relay that breaks (or sends it to a resister) the speaker line on the Rx one.

Another possibility, used in QRP rigs to avoid a clunk when switching from receive to transmit, is to use a transistor switch.

This is smaller, cheaper and quieter than a relay and can be inserted across the volume control.

Just four parts are required - 2 resistors, a capacitor and a transistor.

An example is the circuitry is around Q1 in this transceiver circuit http://www.qsl.net/ea3gcy/pdf/ILER-40%2 ... 0works.pdf

ZL2BMI describes this technique, though in this case switching RF to ground, at https://aa7ee.wordpress.com/2014/07/07/ ... an-update/

In your case you'd have a mute circuit connected across the volume control of each. The lead from the muting circuit's base (via the resistor) would go to the + TX line of the other's transmitter.

[VK6ZFG]

If one opts for or uses external speakers, then an interface box through which the mikes and speakers pass could be arranged to provide the muting requirements without any modifications to the radios.

Arrange the interface box so that PTT 1 from Radio 1 operates Relay 2 to disconnect radio 2 speaker and PTT 2 from Radio 2 to operate Relay 1 to disconnect Radio 1 speaker. No loads are neccessary.

Best to use transistors or FETs to drive the ralays so as to avoid voltage interface problems with the PTT lines. Even better would be opto couplers. Include diodes across the relay coils to suppress voltage switching spikes.

[VK2HRX]

Thanks all,

Both radios have PTT on rear connectors. I think I'll use these on a transister and make the switch happen on the opposite radios speaker line.

Hopefully I can control the smoke......

Compton
VK2HRX