Sound Disconnect During TX

[W0IH]

I used to use some WEB SDRs when a bunch of us would get together on 160m, because the band would stretch out so far. Problem was, that you would hear yourself echoing from the PC speaker from the SDR radio, which drove me nuts!

I built a small relay circuit that would open the audio to the computer speaker, activated by the Key Output on the radio. I had to put a "Y" connector on the RCA output from my rig to run both the Amp and the relay circuit.

The circuit is a 2.2K resistor from the Key Output circuit to the base of the PNP transistor with the emitter going to +12v and the collector going to one side of the relay coil. The other side of the relay goes to ground. Use a snubber diode across the relay coil. The sound input & Output are connected to the Common and Normally Closed contacts of a DPDT relay with the shield of the cables connected together (Not to ground). Reference the attached file.

When using RM Noise, you not only get the echo when you are transmitting, but you also get feedback into the mic. I used this same circuit for the RM Noise on my PC and it works well.
It works AMAZING when there is a storm going on and there is a lot of QRM on 75m!

It could use a little bit of a delay when you release the mic button, because you hear about the last 200ms of your transmission, but that is very minor.

Mike, W0IH