QRP Radio Microphone

This project is to build a microphone that is compatible with my QRP-Labs QMX+. It will also incidentally be compatible with the popular uSDX radios as well as the Elecraft KX2/3.

For this microphone to work, the microphone element must be an electret. It also needs a PTT push button. The operating manual of the QMX states that an internal pullup resistor is provided, and that no decoupling capacitor is required. Below is my schematic for the QMX microphone assembly:

Version 1.0

I wanted the microphone to be a similar form factor to standard speaker/mic accessories that come with other radios. I decided on using a 2.8″x1.7″x0.9″ plastic project box for the housing. It was thick enough to put a push button on the side and have the mic element on the front.

I decided to use a panel mount female jack for the microphone assembly. This allows the mic to be more compact, and I can use the same stereo audio cable as my CW paddle for this.

I got a number of contacts with this microphone, and all of them reported that my audio sounded good.

Version 2.0

After building Version 1.0 and testing it, I decided to make another smaller version. I used KiCAD to design a small PCB that would have an electret mic, push button, and audio jack in a compact form factor. The PCB can accommodate either a standard tactile thru-hole button or a mechanical keyboard key.

This design is meant to be used without an enclosure, eliminating the need for a 3d printer. The kits can be assembled with minimal soldering. I recommend a single piece of electrical tape on the back to protect your fingers from the pointy thru-hole wires.

Version 2.1/2.2

After having some v2.0 boards made, I had a number of ideas for improvements.

For starters, I eliminated the option for a mechanical key and went with the tactile switch only. Then, I reduced the size by quite a bit. I also realized that this board could function for the Elecraft KX2/3, simply by installing the audio jack on the opposite side of the board. This effectively swaps the tip and ring terminals.

I reduced the width of the part of the board that holds the mic element so it can accommodate a small foam lapel mic wind cover.