Icom IC-7300 External Keyboard


Endlessly calling CQ during a contest or special call activation can give you a sore throat. Voice keyers were invented for this particular matter. A voice keyer is even built in in the IC-7300, so at first there is no need for an external device.

This voice keyer has 8 presets and can be used as a keyer for voice, CW or RTTY. The only drawback is that this keyer is only accessible when the voice keyer option is visible on the display. And at that time you can’t see any other screen that might me more of an interest to you than the voice keyer buttons such as a largere scope, the audio in- and output and your meters (SWR, ALC, COMP and I). An external keyboard would be of great help.

Strange enough this external keyboard is not provided by Icom, you are forced to buy an aftermarket device, or… build it yourself. The schematics for this are made available by Icom in their manual on page 12-2.

A prerequisit for me was that I could still use the original mic when the keyboard was attached, and that when I don’t use the original mic, I still have the same capabilities as if I’m using the original mic. So both schematics need to be combined.

Gather the needed components


Except for the resistors all I needed was bought on AliExpress. For the enclosure I choose for a aluminum box measuring 122(W) x 66.5(H) x 39.5(L)mm. Guitar enthousiast use these enclosures to make so call stomp boxes or effects units. Manufacturer Hammond brought an enclosure with these dimension to the market as model 125B/1590N1. If you search on AliExpress with these model numbers, you get some options to choose from.



You can choose whatever momentary switch you like for this project. I went for black plastic 12 mm momentary push-buttons.

Microphone connectors

Icom uses a 8-pin microphone connector. These GX16 connectors, sometimes also referred to as circular aviation socket plug, can be found in abundance on AliExpress. Search for GX16 8 male female because we want two male sockets and 2 female sockets. The male sockets are to be place on the enclosure, the female sockets are needed to build the cable to connect the external keyboard to the radio.


Finding a suitable cable that has sufficient inner strands, is not to thick and looks good was not so easy. Mini din 8 pin extension cables can be found easily, but they do often come in an ugly beige color. As we only need 6 inner strands, I figured out a mini din 6 pin cable would do the trick as well. I still had 1 meter of this cable in my stock as I once used it to build a data interface for my trusty Yaesu FT857-D.


We need one 470 Ohm, one 4,7k Ohm, one 2,2k Ohm and two 1,5k Ohm resistors. All 5% and 1/4 Watt.

Audio Jack Sockets

When looking for audio jack sockets, look for those with a screw on the inside of the enclosure. Not only do they look better, I also have the impression the quality is a bit better.

Preparing the enclosure


On the top of the box 7 holes needed to be drilled. 4 on the top row, 3 on the bottom row. Each hole has to be 12mm.


On the left two 20mm holes are drilled for the GX16 connectors and on the front 2 7mm holes were made for the 3.5mm stereo jacks.


On the back, another 7mm hole was drilled for the 3.5mm jack that will be used to connect a foot-pedal for handsfree PTT operation.

Once all holes are drilled and all components are test fitted, you can start sanding the box and give it some layers of spray paint.

Put everything together

First make sure you solder long ends of wire to the GX16 connectors. It would be a real challenge to solder them when they are already mounted in the enclosure.


I opened the original Icom MH-219 to know what color code they use and tried to use the same as much as possible.

Pin 1: Mic input = white
Pin 2: 8V = not used for this project
Pin 3: Frequency up and down = red
Pin 4: Squelch = not used for this project
Pin 5: PTT = brown
Pin 6: PTT Ground = green
Pin 7: Mic Ground = Black
Pin 8: AF output = Blue

Everything wired up.

Now fix a connection cable with two female GX16-8 connectors, using a SP/2 extension cable and some clear tubing as stress relief. The color scheme of this cable is different from that of Icom, but as long as you connect each wire to the same pin on the opposite side of the cable, you’re good to go.


The finished product


In this picture, the original mic and the foot pedal are not connected. I’m using an in-ear Sennheiser and a 1€ condenser boom mic from AliExpress. Maybe not the “best” solution, but for the moment good enough.

Everything works as it should and the magic smoke remained in the components where it belongs 😉

I will put this keyer to the test during the March 2019 CQ WPX contest. Hope to meet you on the band!

73 de ON5IA

Automatic Magnetic Loop Tuner – Another Soldering Session

I took some time to solder another PCB for an Automatic Magnetic Loop Tuner. I made some pictures of the final result which I would like to share with you.

This is a view from the top of a populated PCB. The Teensy 3.2 and the A4988 stepper module are not yet installed. This loop controller won’t need the end stop feature. Therefor D2, D3, R25, R26, C19, C20, C21, C22, T3 and the 3 pin header for the end stop connector, are not installed.

C1 is located underneath the Teensy 3.2. This capacitor can be soldered upright. There is plenty of space, so no need to lay it flat on the board.

Populated PCB for Automatic Magnetic Loop Tuner

Here we have both the Teensy 3.2 and the A4988 stepper module installed. Note that a jumper is placed over JP1, but that JP2 is left open. JP1 connects “Sleep” and “Reset”. JP2 is for future use. When using a DRV8825 stepper module it gives us the possibility to connect the unused Teensy 3.2 pin 19 with pin MS3 of the DRV8825. With some additional programming to the software, this could enable the 1/32 step stepper resolution. This however has not yet been programmer, nor tested.

Populated PCB for Automatic Magnetic Loop Tuner

If there is one thing I would change to this board it’s the re-positioning of the LM7805 voltage regulator. The ground plane in facing inward which makes it difficult to attach a heat-sink. This can be solved easily by bending the legs of the LM7805 so the ground will face upwards, or by connecting it from the underside of the PCB and connecting the ground to the metal enclosure the whole PCB will be put in.

Populated PCB for Automatic Magnetic Loop Tuner

On this last picture, you can see capacitor C1 has plenty of space and is enjoying the company and security of the Teensy 3.2 😉

Populated PCB for Automatic Magnetic Loop Tuner