PROJECTS & KITS - Amateur Radio by 2E0MDS

Internal view showing PCB and other components

Morse code practice oscillator project

The completed CW Practice Oscillator with Morse Key

WIRING A CABLE FOR A DIFFERENT MICROPHONE

I decided to use my existing Leson (Altai) TW-232 Desk Microphone as an alternative to the Icom HM-103 hand mic that is supplied with the Icom IC-706MK2G transceiver.

The TW-232 desk mic is fitted with a standard type 6 pin mic plug wired for my Midland 48 Excel CB radio. The Icom 706 has a completely different RJ45 type mic socket. I needed to make a 'cross-over cable' to fit between the mic plug on the TW-232 and the Icom 706 transciever.

Looking at the circuit diagram for the Icom IC706, the basic wiring only needs four wires: PTT (Push To Talk transmit switch), PTT Ground, Microphone Audio and Microphone Audio Ground.

This is slightly different to CB wiring which does not have separate grounds for PTT and Mic, inside the plug on the TW-232 microphone these two ground wires were connected together. I therefore I separated the MIC Ground and PTT Ground within that plug.

This would require two Cross-over cables; one for the CB that re-combined the two grounds together to match the wiring scheme required for CB and the second cross-over cable for the connection to the IC706Mk2G.

Here is the wiring scheme for the TW-232 mic and the Icom transceiver:

The Leson (Altai) TW-232 desk microphone wiring is as follows:

White = PTT
Black = PTT / Receive Ground
Blue = Receive
Red = Mic audio
Shield = Shield (mic audio shield)

Icom IC706Mk2G microphone plug wiring for RJ45 plug:

1 = +8 volts d.c. *** Do not connect & be careful NOT to short out otherwise the radio will be damaged ***
2 = Frequency up/down buttons
3 = Audio output
4 = PTT >>>>>>>>>>>>>>>>>>>> Connects to the White wire of the TW-232 Mic
5 = GND - Microphone Ground >>>>>> Connects to the Shield wire of the TW-232 Mic
6 = Microphone audio input >>>>>>>> Connects to the Red wire of the TW-232 Mic
7 = GND - PTT Ground >>>>>>>>>> Connects to the Black wire of the TW-232 Mic
8 = Squelch control

Leson / Altai TW-232 wiring diagram

Wiring diagram for Icom HM-103 microphone
shows the microphone socket as seen from the front of the radio
(Icom Corporation)

The Up / Down frequency buttons are not wired in my cross-over cable, but could be used if required if additional switches were fitted into the desk mic. The basic wiring only requires four wires to pins 4,5,6 & 7 in the RJ45 plug - as seen below:

The RJ45 plug fitted to a short piece of mic cable

Fitting the RJ45 plug to the mic cable

Fitting the RJ45 plug to the mic cable

Fitting the mic socket on the other end of the cable

The completed cross-over cable

Thanks to Alex and Dave at the Charlie Delta ARC for the necessary plugs that enabled me to make this cross-over lead. Cheers guys!!

OTHER PROJECTS

There are many other useful devices that can be made, such as an ATU for portable QRP use, various types of receivers, pocket sized QRP CW transmitters, complex transceivers - the list is endless. Some projects have to be built from scratch which involves making the necessary PCB, other designs provide a pre-etched PCB while many are available in complete kit form.

Another project that I wish to make in the future is a Noise Bridge. I even fancy having a go at a Crystal Calibrator - and more experimental antennas - of course!

Looks like my soldering iron may be busy!