TuneMate  for Icom transceivers


The problem

A common operational procedure using HF transceivers with a manual ATU is to transmit a low power (~10W) steady carrier to allow manual adjustment of the antenna tuner. This is usually done by keying the transmitter up in FM mode (or other steady carrier mode) at reduced power.

The designers of the Icom IC706IIG did not make convenient provision for this common operation. It takes multiple presses of the mode switch, activation of the setup menu, selecting the power setting option from that menu, rotating the dial several times to reduce power, exiting the menu to regain metering and then keying the transmitter up. When tuning is completed the reverse needs to be performed.

A solution

The IC706IIG does however contain a facility for integration of a proprietary automatic remote ATU (AH-4) on HF and 6m. In operation, the front panel TUNE button is pressed, which sends a START signal to the AH-4, prepares the transceiver at 10W in CW mode and awaits a KEY signal from the AH-4 to key up. When the AH-4 is tuned, it removes the KEY signal and the transceiver reverts to the pre-tune operating mode. The tune process can be aborted by pressing the TUNE button on the IC706IIG, which sends a reset signal to the AH-4.

The TuneMate emulates the AH-4 to trick the transceiver into transmitting a low power CW signal for a brief period.  When the transceiver is powered-up with the TuneMate attached, it thinks it has an AH-4 attached and allows the TUNE button to work. The TuneMate awaits a START signal and returns the KEY signal to key the carrier up. If the TUNE button again whilst tune is active, the transceiver will abort the tune process and reset the TuneMate, otherwise the TuneMate will abort the tune process (sending a reset to the IC706IIG) after 18 seconds. 

The TuneMate uses a Microchip PIC12C508A microcontroller to perform the logic and timing operations. To minimise the risk of RFI, the 12C508A is put to sleep between operations, which stops the clock oscillator, and wakes on a change on the ~START  or ~STOP pins.

 Figure 1 shows the TuneMate implemented on a small piece of vero-board and enclosed in heat shrink to protect the circuit.

Figure 1: TuneMate implementation

Figure 2 is a schematic of the TuneMate which is also available as a higher resolution  PDF file.

Figure 2: TuneMate circuit schematic

Compatibility with other Icom transceivers

The TuneMate has been tested on other Icom transceivers. Two types of behaviour have been observed, Table 1 sets out the behaviour of some models of Icom transceivers.

Table 1: Radio model behaviour
Model Behaviour
  • Tune on radio initiates tune process if tune inactive
  • Tune on radio cancels tune process if tune active and resets TuneMate
  • TuneMate times out after 18s activity and resets itself and radio
  • STOP button on TuneMate initiates tune process if tune inactive
  • STOP button on TuneMate cancels tune process if tune active and resets itself and radio
IC7400, IC746PRO,IC7000, IC718
  • Tune on radio initiates tune process if tune inactive
  • TuneMate times out after 18s activity and resets itself and radio
  • STOP button on TuneMate initiates tune process if tune inactive
  • STOP button on TuneMate cancels tune process if tune active and resets itself and radio

Figure 2 is a schematic of the TuneMate which is also available as a higher resolution  PDF file.

My own implementation of the TuneMate has a 3.5mm phone jack for a remote START/STOP switch. Figure 3 shows a remote START/STOP button added to a commercial tuner for convenient control of the tune power source, the button is the top red button. The momentary normally OFF switch is wired to a 3.5mm phone jack on the back panel using shielded cable and 0.001μF bypass capacitor on the jack. RF suppression sleeves may be necessary on the TuneMate cable and the remote switch cable in some situations.

Figure 3: Remote tune START/STOP button added to ATU.

Compatibility with other brand transceivers

The design of the Tune Mate was motivated by the IC706's awful tuning procedure. The argument for using such a device probably does not exist with other transceivers that offer a convenient and fast means of flashing up a low power carrier for tuning. For example, the Alinco DX-70TH requires only two button pushes.

Note that the external tuner control protocol is proprietary, and unpublished. Although some tuners do similar things, there is no reason to expect the TuneMate to work on other brand transceivers.


The TuneMate works a treat, adjustment of a manual ATU is much more convenient and so much faster using the device. Without the TuneMate, it can be a real challenge to tune up and return a call to a station before they have given up and moved off the frequency.

Sourcing parts

I will make a programmed chip and a Molex plug and pins available to constructors at a price of A$15 including postage within Australia.


A simple test jig can be built by connecting 12 V to the 12V and Ground connections, a momentary switch from the START line to Ground, two resistors of 10K and 4.7K from 12V to Ground (in that order), and an LED anode to the junction of the resistors and cathode to the KEY line. A momentary earth of more than 250mS should trigger the device, turning the LED on for 18 seconds before timeout. A momentary earth while the LED is on should reset it.


Modifying your radio may damage it. No warranty is expressed or implied. Use this information and / or this device entirely at your own risk.


Whilst I developed this independently, I was not surprised to find others had addressed the same problem and come up with a range of solutions generally around tricking the transceiver into tuning a non existent remote ATU. Most use an resistor and capacitor to provide a fixed time carrier, and they typically cannot be reset or restarted without waiting for a full charge and discharge cycle.

I did find one other device that probably takes the same approach as TuneMate, and it retails for around US$35.

Correspondence suggests that the IC-7000 also uses the KEY control line for part of the temperature sensing / fan control function, and that the simple resistor / capacitor tuning devices that were often used on IC706IIGs do not work properly with the IC-7000. The TuneMate does NOT disrupt the temperature sensing / fan control function of the IC-7000, TuneMate uses a tri-state output pin which either pulls the key line to ground or is in the "open" state which is equivalent to the open collector output from the IC-AH4.


Tune power output is not 10W

One correspondent found that the tune power output of the IC706IIG was 100W with the TuneMate. The TuneMate does nothing special to set the power level, it uses the standard feature of the tuner control interface. The "tune power" on 50 MHz and HF is adjustable using the Set mode adjustment described in the Service Manual on page 4-10, and should be set to 10W. Note that the TuneMate will only work on HF and 6m bands, as they are the only bands where the IC706IIG supports the auto-tuner.

V 1.03 (01/05/03)

Version 1.03 firmware was modified to allow abort of the TuneMate timer by a ground on pin 4. Though the IC706 TuneMate was developed specifically to provide a convenient tuning carrier from the IC706, it does work on some other Icom transceivers that support the AH-4. The implementation of the tuner interface is a little different on some other Icom transceivers, and it is convenient on those radios to be able to abort the TuneMate by a switch on the TuneMate (as it is not aborted by pressing the Tune button whilst tuning is in progress). The optional STOP switch circuit is shown on the schematic.

V 1.04 (29/06/06)

Version 1.04 firmware was modified to allow the TuneMate to be started or stopped by a ground on pin 4.

If the switch is closed when the TuneMate is inactive, it will start the CPU, and on release of the switch, will activate tune carrier.

Closing the switch whilst tuning will abort the tune.

V 1.05 (11/08/06)

Version 1.05 firmware was modified to change the pin assignments and C1 to better suit ICSP.

Last update: 16 October 2006 15:05

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