Using antenna tuner AH-4 with IC-705

Using antenna tuner AH-4 with IC-705

The antenna tuner for the IC-705 is “to be released”, but “I want to use the wire antenna with the IC-705 soon”, so I tried to verify whether the AH-4 can be used with the IC-705.


Antenna tuner AH-4 with IC-705

IC-705 TUNER Jack and plug pin assignment

The IC-705 has a “TUNER jack” on the right side, and is said to be “connectable to an IC-705 dedicated antenna tuner that will be released at a later date.”

The TUNER plug is a 3-pole stereo plug with [KEY], [START], and [GND] assigned from the tip.

To connect AH-4 to IC-705

IC-705 does not have AH-4 connector like IC-7610 or IC-7300, but connect each control line from AH-4 side and GND to TUNER jack, and separately add 13.8V to AH-4. Once supplied, the IC-705 will also be able to use the AH-4…

IC-705 tuner mod
Connection diagram of AH-4 and IC-705. Connect AH-4 and IC-705 to the same external power supply, and ground properly from the GND terminal.

To connect AH-4 to IC-705, connect each control line (KEY and START) and GND line from AH-4 side to the tip and ring of Φ3.5 stereo plug so that 13.8V can be supplied separately. To process. You can get a Φ3.5 stereo plug at a parts shop, but if you just want to verify the operation, a screw-type conversion connector is convenient.

The screw-type conversion connector that can be wired directly to the 3-pin terminal is convenient for wiring confirmation.

To connect the IC-705 and AH-4, prepare either of the following cables.

(1) AH-4 control cable that is specially processed for IC-705 connection using Φ3.5mm plug.

(2) Conversion cable that is attached to the AH-4 control cable connector using the AH-4 connector (female side) parts.

In the case of (1), the control cable attached to the AH-4 will be processed, so I would like to avoid this, and use one side of the separately purchased 4-core shielded cable as the J2 connector of the AH-4 and the other side. Processed so that it can be connected to IC-705. (Red part of the above connection diagram)

In the case of (2), a cable of several tens of centimeters is sufficient, so if there is no problem with shortening the control cable that comes with the AH-4 standard, cut the required length from the AH-4 main unit side before using. Would be fine. The shell and pin of the AH-4 side connector (female side) of the conversion cable can be requested for purchase (cash on delivery) from the Icom Support Center mail form.

IC-705 tuner mod
A conversion cable that I made by ordering the AH-4 connector (female side) parts.

Connection and operation check

Since the IC-705 has not arrived at hand, I borrowed an ham shop display machine to check the operation. If you check the IC-705 function screen before connecting the AH-4, it is natural that you cannot select [TUNER].

IC-705 tuner mod
IC-705 function screen before AH-4 connection.

Next, connect both AH-4 and IC-705 to the same stabilized power supply with the power off, and turn on the power in the order of AH-4 → IC-705. When I checked the function screen of IC-705, the text [TUNER] was displayed in white this time, and when I touched it for a long time (about 1 second), it changed from OFF to ON.

IC-705 tuner mod
IC-705 function screen after connecting AH-4.

When tuning is started with the external antenna tuner, the [TUNE] display flashes red in the upper left of the IC-705 screen, and when tuning is completed, the [TUNE] display changes to lit.

TUNE display on the upper left of the IC-705 screen. When tuning is done, it lights up as shown in the figure.

Precautions when using the AH-4 and expectations for a dedicated antenna tuner

It was confirmed that AH-4 was connected to IC-705 and operated theoretically. I was able to tune without any problems, but it seems that there are some bands whose detection of tuning completion is more severe than other radios.

The tuning power of the AH-4 is 10W, and the instruction manual for the AH-4 also states “If you are using a 10W machine, set the transmission output to high power (10W).” In conclusion, I feel that it is possible to operate with IC-705 connected to AH-4, but it is also necessary to divide it from provisional operation.

The IC-705 is compact and can be operated with a battery. In order to maximize the enjoyment, I wanted a dedicated antenna tuner as soon as possible! – JK3AZL

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