Elecraft: Elecraft K3S: Will it work with an ICOM AH-730 ATU?

[k2mm]

Hello, I use an LDG AT-100ProII ATU at my EFHW wire antenna before the coax runs to my Elecraft K3S transceiver in the shack. At this time, I am using FT8 and WSJT. After launching WSJT, I click on its "Tune" button and make any adjustments to improve quality. When this signal reaches the LDG ATU, it automatically adjusts itself for an optimal matching.

I have been thinking about buying a proper, external automatic ATU, such as the ICOM AH-730. However, there seems to be a dearth of information about how to connect the K3S with the AH-730. I have seen a lot of discussions about the need to create a custom interface circuit to make my K3S send commands to the ATU. Is this really necessary? Since the ATU is automatic, why would it need control commands from my transceiver? Won't it work like my LDG with just the coax connection and power?

If control commands must be sent to the ATU, will the K3S be able to provide the proper signals to some kind of interface circuit?

If a custom control interface circuit must be created for the K3S to work with the AH-730, does anyone have a schematic and list of parts, or know where a commercial interface can be purchased? I have found very little information about using the K3S with an ICOM AH-4 and no information about using it with an AH-730.

I'd appreciate any help and thank you for your interest and time.

Mike

 

[AK9R]

As a long-time Icom AH-4 user, maybe I can provide some input.

The AH-730 and AH-4 use the same tuning process. The control cable between the radio and tuner has four wires: KEY, START, DC 13V, Ground. Without power applied, the tuner is effectively "off" and bypasses the RF from the SO-239 connector to the "hot" terminal on the top of the tuner. When the "TUNE" button on the radio is pressed, the START line is asserted, taken low, and the tuner is prepared to start the tuning process. 250ms after the START line goes low, the tuner asserts, takes low, the KEY line. This tells the radio to start transmitting a CW carrier at about 10 watts. The tuner senses the RF and switches appropriate inductors and capacitors in and out to match the impedance of the attached antenna to 50 ohms. The tuning cycle is assumed by the circuitry to take 560 to 2000ms. When the KEY line is released, goes back high, the radio stops transmitting and the radio assumes that the tuner is tuned. If the tuner can't get a match in 2000ms, the tuner "flashes" the KEY line which tells the radio that no match was achieved.

So, after reading the previous paragraph, I think you'll come to the conclusion that the AH-4 or AH-730 really isn't suitable for use with your Elecraft as an automatic tuner controlled by the radio. The AH-4 and AH-730 are not general purpose automatic antenna tuners like you've been used to with your LDG. These tuners are specifically designed to work with Icom radios and the interface between radio and tuner has remained the same for well over 20 years.

There are home-brewed interfaces out there intended to make the Icom tuners more universal, but I don't have experience with them. I've found documents online from John Rowing M0NRZ and Chris Peterson K9EQ that give some background into the timing and signal levels for controlling the Icom tuners. K9EQ also designed and prototyped an interface.

Good luck.

FWIW, I used an Elecraft KAT500 tuner and a KPA500 amplifier for a while. The KAT500 is a fine automatic tuner, though not intended for use outside.

 

[k2mm]

Thank you for sharing the information about how Icom's remote ATUs work, Bob. I will check out the interface projects you've mentioned, but I suspect I will keep using my LDG-AT100PROII at my antenna. I live in Arizona and only operate when the weather is good, so the tuner should have minimal wear-n-tear. One of the ARRL's antenna books showed a project where someone put the tuner into a plastic container, added coax ports to the container, and fed power over the coax to the tuner. I may implement something similar. Thanks again, for your help!