Super simple tune-button

When using the ICOM IC-705 with an external auto-tuner without communication with the radio, switching to e.g. AM or FM and starting transmission every time you need to re-tune can be somewhat tedious. Yukiji 7L1WCX has designed a brilliantly simple circuitry for a button that immediately brings the radio into tuning mode, putting out a constant carrier. Just like when ICOM’s own AH-705 is connected, it transmits at maximum output power. (Original blog post.)

Yukiji’s schematics together with photos of my own design can be found below. Since the voltage drop across the diode approaches zero when the capacitor becomes fully charged, I decided to use a cheap 1N4148 silicon diode instead of a somewhat hard to find Schottky diod. Also, since the radio only samples the START voltage when KEY goes low, the size of the capacitor is almost irrelevant. I used 1uF which is physically small and cheap. The voltage in the circuit is less than 4V so a 15V capacitor has good safety margin.

If the button is not recognized by the radio when connected, just press the “Function” key and touch the “Tuner” button on the screen.

Schematics by Yukiji 7L1WCX. I use 1N4148 and 1uF with good results.
Inside. The indentation for the cable was done by just pressing the soldering iron into the side of the box. The enclosure is Hammond 1551FBK.
The finished tune button

Interface for Elecraft T1 tuner

Yukiji 7L1WCX has also designed a direct interface for the super compact Elecraft T1 tuner. (Orginal blog post.) The interface allows the radio and the tuner to communicate, making it possible to to initiate a tuning cycle from either. It even shows the battery status of the interface at power down.

Yukiji’s schematics together my own design can be found below.

In case you have trouble reaching Yukiji’s blog, you can download the PIC source here, the programming hex file here, and a basic manual here.

Yukiji has also made some nice YouTube videos demonstrating the functionality that can be viewed here, here, and here.

Schematics by Yukiji 7L1WCX.
Prototype on experiment board.
Elecraft T1 connected to ICOM IC-705 via the prototype interface.
Interface electronics built on a small circuit board.
Wrapped in plastic cling wrap and with strain-reliefs added to cables. The case is a simple snap-lock plastic box. Not very weather-proof but probably more so than the IC-705 itself.
Finished interface.