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Tuner Switch

One of the problems I ran into with the SGC-239 tuner was operating the tuner with the Kenwood TS-520S. The Icom has the tuner interface that makes the SGC tuner emulate the Icom AH4 tuner. It provides tuner control and feedback to the Icom 706, and provides a tuner lock switch on the front of the interface. The SGC tuner is powered through the Icom, I needed a way to power the tuner when using the Kenwood, and to have feedback to let me know that the tuner has found a match.

The other issue is when dipping the plate current on the Kenwood, the tuner thinks the antenna environment is changing and starts the retune process, making it difficult to properly tune the finals of the hybrid radio. SGC sells a Smartlock for the tuner, and they also provide a schematic and instruction for home brewing one.

Using a Simplified Version of the smart lock designed by AD5X, Phil Salas, I set off to build an interface that would suit my needs. The Icom is in my EMCOMM box, and wanted the tuner interface to be standalone, and un modified for field use. I needed a way to power the tuner in the shack, independent from the Icom interface, and isolate the Icom interface and the AD5X smart lock.

http://www.ad5x.com/images/Articles/SG239SmartLock.pdf

I used the AD5X smartlock, and added a DPDT switch, and a power switch. The additional DPDT switch was used to isolate the Icom from the tuner interface.

Here is the schematic.

The power and ground is provided by the homebrew smartlock, instead of bringing power from the Icom Interface. The Tune line and Hold/Reset Line are brought over from the Icom to the DPDT switch, allowing me to switch from the Icom or Kenwood.

My Original design had the Tune LED connected to the tuner output with the idea that the tune LED would work on either the Kenwood or Icom radio, but found that although the tuner reaches a match, the Icom does not receive the signal and stays in tune mode. This was solved by wiring the LED to the DPDT switch and isolating from the Icom. It allows the tuned LED to work with the kenwood and bypasses it when the Icom is being used.

I also added an LED for the power on, letting me know when the tuner is powered. The tuner is interfaced with the smartlock with a 4 wire line and a 4 pin microphone connector just like the EMCOMM box. I am able to simply unplug the line from the smartlock and plug directly into the EMCOMM box and I am up and running.

Here is the picture of the completed Interface.

Sitting side by side with the antenna switch allows for switching of the antenna between rigs and allows me to utilize the SGC tuner on either rig.