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Recently, I purchased an LDG RT-100/RC-100 (hence RT-100) for use with my Yaesu FTDX10 in the field. As I have said previously, The FTDX10 now resides on the desk at the home QTH. It is better suited there. My main field radio is my trusted Icom IC-7300 so why not adapt this tuner to it.
The RT-100 is an auto tuner and doesn’t require a special tuning circuit. Icoms are set up in such a way that when using a tuner such as the LDG Z11 Pro or the Icom AH-4, the radio automatically detects the tuner and switches off the internal tuner. It also supplies power at the tuner port through pins 3 and 4. With the RT-100, there isn’t a way to make this switch since it only requires power to operate. What I wanted was to use the power from the tuner port on the back of the IC-7300 to power the tuner and turn off the internal tuner. I had to “trick” the IC-7300 into thinking there was a tuner there in order to get it to supply power to the RT-100 through the tuner port.
This is accomplished a lot easier than it sounds. Starting with a diagram created by KC2WI http://www.prnewell.com/kc2wi/Icom_tune_control/)
I only needed pins 2, 3, and 4. Pin 4 is the ground, pin 3 is power and pin 2 is what tells the radio an external tuner is present. It requires a resister in series and I used a 47K ohm 1/2 watt resistor. I did not incorporate the switch and I did not utilize pin 1. Here is a parts list:
Molex Connector https://tinyurl.com/mw24chcc
47K Ohm Resistor https://tinyurl.com/43ax8kc9
2.5mm Power Cable https://tinyurl.com/2p8d466j
Starting with the basic parts.
It’s just a matter of soldering the parts to the pins.
And putting the pins in the right holes.
The pointy end of the connector is facing up.
I added a little heat shrink and electrician’s tape and viola!
When assembling, make sure you put the pins in the right holes and in the right direction. The pins will go in either way as I found out.
How does it work? It works well. The Icom power at the tuner port is rated at 1 amp and the tuner draws about 500 milliamps. This saves me from having to make an extra power connection. The RT-100 is a tune as you go type tuner so the tune button on the radio does not work. The way I tune when not using a digital mode (software has its own tune function), is to switch the mode to AM and then hit the transmit button or PTT button if a microphone is attached. This transmits a carrier at about half the wattage of your current power level. When the tuner finishes, stop the transmit, switch the mode back, and you are ready.
My next adventure will be the first weekend in April during the GA Parks on the Air Contest. I will not be contesting, but I will be operating portable at a park using FT8 and CW. I may try some FT4 to. Hope to hear you out there – 73 – Scott