New (to me) radio arrived

[Brian D]

I finally purchased a radio to replace my Kenwood TS-50S which gave up the ghost. The replacement is an Icom IC-707. It was made between 1993 and maybe 1995, so it is an older radio. A very simple radio with no bells or whistles. The TS-50S was the same way, no bells or whistles.

The 707 does have the ability to activate an auto antenna tuner via a 4-pin Molex connector on the back. The four pins have 13vdc, Gnd, Key, and Start. The Key and Start are functions of the antenna tuner. I already have a tuner that will be installed in the boat later. It is an MFJ939. A very simple auto antenna tuner that works great. I do not have the cable to control the tuner though. So I have to select AM mode, key the radio to tune, then go back to SSB. A real pain.

While doing some research a few months back, I seem to recall that I could trick the radio into thinking it was connected to an auto antenna tuner. The key was to connect a resistor between the Key and Start lines. I went to my bench and found a 330Ω resistor and put it in the two pins for Key and Start. Turned on the radio and sure enough, the radio detected a tuner connected. Pressing the Tune button on the radio started the tune process and after about 1/2 second, stopped. The tuner was tuned to the frequency of the radio. Impressive.

So now the next process is to rebuild my box to fit this radio. I had fun before but made too many error. I actually get to correct those errors this time. Lesson learned and applied.

Thanks for listening.

 

[JamesG161]

found a 330Ω resistor and put it in the two pins for Key and Start

Did it get hot?
Curious, does you tuner transmit ERP? Way back, I had to use a dummy load when tuning but mine was 600 Watts.
Jim...

 

[Brian D]

No, in theory, the 330Ω resistor is only passing 15ma of current. Power wise that is 75mw. But this is not a dummy load. It is a means to tell the radio that a tuner is connected. It provide a voltage drop on the start signal to the tuner and the radio detects this as a tuner connected.

I do not need a dummy load to tune the tuner because it is always connected to my antenna. So nothing is heating in the radio, turner or my shack. LOL

 

[JamesG161]

I do not need a dummy load to tune the tuner because it is always connected to my antenna. So nothing is heating in the radio, turner or my shack. LOL

Well you see I am dated. but.
It was illegal or poor practice to tune on the air ways, 16 years ago.

Although I have never had multi-frequency antennae turner, I understood your purpose of a trigger. So basically it is a bias current, but does it stay alive after tuning?

The PO of my boat was a Ham, he offered up his full set up for $1000 at time of purchase. I offered $600, since I found 2 online for $800 and I had no knowledge of his set up's condition.
So....
All I have is his power set up and NMEA tie in to his computer.

As you can tell, I have a longgg way to go to my rival of General License.
Jim...

 

[Brian D]

I am not presuming to lecture here, so if you already know this, my apologies.

Automatic tuners use low power for tuning. Usually less than 10w. Once they have found the correct combination of C and L, this goes into memory and every time I return to that frequency, that combination of C and L will be recalled. Tuning takes about 500ms or less. It is just a low power beep if I may. When I press the tune button, it too last about 500ms or so. The tuner is very quick.

I am sure the PO of your boat had an auto tuner. What kind of antenna was he using? Most sailboat use their backstay as the antenna.