Rethinking the Icom IC-7600 Interface to Elecraft KPA/KAT-500

I have been using this combo for a number of years. I have been using the AH-4 4-pin connector to connect the 7600 to the KAT-500 Antenna Tuner. When I would change frequencies, I would often hit the TUNE button quickly, to get the best possible match. A few months ago, I started having some strange things happening with my Tuner. I was using two antennas, and started having some trouble with tuning at times. It was not predictable, or clear to me what was happening. So I had to investigate and also contacted Elecraft.

Elecraft Feedback on the AH-4 Interface

I spoke to Elecraft and one of their Technicians offered to look at my KAT-500 Config file, to see if they could identify any problems. There has always been varying opinions on the use of the KAT-500 AH-4 interface with non-Elecraft radios. If you read the Elecraft documents, you can find comments that using the TUNE button, the 7600 does not generate sufficient RF to get an optimal antenna match. They say that using 20 – 100 watts for tuning is recommended. BUT, you can also find wiring diagrams in the Elecraft documents that show exactly this setup, using the AH-4 interface.

Elecraft told me that they do NOT recommend using the AH-4 interface. They say that the 8-10 watts generated during tuning is just not enough to assure an “optimal match” with the KAT-500. They say that the first match that is found, is not always the best and final match. From my Config file, it appeared that my TUNE cycles were not always saving good match values in the memories. I still can’t say that I understand what was happening, but I asked for their advice for best operation of my station, which is mainly used for Contests with several multi-band antennas.

Recommended Approach

The recommended approach is to connect your antennas and then “train” the tuner at various frequencies across the Bands that will be used for each antenna. This is a bit of a pain, as it forces me to keep track of which antenna was connected to each of the KAT-500 antenna connectors, and for which Bands a given antenna-connector combination had be trained. It is also recommended to keep the tuner in the “MAN” mode. I decided to give this a try.

My Current Operating Procedure

I have now started to use this antenna training approach. There is a table available in the KAT-500 manual that provides the list of frequency sub-bands where training is needed. The training is a little tricky, but it does seem to work well. Once I train an antenna-connector pair, no additional tuning is necessary unless something changes with the antenna or the feedline. I sometimes use a different feedline to get a particular antenna connected to my radio into the shack. Now if I change the feedline at all, I have to retrain the tuner in some cases.

I have found a fairly simple way to complete the tuner training. I use N1MM+ to control my station during contests. Pressing CTRL-T puts the radio into transmit mode when operating CW. So I go to CW Mode, press CTRL-T and then set the power output for approximately 25 watts. Then I press the TUNE button on the KAT-500 to get a match. Then I walk up the Band and repeat this at the frequency intervals found in the KAT-500 manual

But What about the “Old” Method?

I thought for a long time that the previous approach using the AH-4 interface was working fine. And it still seems to be usable. But what I have found is that the Training method results in spending less time getting antennas tuned throughout a contest. It does make me wonder why the AH-4 interface is present on the KAT-500, and if the implementation details might have been better. The ICOM AH-4 standard has been around for a long time and of course it works great with my AH-4 antenna tuner.

For those who have followed my suggestions in the past, I hope your setups are still working and I would suggest that you consider changing to the Tuner Training approach like I have. I have found that it actually saves time during a contest, if you have connected and tuned your antennas properly before the starting gun.