Building an Elecraft KAT-500 Antenna Tuner

I have had a number of automatic Antenna Tuners in recent years.I have had  MFJ tuners, LDG tuners and the built-in tuners in my TS-930s, Elecraft K2, ICOM IC-7600, and Yaesu FTDX-3000. They have all worked pretty well. The first LDG tuner, the IT-1100 has been a real survivor. I put it in my mobile rig, and about 6 years later, it just continues to work flawlessly. The best tuner I have ever had was the internal tuner in my K2. It was one of the few rigs to have an internal tuner that could handle 10:1 SWR mismatches. So it can’t be beat when you need to use one wire antenna on many Bands.

I wanted to get a tuner that is a little more flexible and more capable of handling power excesses that occur during tuning. Since I liked the Elecraft K2 tuner so much, I looked for an external Elecraft tuner. I like the built-in 3-antenna switch and the wide tuning range. I am sure the tuner will be fast and accurate, based upon experience with the K2 tuners. So I bought the KAT-500 Antenna Tuner “kit.” Here is my experience, and a few recommendations for building it.

I decided to go the “kit” route to save a few dollars. I also like the idea that when I built it, I will know all about what is inside, in case there is ever a need to service or upgrade the tuner.  As far as the kit goes – I had a great time building the K2 and the 100W amp and K2 antenna tuner. You start with a box of parts, and end up with a great transceiver and all the accessories. Elecraft no longer makes what I would consider a kit, but you can do the mechanical assembly yourself. That is what they mean now when they say kit. I find the mechanical assembly to be the less fun part, and really prefer building the PC boards, etc. But I understand that Elecraft has to face the realities of the Market.

A couple things I recommend if you are building the KAT-500 kit:

  1. Do the parts inventory and be sure to separate the various screw types. Most are the same length, but there are 3 or 4 that are different, and you want to make sure you don’t use the shorter ones at the wrong time.
  2. DON’T open the SO-239 packages until they are called for. Each one has a different arrangement of the solder-lug that has been pre-assembled for you. If you mix these up, you will not have a good time when you go to attach the rear panel to the PC board.

As I have seen in the past, Elecraft Engineers are masters of the chassis. Everything aligns almost surprisingly well. No fighting with screw holes that are off a hair in this kit. And all of the solder lugs from the RF connectors aligned perfectly when the rear panel was attached to the main PC board. And the instructions were outstanding, with even more photos than you need to get the job done.

The finished product looks great and seems to work very well. I am using it with an Icom IC-7600 and it integrates seemlessly, using the standard Yaesu AH-4 antenna tuner interface. You will need a cable for this interface, and they are available from LDG and others. The Tuner senses the RF and quickly determines which antenna to select, and searches for a match in its memory. This all happens very quickly.

There are only a couple things that could be better for me.:

  1. This thing is LOUD when searching for an initial match, which can take many seconds. Once it finds a match for an antenna, it remembers it and subsequent tuning cycles are very short. So this is really not a major issue, but I would consider adding some sound deadening material if I ever had to take it apart.
  2. If I turn-ON the IC-7600 and the Tuner is OFF, the 7600 goes into TUNE mode and seems to hang. This is at a low power level, but still makes me nervous. I have since learned to not turn-off the tuner, and all is well.

I am still experimenting with the KAT-500 but it is a great fit in my station and it will probably be there for a long time. This tuner, like all Elecraft gear, is not inexpensive. The KAT-500 hardware and software seem to be very well designed, and I have not even tried the remote-station-control software yet. The ultimate would be to pickup a KPA-500 Linear Amp and add that to the station. I never really thought I would go beyond the 100W level, but if prices drop enough on the KPA-500 once the KPA-1500 Amp is selling, you just never know.

I had an email exchange with Elecraft about using this Tuner with the IC-7600. The AH-4 interface includes a power cable that CAN provide the 12 VDC to power the Tuner. However, the IC-7600 is rated to provide up to 1 Amp on the +12 VDC Line. The Tuner can draw up to ~ 800 mA, if all the relays are in the powered state. I am guessing that is not the normal case, and it seems to work fine. Still, Elecraft suggested that I power the Tuner from my Station’s 12 Volt supply instead. I plan to do that, and not force the IC-7600 to provide the power.


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