I have continued to investigate the various ways to connect my Icom IC-7300 or IC-7600 to the Elecraft KAT/KPA-500 Tuner and Amplifier. I have received some very helpful communication from a number of other Hams using Icom Radios with the Elecraft KPA-500 Amplifier and KAT-500 Tuner. It appears that there are several different ways to do this, including a couple of required connections and some options that may also be chosen.

The connections that should be considered are:

  1. Amplifier KEYING (and inhibit)
  2. Band Switching
  3. Antenna Tuning

Here is what I have found about each of these topics

Amplifier KEYING and inhibit

There must be a means of keying the Amplifier when it needs to transmit. It may be called PTT, SEND, or KEY in various documents and discussions. A single KEY line from the Transmitter to the Tuner is used, combined with a line from the Tuner to the Amplifier’s PA KEY line. This line is a critical connection, as the KAT-500 uses it to protect the KPA-500 from bad antenna situations. When this line is pulled to GROUND, the KPA-500 will amplify the transmitted signal. While the Tuner is in direct control of this signal, you may actually have several other components that must also be “ready” to transmit before this line is driven LOW. This provides protection against transmitting high power into a bad Antenna or load. The Tuner has the ultimate protection, being able to instantly inhibit the KPA-500 from putting out power.

What I have discovered is that there are multiple lines on each of the Icom Radios (7300 and 7600) that can be used for this purpose. You can use the most-often-recommended ACC port (DIN connector) KEY line, or you can use the RCA jack labeled SEND on the rear panel. While the ACC connector approach seems to be recommended, there appears to be no reason that this must be used. However, in applications where high voltage or current are used for Amplifier keying, you MUST use the RCA jack for KEYING. More details are available in the Operating Manual for each Radio. There appears to be no reason NOT to use the simple RCA-connector and the SEND line of the 7600 or 7300 for KEYING..

Band Switching

The KAT-500 and KPA-500 are both capable of quickly measuring an applied RF signal, and determining the correct Band. You could probably also connect Band Data from the transmitter to the Amplifier, if you want it to change Bands when you change Band selection on your Radio. Per the KPA-500 Operating manual – “The automatic Band selection function is active whenever the PA KEY is LOW (transmit mode) and the Transmitter is delivering RF drive to the KPA-500.” So while you may choose to connect Band Data to the KPA-500 so it picks up Band changes when you make them on the Radio, this will be overridden by the automatic RF-sensing used by the KPA-500 to avoid using incorrect Band circuitry when you transmit. To me, that means it is pointless to connect the Band Data, other than for the satisfaction of seeing the Band LEDs change on the Amp when I change Bands on the Radio.

Antenna Tuning

Like the KPA-500 Amplifier, the KAT-500 Tuner can perform automatic RF-sensing for determining the correct Band. The Elecraft documents recommend “Training” the Tuner for each antenna and frequency Band that you plan to use. There are detailed instructions available for doing this in Elecraft App Notes. While I may do that, I also want the ability to tell the Tuner to TUNE NOW, on the current Band and with the selected antenna. For that reason, I plan to connect the 4-pin AH-4 Tuner connector on the Icom Radio to the Tuner.

While using the TUNE button on the radio is my preference, there is a problem with that approach. The KAT-500 manual recommends using 25W or more for tuning, to get the best match. If you press the TUNE button on the radio, I think both the IC-7300 and the IC-7600 put out only a 10W carrier. To get 25W, you need to do something like selecting RTTY/PSK mode, and setting the power output level for 25W or more.

Transmit Delay

One other thing that was mentioned to me by several people, is to set a Transmit delay of 10-15 mS. That should give the switching enough time to settle before transmission.

Summary

There is much documentation on this subject, some of it being inconsistent. After looking at all the documents and speaking to several people, I decided that my first attempt will be to connect my IC-7600 to the KAT/KPA-500 “power combo.” I will be using the diagram on Page 12 of the KAT-500 manual. The only difference will be that I will use the SEND line (RCA connector) instead of the ACC connector (DIN connector).

I will publish the results of my effort to integrate these two Icom radios with the KAT/KPA-500 in future posts. I would also love to hear about experience others have had using this equipment.