[Elecraft] KPA1500 SWR Tolerance

Paul Baldock

I keep the SWR below 1.2, using Autotune and manual tweaking. This is necessary to keep the gain reasonably constant across a band. I store values for Wet and Dry if necessary , and then use the ^OS ^PB function assigned to PF1 to select between them. I set/store my max drive power level to achieve 1.3KW PEP (on an external meter) and never turn it up even if the output power drops a little. So far the amplifier's finals have survived.

- Paul KW7Y

At 07:43 PM 3/16/2020, you wrote:
I've long been aware that my KPA1500 would not run at full power (1.5 kW) unless the SWR was very low. (This is SWR at the input to the ATU, if used.) The current ATU firmware does a pretty good job of keeping the SWR below about 1.3:1, which usually is low enough. In any case, I just ran a simple test on 160, where I have an antenna I can easily tune to 1:1, or deliberately higher. The ATU was engaged, but it's settings were not changed during the test. The SWR indicated was that at the ATU input (amplifier output). I found that the output power remained nearly constant up to 1.4:1, but the current increased from 58 to 62 A. (This with no adjustment of the K3 power, though the indicated input power varied slightly.) At 1.5:1, the current exceeded 65 A and the amplifier faulted. By reducing drive, I was able to run it at 1.4 kW output and 60 A. The above is typical of my experience on other bands, etc. The effect of SWR on the amplifier, of course, depends on the actual impedance at the amplifier, so in some cases it may be more or less sensitive to SWR. Do others see similar effects? 73, Scott K9MA -- Scott K9MA k9ma@... ______________________________________________________________ Elecraft mailing list Home: Help: Post: mailto:Elecraft@... This list hosted by: Please help support this email list: Message delivered to paul@...