[Elecraft] K3S - Alpha 87a combo - loss of keying amp

[Jim Brown]

On 10/20/2020 4:22 AM, Kimo Chun wrote:
> In a K3S tested with two Alpha 87a amps using RF sensing to change band and
> tuning the K3S appears to easily trip the amp into Fault mode.

For a couple of years, I have had two 87As on my operating desk, each 
driven by a K3, and I the only time I experienced any issues when 
changing bands was when I screwed up and transmitted into the wrong 
antenna.Both of those 87As have the auto-tuning feature, which was added 
several years after the amp was introduced. Not all 87As have it, older 
amps require the replacement of a PROM, and after the company has been 
sold several times, it's no longer available.

The auto-tuning system must be trained, by band segment. It's covered in 
the manual, which can be downloaded. That training can be tricky, 
depending on what the previous owner might have done. And the feature 
must be turned on, by simultaneously pushing two of the buttons. I found 
that it works quite well when working into reasonably well matched 
loads, but its tuning range is pretty limited, and falls apart as the 
mismatch approaches 2:1. It's a Pi-L output network, not an antenna 
tuner.

One of those 87As has been replaced by a KPA1500, and it DOES 
occasionally go into Fault mode when changing bands, but it matches a 
FAR greater range of loads. I didn't replace the 87A because I was 
unhappy with it, but to get legal limit on 6M.

73, Jim K9YC