[Elecraft] KPA500 High Reflected Power Fault

[Nels Anderson]

Well, I found a solution to the problem. I had been using my old MFJ 
manual tuner simply for its balun and antenna switch (tuning circuitry 
bypassed). It appears at some point there was a failure in the metering 
circuit. While trying things I noticed a burned resistor smell and when 
I opened the box found several burned out parts on the sensor board. I 
removed the board and just ran a bypass where it had been and the 
problem is now gone. Had a long rag chew on 40m at 500w at the end of 
the day and no issues at all.

I know antennas are often a compromise, but I've been using this one for 
years and made lots of contacts on it (also have a triband yagi for 
20/15/10). I'm the opposite of you, I spend most of my available time 
operating rather than worrying about a better antenna. There's no one 
solution that works for everyone.

73 Nels K1UR

On 5/15/2011 10:48 PM, Mike WA8BXN wrote:
>
> If a tuner gets you to a good match at low power where there is a balun
> involved, but you run into problems at high power, I would first suspect
> that the balun is getting saturated. Using a balun between an antenna and
> the tuner many times is not a good thing to do. Using a balanced line tuner
> is really the best thing to do. Changing the length of feedline from antenna
> to balun does change the impedance that the balun or tuner has to deal with.
> And that chance can help at a specific frequency that has problems.
>
> Using a single antenna on multiple bands is very attractive. Unfortunately
> it is sometimes not an easy thing to do efficiently. In most cases antennas
> are always a tradeoff. There are so many constraints we deal with. Lot sizes
>   deed restrictions, supports available, how much we can spend. You want a
> great antenna system and unlimited budget? I'm sure someone can sell you the
> land needed, someone can clear it, someone can put up multiple support
> structures and good antennas for the bands of interest.
>
> Most often what we wind up with is a compromise in one way or another. In
> many cases that compromise, with careful study and understanding, can result
> in a quite respectable antenna. The other trade off to consider is the time
> spent in getting the best antenna versus getting on the air a lot with a
> variety of antennas (or maybe just one).
>
> I must confess that I probably spend more time brooding over what could be a
> better antenna than getting on the air and making contacts with the fairly
> decent antennas that I do have here.
>
> 73 - Mike WA8BXN
>
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