[Elecraft] UPDATE KPA1500 on 160M

[Adrian]

Bill, ok on that, yes more electronic amplifiers especially use a swr 
limit to protect against the high voltages

generated at high swr. Sometimes you are better off using a robust 
manual tuner made for the job external to the amp.

High swr between a remote balun and atu at amp, will emphasis balun 
heating loss as the signal passes the feedline length many times before

totally dissipating in the coax loss & balun core,some as heat loss, and 
some as desired induced balun current to antenna radiated RF.

Ladder line back to a close-by matchbox, which can handle KV, close to 
amp, would give best power efficiency, as ladder line has minimal 
feedline loss.

I would be using a manual ext tuner with this type of antenna, also 
taking away risk of damaging the amp.



On 3/9/20 2:19 pm, K8TE wrote:
> Nowhere has there been a mention of what VSWR the tuner sees, only the result
> of its match which is 2.5:1.
>   That means the VSWR it sees is beyond its capability to tune properly and
> run full power.  This information is available on the KPA1500 panel display.
> It will also state the maximum allowable power output.  What are those
> values?
>
> I suspect the VSWR is quite high and the allowable power well below 1,500
> Watts.  It's likely you're expecting more power-handling capability than the
> BALUN, either one, can handle.
>
> When one writes "quickly" that is interpreted differently by all those who
> read it.  Obviously, 20 to 30 seconds is not "quickly", at least to me, but
> a very good indications of something overheating, but not instantly.  The
> latter could lead toward a very different conclusion.
>
> My current (pun intended) conclusion is don't run over 800 Watts on 160m!
> That is about the same level you run with your other amplifier without a
> failure, maybe, if you don't run it too long at that level.  I'm glad you
> concluded it's an antenna system problem.
>
> BTW, W8JI has written about this antenna and recommends an 80-20% ratio,
> rather than the typical 67-33% ratio.  He has modeled it for various bands
> on his web site.  I don't know why the common 67-33% values are used when
> someone has shown there is a better choice.  Old habits, good and bad, die
> hard.
>
> 73, Bill, K8TE
>
>
>
> --
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