[QRO] KPA500 PIN diodes / High SWR

[W5UXH]

Back in Feb, Guy (K2AV) wondered in another thread:
------------------
I still wonder what happens to the KPA500 pin diodes when you open with a dit into an unterminated coax and a 20:1 SWR.  Wayne and Co are working their magic into a problem that has taken most amps down.
------------------

I would also like to know if they have been able to provide sufficient protection, magical though it would be.  That would be a terrific selling point.  I know I will eventually hit the key while in a confused state with the KPA500.  

Chuck, W5UXH

[Eric Swartz - WA6HHQ]

Hi Chuck,

We immediately protect the amp by going into bypass mode. The
microprocessor detects the extreme SWR event and immediately routes the
drive signal around the amp, initially though the diodes, and then
through the bypass relay after it has switched. This happens in a few
milliseconds.

While I do not recommend this as a normal operation test, we even have
pulled the coax out of the dummy load at 500W during tx to test this,
with no ill effects. (If you were at our contest university demo in
Italy, you may know how I know this..  ;-)

We have not been able to kill the t/r diodes during lab destructive
testing or in on-air operation.

73, Eric  WA6HHQ
----

On 4/26/2011 5:29 PM, W5UXH wrote:

> Back in Feb, Guy (K2AV) wondered in another thread:
> ------------------
> I still wonder what happens to the KPA500 pin diodes when you open with a
> dit into an unterminated coax and a 20:1 SWR.  Wayne and Co are working
> their magic into a problem that has taken most amps down.
> ------------------
>
> I would also like to know if they have been able to provide sufficient
> protection, magical though it would be.  That would be a terrific selling
> point.  I know I will eventually hit the key while in a confused state with
> the KPA500.
>
> Chuck, W5UXH

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[W5UXH]

Hi Eric,

That is what I hoped to hear.  I also had a response off list from a dedicated tester who "tested" this.  It is good to know there is a good chance of surviving an occasional oops.

73,

Chuck, W5UXH

Eric Swartz - WA6HHQ, Elecraft wrote

Hi Chuck,

We immediately protect the amp by going into bypass mode. The
microprocessor detects the extreme SWR event and immediately routes the
drive signal around the amp, initially though the diodes, and then
through the bypass relay after it has switched. This happens in a few
milliseconds.

While I do not recommend this as a normal operation test, we even have
pulled the coax out of the dummy load at 500W during tx to test this,
with no ill effects. (If you were at our contest university demo in
Italy, you may know how I know this..  ;-)

We have not been able to kill the t/r diodes during lab destructive
testing or in on-air operation.

73, Eric  WA6HHQ

[otto]

Chuck,
I want tell you a little story:

Last month I was with Eric at an Italian exhibition to show the KPA500 to the ham community.
The KPA was, and is s/n 10 without of course the latest fw.

One customer asked to me what happens if the antenna is disconnected from the PA.

I grabbed the PL259 and I disconnected it from the dummy load.

In the same moment, Eric was showing something to another customer keyng the K3 and the KPA at full power.

A nice RF spark  drilled one of my fingers, the KPA turned in stand by and the only consequence of the experiment was a smell of fried chicken coming from my finger.

I can say that the protections are very efficient :-))

73, Carlo IK4ISQ