[Elecraft] Excessive SWR Faulting KPA500

Sat Apr 18 17:16:21 EDT 2020

Hi Ed, 

At a distance of only six feet to your antenna, perhaps your amplifier is 
trying to warn you that you may also have a human RF safety issue. 

73 
Frank 
W3LPL 

----- Original Message -----

From: k2te at juno.com 
To: rmcgraw at blomand.net 
Cc: elecraft at mailman.qth.net 
Sent: Saturday, April 18, 2020 7:53:06 PM 
Subject: Re: [Elecraft] Excessive SWR Faulting KPA500 

Bob, 

You mentioned: 

"Also you can bypass the KPA500 to STBY mode and check the system by 
observing the SWR on the K3." 

I think you meant the KAT500 instead of the K3. The K3 has to be 
bypassed to work with the tuner. Anyway, I have made some progress. I 
tried running through my dummy load and I got the run-up condition to 
fault on 17 and 20. I had to run reduced power since the load is only 
rated for 300W. The odd thing is that I had to use the tuner to make 
things happy with the load. 

Thanks to AI4VZ, I have the schematics for the KPA500 and the LPF 
details. The schematics are from 2011 or so and my gear is from 2017 but 
I doubt the design changed significantly. 

After testing with the dummy load, I re-connected to my patch panel only 
to find that all the settings in the KAT500 were gone. I had to retune 
from 80 through 10; what a PITA! However, my efforts were rewarded with 
the amp working fine on CW everywhere except 12 meters. I may have an 
intermittent on 12 since the best I can do is 2.9:1 SWR after the tuner 
shuts up. Since both the 12 and 17 meter Vs are off the same feed point, 
the 17 may be guilty as well; it settles around 1.9:1. 

As for the amp faulting, I may have an RFI issue. The 6BTV is only six 
feet from the shack. Another possibility: the fault surfaced when 
running the amp on FT8. The long duty cycle plus RFI may have done me 
in. 

Tnx for your help. 

73 de Ed 

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