[Elecraft] KPA1500 PA Current

[Bill Johnson]

On this list the subject comes up regularly.  I have some issues when a feedline or antenna looks great, until I hit it with 1500 watts.  Check you antennas and connectors, then come back let us know what you then find.  Antennas and feedlines can fail or cause what you are seeing.  10-100 watts is simple, or looks to be so.  With 1500 watts you will find issues you didn't know you had.

72 & 73,
Bill
K9YEQ
FT’er for K2, KX1, KX3, KXPA100,  KAT500, W2, etc. 

-----Original Message-----
From: elecraft-bounces at mailman.qth.net <elecraft-bounces at mailman.qth.net> On Behalf Of Gary J Ferdinand
Sent: Friday, March 15, 2019 2:26 PM
To: elecraft <elecraft at mailman.qth.net>
Subject: [Elecraft] KPA1500 PA Current

I’m in the process of checking out my amp.  I have two dipoles (40 and 80).  At resonance both show a 1.2:1 SWR with ATU totally bypassed.  With ATU on, it remains bypassed on 80, but shows only the ATU ON LED on 40.  In both cases the resultant SWR is 1.2:1.   SWR measurements are from the KPA1500 display.

When I use the amp with my K3 and drive it up to 1500W, I am occasionally getting an excessive PA current fault at 63A.  From a cold start it’s 60A, but as it warms up in contest usage I find the power drops off, so I have to adjust the K3 to bring it back up to 1500W.  At that point the PA current goes over 60A.

Interestingly, into a dummy load the 1500W point shows a PA current of only 55A.  So the 1.2:1 SWR, be it via a bypassed ATU or using the ATU, is sufficient to raise the PA current eventually to excessive levels.

Suggestions?   I don’t want this to be flipping out during a contest.  I also don’t want to reduce power into what should be a totally acceptable load.

73

Gary W2CS


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