No antenna issue here. No SWR variations when
antenna under continuous power (measured on a
real SWR meter). Same effect into a high power
cool dummy load. It's the amp without doubt.
- Paul
At 03:09 PM 3/15/2019, Bill Johnson wrote:
Paul, I do not witness what you are seeing. You
may also have an antenna issue, slight but problematic?
72 & 73,
Bill
K9YEQ
FTâer for K2, KX1, KX3, KXPA100, KAT500, W2, etc.
-----Original Message-----
From: elecraft-boun...@mailman.qth.net
<elecraft-boun...@mailman.qth.net> On Behalf Of Paul Baldock
Sent: Friday, March 15, 2019 4:47 PM
To: donw...@embarqmail.com; Gary J Ferdinand
<alapa...@w2cs.net>; elecraft <elecraft@mailman.qth.net>
Subject: Re: [Elecraft] KPA1500 PA Current
I believe its universal that as the KPA1500
warms up the gain drops. I have mine set up on
each band for around 1500WPEP when cold. If I
operate it enough by the time the amp gets up to
70C its down to around 1300W. I try to
operate the amp conservatively so I don't
increase the input to raise the output back to 1500W, I just leave at 1300W,.
The issue is in the amp, not in your antenna or feeder, balun etc.
I had a SPE1.5K for a short time and this exhibited a similar effect.
-Paul KW7Y
At 02:10 PM 3/15/2019, Don Wilhelm wrote:
>Gary, Have you considered that there may be something in your antenna
>system that is heating up or otherwise changing with the 1500 watts
>power? The first thing I would suspect is a balun that is heating, or a
>connector that is not quite tight enough. Those kind of problems will
>not show up at lower power, but at 1500 watts may become troublesome.
>73, Don W3FPR On
>3/15/2019 3:25 PM, Gary J Ferdinand wrote: > Iâm in the process of
>checking out my amp.mp. 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 itâs 60A, but as it wa 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. >
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