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. 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 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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