Jim I don't have a KPA1500, but do have a KPA500. I'm not particularly surprised
at your observations based on mine with the '500.
After a recent thread about amplifier efficiency I ran some tests on mine, using
a well characterized dummy load and an LP-100A wattmeter, at rated output.
Although I only tested at the bottom of each band, I observed a variation in
efficiency of a bit under 55% at 21 MHz to 75% at 3.5 MHz. The gain varied from
12.7 dB to 15.8 dB over the HF range (excluding 50 MHz) Additionally, I see
power jitter of several watts. In past two-tone IMD testing I've seen the
spectrum break up due to (according to headquarters) the K3 ALC loop hunting.
As you no doubt have noticed adjusting output power by tweaking the input power
isn't a smooth operation either. In short, this combination is anything but stable.
I believe that additional attenuation might be helpful if you can implement it
without upsetting the RX path, although on most bands 2 or 3 dB extra
attenuation wouldn't matter.
Wes N7WS
On 8/24/2019 11:45 AM, Jim McCook wrote:
I'm using my K-3 with the KPA-1500 and have a problem with extreme changes in
power output with a given drive level on 40m CW. This happens to a lesser
extent on other bands with different antennas. My 40m antenna is tuned to
7.025 where SWR is 1.1:1. On 7.000 it is 1.4:1 and at 7.050 it's 1.3:1.
Within that range of frequencies the output _without_ the tuner at a given
drive level (30w) varies from 1300w to well over 1700w. Using careful _tuner_
settings it's only slightly better. I have to reduce drive to 24 or 25w to
get below 1500w, depending on the temperature of the amplifier (power output
varies a lot with temperature changes). Higher temp = lower output.
I have tried to compensate in the segments where output is excessive by using
manual settings via the Utility. This has helped slightly, but still isn't
adequate. I've resisted using ALC because of concern for generating
distortion. Having to ride the drive level from the K-3 is a PIA, especially
during contests.
It seems to me a good answer would be to have higher input attenuation so
drive requirement would be higher, maybe around 70+ watts. I'd expect
changing drive level by the same number of watts (5 or 6) would not affect
output as much. I'd also assume the power output would not vary nearly so
much with a given drive level.
Is this a possible solution? I've also understood that most transmitters
(even the K-3) have cleaner output near highest rated output.
Help!
Jim W6YA
______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[email protected]
This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html
Message delivered to [email protected]
