Posted by
Wes Stewart-2 on
Aug 24, 2019; 9:40pm
URL: http://elecraft.85.s1.nabble.com/KPA-1500-Power-Output-Variation-tp7654657p7654663.html
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/elecraftHelp:
http://mailman.qth.net/mmfaq.htmPost: mailto:
[hidden email]
This list hosted by:
http://www.qsl.netPlease help support this email list:
http://www.qsl.net/donate.htmlMessage delivered to
[hidden email]