Posted by
Roger D Johnson on
Aug 24, 2019; 9:14pm
URL: http://elecraft.85.s1.nabble.com/KPA-1500-Power-Output-Variation-tp7654657p7654662.html
I just did some experiments with my K3/KPA1500 combo into a dummy load.
I used my LP-700 for power measurements. Drive from K3 was set to 30W
(28 on K3 indication).
I started at 35C with PO at 1362 watts. At 70C, the PO dropped to 1277
watts...about a 6% decrease. K3 output remained steady at 30W.
What we need is someone with a separate tuner that can set up loads
greater and lesser than 50 Ohms and with Xc and Xl components. We may
find greater output with loads less than 50 Ohms and/or loads with Xl
rather than Xc. This is one of the disadvantages of having a fixed output
network. With the old AL-1200, I could just tune for max smoke and set
the drive accordingly!
73, Roger
On 8/24/2019 2:45 PM, 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
>
>
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