I just repeated the linearity measurements, on both 40 and 15 meters. I
used the KPA1500 meter to measure output, and the K3 power setting for
input. Results on the two bands were similar, though 15 required much
more drive.
On 40, the maximum gain occurred at about 800 W out, 17.2 dB. At 1 kW,
it was 16.9 dB, and at 1.5 kW it was 15.7 dB. However, at 1.45 kW the
gain was 16.2 dB, so there was a lot of compression in that last 55 W.
The gain compression at 1.5 kW vs 1 kW is 1.2 dB, but only 0.7 dB at
1.45 kW. Overall, I'm told this compression is typical of the KPA1500,
and probably doesn't indicate excessive IMD, at least compared to other
solid-state amplifiers. It's probably a good idea to be very careful not
to overdrive it on SSB, though.
The gain drops off at low power, to 16.0 dB at 200 W. This is
consistent with the BLF188 data sheet. However, the data sheet shows the
gain almost perfectly flat to over 1 kW per device. They show maximum
gain, in fact, at about 1 kW per device, which means gain ought to be a
bit HIGHER at 1.5 kW than 1 kW for two devices. Since there are two of
them in the KPA1500, the compression at 1.5 kW is a bit surprising.
(That's about what one would expect from ONE device at 1.5 kW.) Yes, the
data sheet curves are for a specific test circuit at 108 MHz, but it's
still surprising. On the other hand, anyone who has designed electronics
knows to take the published data sheets skeptically. Elecraft has, no
doubt, tested lots of them, and knows their REAL characteristics.
73,
Scott K9MA
--
Scott K9MA
k...@sdellington.us
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