[Elecraft] Looking at KPA1500

[Erik Basilier]

The KPA1500 is right now outside my budget, but there is nothing wrong with
dreaming and planning, right? The latest QST reviews the new Palstar amp,
which first seemed attractive, but I soon noticed that its continuous
carrier capacity is no better than the KPA500. Also, when you add the price
of the matching tuner, you are looking at a total price of $5k, which makes
the full legal power KPA1500 with included tuner look good at $6k. However,
what does dampen my enthusiasm is that the KPA1500 tuner handles swr only up
to 3:1 at full power. My main 40m antenna meets that requirement over a
significant portion of the band, but at band edges swr can be 4.5:1 or so.
The lower bands are where high power is most commonly needed, so it doesn't
make much sense to upgrade from my KPA500 only to have to throttle back to
500W on 40m. That begs the question exactly how much power the KPA1500 tuner
can handle on 40m. Also, it would be desirable to use higher power on the
portion of the band where swr does stay under 3:1. I could set the power to
a lower value on the K3 for 40m, but it would be helpful to be able to set
the power separately for different band segments. The actual power limit at
a higher swr probably depends on the actual impedance presented to the
tuner, and not just the swr value. One could perhaps use an antenna analyzer
to measure the complex impedance at different frequencies within the band,
and then program different drive power levels for the corresponding band
segments (if that capability were implemented). Maybe a future tuner design
could incorporate sensing of complex load impedance and signal the
transceiver to limit drive power accordingly. Or, instead of basing it on
load impedance, the design could directly measure voltages and currents
within the tuner to prevent excessive voltages and currents from being
produced (not dynamically a la ALC, but as a calibration using steady
carrier). 

73,
Erik K7TV