Posted by
Don Wilhelm-4 on
Oct 06, 2007; 12:58pm
URL: http://elecraft.85.s1.nabble.com/KPA100-KAT100-trouble-tp453506p453509.html
Chris,
I am pleased to learn that you have had success with the diode
replacement. They are a bit difficult to reach, and there is no reason
they cannot be placed on the bottom of the board as you have done.
Do correct the power supply situation before drawing any further
conclusions about maximum power output, but you can calibrate the
wattmeters even with your limited current battery.
You can calibrate the wattmeter in the KPA100 and the KAT100 at 10 watts
and that typically provides good results over the entire range. The
KAT100 manual gives you voltage measurements to do that calibration and
will normally yield quite acceptable calibration results - just follow
the manual instructions.
Actually doing the KPA100 wattmeter calibration at 10 watts will provide
good accuracy over the entire range too (there is scaling at high power
built into the KPA100). Power only the base K2 and the power control
steps will provide more resolution during the calibration, and if you
have an accurate dummy load, you can read the RF voltage across the
dummy load with an RF Probe and calculate the actual power.
The K2 LED bargraph does not have sufficient resolution to measure the
actual power output - if you have the Elecraft DL1, you can use it with
the built-in detector to determine the actual power, but lacking that
tool, use an RF Probe and a good 50 ohm non-reactive dummy load to
calculate the power - most RF Probes will withstand RF voltages across a
50 ohm load for up to about 18 watts.
73,
Don W3FPR
Christopher A. Kantarjiev wrote:
> Don,
>
> It's taken me several weeks to get to this, but tonight was the night.
> I had tested and determined that the base K2 was fine, but neither the
> KPA nor KAT controlled power correctly. The parts folks had sent me
> diodes.
>
> Boy, what a nuisance these are to replace! Julius N2WN had suggested
> putting the KPA's diodes on the underside of the board, where they are
> easier to get at, and I followed that advice. For the KAT, there's
> just no good way to get at the backside of the board w/o removing all
> the connectors. I used a stainless dental pick to clean out the holes
> from the front, and soldered from that side, too.
>
> Power control works great now. Both bridges seem to want to be
> recalibrated - the max output is about 75W, even when I have 100+
> dialed in. I didn't do the original calibration on these, so I'm not
> certain of how close they were ... and I guess I'm not sure that I
> measured for full power out when I bought them.
>
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