[Elecraft] K2 Assembly part 3 check: Power output on transmit varies

[Ron D'Eau Claire]

Vic, KG4HTT wrote:
verything seems to be fine, except for one thing - the power output is
inconsistent on transmit.  It doesn't fluctuate much once it starts, but it
starts at different levels.  For example, when you set the power level to 2
watts, maybe one out of 5 times it will transmit 1.9 or 2.0 watts when you
push the "tune" button.  Other times, it will transmit 2.5, 3.0, maybe even
4.0 watts, and hold it pretty consistent (+-.1 watt) for the few seconds I
hold it in "tune" into a dummy load.  Wherever the watt meter shows, it
corresponds on the MFJ dummy load, so the power is going into the dummy
load... it just doesn't seem to reliably put out the right amount of power.


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That's because in "TUNE" the power control circuitry in the K2 is disabled,
Vic. The power will jump all over the place based on several things,
including the load. 

Key the rig in CW if you want to see the power stay stable. Still, it'll
shift a little bit as the finals warm up. 

That brings up another point that surprises ops sometimes. The K2 sets the
output power by measuring the RF voltage delivered to the load, compares it
with the power level you have requested with the POWER control, and adjusts
the gain of the transmitter circuits accordingly. So, when you first key up
the rig after turning the power on or after adjusting the POWER setting, it
will NOT produce the expected power for a moment until the circuit has a
chance to monitor the power out and adjust the level accordingly. 

When doing a Power On, the default is minimum output. That means that after
turning on the rig, if you hit the key you might see a short delay before
the RF appears. It might be enough to lose several dits if you are starting
with dits on the key. Same is  true when you change the POWER setting. If
you turn it up or down, the first few dits or part of a dash will be at the
original higher power before the circuits react. 

Also, since the power is monitored by an RF voltmeter, the accuracy of the
power display is based on the accuracy of the load. The closer it is to 50
ohms non-reactive, the better the power accuracy. 

Ron AC7AC