K2 Assembly part 3 check: Power output on transmit varies

[Vic Dively]

Well, it's all put together and I'm running through the checks.
Everything 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.  

So when I do the amp checks for 5 watts, it reads high, because it will
actually be putting out usually 6 or 7 watts.  So it isn't drawing too
much current, per se, it's just that the output doesn't correspond
reliably with the power setting.  Usually it is 1 to 2 watts higher than
the power setting, but just to be confusing, every so often it is exactly
right... rarely, it may be low, but will again be stable... or climb
slowly.

On the positive side, the receiver seems to work good.  With good advice
offered here, I picked up the XG1 signal generator and the noise
generator.  I'm going to pick up Spectragram and re-do the filters.  With
the XG1 I can pick up the 28.160 harmonic, even with the attenuator on...
it's extremely quiet, but it is still barely detectable.  All the
controls seem to work, the peaking of the various inductors and caps
seems to go as it should.  I've looked closely at all the toroids in the
XMTR section, and even re-did T2, because the leads didn't look the best.
 Same problem.  I've checked the toroids for continuity by touching the
pad, and not the wire, to verify that the leads are conducting through
the pads.

Could this possibly be a I/O Controller issue?  When it gets the power
level correct, I notice that there sometimes is a very quick blip at
transmit - for example, I'll have the power level set at 2.0 watts, and
it will say something like 4.0 watts for just a tiny fraction of a
second, then immediately stabilize at 1.9 watts... so it's as if it
sometimes jumps in and corrects the power level correctly, and other
times lets it go wherever it starts.. .usually not too high, no HI
CURRENT problems at the 2 and 5 watt level, but the power out seems to be
1 to 2 watts higher than the power setting... but not always.

Thanks again.  I enjoyed listening a bit to the bands, I'm getting close
now... probably could use it like this, but I'll wait until I get things
all set up right.

Vic  KG4HTT
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[Ron D'Eau Claire-2]

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.


----------------

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


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