RE: Peculiar problem on 80 M

Posted by Don Wilhelm-3 on Sep 25, 2006; 12:28pm
URL: http://elecraft.85.s1.nabble.com/More-information-Need-help-with-fluctuating-power-output-on-K2-tp386379p386396.html

Steve,

Have you perhaps increased the value of R98 on the bottom of the RF Board to
give you a more stable power control at high power?  If so, it will make the
power control at lower power more sluggish.  That is the only thing I can
think of which would make a difference.

There is nothing band dependent about the power control that I am aware of,
but the overall gain of the transmitter does vary from band to band, and
that combined with the granularity of the power control may be causing the
effect. The K2 remembers the power setting unless the power request is
changed or the band is changed.  So the real power output that you are
observing may be dependent on the exact steps that you are using to observe
this phenonomon.

You did say that you verify the power output level on the K2 display?  Can
you provide the sequence you are using to do that?  The normal transmit
display does not show the power output level, so you must be doing something
other than a keydown.

It would also be of interest to know if the same thing happens with the
wider range QRP levels - power the K2 through the low power jack only
(disconnect or turn off the power to the KPA100).

73,
Don W3FPR

> -----Original Message-----
>
> I have a strange problem with my K2/100 on 80 meters.
>
> The situation is as follows:
>
> I work QRP DX at the low end of 80 M, (say 3508 kHz or thereabouts)
> with a requested power of 4.5 watts, and get an indicated 5 watts out.
>
> I then check into the Pine Tree Net on 3596 kHz and crank up the
> requested power to 10 watts (this is before the relay clicks; I'm
> still in QRP mode), and I get about 10 watts out. So far so good, right?
>
> Then I go back to 3508 kHz, without resetting the power request level
> knob, but the rig puts out 5 watts, even though the display
> acknowledges my ten watt request. If I go back to 3596 the output
> goes back to 10 watts in agreement with the requested level.
>
> Note the essential point, when I make a big excursion in frequency,
> the radio is putting out a level of power substantially different
> from the requested level.
>
> I can correct the output level at the low end by sweeping the
> requested level either low (near 0) or high enough to make the QRO
> relay click, and then adjust it down to and desired QRP level, and
> the rig will put out approximately the requested level of power.
>
> The phenomenon occurs whether I change frequency by switching VFOs
> preset to the two frequencies, or if I retune one VFO using the
> tuning knob.
>
> This is not an issue of varying antenna impedance. I get this effect
> with a commercial dry dummy load as well as a real (very well
> matched) antenna.
>
> I can also create the effect the other way around. If I request 5
> watts at the 3596 then go to the low end and request 10 watts, then
> go back to 3596 with the knob in the 10 watt position, I still get 5
> watts until I jigger the power level request knob.
>
> I have tried to reproduce this effect on 40 meters, requesting 5 and
> 10 watt levels at frequencies differing by about 100 kHz. In that
> case I get what I would regard as normal behavior. The rig always
> puts out the approximately the requested level of power irrespective
> of when I set the power level request knob.
>
> Has anyone else run into this phenomenon?
>
> Is it a quirk in the software?
>
> Is something wrong with the radio?
>
> 73,
>
> Steve Kercel
> AA4AK
>
>
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