[Elecraft] Question about K2 power meter

Mon Apr 23 13:03:11 EDT 2007

Thanks Don, I'll begin looking...

Jeff

On 4/23/07, Don Wilhelm <w3fpr at earthlink.net> wrote:
> Jeff,
>
> I was really asking if the power jumped to 160 watts regardless of the
> setting of the power control so I could better suggest where the problem
> might be - apparently it does not go to 160 watts if you set the power
> lower.
>
> That behavior is not normal, and right now I would strongly suspect that
> there is a bad solder connection in the KPA100 wattmeter section or in
> the VRFDET signal path back to the K2 microprocessor.  Do the trimmer
> pots R26 and R27 look OK?  I have found some that were damaged when
> soldering the transformers cores in the PA - a damaged trimmer could
> have an intermittent contact at the wiper and cause the results you are
> seeing.  Check the entire path for FWD power indication from the KPA100
> wattmeter to the VRFDET signal output (look at the schematic to identify
> the components - and don't forget about the scaling resistors and the
> scaling switches Q10 and Q11).  Since this is an intermittent condition,
> it will be difficult to know when it is fixed - that is what makes
> intermittents so hard to deal with - try tapping on things to try to
> induce a failure.
>
> 73,
> Don W3FPR
>
> Jeff Kinzli N6GQ wrote:
> > Don, thanks.
> >
> > I do have a recently-made KPA100 (~3 months) and have installed the
> > upgraded C31 to combat the parasitic.
> >
> > When in QSO, I see the power jump up, and it seems to stay there until
> > I enter a TUNE operation or manually drop the power level via the
> > power knob.
> >
> > I spend a lot of time on 40M, so that's where I usually see the
> > problem. I do believe it happens on other bands though.
> >
> > If an occasional jump to 150W is ok, then I won't worry about it. I
> > can leave the power knob lower so that the maximum power reached is
> > less than 130W on those transients.
> >
> > 73,
> >
> > Jeff
> >
> > On 4/23/07, Don Wilhelm <w3fpr at earthlink.net> wrote:
> >> Jeff,
> >>
> >> If you are saying that you see an occasional jump from 120 watts power
> >> to 140 or even 160, I would say that *MAY* be possible, but if it jumps
> >> from 50 (or even 80) watts to 160, then you do have a problem - and my
> >> first reaction is that it is an indication of a transient oscillation.
> >>
> >> How long does the power stay at 160 watts?  Is this on 40 meters, or
> >> does it occur on all bands?  What level is your KPA100?  If it has RFC10
> >> installed and the L15 position has a toroid and L16 has a toroid with a
> >> red core - you do not have the latest update - that update was designed
> >> to combat a parasitic on 40 meters.  In your case, I would recommend the
> >> KPA100UPKT if it is not already installed just to be rid of the
> >> possibility that the 40 meter parasitic is what is causing your problem.
> >>
> >> 73,
> >> Don W3FPR
> >>
> >> Jeff Kinzli N6GQ wrote:
> >> > Thanks Don and others for the answers.
> >> >
> >> > In my case, I'm trying to run down a proble where the KPA100 will be
> >> > fine, then all of a sudden it's output will jump up over 140W. I
> >> > thought that the high output in the base K2 might be the cause. So are
> >> > we saying that some variation is ok, and once in a while if the KPA100
> >> > gets up over 150W then we're ok? This is not apparently an oscillation
> >> > issue, as I don't see high SWRs.
> >> >
> >> > Thanks,
> >> >
> >> > Jeff
> >> >
> >> > On 4/23/07, Don Wilhelm <w3fpr at earthlink.net> wrote:
> >> >> Jeff,
> >> >>
> >> >> That is normal behavior - the power will climb a bit if left in
> >> TUNE for
> >> >> a period of time.  It is mostly the result of heating in the PA
> >> >> transistors.  In normal operation, either with CW or SSB, there is
> >> not a
> >> >> constant carrier being transmitted and the same conditions will not be
> >> >> present.
> >> >>
> >> >> Do not leave the K2 in TUNE at high power for any significant
> >> length of
> >> >> time - remember that TUNE is transmitting at a 100% duty cycle.  OK
> >> for
> >> >> short bursts, but not good for longer periods.  The base K2 shoud be
> >> >> limited to 5 watts or less for a 100% duty cycle transmission and
> >> to 35
> >> >> watts or less with the KPA100.
> >> >>
> >> >> 73,
> >> >> Don W3FPR
> >> >>
> >> >> Jeff Kinzli N6GQ wrote:
> >> >> > Hi Don,
> >> >> >
> >> >> > Thanks for the replies.
> >> >> >
> >> >> > To answer your questions, the problem occurs into a dummy load.
> >> >> >
> >> >> > I set the base K2 (without KPA100 connected) to 5.0W, and then TUNE,
> >> >> > and it starts at 5.0W and heads upwards to 5.7-6.0W (read from the
> >> >> > display, as well as the S-meter). After about 10 seconds in TUNE,
> >> it's
> >> >> > up to 5.7 or 6W and the next LED on the S-meter is starting to
> >> flicker
> >> >> > some.
> >> >> >
> >> >> > Moving the power knob will allow me to bring it back to 5.0W, but
> >> the
> >> >> > next TUNE will see the power climb back up again.
> >> >> >
> >> >> > I'm not sure if I should still be looking on the RF board at this
> >> >> > point, or start focusing on the control board...?
> >> >> >
> >> >> > Thanks, 73,
> >> >> >
> >> >> > Jeff
> >> >> >
> >> >> > On 4/22/07, Don Wilhelm <w3fpr at earthlink.net> wrote:
> >> >> >> Jeff,
> >> >> >>
> >> >> >> Another thought and a question - does the K2 control power properly
> >> >> >> (check with TUNE) when the requested power is set to 5 watts?
> >> If you
> >> >> >> get somewhere between 4.5 and 5.5 watts output with the requested
> >> >> power
> >> >> >> set to 5, then the power control circuits are working as they
> >> >> should be.
> >> >> >>
> >> >> >> Setting the power to maximum will not readily reveal any
> >> problems with
> >> >> >> the power control.
> >> >> >>
> >> >> >> OTOH, if the power output is always high then you do have a
> >> problem in
> >> >> >> the power control (ALC) loop.
> >> >> >>
> >> >> >> 73,
> >> >> >> Don W3FPR
> >> >> >>
> >> >> >> Jeff Kinzli N6GQ wrote:
> >> >> >> > Don and others,
> >> >> >> >
> >> >> >> > A few weeks back, a user posted about an issue with low power
> >> output
> >> >> >> > with his K2. Don said:
> >> >> >> >
> >> >> >> >> If you do not have either the KAT2, the KPA100, or the KAT100
> >> >> >> >> installed, the
> >> >> >> >> K2 does not display the actual power output on the LCD (the
> >> >> requested
> >> >> >> >> power
> >> >> >> >> is displayed briefly when the power control is changed). What is
> >> >> the
> >> >> >> >> indication on the LED bargraph during transmit?
> >> >> >> >
> >> >> >> > I'm going through an issue with my K2 where it *appears* to be
> >> >> putting
> >> >> >> > out too much power. With the KPA100 installed, the output
> >> sometimes
> >> >> >> > jumps up to 150+W.
> >> >> >> >
> >> >> >> > I removed the KPA100 from the picture and have been seeing if
> >> I can
> >> >> >> > reproduce higher than normal output with just the base K2. So
> >> >> far, the
> >> >> >> > behavior is that if I enter TUNE mode, the indicated power on the
> >> >> >> > display of the K2 will rise to 16-17W. My watt meter isn't
> >> accurate
> >> >> >> > enough to tell me what it's *really* putting out though, although
> >> >> with
> >> >> >> > the KPA100 it is accurate enough to see the 150W+ peaks.
> >> >> >> >
> >> >> >> > So I was trying to think if it's really putting out 16+W, or
> >> if the
> >> >> >> > power meter is really telling me it's TRYING to put it out
> >> >> (because my
> >> >> >> > external wattmeter looks like actually less, but again not
> >> >> accurate).
> >> >> >> >
> >> >> >> > I also thought maybe it's an ALC issue, because if I rotate the
> >> >> power
> >> >> >> > knob back then back up to max, the indicated power on the K2
> >> will go
> >> >> >> > to about 15W, but the next time I do TUNE again, it again goes
> >> >> back up
> >> >> >> > to 16+W.
> >> >> >> >
> >> >> >> > Any thoughts on this? Should I keep chasing ALC issues? I've
> >> already
> >> >> >> > gone through the base K2 RF board resoldering T1-T4, reheating
> >> >> >> > anything that looks suspect, etc. to no avail.
> >> >> >> >
> >> >> >> > I also sent something to this effect to Gary at Support, I'm just
> >> >> hoping
> >> >> >> > someone might have any ideas that I could chase down.
> >> >> >> >
> >> >> >> > Thanks,
> >> >> >> >
> >> >> >> > Jeff
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