[Elecraft] Question about K2 power meter

Don Wilhelm w3fpr at earthlink.net
Mon Apr 23 12:58:31 EDT 2007 

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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