K3: Still unable to set power correctly in DATA A (sigh)

[Julian, G4ILO]

I recently installed the latest firmware and ran the TX Power calibration wizard - nice work. However while running WSPR (a sound card data mode) I was somewhat annoyed to find the K3 power meter showing about twice the output power I had selected. Checks using my own power meter confirmed that the K3 is putting out about twice the amount of power specified by the power control when DATA A is used (though the exact difference seems to vary a bit from band to band.)

Using TXG VCE is NOT the answer, as the output power in SSB (and in CW) is regulated correctly. Using the maximum TXG VCE -3.0dB I still can't quite get the power down to what it should be, but if I do that, SSB output is too low.

Forgive the note of frustration but I am frankly very annoyed and fed up that after all this time and numerous reports of this issue from me and several other people going back several months, the K3 is still not capable of performing a simple basic function like regulating the output power to the level the operator requests. I am seriously considering selling the K3 at this point, as I am losing confidence that Elecraft has any intention of fixing this issue.

[Stephen Prior]

I can report the identical problem to that which Julian describes.  I don't
remember the firmware version where this started but it was certainly not
always the case that the actual power output in Data A mode was so much
greater than the requested power.  I can set for 5W and get a displayed (K3
meter) output in excess of 10W. No problems at all with the other modes that
I have tried.

Stephen G4SJP


On 03/01/2009 16:36, "Julian, G4ILO" <[hidden email]> wrote:

>
>
> I recently installed the latest firmware and ran the TX Power calibration
> wizard - nice work. However while running WSPR (a sound card data mode) I
> was somewhat annoyed to find the K3 power meter showing about twice the
> output power I had selected. Checks using my own power meter confirmed that
> the K3 is putting out about twice the amount of power specified by the power
> control when DATA A is used (though the exact difference seems to vary a bit
> from band to band.)
>
> Using TXG VCE is NOT the answer, as the output power in SSB (and in CW) is
> regulated correctly. Using the maximum TXG VCE -3.0dB I still can't quite
> get the power down to what it should be, but if I do that, SSB output is too
> low.
>
> Forgive the note of frustration but I am frankly very annoyed and fed up
> that after all this time and numerous reports of this issue from me and
> several other people going back several months, the K3 is still not capable
> of performing a simple basic function like regulating the output power to
> the level the operator requests. I am seriously considering selling the K3
> at this point, as I am losing confidence that Elecraft has any intention of
> fixing this issue.
>
> -----
> Julian, G4ILO. K2 #392  K3 #222.
> http://www.g4ilo.com/ G4ILO's Shack   http://www.ham-directory.com/ Ham
> Directory    http://www.g4ilo.com/kcomm.html KComm for Elecraft K2 and K3

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[Joe Subich, W4TV-4]

> I can report the identical problem to that which Julian
> describes.  I don't remember the firmware version where this
> started but it was certainly not always the case that the
> actual power output in Data A mode was so much greater than
> the requested power.  I can set for 5W and get a displayed (K3
> meter) output in excess of 10W. No problems at all with the
> other modes that I have tried.

So?  Reduce the power you request to get the required output.
What other radio has a "calibrated" power output control?  

The wattmeter in the K3 is relative ... there is a documented
power vs. frequency slope.  Testing seems to indicate there
are also nonlinearities with changes in peak to average ratio
and as the power level moves away from the calibration points.
The directional coupler in the K3 does not have the high level
of directivity and compensation of a product like the Telepost
LP-100 nor does it have the high quality detectors.

If you want a bloody laboratory grade meter, buy a laboratory
grade power meter.
 

> -----Original Message-----
> From: [hidden email]
> [mailto:[hidden email]] On Behalf Of Stephen Prior
> Sent: Saturday, January 03, 2009 11:45 AM
> To: elecraft
> Subject: Re: [Elecraft] K3: Still unable to set power
> correctly in DATA A(sigh)
>
>
> I can report the identical problem to that which Julian
> describes.  I don't remember the firmware version where this
> started but it was certainly not always the case that the
> actual power output in Data A mode was so much greater than
> the requested power.  I can set for 5W and get a displayed (K3
> meter) output in excess of 10W. No problems at all with the
> other modes that I have tried.
>
> Stephen G4SJP
>
>
> On 03/01/2009 16:36, "Julian, G4ILO" <[hidden email]> wrote:
>
> >
> >
> > I recently installed the latest firmware and ran the TX Power
> > calibration wizard - nice work. However while running WSPR (a sound
> > card data mode) I was somewhat annoyed to find the K3 power meter
> > showing about twice the output power I had selected. Checks
> using my
> > own power meter confirmed that the K3 is putting out about
> twice the
> > amount of power specified by the power control when DATA A is used
> > (though the exact difference seems to vary a bit from band to band.)
> >
> > Using TXG VCE is NOT the answer, as the output power in SSB (and in
> > CW) is regulated correctly. Using the maximum TXG VCE
> -3.0dB I still
> > can't quite get the power down to what it should be, but if
> I do that,
> > SSB output is too low.
> >
> > Forgive the note of frustration but I am frankly very
> annoyed and fed
> > up that after all this time and numerous reports of this
> issue from me
> > and several other people going back several months, the K3 is still
> > not capable of performing a simple basic function like
> regulating the
> > output power to the level the operator requests. I am seriously
> > considering selling the K3 at this point, as I am losing confidence
> > that Elecraft has any intention of fixing this issue.
> >
> > -----
> > Julian, G4ILO. K2 #392  K3 #222.
> > http://www.g4ilo.com/ G4ILO's Shack  
> http://www.ham-directory.com/ Ham
> > Directory    http://www.g4ilo.com/kcomm.html KComm for
> Elecraft K2 and K3
>
>
>
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[Stephen Prior]

>
> So?  Reduce the power you request to get the required output.
> What other radio has a "calibrated" power output control?
>
> The wattmeter in the K3 is relative ... there is a documented
> power vs. frequency slope.  Testing seems to indicate there
> are also nonlinearities with changes in peak to average ratio
> and as the power level moves away from the calibration points.
> The directional coupler in the K3 does not have the high level
> of directivity and compensation of a product like the Telepost
> LP-100 nor does it have the high quality detectors.
>
> If you want a bloody laboratory grade meter, buy a laboratory
> grade power meter.
>  
>
>
>

I'm sorry, but profanities end the conversation for me.  I was merely
pointing out that something has changed.


73 Stephen G4SJP



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[Leigh L. Klotz Jr WA5ZNU]

There's a thread on a related topic (PSK TX IMD) on the Elecraft K3 list
at Yahoo Groups.
Rich VE3KI posted some measurements done with the PSKMeter that show
poor IMD above about 50W.
I've suggested he re-run the tests with a 3dB pad to compare
apples-to-apples and reduce the effect of non-linear response in the
PSKMeter, but Rich has suggested that perhaps the peak power is
exceeding 100W when the TX PWR setting is above 50W.  Your observations
would seem to confirm that.

Leigh/WA5ZNU

> I recently installed the latest firmware and ran the TX Power calibration
> wizard - nice work. However while running WSPR (a sound card data mode) I
> was somewhat annoyed to find the K3 power meter showing about twice the
> output power I had selected. Checks using my own power meter confirmed that
> the K3 is putting out about twice the amount of power specified by the power
> control when DATA A is used (though the exact difference seems to vary a bit
> from band to band.)
>
> Using TXG VCE is NOT the answer, as the output power in SSB (and in CW) is
> regulated correctly. Using the maximum TXG VCE -3.0dB I still can't quite
> get the power down to what it should be, but if I do that, SSB output is too
> low.
>
> Forgive the note of frustration but I am frankly very annoyed and fed up
> that after all this time and numerous reports of this issue from me and
> several other people going back several months, the K3 is still not capable
> of performing a simple basic function like regulating the output power to
> the level the operator requests. I am seriously considering selling the K3
> at this point, as I am losing confidence that Elecraft has any intention of
> fixing this issue.
>
> -----
> Julian, G4ILO. K2 #392  K3 #222.
> http://www.g4ilo.com/ G4ILO's Shack   http://www.ham-directory.com/ Ham
> Directory    http://www.g4ilo.com/kcomm.html KComm for Elecraft K2 and K3
>  

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[wayne burdick]

On Jan 3, 2009, at 1:02 PM, Leigh L. Klotz, Jr WA5ZNU wrote:

> There's a thread on a related topic (PSK TX IMD) on the Elecraft K3
> list at Yahoo Groups.
> Rich VE3KI posted some measurements done with the PSKMeter that show
> poor IMD above about 50W.

Greg, AB7R, was unable to duplicate this. He'll be contacting Rich
about it.

73,
Wayne
N6KR

---

http://www.elecraft.com

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[Julian, G4ILO]

Joe Subich, W4TV-4 wrote

So?  Reduce the power you request to get the required output.
What other radio has a "calibrated" power output control?  

If you want a bloody laboratory grade meter, buy a laboratory
grade power meter.

Er, my K2 has always been able to do this. My FT-817 will also not put out more than the power level requested.

Nobody has asked for laboratory grade standard of accuracy. But a radio that puts out 10W when 5W is requested clearly has a design fault, especially when it is demonstrably capable of regulating the power correctly in other modes (though private mail suggests that certain people aren't happy with the repeatability of the SSB level control either.)

[Julian, G4ILO]

Leigh L. Klotz Jr WA5ZNU wrote

There's a thread on a related topic (PSK TX IMD) on the Elecraft K3 list
at Yahoo Groups.
Rich VE3KI posted some measurements done with the PSKMeter that show
poor IMD above about 50W.
I've suggested he re-run the tests with a 3dB pad to compare
apples-to-apples and reduce the effect of non-linear response in the
PSKMeter, but Rich has suggested that perhaps the peak power is
exceeding 100W when the TX PWR setting is above 50W.  Your observations
would seem to confirm that.

I don't do Yahoo so I haven't seen that thread, but I observed exactly the same phenomenon using my KK7UQ IMD meter. However it is blatantly obvious that the K3 is putting out too much power when this occurs, because its own power meter shows this.

[wayne burdick]

Could I suggest that we table this topic until Lyle and I can work
together to resolve it? We'll be looking into the RTTY anomalies as
well.

Thanks,
Wayne
N6KR

---

http://www.elecraft.com

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[Trevor Smithers]

Stephen G4SJP said:
> I don't
>remember the firmware version where this started but it was certainly not
>always the case

The problem first appeared last September with "production release"  2.38/1.90. The previous
"production release", which I believe was 2.02, was stable.

73 to all
Trevor  G0KTN
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[Joe Subich, W4TV-4]

> > Rich VE3KI posted some measurements done with the PSKMeter
> that show poor IMD above about 50W.

The K3 wattmeter is essentially an average responding device.
PSK31 has a relatively high peak to average ratio ... as much
as 6 dB or more depending on the particular data but generally
running at least 3 dB at idle.  Since the KPA3 will clip at an
output power much above 110 watts, indicated power output on
PSK31 idle should never exceed 50 watts with 30 to 40 watts
being a "safe" value.  

> I've suggested he re-run the tests with a 3dB pad to compare
> apples-to-apples and reduce the effect of non-linear response
> in the PSKMeter, but Rich has suggested that perhaps the peak
> power is exceeding 100W when the TX PWR setting is above 50W.

I've made similar measurements to those of VE3KI using a
soundcard and software detectors on a separate receiver while
monitoring the K3 power output with a factory calibrated LP-100.
In fact, the K3's peak power output is around 110 watts when
the indicated (average) power is about 50 watts with PSK31
idle modulation.  Increasing the power output simply results
in extreme overdrive of the KPA3 (and/or the IPA since I did
not make separate measurements below the 12 watt level).  The
excess drive results in a higher average power output due to
clipping in the amplifier chain.  The clipping results in
greatly increased IMD products.

Similar sets of measurements should be made for EVERY digital
mode - particularly modes that use phase shift and/or multi-tone
modulation.  Every one of those modes will have unique peak to
average ratios and duty cycles.  Increasing the power output
beyond the point of peak clipping (more specifically the 1 dB
compression point) will, at best, only cause IMD and interference
to other users and will, at worst, result in decoding errors in
reception.  

Since the K3 power control is based on average power and not
instantaneous (absolute) peak power, the power level (both
requested and reported) can not be relied on as a gauge of
proper operation unless the user knows with certainty how much  
headroom is required to handle the peak power without compression
or clipping.

73,

   ... Joe, W4TV
 

> -----Original Message-----
> From: [hidden email]
> [mailto:[hidden email]] On Behalf Of Leigh
> L. Klotz, Jr WA5ZNU
> Sent: Saturday, January 03, 2009 4:03 PM
> To: Julian, G4ILO
> Cc: [hidden email]
> Subject: Re: [Elecraft] K3: Still unable to set power
> correctly in DATA A(sigh)
>
>
> There's a thread on a related topic (PSK TX IMD) on the
> Elecraft K3 list
> at Yahoo Groups.
> Rich VE3KI posted some measurements done with the PSKMeter that show
> poor IMD above about 50W.
> I've suggested he re-run the tests with a 3dB pad to compare
> apples-to-apples and reduce the effect of non-linear response in the
> PSKMeter, but Rich has suggested that perhaps the peak power is
> exceeding 100W when the TX PWR setting is above 50W.  Your
> observations
> would seem to confirm that.
>
> Leigh/WA5ZNU
> > I recently installed the latest firmware and ran the TX Power
> > calibration wizard - nice work. However while running WSPR (a sound
> > card data mode) I was somewhat annoyed to find the K3 power meter
> > showing about twice the output power I had selected. Checks
> using my
> > own power meter confirmed that the K3 is putting out about
> twice the
> > amount of power specified by the power control when DATA A is used
> > (though the exact difference seems to vary a bit from band to band.)
> >
> > Using TXG VCE is NOT the answer, as the output power in SSB (and in
> > CW) is regulated correctly. Using the maximum TXG VCE
> -3.0dB I still
> > can't quite get the power down to what it should be, but if
> I do that,
> > SSB output is too low.
> >
> > Forgive the note of frustration but I am frankly very
> annoyed and fed
> > up that after all this time and numerous reports of this
> issue from me
> > and several other people going back several months, the K3 is still
> > not capable of performing a simple basic function like
> regulating the
> > output power to the level the operator requests. I am seriously
> > considering selling the K3 at this point, as I am losing confidence
> > that Elecraft has any intention of fixing this issue.
> >
> > -----
> > Julian, G4ILO. K2 #392  K3 #222.
> > http://www.g4ilo.com/ G4ILO's Shack  
> http://www.ham-directory.com/ Ham
> > Directory    http://www.g4ilo.com/kcomm.html KComm for
> Elecraft K2 and K3
> >  
>
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[AD6XY]

Joe Subich, W4TV-4 wrote

Since the K3 power control is based on average power and not
instantaneous (absolute) peak power, the power level (both
requested and reported) can not be relied on as a gauge of
proper operation unless the user knows with certainty how much  
headroom is required to handle the peak power without compression
or clipping.

73,

   ... Joe, W4TV

Unfortunately, the life of amplifier power transistors and to a lesser extent valves is based on the peak power. Most license conditions are also based on peak power.

A power control based on average power is therefore, irrespective of any technical merit, inappropriate. It is theoretically illegal in many countries to use with a following amplifier as well as being likely to result in damage to that PA.

This is why it is such a serious issue and why we keep banging on about it.

Mike

[Julian, G4ILO]

AD6XY wrote

Joe Subich, W4TV-4 wrote

Since the K3 power control is based on average power and not
instantaneous (absolute) peak power, the power level (both
requested and reported) can not be relied on as a gauge of
proper operation unless the user knows with certainty how much  
headroom is required to handle the peak power without compression
or clipping.

Unfortunately, the life of amplifier power transistors and to a lesser extent valves is based on the peak power. Most license conditions are also based on peak power.

A power control based on average power is therefore, irrespective of any technical merit, inappropriate. It is theoretically illegal in many countries to use with a following amplifier as well as being likely to result in damage to that PA.

This is why it is such a serious issue and why we keep banging on about it.

Mike

If what Joe claims is true then this is a more serious issue than even I imagined, since it affects SSB operation as well as data modes. It would be so serious that I suspect he is wrong about it.

If I dial up 100W in SSB or data I expect the power to be limited to 100W PEP, not 100W average power.

One reason I suspect he is wrong is that the observation of getting around twice the requested power applies to any data mode, not just PSK31. I can feed a pure sine wave in, request a power of 5W, and get 10W out. If the K3 power meter was indeed average level then it should still limit the power to 5W as it does in SSB.

The issue here is not how the K3 power control works. It is that it is not working in DATA A as it does in SSB. DATA A ought simply to be treated as another SSB mode that just allows a different choice of audio input and filter settings. I believe that it did originally work like that in early versions of the firmware.

Sorry to continue the topic after Wayne requested we call a halt on it, but the assertion made by Joe opens up a whole new can of worms if he is indeed correct about it.

[Mike Scott-7]

>Setting a power control calibrated for CW and expecting that level to be
accurate for PSK31 or any other arbitrary digital modulation is complete
folly and utter hubris.


I also read another post that the K3 watt meter is an average power
responding device and there in lies a problem of setting power for an
arbitrary waveform that will not create IM products.

In the old days we could use a monitor scope to make sure we weren't
clipping. An interesting thought about a future K3 band scope is to provide
a station monitor mode...

I also wonder why the internal K3 wattmeter does not have a peak detecting
mode and set the PEP power to the requested level. That doesn't take care of
directional coupler errors but I suspect it would drop the complaint level
down 6 dB. K3 output power vs. requested power has been a continuous theme
on the reflector.

What is wrong about setting and displaying peak envelope power or at least
have the ability to switch to a peak detecting mode? It seems to me that if
we are worried about IM products when approaching PA clipping levels that
PEP is what we should be monitoring for any transmitted waveform.

Mike Scott - AE6WA
Tarzana, CA (DM04 / near LA)
K3-100 #508/ KX1  #1311


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[Jim Garland]

One way to resolve the confusion over interpreting the K3's power output
display would be to implement a peak reading/average reading feature, like
that in the s-meter.  The S-meter can show both peak and average signal
strength simultaneously. Perhaps something like that could be done with the
power output meter.

I also like the suggestion to blink the red TX LED when the K3 is is in the
test mode. I, too, often fail to note the LCD indicator.

Jim W8ZR

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[Joe Subich, W4TV-4]

> If what Joe claims is true then this is a more serious issue
> than even I imagined, since it affects SSB operation as well
> as data modes. It would be so serious that I suspect he is
> wrong about it.
>
> If I dial up 100W in SSB or data I expect the power to be
> limited to 100W PEP, not 100W average power.

The K3, like any other peak reading wattmeter uses a time
constant appropriate for "normal" voice.  As such in SSB
the K3 adjusts for the typical peak to average of voice -
one of the reasons for TXG VCE.  Serious investigation will
show that TXG VCE will vary with the particular voice and
the level of compression (clipping) prior to the power control
circuitry.  Watching the output with a scope or fast peak
reading wattmeter like the LP-100 will also show the differences
(and deviations) with voice characteristics and compressions
levels.

However with digital modes like PSK31 the peak to average
ratio varies with modulation and compression/clipping can
not be tolerated if IMD is to be avoided.  To be accurate
with arbitrary digital modulation, the wattmeter must be able
to respond to peaks in the fraction of a millisecond range.
To adequately control the power level and must be able to
predict the required peak to average ratio (headroom).  In
commercial applications (cellular telephone, digital TV,
etc.) the power amplifiers are regularly operated at
average power levels 10 to 20 dB OR MORE below saturation
(the 1 dB compression point) with long time constant average
power control due to the high peak to average ratios.    
 
> One reason I suspect he is wrong is that the observation of
> getting around twice the requested power applies to any data
> mode, not just PSK31. I can feed a pure sine wave in, request
> a power of 5W, and get 10W out. If the K3 power meter was
> indeed average level then it should still limit the power to
> 5W as it does in SSB.

No.  If you were operating in SSB (and DATA A is SSB), the
internal "adjustment" for peak to average in a voice signal
would cause the gain in the amplifier chain to be increased
to provide approximately twice the requested power output.
I can create almost any arbitrary level of "overpower" for
a single tone in DATA A simply by adjusting TXG VCE.  If it
is set (as I normally do) for +1.5 dB, I will see just about
3dB of "overpower" when driving the k3 with a single tone
and adjusting the line input for five bars of ALC.  If, on
the other hand, I reduce TXG VCE to -1.5 dB, the power level
will be almost exactly the requested level (15.8 for 15, 98
for 100 on 20 meters).  This has nothing to do with the peak
to average ratio since this is with tone ... only with the
way the K3 controls power in SSB modes.

Again, the K3 wattmeter is essentially average responding
(as you would expect for CW and to be used with the tuner).
The MCU then makes an "educated" guess bout the peak to
average power and duty cycle in SSB.  TXG VCE then allows
the user to "tune" that adjustment for their own voice and
level of compression.  

TXG VCE does not seem to effect the power level for a single
tone in SSB (as expected) but it seems to have a significant
effect in DATA A.  That appears to be as expected if the power
control is based on an average reading wattmeter with a
compensation factor.  Perhaps the MCU needs another control -
TXG DTA anyone?  By the way, AFSK A behaves exactly like SSB
and does not show the "overpower" with tone.

73,

   ... Joe, W4TV
 

> -----Original Message-----
> From: [hidden email]
> [mailto:[hidden email]] On Behalf Of Julian, G4ILO
> Sent: Sunday, January 04, 2009 5:50 AM
> To: [hidden email]
> Subject: RE: [Elecraft] K3: Still unable to set power
> correctly in DATA A(sigh)
>
>
>
>
>
> AD6XY wrote:
> >
> >
> >
> > Joe Subich, W4TV-4 wrote:
> >>
> >>
> >> Since the K3 power control is based on average power and not
> >> instantaneous (absolute) peak power, the power level (both
> >> requested and reported) can not be relied on as a gauge of
> >> proper operation unless the user knows with certainty how much  
> >> headroom is required to handle the peak power without compression
> >> or clipping.
> >>
> >>
> >
> > Unfortunately, the life of amplifier power transistors and
> to a lesser
> > extent valves is based on the peak power. Most license
> conditions are
> > also based on peak power.
> >
> > A power control based on average power is therefore,
> irrespective of
> > any technical merit, inappropriate. It is theoretically illegal in
> > many countries to use with a following amplifier as well as being
> > likely to result in damage to that PA.
> >
> > This is why it is such a serious issue and why we keep banging on
> > about it.
> >
> > Mike
> >
> >
>
> If what Joe claims is true then this is a more serious issue
> than even I imagined, since it affects SSB operation as well
> as data modes. It would be so serious that I suspect he is
> wrong about it.
>
> If I dial up 100W in SSB or data I expect the power to be
> limited to 100W PEP, not 100W average power.
>
> One reason I suspect he is wrong is that the observation of
> getting around twice the requested power applies to any data
> mode, not just PSK31. I can feed a pure sine wave in, request
> a power of 5W, and get 10W out. If the K3 power meter was
> indeed average level then it should still limit the power to
> 5W as it does in SSB.
>
> The issue here is not how the K3 power control works. It is
> that it is not working in DATA A as it does in SSB. DATA A
> ought simply to be treated as another SSB mode that just
> allows a different choice of audio input and filter settings.
> I believe that it did originally work like that in early
> versions of the firmware.
>
> Sorry to continue the topic after Wayne requested we call a
> halt on it, but the assertion made by Joe opens up a whole
> new can of worms if he is indeed correct about it.
>
> -----
> Julian, G4ILO. K2 #392  K3 #222.
> http://www.g4ilo.com/ G4ILO's Shack  
> http://www.ham-directory.com/ Ham
> Directory    http://www.g4ilo.com/kcomm.html KComm for
> Elecraft K2 and K3
> --
> View this message in context:
> http://n2.nabble.com/K3%3A-Still-unable-to-set-power-correctly

-in-DATA-A-%28sigh%29-tp2106260p2108786.html
Sent from the Elecraft mailing list archive at Nabble.com.

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[wayne burdick]

The K3's internal wattmeter *is* intended to be peak-reading. I'm
looking into whether I need to sample the ADC faster and/or increase
the size of the filter capacitor at the cathode of each diode in the
detector. ALC is a separate issue. In some cases (e.g., data modes), we
have to apply ALC sparingly, if at all, to minimize distortion. Adjust
PWR and MIC levels accordingly.

As I said earlier, Lyle and I will be reviewing the issues when he
returns.

Thanks for all the input.

73,
Wayne
N6KR


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