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

[Steve Ward]

"Joe Subich, W4TV" Wrote:

>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.

The point is it was providing the correct power output levels before the last couple of firmware revisions.  Something changed that made it go from putting out approximately the right power level, to putting out WAY TOO MUCH (i.e. causing splatter) power.

Setting TXG VCE to -3 dB gets DATA A output almost to where it should be, but of course adversely affects SSB.

This is NOT about the accuracy of the wattmeter, its about overdriving the PA.

73,
Steve
AD7OG
K3 #1544

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[Joe Subich, W4TV-4]

> The point is it was providing the correct power output levels
> before the last couple of firmware revisions.  Something
> changed that made it go from putting out approximately the
> right power level, to putting out WAY TOO MUCH (i.e. causing
> splatter) power.

Not true ... in spite of careful calibration at both 5 and 50
watt levels neither of my K3s has ever produced exactly the
power requested on any band other than 20 meters, on any mode
other than CW and at any power other than 5 or 50 watts.  The
variations can be as much as 3 dB on SSB depending on the peak
to average ratio of the driving audio and amount of compression
used.  

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.  Among other
issues the wattmeter does not know if you are setting peak
or average power and it does not know what the average power
should be for the arbitrary data and arbitrary modulation.  

For the K3 to accurately control the power level in all modes
the its directional coupler would probably need to be improved
by at least an order or magnitude.  The response flatness would
need to be improved by at least an octave and the detectors would
need to be substantially more linear ... and that's just for CW.
To handle arbitrary audio inputs takes some knowledge of the
peak to average ratio as well as the peak duration (duty cycle)
in order to select the proper detector time constants.  Every
voice every  digital mode and every arbitrary data stream will
have different peak to average ratios and duty cycles.  Do you
expect the DSP to calculate those values on the fly?  Perhaps
the power metering should be derived from a DSP based spectrum
analyzer?

Accept the fact that the power level control is relative.  If  
Wayne and Lyle can improve on it that's great.  However, trying
to hold .1 dB or even 1 dB accuracy from 1 mW to 120 W, 1.8 MHz
to 54 MHz with arbitrary modulation sources in a reasonably
priced amateur transceiver is a fool's errand.

73,

   ... Joe, W4TV
 

> -----Original Message-----
> From: [hidden email]
> [mailto:[hidden email]] On Behalf Of Steve Ward
> Sent: Saturday, January 03, 2009 2:54 PM
> To: [hidden email]
> Subject: [Elecraft] K3: Still unable to set power correctly
> in, DATA A(sigh)
>
>
> "Joe Subich, W4TV" Wrote:
>
> >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.
>
> The point is it was providing the correct power output levels
> before the last couple of firmware revisions.  Something
> changed that made it go from putting out approximately the
> right power level, to putting out WAY TOO MUCH (i.e. causing
> splatter) power.
>
> Setting TXG VCE to -3 dB gets DATA A output almost to where
> it should be, but of course adversely affects SSB.
>
> This is NOT about the accuracy of the wattmeter, its about
> overdriving the PA.
>
> 73,
> Steve
> AD7OG
> K3 #1544
>
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[G4LNA]

CONTENTS DELETED

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[Pete Connors F5VNB]

CONTENTS DELETED

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[Julian, G4ILO]

Peter Connors, F5VNB wrote

Joe

Thank you for pointing out the difficulties in setting average power
across a range of modulation types.
Whatever the peak/average ratio of the modulation, the output power from
the PA is peak limited - so wouldn't the answer be a K3 power meter and
power control that shows/sets peak rather than average power?

That would certainly be the answer, and I suspect that if you took a poll of K3 owners, the majority would have thought that is what they already had.

How close the actual power is to the level dialled up on the control is, within reason, a side issue. I think everyone would expect that the ALC of any transceiver to be capable of limiting the *peak* output power to below the point at which clipping occurs. If you have a front panel control that is linked to the ALC then it should also be able to limit the peak output power to any lower value.

Whether the control has some arbitrary scale of 0 to 10 or an approximation of actual output power is really beside the point. Most amateur power meters only have a specification of within 10% FSD or something quite broad, and I don't think anyone expects the K3 to do better than that.

My point is that one expects the power control to control the peak power, not the average power, because it is excessive peaks that cause splatter and violation of one's license conditions.

To assert that every K3 owner needs an oscilliscope or laboratory grade peak reading meter in order to ensure that they never exceed a given peak power because the K3 internal circuits are incapable of doing so is a very serious criticism indeed.

[Joe Subich, W4TV-4]

> Whatever the peak/average ratio of the modulation, the output
> power from the PA is peak limited - so wouldn't the answer be
> a K3 power meter and power control that shows/sets peak rather
> than average power?

While that might be a solution, it causes other problems. The
wattmeter is used to measure SWR.  If the wattmeter reads peak
power in forward it must also be beak reading in reverse in
order to calculate/display SWR instead of reflected power.  Peak
reading reflected power makes it difficult for the MCU to adjust
the tuner (if installed) and makes it nearly impossible to adjust
while in operation rather than "tune" mode due to the time
constant of the peak reading circuits.  I don't know of any
transceiver that combines a peak reading wattmeter with a tuner.

73,

   ... Joe, W4TV
 

> -----Original Message-----
> From: [hidden email]
> [mailto:[hidden email]] On Behalf Of Peter
> Connors, F5VNB
> Sent: Sunday, January 04, 2009 3:46 AM
> To: [hidden email]
> Subject: Re: [Elecraft] K3: Still unable to set power
> correctly in,DATA A(sigh)
>
>
> Joe
>
> Thank you for pointing out the difficulties in setting average power
> across a range of modulation types.
> Whatever the peak/average ratio of the modulation, the output
> power from
> the PA is peak limited - so wouldn't the answer be a K3 power
> meter and
> power control that shows/sets peak rather than average power?
> The power
> control would then be set just once and the average power would be an
> unavoidable consequence of the choice of modulation.
>
> 73, Pete F5VNB
>
> Joe Subich, W4TV wrote:
> >
> >
> > 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.  Among other
> > issues the wattmeter does not know if you are setting peak
> > or average power and it does not know what the average power
> > should be for the arbitrary data and arbitrary modulation.  
> >
> > For the K3 to accurately control the power level in all modes
> > the its directional coupler would probably need to be improved
> > by at least an order or magnitude.  The response flatness would
> > need to be improved by at least an octave and the detectors would
> > need to be substantially more linear ... and that's just for CW.
> > To handle arbitrary audio inputs takes some knowledge of the
> > peak to average ratio as well as the peak duration (duty cycle)
> > in order to select the proper detector time constants.  Every
> > voice every  digital mode and every arbitrary data stream will
> > have different peak to average ratios and duty cycles.  Do you
> > expect the DSP to calculate those values on the fly?  Perhaps
> > the power metering should be derived from a DSP based spectrum
> > analyzer?
> >
> > Accept the fact that the power level control is relative.  If
> > Wayne and Lyle can improve on it that's great.  However, trying
> > to hold .1 dB or even 1 dB accuracy from 1 mW to 120 W, 1.8 MHz
> > to 54 MHz with arbitrary modulation sources in a reasonably
> > priced amateur transceiver is a fool's errand.
> >
> > 73,
> >
> >    ... Joe, W4TV
>
>
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[dj7mgq]

> While that might be a solution, it causes other...

Why should the firmware not be able to both? Assuming that there are no
hardware limitations, I would think it should fairly easily be possible
to do peak readings and average readings as needed by the firmware, in
the firmware, for the firmware.

BTW: I've always felt that the power control in SSB could be better and
way back when (i.e. I can't remember which firmware version) it was not
very good at all, to put it mildly. At least in SSB the power control
has been improved markedly over the last year, even if it is not 100%
perfect (yet).

I've only used DATA-A once, for a quick experimental PSK QSO several
months ago, and at the time I didn't notice any problems.

I'm sure that Wayne & Lyle will find a good solution...

vy 73 de toby
--
DD5FZ
K2 #885
K2/100 #3248
k3/100 #67
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[G4LNA]

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[Julian, G4ILO]

G4LNA wrote

I'm not asserting anything, what I said applies to any rig you care to mention, I don't believe meters. No matter what magic wizardry circuits or software is contained in the rig to deceive to meter into reading power, you can't beat seeing the peak power reading on an oscilloscope.

I did have a look at the peak output of my rig and notice the meter doesn't correspond to the peak power reading on the K3, it doesn't even come close, that doesn't worry me in the slightest because I don't use the meter for power setting on anything apart from CW.

What I will assert is that every radio amateur should at least have an oscilloscope as basic test equipment and learn how to use it, perhaps there wouldn't be so many rubbish signals on the air, there again, if pigs fly...........

I'm not pointing a finger at you Julian, I think you may agree there are a lot of amateurs who do rely on meters without understanding what is really happening in the real world, because now a days they are not taught basic understanding of what is happening to a modulated RF signal.

An oscilloscope is one of the main bits of test gear an RF engineer can own, after all, that's what we are, RF engineers and oscilloscopes are cheap to buy.

It would be very nice if we were all able to do this, but your statement takes no account of individuals' circumstances. You are from the UK, so you know what most of our houses are like. Take a look at the picture on the front page of my website. My "shack" has to share desk space with my home office, and meet the aesthetic criteria of my XYL. I don't have the luxury of a dedicated radio room I can cram with test equipment, and there are a lot of us like that. If radio manufacturers required customers to have a lab full of test gear then the market for their products would be so limited they'd be out of business.

Elecraft does not recommend never mind require an oscilloscope not even when constructing a K2 from parts. I successfully built one using nothing more in the way of test equipment than a £5 DMM and a home made power meter. If you are building gear from scratch then a scope probably is very useful, but if you are paying $3,000 for a factory aligned transceiver from any manufacturer then you ought to be confident that it puts out a clean signal as long as you operate it in accordance with the instructions.

[Joe Subich, W4TV-4]

> If the onboard meter _thought_ the K3 was making the requested
> power, that would be one thing.  But in this case the onboard
> meter thinks it's putting out 2x the power, which it is.

It depends on what part of the system thinks what.  In this
case the MCU is reading a given value but interpreting it
as something else thanks to TXG VCE.  

TXG VCE does not effect the peak power in SSB or AFSK A with
single tone modulation.  It does effect peak power in DATA A.

If you are seeing about 2x the power called for, decrease
TXG VCE by 3 dB and see if the situation does not resolve
itself (at the expense of power output in USB/LSB).  Although
the wattmeter is peak reading according to Wayne, TXG VCE
still provides an inappropriate "adjustment."

73,

   ... Joe, W4TV
 
 

> -----Original Message-----
> From: Steve Ward [mailto:[hidden email]]
> Sent: Monday, January 05, 2009 3:38 AM
> To: [hidden email]
> Subject: Re: [Elecraft] K3: Still unable to set power
> correctly in, DATA A(sigh)
>
>
> Joe,
>
> If the onboard meter _thought_ the K3 was making the requested power,
> that would be one thing.  But in this case the onboard meter
> thinks it's
> putting out 2x the power, which it is.  So, I dial in 40w and
> I get 80w
> both by the internal meter and by my admittedly less than lab-quality
> MFJ dummy load+meter.
>
> It did not do this before the most recent firmware.  
> Something got broken...
>
> 73,
>
> Steve AD7OG
>
> Joe Subich, W4TV wrote:
> >  
> >> The point is it was providing the correct power output levels
> >> before the last couple of firmware revisions.  Something
> >> changed that made it go from putting out approximately the
> >> right power level, to putting out WAY TOO MUCH (i.e. causing
> >> splatter) power.
> >>    
> >
> > Not true ... in spite of careful calibration at both 5 and 50
> > watt levels neither of my K3s has ever produced exactly the
> > power requested on any band other than 20 meters, on any mode
> > other than CW and at any power other than 5 or 50 watts.  The
> > variations can be as much as 3 dB on SSB depending on the peak
> > to average ratio of the driving audio and amount of compression
> > used.  
> >
> > 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.  Among other
> > issues the wattmeter does not know if you are setting peak
> > or average power and it does not know what the average power
> > should be for the arbitrary data and arbitrary modulation.  
> >
> > For the K3 to accurately control the power level in all modes
> > the its directional coupler would probably need to be improved
> > by at least an order or magnitude.  The response flatness would
> > need to be improved by at least an octave and the detectors would
> > need to be substantially more linear ... and that's just for CW.
> > To handle arbitrary audio inputs takes some knowledge of the
> > peak to average ratio as well as the peak duration (duty cycle)
> > in order to select the proper detector time constants.  Every
> > voice every  digital mode and every arbitrary data stream will
> > have different peak to average ratios and duty cycles.  Do you
> > expect the DSP to calculate those values on the fly?  Perhaps
> > the power metering should be derived from a DSP based spectrum
> > analyzer?
> >
> > Accept the fact that the power level control is relative.  If
> > Wayne and Lyle can improve on it that's great.  However, trying
> > to hold .1 dB or even 1 dB accuracy from 1 mW to 120 W, 1.8 MHz
> > to 54 MHz with arbitrary modulation sources in a reasonably
> > priced amateur transceiver is a fool's errand.
> >
> > 73,
> >
> >    ... Joe, W4TV
> >  
> >
> >
> >
> >  
> >> -----Original Message-----
> >> From: [hidden email]
> >> [mailto:[hidden email]] On Behalf Of Steve Ward
> >> Sent: Saturday, January 03, 2009 2:54 PM
> >> To: [hidden email]
> >> Subject: [Elecraft] K3: Still unable to set power correctly
> >> in, DATA A(sigh)
> >>
> >>
> >> "Joe Subich, W4TV" Wrote:
> >>
> >>    
> >>> 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.
> >>>      
> >> The point is it was providing the correct power output levels
> >> before the last couple of firmware revisions.  Something
> >> changed that made it go from putting out approximately the
> >> right power level, to putting out WAY TOO MUCH (i.e. causing
> >> splatter) power.
> >>
> >> Setting TXG VCE to -3 dB gets DATA A output almost to where
> >> it should be, but of course adversely affects SSB.
> >>
> >> This is NOT about the accuracy of the wattmeter, its about
> >> overdriving the PA.
> >>
> >> 73,
> >> Steve
> >> AD7OG
> >> K3 #1544
> >>

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