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Phil Hystad

W2 Questions

A few questions about the W2 meter:

1. The posted accuracy is +- 0.5 dB which I calculate as about +- 12 %. Is this full scale accuracy and if so is half scale possibly more accurate or is this the most accurate the meter is likely to be. I am not even sure if it makes a difference for full scale or half scale for a digital meter so that part of my question may be moot.

2. What does it take to achieve an accuracy better then 5 % (for example), and is it possible to achieve an accuracy of 1 % or better? I am curious as to where the money needs to be spent in achieving such accuracy. Is it in the directional coupler?

3. I am thinking that the company that can build the best receiver on the market (the K3) can also build the best meter. So, would Elecraft principles consider a future super-accurate, best on the planet, amateur radio RF/SWR power meter? Oh, I think a current meter would be cool too.

And, I know that having meter accuracy is of little importance in ham radio but there is some kind of deep seated quirk in me that wants accuracy just for the heck of it. Certainly 5 % is achievable, right?

73,
phil, K7PEH
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P.B. Christensen

Re: W2 Questions

Phil,

With each LED representing 100-watts on the 2KW scale, it may be of some
help to go from 10% to 5% in accuracy, but in the case of the W2, the
display resolution is limited to 50-watts in between mid power ranges (e.g.,
250-watts) but a display of 200-watts with two LEDs showing may actually
mean 151 watts or 249 watts.

50-watts is mid-way between any two LEDs at the 2KW range and I'm making an
assumption that levels less than any 50-watt range (e.g., 240-watts) will
result in the preceding element being lit which shows 200-watts. If it's
more than the mid point (e.g., 260-watts) then the next LED should be lit.
So, at the low-end of the W2's range at say the 200-watt level, the meter
can at best resolve to only 50/200 = 25% and seemingly 100/200 = 50% at
worst (using the 149W to 249W example). I don't want to confuse resolution
with accuracy but the two parameters go hand-in-hand. That said, I see no
real benefit of going from 10% to 5% in accuracy when resolution
deficiencies can easily mask the error in accuracy. I may be completely
wrong with the manner in which the W2 resolves, so someone set me straight
if my assumptions aren't correct.

You asked the question about what it takes to achieve better accuracy. You
may want to read N8LP's excellent article in QEX from a few years ago, along
with articles from Warren Bruene, Roy Lewallen, John Grebenkemper, and
others who have published on the accuracy subject.

Paul, W9AC

----- Original Message -----
From: "Phil Hystad" <[hidden email]>
To: "Elecraft" <[hidden email]>
Sent: Wednesday, December 09, 2009 7:51 PM
Subject: [Elecraft] W2 Questions

>A few questions about the W2 meter:
>
> 1. The posted accuracy is +- 0.5 dB which I calculate as about +- 12 %.
> Is this full scale accuracy and if so is half scale possibly more accurate
> or is this the most accurate the meter is likely to be. I am not even
> sure if it makes a difference for full scale or half scale for a digital
> meter so that part of my question may be moot.
>
> 2. What does it take to achieve an accuracy better then 5 % (for
> example), and is it possible to achieve an accuracy of 1 % or better? I
> am curious as to where the money needs to be spent in achieving such
> accuracy. Is it in the directional coupler?
>
> 3. I am thinking that the company that can build the best receiver on the
> market (the K3) can also build the best meter. So, would Elecraft
> principles consider a future super-accurate, best on the planet, amateur
> radio RF/SWR power meter? Oh, I think a current meter would be cool too.
>
> And, I know that having meter accuracy is of little importance in ham
> radio but there is some kind of deep seated quirk in me that wants
> accuracy just for the heck of it. Certainly 5 % is achievable, right?
>
> 73,
> phil, K7PEH
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>

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Phil Hystad

Re: W2 Questions

Paul,

Thanks for your comments. And, in followup, if Elecraft were to make
a meter with reasonably high accuracy I presume that another display
method, other then LEDs, would be required. I think a high-resolution
LCD with nice color graphic renditions of power information. OK, sort
of kidding here, I presume that a computer interface could handle that
kind of information display.

peh

On Dec 9, 2009, at 5:23 PM, Paul Christensen wrote:

> Phil,
>
> With each LED representing 100-watts on the 2KW scale, it may be of some
> help to go from 10% to 5% in accuracy, but in the case of the W2, the
> display resolution is limited to 50-watts in between mid power ranges (e.g.,
> 250-watts) but a display of 200-watts with two LEDs showing may actually
> mean 151 watts or 249 watts.
>
> 50-watts is mid-way between any two LEDs at the 2KW range and I'm making an
> assumption that levels less than any 50-watt range (e.g., 240-watts) will
> result in the preceding element being lit which shows 200-watts. If it's
> more than the mid point (e.g., 260-watts) then the next LED should be lit.
> So, at the low-end of the W2's range at say the 200-watt level, the meter
> can at best resolve to only 50/200 = 25% and seemingly 100/200 = 50% at
> worst (using the 149W to 249W example). I don't want to confuse resolution
> with accuracy but the two parameters go hand-in-hand. That said, I see no
> real benefit of going from 10% to 5% in accuracy when resolution
> deficiencies can easily mask the error in accuracy. I may be completely
> wrong with the manner in which the W2 resolves, so someone set me straight
> if my assumptions aren't correct.
>
> You asked the question about what it takes to achieve better accuracy. You
> may want to read N8LP's excellent article in QEX from a few years ago, along
> with articles from Warren Bruene, Roy Lewallen, John Grebenkemper, and
> others who have published on the accuracy subject.
>
> Paul, W9AC
>
>
> ----- Original Message -----
> From: "Phil Hystad" <[hidden email]>
> To: "Elecraft" <[hidden email]>
> Sent: Wednesday, December 09, 2009 7:51 PM
> Subject: [Elecraft] W2 Questions
>
>
>> A few questions about the W2 meter:
>>
>> 1. The posted accuracy is +- 0.5 dB which I calculate as about +- 12 %.
>> Is this full scale accuracy and if so is half scale possibly more accurate
>> or is this the most accurate the meter is likely to be. I am not even
>> sure if it makes a difference for full scale or half scale for a digital
>> meter so that part of my question may be moot.
>>
>> 2. What does it take to achieve an accuracy better then 5 % (for
>> example), and is it possible to achieve an accuracy of 1 % or better? I
>> am curious as to where the money needs to be spent in achieving such
>> accuracy. Is it in the directional coupler?
>>
>> 3. I am thinking that the company that can build the best receiver on the
>> market (the K3) can also build the best meter. So, would Elecraft
>> principles consider a future super-accurate, best on the planet, amateur
>> radio RF/SWR power meter? Oh, I think a current meter would be cool too.
>>
>> And, I know that having meter accuracy is of little importance in ham
>> radio but there is some kind of deep seated quirk in me that wants
>> accuracy just for the heck of it. Certainly 5 % is achievable, right?
>>
>> 73,
>> phil, K7PEH
>> ______________________________________________________________
>> Elecraft mailing list
>> Home: http://mailman.qth.net/mailman/listinfo/elecraft
>> Help: http://mailman.qth.net/mmfaq.htm
>> Post: mailto:[hidden email]
>>
>> This list hosted by: http://www.qsl.net
>> Please help support this email list: http://www.qsl.net/donate.html
>>
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html

P.B. Christensen

Re: W2 Questions

It's kinda' hard to beat numerical digits when you want the best possible
resolution displayed. By the way Phil, I should re-phrase my earlier
statement when I referred to a resolution "deficiency." I really meant to
imply a resolution "limitation." There's nothing wrong with that form of
wattmeter display, even with the set limitation on resolution. I prefer a
bargraph display as a quick indicator of what's going on rather than
interpolating quickly flashing numbers on a display.

Here's a link to N8LP's article in QEX. Accuracy is highly dependent on
directional coupler design and construction technique as well as detector
design.

http://www.telepostinc.com/Files/phipps-1.pdf

Paul, W9AC

----- Original Message -----
From: "Phil Hystad" <[hidden email]>
To: "Paul Christensen" <[hidden email]>
Cc: "Elecraft" <[hidden email]>
Sent: Wednesday, December 09, 2009 8:37 PM
Subject: Re: [Elecraft] W2 Questions

Paul,

Thanks for your comments. And, in followup, if Elecraft were to make
a meter with reasonably high accuracy I presume that another display
method, other then LEDs, would be required. I think a high-resolution
LCD with nice color graphic renditions of power information. OK, sort
of kidding here, I presume that a computer interface could handle that
kind of information display.

peh

On Dec 9, 2009, at 5:23 PM, Paul Christensen wrote:

> Phil,
>
> With each LED representing 100-watts on the 2KW scale, it may be of some
> help to go from 10% to 5% in accuracy, but in the case of the W2, the
> display resolution is limited to 50-watts in between mid power ranges
> (e.g.,
> 250-watts) but a display of 200-watts with two LEDs showing may actually
> mean 151 watts or 249 watts.
>
> 50-watts is mid-way between any two LEDs at the 2KW range and I'm making
> an
> assumption that levels less than any 50-watt range (e.g., 240-watts) will
> result in the preceding element being lit which shows 200-watts. If it's
> more than the mid point (e.g., 260-watts) then the next LED should be lit.
> So, at the low-end of the W2's range at say the 200-watt level, the meter
> can at best resolve to only 50/200 = 25% and seemingly 100/200 = 50% at
> worst (using the 149W to 249W example). I don't want to confuse
> resolution
> with accuracy but the two parameters go hand-in-hand. That said, I see no
> real benefit of going from 10% to 5% in accuracy when resolution
> deficiencies can easily mask the error in accuracy. I may be completely
> wrong with the manner in which the W2 resolves, so someone set me straight
> if my assumptions aren't correct.
>
> You asked the question about what it takes to achieve better accuracy.
> You
> may want to read N8LP's excellent article in QEX from a few years ago,
> along
> with articles from Warren Bruene, Roy Lewallen, John Grebenkemper, and
> others who have published on the accuracy subject.
>
> Paul, W9AC
>
>
> ----- Original Message -----
> From: "Phil Hystad" <[hidden email]>
> To: "Elecraft" <[hidden email]>
> Sent: Wednesday, December 09, 2009 7:51 PM
> Subject: [Elecraft] W2 Questions
>
>
>> A few questions about the W2 meter:
>>
>> 1. The posted accuracy is +- 0.5 dB which I calculate as about +- 12 %.
>> Is this full scale accuracy and if so is half scale possibly more
>> accurate
>> or is this the most accurate the meter is likely to be. I am not even
>> sure if it makes a difference for full scale or half scale for a digital
>> meter so that part of my question may be moot.
>>
>> 2. What does it take to achieve an accuracy better then 5 % (for
>> example), and is it possible to achieve an accuracy of 1 % or better? I
>> am curious as to where the money needs to be spent in achieving such
>> accuracy. Is it in the directional coupler?
>>
>> 3. I am thinking that the company that can build the best receiver on
>> the
>> market (the K3) can also build the best meter. So, would Elecraft
>> principles consider a future super-accurate, best on the planet, amateur
>> radio RF/SWR power meter? Oh, I think a current meter would be cool too.
>>
>> And, I know that having meter accuracy is of little importance in ham
>> radio but there is some kind of deep seated quirk in me that wants
>> accuracy just for the heck of it. Certainly 5 % is achievable, right?
>>
>> 73,
>> phil, K7PEH
>> ______________________________________________________________
>> Elecraft mailing list
>> Home: http://mailman.qth.net/mailman/listinfo/elecraft
>> Help: http://mailman.qth.net/mmfaq.htm
>> Post: mailto:[hidden email]
>>
>> This list hosted by: http://www.qsl.net
>> Please help support this email list: http://www.qsl.net/donate.html
>>
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html

Don Wilhelm-4

Re: W2 Questions

In reply to this post by Phil Hystad

Phil,

The W2 wattmeter is similar in its detector accuracy to the Tandem Match
(by John Grebenkemper KI6WX) in that its accuracy depends on matching
the detector diodes with the compensation diodes.
The "Gold Standard" of power measuring devices is the HP436A wattmeter,
and it has a stated accuracy of +/-0.05 dB. That amounts to a +/-1.16%
accuracy - you are not going to get much better than that lab instrument
in an amateur grade instrument.
The Tandem Match that KI6WX built tracks the HP436A within +/- 0.5 dB
over a range of 10 mW to 100W (your 11.2% error), and also tracks the
HP436A within +/-0.1 dB over a 1W to 100W range for a 2.33 % difference.

Power measurement is tough on accuracy as expressed in percentage. Most
ham grade wattmeters specify 20% of full scale. The Tandem Match and
the W2 wattmeter are percentages of actual readings.

Since power is normally best expressed in dB (because the apparent
signal strength is related in dB), a specification of 0.5 dB is not bad
at all.
BTW - I believe that is the accuracy of the power reported using the PC
link. The resolution of the LED scale is not adequate to indicate the
degree of precision available.

The directional coupler will have frequency dependencies as well as
accuracy implications.

73,
Don W3FPR

Phil Hystad wrote:

> A few questions about the W2 meter:
>
> 1. The posted accuracy is +- 0.5 dB which I calculate as about +- 12 %. Is this full scale accuracy and if so is half scale possibly more accurate or is this the most accurate the meter is likely to be. I am not even sure if it makes a difference for full scale or half scale for a digital meter so that part of my question may be moot.
>
> 2. What does it take to achieve an accuracy better then 5 % (for example), and is it possible to achieve an accuracy of 1 % or better? I am curious as to where the money needs to be spent in achieving such accuracy. Is it in the directional coupler?
>
> 3. I am thinking that the company that can build the best receiver on the market (the K3) can also build the best meter. So, would Elecraft principles consider a future super-accurate, best on the planet, amateur radio RF/SWR power meter? Oh, I think a current meter would be cool too.
>
> And, I know that having meter accuracy is of little importance in ham radio but there is some kind of deep seated quirk in me that wants accuracy just for the heck of it. Certainly 5 % is achievable, right?
>
> 73,
> phil, K7PEH
>
>

Eric Swartz - WA6HHQ

Re: W2 Questions

Administrator

In reply to this post by Phil Hystad

Within 0.5 dB worst case of the actual power being measured. Not of full
scale.

We actually do much better than that.

73, Eric

Phil Hystad wrote:
> A few questions about the W2 meter:
>
> 1. The posted accuracy is +- 0.5 dB which I calculate as about +- 12 %. Is this full scale accuracy and if so is half scale possibly more accurate or is this the most accurate the meter is likely to be. I am not even sure if it makes a difference for full scale or half scale for a digital meter so that part of my question may be moot.
>
>
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n7ws

Re: W2 Questions

In reply to this post by P.B. Christensen

And take a look at HP's note AN64 (cp.literature.agilent.com/litweb/pdf/5965-6630E.pdf), particularly chapter VII. After that, the question about whether more resolution is necessary or meaningful might be moot.

--- On Wed, 12/9/09, Paul Christensen <[hidden email]> wrote:

>
> You asked the question about what it takes to achieve
> better accuracy. You
> may want to read N8LP's excellent article in QEX from a few
> years ago, along
> with articles from Warren Bruene, Roy Lewallen, John
> Grebenkemper, and
> others who have published on the accuracy subject.
>
> Paul, W9AC
>
>
> ----- Original Message -----
> From: "Phil Hystad" <[hidden email]>
> To: "Elecraft" <[hidden email]>
> Sent: Wednesday, December 09, 2009 7:51 PM
> Subject: [Elecraft] W2 Questions
>
>
> >A few questions about the W2 meter:
> >
> > 1. The posted accuracy is +- 0.5 dB which I
> calculate as about +- 12 %.
> > Is this full scale accuracy and if so is half scale
> possibly more accurate
> > or is this the most accurate the meter is likely to
> be. I am not even
> > sure if it makes a difference for full scale or half
> scale for a digital
> > meter so that part of my question may be moot.
> >
> > 2. What does it take to achieve an accuracy
> better then 5 % (for
> > example), and is it possible to achieve an accuracy of
> 1 % or better? I
> > am curious as to where the money needs to be spent in
> achieving such
> > accuracy. Is it in the directional coupler?
> >
> > 3. I am thinking that the company that can build
> the best receiver on the
> > market (the K3) can also build the best meter.
> So, would Elecraft
> > principles consider a future super-accurate, best on
> the planet, amateur
> > radio RF/SWR power meter? Oh, I think a current
> meter would be cool too.
> >
> > And, I know that having meter accuracy is of little
> importance in ham
> > radio but there is some kind of deep seated quirk in
> me that wants
> > accuracy just for the heck of it. Certainly 5 %
> is achievable, right?
> >
> > 73,
> > phil, K7PEH
> >
> ______________________________________________________________
> > Elecraft mailing list
> > Home: http://mailman.qth.net/mailman/listinfo/elecraft
> > Help: http://mailman.qth.net/mmfaq.htm
> > Post: mailto:[hidden email]
> >
> > This list hosted by: http://www.qsl.net
> > Please help support this email list: http://www.qsl.net/donate.html
> >
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>

Jack Smith-6

Re: W2 Questions

In reply to this post by Don Wilhelm-4

Don:

All I've done is read the spec sheet, but Minicircuits has a relatively
new sensitive termination wattmeter with USB interface for a quite
reasonable price, at least by Agilent standards.
http://www.minicircuits.com/pdfs/PWR-6G+.pdf -- it's a "virtual"
instrument as it consists of the sensor and a USB port to plug into
your computer. At $700, it isn't much more than you might pay for a
single used Agilent sensor in decent shape and calibration.

Depending on frequency and power range, the "typical" error runs from
+/- 0.1 db to +/- 0.35 dB. power range from -30 to +20 dBm, frequency
range 1 MHz - 6 GHz.

If I didn't already have a 437B and 8481A and 8482A sensors, I would
give the Minicircuits product serious consideration.

Jack K8ZOA

Don Wilhelm wrote:

> Phil,
>
> The W2 wattmeter is similar in its detector accuracy to the Tandem Match
> (by John Grebenkemper KI6WX) in that its accuracy depends on matching
> the detector diodes with the compensation diodes.
> The "Gold Standard" of power measuring devices is the HP436A wattmeter,
> and it has a stated accuracy of +/-0.05 dB. That amounts to a +/-1.16%
> accuracy - you are not going to get much better than that lab instrument
> in an amateur grade instrument.
> The Tandem Match that KI6WX built tracks the HP436A within +/- 0.5 dB
> over a range of 10 mW to 100W (your 11.2% error), and also tracks the
> HP436A within +/-0.1 dB over a 1W to 100W range for a 2.33 % difference.
>
> Power measurement is tough on accuracy as expressed in percentage. Most
> ham grade wattmeters specify 20% of full scale. The Tandem Match and
> the W2 wattmeter are percentages of actual readings.
>
> Since power is normally best expressed in dB (because the apparent
> signal strength is related in dB), a specification of 0.5 dB is not bad
> at all.
> BTW - I believe that is the accuracy of the power reported using the PC
> link. The resolution of the LED scale is not adequate to indicate the
> degree of precision available.
>
> The directional coupler will have frequency dependencies as well as
> accuracy implications.
>
> 73,
> Don W3FPR
>
> Phil Hystad wrote:
>
>> A few questions about the W2 meter:
>>
>> 1. The posted accuracy is +- 0.5 dB which I calculate as about +- 12 %. Is this full scale accuracy and if so is half scale possibly more accurate or is this the most accurate the meter is likely to be. I am not even sure if it makes a difference for full scale or half scale for a digital meter so that part of my question may be moot.
>>
>> 2. What does it take to achieve an accuracy better then 5 % (for example), and is it possible to achieve an accuracy of 1 % or better? I am curious as to where the money needs to be spent in achieving such accuracy. Is it in the directional coupler?
>>
>> 3. I am thinking that the company that can build the best receiver on the market (the K3) can also build the best meter. So, would Elecraft principles consider a future super-accurate, best on the planet, amateur radio RF/SWR power meter? Oh, I think a current meter would be cool too.
>>
>> And, I know that having meter accuracy is of little importance in ham radio but there is some kind of deep seated quirk in me that wants accuracy just for the heck of it. Certainly 5 % is achievable, right?
>>
>> 73,
>> phil, K7PEH
>>
>>
>>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>
>

Phil Hystad

Re: W2 Questions

In reply to this post by n7ws

Wes,

Thanks for the link to what looks like a very interesting document. Just what I have been looking for. And, thanks to others for the suggested resources.

phil

On Dec 9, 2009, at 7:01 PM, Wes Stewart wrote:

> And take a look at HP's note AN64 (cp.literature.agilent.com/litweb/pdf/5965-6630E.pdf), particularly chapter VII. After that, the question about whether more resolution is necessary or meaningful might be moot.
>
>
>
> --- On Wed, 12/9/09, Paul Christensen <[hidden email]> wrote:
>
>
>>
>> You asked the question about what it takes to achieve
>> better accuracy. You
>> may want to read N8LP's excellent article in QEX from a few
>> years ago, along
>> with articles from Warren Bruene, Roy Lewallen, John
>> Grebenkemper, and
>> others who have published on the accuracy subject.
>>
>> Paul, W9AC
>>
>>
>> ----- Original Message -----
>> From: "Phil Hystad" <[hidden email]>
>> To: "Elecraft" <[hidden email]>
>> Sent: Wednesday, December 09, 2009 7:51 PM
>> Subject: [Elecraft] W2 Questions
>>
>>
>>> A few questions about the W2 meter:
>>>
>>> 1. The posted accuracy is +- 0.5 dB which I
>> calculate as about +- 12 %.
>>> Is this full scale accuracy and if so is half scale
>> possibly more accurate
>>> or is this the most accurate the meter is likely to
>> be. I am not even
>>> sure if it makes a difference for full scale or half
>> scale for a digital
>>> meter so that part of my question may be moot.
>>>
>>> 2. What does it take to achieve an accuracy
>> better then 5 % (for
>>> example), and is it possible to achieve an accuracy of
>> 1 % or better? I
>>> am curious as to where the money needs to be spent in
>> achieving such
>>> accuracy. Is it in the directional coupler?
>>>
>>> 3. I am thinking that the company that can build
>> the best receiver on the
>>> market (the K3) can also build the best meter.
>> So, would Elecraft
>>> principles consider a future super-accurate, best on
>> the planet, amateur
>>> radio RF/SWR power meter? Oh, I think a current
>> meter would be cool too.
>>>
>>> And, I know that having meter accuracy is of little
>> importance in ham
>>> radio but there is some kind of deep seated quirk in
>> me that wants
>>> accuracy just for the heck of it. Certainly 5 %
>> is achievable, right?
>>>
>>> 73,
>>> phil, K7PEH
>>>
>> ______________________________________________________________
>>> Elecraft mailing list
>>> Home: http://mailman.qth.net/mailman/listinfo/elecraft
>>> Help: http://mailman.qth.net/mmfaq.htm
>>> Post: mailto:[hidden email]
>>>
>>> This list hosted by: http://www.qsl.net
>>> Please help support this email list: http://www.qsl.net/donate.html
>>>
>>
>> ______________________________________________________________
>> Elecraft mailing list
>> Home: http://mailman.qth.net/mailman/listinfo/elecraft
>> Help: http://mailman.qth.net/mmfaq.htm
>> Post: mailto:[hidden email]
>>
>> This list hosted by: http://www.qsl.net
>> Please help support this email list: http://www.qsl.net/donate.html
>>
>
>
>
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Don Wilhelm-5

Re: W2 Questions

In reply to this post by Jack Smith-6

Jack,

At $700 I will stick with my W7ZOI power meter with its 40 dB power tap
and my Tandem Match! I have calibration data that Bob Friess provided
on my Power meter from 1 MHz to 500 MHz (and ham band intervals in
between). The Tandem Match tracks that data quite well in its basic
metering, but is limited to 30 MHz with the couplers available. I
really like the Tandem Match for general purposes, but the parallax from
the analog meters must be taken into consideration too (op amp accuracy
is a great thing indeed, nothing like analog computers using precision
resistors - but then I am partly "old school").

That is certainly good enough to give me +/- 5% power measurement
accuracy from 1 MHz to 500 MHz, and that is more than I require at the
moment.

The world of Power measurement is getting better, but it still is not
down to really precise accuracy, no matter what the instrument.

Thanks for the information. Perhaps one day when the ham budget allows
and I have a purpose for it, I will make the investment.

73,
Don W3FPR

Jack Smith wrote:

> Don:
>
> All I've done is read the spec sheet, but Minicircuits has a
> relatively new sensitive termination wattmeter with USB interface for
> a quite reasonable price, at least by Agilent standards.
> http://www.minicircuits.com/pdfs/PWR-6G+.pdf -- it's a "virtual"
> instrument as it consists of the sensor and a USB port to plug into
> your computer. At $700, it isn't much more than you might pay for a
> single used Agilent sensor in decent shape and calibration.
>
> Depending on frequency and power range, the "typical" error runs from
> +/- 0.1 db to +/- 0.35 dB. power range from -30 to +20 dBm, frequency
> range 1 MHz - 6 GHz.
>
> If I didn't already have a 437B and 8481A and 8482A sensors, I would
> give the Minicircuits product serious consideration.
>
> Jack K8ZOA
>
>
> Don Wilhelm wrote:
>> Phil,
>>
>> The W2 wattmeter is similar in its detector accuracy to the Tandem
>> Match (by John Grebenkemper KI6WX) in that its accuracy depends on
>> matching the detector diodes with the compensation diodes.
>> The "Gold Standard" of power measuring devices is the HP436A
>> wattmeter, and it has a stated accuracy of +/-0.05 dB. That amounts
>> to a +/-1.16% accuracy - you are not going to get much better than
>> that lab instrument in an amateur grade instrument.
>> The Tandem Match that KI6WX built tracks the HP436A within +/- 0.5 dB
>> over a range of 10 mW to 100W (your 11.2% error), and also tracks the
>> HP436A within +/-0.1 dB over a 1W to 100W range for a 2.33 % difference.
>>
>> Power measurement is tough on accuracy as expressed in percentage.
>> Most ham grade wattmeters specify 20% of full scale. The Tandem
>> Match and the W2 wattmeter are percentages of actual readings.
>>
>> Since power is normally best expressed in dB (because the apparent
>> signal strength is related in dB), a specification of 0.5 dB is not
>> bad at all.
>> BTW - I believe that is the accuracy of the power reported using the
>> PC link. The resolution of the LED scale is not adequate to indicate
>> the degree of precision available.
>>
>> The directional coupler will have frequency dependencies as well as
>> accuracy implications.
>>
>> 73,
>> Don W3FPR
>>
>> Phil Hystad wrote:
>>
>>> A few questions about the W2 meter:
>>>
>>> 1. The posted accuracy is +- 0.5 dB which I calculate as about +-
>>> 12 %. Is this full scale accuracy and if so is half scale possibly
>>> more accurate or is this the most accurate the meter is likely to
>>> be. I am not even sure if it makes a difference for full scale or
>>> half scale for a digital meter so that part of my question may be moot.
>>>
>>> 2. What does it take to achieve an accuracy better then 5 % (for
>>> example), and is it possible to achieve an accuracy of 1 % or
>>> better? I am curious as to where the money needs to be spent in
>>> achieving such accuracy. Is it in the directional coupler?
>>>
>>> 3. I am thinking that the company that can build the best receiver
>>> on the market (the K3) can also build the best meter. So, would
>>> Elecraft principles consider a future super-accurate, best on the
>>> planet, amateur radio RF/SWR power meter? Oh, I think a current
>>> meter would be cool too.
>>>
>>> And, I know that having meter accuracy is of little importance in
>>> ham radio but there is some kind of deep seated quirk in me that
>>> wants accuracy just for the heck of it. Certainly 5 % is
>>> achievable, right?
>>>
>>> 73,
>>> phil, K7PEH
>>>
>>>
>> ______________________________________________________________
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>>
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>> Please help support this email list: http://www.qsl.net/donate.html
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>>
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Don Wilhelm-4

Re: W2 Questions

In reply to this post by Jack Smith-6

Jack,

At $700 I will stick with my W7ZOI power meter with its 40 dB power tap
and my Tandem Match! I have calibration data that Bob Friess provided
on my Power meter from 1 MHz to 500 MHz (and ham band intervals in
between). The Tandem Match tracks that data quite well in its basic
metering, but is limited to 30 MHz with the couplers available. I
really like the Tandem Match for general purposes, but the parallax from
the analog meters must be taken into consideration too (op amp accuracy
is a great thing indeed, nothing like analog computers using precision
resistors - but then I am partly "old school").

That is certainly good enough to give me ± 5% power measurement accuracy
from 1 MHz to 500 MHz, and that is more than I require at the moment.

The world of Power measurement is getting better, but it still is not
down to really precise accuracy, no matter what the instrument.

Thanks for the information. Perhaps one day when the ham budget allows
and I have a purpose for it, I will make the investment.

73,
Don W3FPR

Jack Smith wrote:

> Don:
>
> All I've done is read the spec sheet, but Minicircuits has a relatively
> new sensitive termination wattmeter with USB interface for a quite
> reasonable price, at least by Agilent standards.
> http://www.minicircuits.com/pdfs/PWR-6G+.pdf -- it's a "virtual"
> instrument as it consists of the sensor and a USB port to plug into
> your computer. At $700, it isn't much more than you might pay for a
> single used Agilent sensor in decent shape and calibration.
>
> Depending on frequency and power range, the "typical" error runs from
> +/- 0.1 db to +/- 0.35 dB. power range from -30 to +20 dBm, frequency
> range 1 MHz - 6 GHz.
>
> If I didn't already have a 437B and 8481A and 8482A sensors, I would
> give the Minicircuits product serious consideration.
>
> Jack K8ZOA
>
>