P3TXMON question?

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P3TXMON question?

Bill Breeden

It's important to remember that RF power expressed in watts is always
based on RMS values.  If RF watts are calculated by measuring the
voltage across a known load, the voltage must be expressed as an RMS
value to correctly calculate the power in watts.  Watts are watts.  
There is no such thing as "peak to peak" or "RMS watts" when expressing
RF power in watts.

Peak envelope power (PEP) has nothing to do with the difference between
the peak and average voltage of a sine wave.  It is the measure of the
power of an RF signal at the modulation peak, averaged over one RF
cycle.  The power measurement within that one RF cycle is still based on
RMS values.

73,

Bill - NA5DX
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Re: P3TXMON question?

Stephen G4SJP
Bill,

That's absolutely right.  There's so much confusion about such things and
you have explained it very well.  RMS can only ever be used as a value of
current or voltage, never power.

73 Stephen, G4SJP

On 21 August 2015 at 20:34, Bill Breeden <[hidden email]> wrote:

>
> It's important to remember that RF power expressed in watts is always
> based on RMS values.  If RF watts are calculated by measuring the voltage
> across a known load, the voltage must be expressed as an RMS value to
> correctly calculate the power in watts.  Watts are watts.  There is no such
> thing as "peak to peak" or "RMS watts" when expressing RF power in watts.
>
> Peak envelope power (PEP) has nothing to do with the difference between
> the peak and average voltage of a sine wave.  It is the measure of the
> power of an RF signal at the modulation peak, averaged over one RF cycle.
> The power measurement within that one RF cycle is still based on RMS values.
>
> 73,
>
> Bill - NA5DX
> ______________________________________________________________
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Re: P3TXMON question?

Don Wilhelm-4
In reply to this post by Bill Breeden
Bill's information is entirely correct.  Thank you for that clear
explanation.

Now back to what I think was the intent of the original question - even
if the terms were incorrect.
Hams commonly use two different considerations for power - PEP - Peak
Envelope Power - that is the peak power that we (at least here in the
US) need to use when considering our power limits, and that is the
specified power output for most if not all amateur transceivers and
amplifiers.

The other term is Average Power, and we can use that for a measure of
the amount of compression used in SSB transmissions - more compression
will bring the Average Power up closer to the PEP, but too much will
create muffled speech (listen during a SSB contest for the
unintelligible signals using too much compression).

As Alan Bloom indicated, the narrow bar indicates the PEP value, while
the other bar will be more of an indication of Average Power, although
your eyes may have to interpret the movement to determine the real
average because that indicator will be constantly changing with SSB
speech patterns, but for CW and data modes, the PEP and average should
be equal during keydown intervals.

73,
Don W3FPR

On 8/21/2015 3:34 PM, Bill Breeden wrote:

>
> It's important to remember that RF power expressed in watts is always
> based on RMS values.  If RF watts are calculated by measuring the
> voltage across a known load, the voltage must be expressed as an RMS
> value to correctly calculate the power in watts.  Watts are watts.  
> There is no such thing as "peak to peak" or "RMS watts" when
> expressing RF power in watts.
>
> Peak envelope power (PEP) has nothing to do with the difference
> between the peak and average voltage of a sine wave.  It is the
> measure of the power of an RF signal at the modulation peak, averaged
> over one RF cycle.  The power measurement within that one RF cycle is
> still based on RMS values.
>
> 73,
>
> Bill - NA5DX

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Re: P3TXMON question?

Don Wilhelm-4
In reply to this post by Bill Breeden
In a slightly related note - for those who are using an oscilloscope to
measure the RF voltage at the output, instead  of converting everything
to RMS and doing the power calculation, I can give you a shortcut.  The
formula for power by observing the RF voltage across a 50 ohm dummy load
is Vp-p squared, and then divided by 400.  If the load is not 50 ohms,
then it is Vp-p squared and divided by 8 times R.

The derivation is left to "the student" - Hint, use SQRT 2 in your
derivation rather than 1.414 or .707 because the radicals will cancel
out - the numbers will only cause confusion, but will produce a similar
result.
I use this easy formula at the workbench often when determining power
output, it is especially useful at power levels of 10 watts and below.  
Yes, I do have an oscilloscope probe permanently connected directly
across my dummy load just for this purpose as well as for looking at
relative RF voltages during an alignment.

73,
Don W3FPR

On 8/21/2015 3:34 PM, Bill Breeden wrote:
>
> It's important to remember that RF power expressed in watts is always
> based on RMS values.  If RF watts are calculated by measuring the
> voltage across a known load, the voltage must be expressed as an RMS
> value to correctly calculate the power in watts.  Watts are watts.  
> There is no such thing as "peak to peak" or "RMS watts" when
> expressing RF power in watts.
>

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Re: P3TXMON question?

Bob McGraw - K4TAX
A comment here, has anyone thought to use a Bird 43P with a 100 watt HF
slug?  Or maybe a TelePost LP-100a?  Both are equally good regarding
power measurements but only when the load is 50 ohms resistive.

73
Bob, K4TAX
K3S s/n 10,163

On 8/21/2015 8:15 PM, Don Wilhelm wrote:

> In a slightly related note - for those who are using an oscilloscope
> to measure the RF voltage at the output, instead  of converting
> everything to RMS and doing the power calculation, I can give you a
> shortcut.  The formula for power by observing the RF voltage across a
> 50 ohm dummy load is Vp-p squared, and then divided by 400.  If the
> load is not 50 ohms, then it is Vp-p squared and divided by 8 times R.
>
> The derivation is left to "the student" - Hint, use SQRT 2 in your
> derivation rather than 1.414 or .707 because the radicals will cancel
> out - the numbers will only cause confusion, but will produce a
> similar result.
> I use this easy formula at the workbench often when determining power
> output, it is especially useful at power levels of 10 watts and
> below.  Yes, I do have an oscilloscope probe permanently connected
> directly across my dummy load just for this purpose as well as for
> looking at relative RF voltages during an alignment.
>
> 73,
> Don W3FPR
>
> On 8/21/2015 3:34 PM, Bill Breeden wrote:
>>
>> It's important to remember that RF power expressed in watts is always
>> based on RMS values.  If RF watts are calculated by measuring the
>> voltage across a known load, the voltage must be expressed as an RMS
>> value to correctly calculate the power in watts.  Watts are watts.  
>> There is no such thing as "peak to peak" or "RMS watts" when
>> expressing RF power in watts.
>>
>
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>
>
>


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Re: P3TXMON question?

Phil Hystad-3
I have an LP100A as well as TX Mon for the P3.  But, I also do admit that my reason for having the LP100A is not to have an accurate reading of power but rather to have a reasonable good indicator of power and SWR.  I got the LP100A long before I had my K3 or P3 so if I were doing it all over again, the power meters on the KPA500 or the P3 TX Mon are good enough.  I like to know whether I am putting out 100 watts or 2 watts.  I really don’t care to know if it is 100 watts or 95 or 105 watts.

I think these days, the best thing about the LP100A is that it is yet another lighted up display that looks cool for any visiting guests.

73, phil, K7PEH


> On Aug 21, 2015, at 7:38 PM, Bob McGraw - K4TAX <[hidden email]> wrote:
>
> A comment here, has anyone thought to use a Bird 43P with a 100 watt HF slug?  Or maybe a TelePost LP-100a?  Both are equally good regarding power measurements but only when the load is 50 ohms resistive.
>
> 73
> Bob, K4TAX
> K3S s/n 10,163
>
> On 8/21/2015 8:15 PM, Don Wilhelm wrote:
>> In a slightly related note - for those who are using an oscilloscope to measure the RF voltage at the output, instead  of converting everything to RMS and doing the power calculation, I can give you a shortcut.  The formula for power by observing the RF voltage across a 50 ohm dummy load is Vp-p squared, and then divided by 400.  If the load is not 50 ohms, then it is Vp-p squared and divided by 8 times R.
>>
>> The derivation is left to "the student" - Hint, use SQRT 2 in your derivation rather than 1.414 or .707 because the radicals will cancel out - the numbers will only cause confusion, but will produce a similar result.
>> I use this easy formula at the workbench often when determining power output, it is especially useful at power levels of 10 watts and below.  Yes, I do have an oscilloscope probe permanently connected directly across my dummy load just for this purpose as well as for looking at relative RF voltages during an alignment.
>>
>> 73,
>> Don W3FPR
>>
>> On 8/21/2015 3:34 PM, Bill Breeden wrote:
>>>
>>> It's important to remember that RF power expressed in watts is always based on RMS values.  If RF watts are calculated by measuring the voltage across a known load, the voltage must be expressed as an RMS value to correctly calculate the power in watts.  Watts are watts.  There is no such thing as "peak to peak" or "RMS watts" when expressing RF power in watts.
>>>
>>
>> ______________________________________________________________
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>>
>>
>
>
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Re: P3TXMON question?

Ken G Kopp
In reply to this post by Bob McGraw - K4TAX
Bird accuracy is specified to be +/- 5% of meter full scale ... a 100W
element would be a poor choice to measure a 100W output level.  Take a look
at any Bird's meter scale.  It's not linear and can be read with the most
accuracy to the left of center scale.  A 250W element is much better for
measuring 100W.

Wanna chase your tail?  Measure the same power source with identical Bird
elements......

Don's method is better, but all methods are obviously subject to the
accuracy of the final indicating instrument.

FWIW .....

73l

Ken Kopp - K0PP
On Aug 21, 2015 8:39 PM, "Bob McGraw - K4TAX" <[hidden email]> wrote:

> A comment here, has anyone thought to use a Bird 43P with a 100 watt HF
> slug?  Or maybe a TelePost LP-100a?  Both are equally good regarding power
> measurements but only when the load is 50 ohms resistive.
>
> 73
> Bob, K4TAX
> K3S s/n 10,163
>
> On 8/21/2015 8:15 PM, Don Wilhelm wrote:
>
>> In a slightly related note - for those who are using an oscilloscope to
>> measure the RF voltage at the output, instead  of converting everything to
>> RMS and doing the power calculation, I can give you a shortcut.  The
>> formula for power by observing the RF voltage across a 50 ohm dummy load is
>> Vp-p squared, and then divided by 400.  If the load is not 50 ohms, then it
>> is Vp-p squared and divided by 8 times R.
>>
>> The derivation is left to "the student" - Hint, use SQRT 2 in your
>> derivation rather than 1.414 or .707 because the radicals will cancel out -
>> the numbers will only cause confusion, but will produce a similar result.
>> I use this easy formula at the workbench often when determining power
>> output, it is especially useful at power levels of 10 watts and below.
>> Yes, I do have an oscilloscope probe permanently connected directly across
>> my dummy load just for this purpose as well as for looking at relative RF
>> voltages during an alignment.
>>
>> 73,
>> Don W3FPR
>>
>> On 8/21/2015 3:34 PM, Bill Breeden wrote:
>>
>>>
>>> It's important to remember that RF power expressed in watts is always
>>> based on RMS values.  If RF watts are calculated by measuring the voltage
>>> across a known load, the voltage must be expressed as an RMS value to
>>> correctly calculate the power in watts.  Watts are watts.  There is no such
>>> thing as "peak to peak" or "RMS watts" when expressing RF power in watts.
>>>
>>>
>> ______________________________________________________________
>> Elecraft mailing list
>> Home: http://mailman.qth.net/mailman/listinfo/elecraft
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>> Post: mailto:[hidden email]
>>
>> This list hosted by: http://www.qsl.net
>> Please help support this email list: http://www.qsl.net/donate.html
>> Message delivered to [hidden email]
>>
>>
>>
>>
>
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Re: P3TXMON question?

Wes (N7WS)
So by your "logic" it would be best to measure one Watt using a 100W element.

On 8/21/2015 8:03 PM, Ken G Kopp wrote:

> Bird accuracy is specified to be +/- 5% of meter full scale ... a 100W
> element would be a poor choice to measure a 100W output level.  Take a look
> at any Bird's meter scale.  It's not linear and can be read with the most
> accuracy to the left of center scale.  A 250W element is much better for
> measuring 100W.
>
> Wanna chase your tail?  Measure the same power source with identical Bird
> elements......
>
> Don's method is better, but all methods are obviously subject to the
> accuracy of the final indicating instrument.
>
> FWIW .....
>
> 73l
>
>

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Re: P3TXMON Question?

Edward R Cole
In reply to this post by Bill Breeden
When I need to know accurate power readings my best instrument is
either scope and good 50-ohm termination, or using my HP432A mw power
meter.  Its about 1/2 dB accurate.  But +10mw is the highest scale so
you need several high power coaxial attenuators to measure
power.  40dB will permit measuring +50-dBm (= 100w).

I have a lot of Bird elements and rely on the Bird for day-to-day
measurements, but do realize the Bird's limitation. I measure from
-20 dBm to +62 dBm in my ham shack.  The latter is 1500w. I use
2500H, 2500B, 1000A or 1000D elements.  5w is my smallest element.

But for really precise SWR I use directional couplers and calibrated
open, short and 50-ohm terms.  They are never subjected to over +10
dBm.  Return loss is what is actually measured and one can use a
conversion chart to determine SWR.  If I had the money then a VNA is
the optimum instrument.  But the average ham does not need that.

73, Ed - KL7UW
http://www.kl7uw.com
     "Kits made by KL7UW"
Dubus Mag business:
     [hidden email]

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Re: P3TXMON Question?

Hank Garretson
On Fri, Aug 21, 2015 at 11:19 PM, Edward R Cole <[hidden email]> wrote:

When I need to know accurate power readings my best instrument is either
> scope and good 50-ohm termination, or using my HP432A mw power meter.  Its
> about 1/2 dB accurate.


Isn't "1/2 dB accurate" the same as "12 percent accuracy"?

73,

Hank, W6SX
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Re: P3TXMON Question?

Wes (N7WS)
In reply to this post by Edward R Cole
Maybe "really precise" is a stretch when you're using scalar instrumentation.

Considering the money we put into rigs and antennas, the ~$500 price of the
DG8SAQ Vector Network Analyzer is affordable.

I can remember the days when I had to have some precision attenuation
measurements made on a piece of equipment and it took an airplane ride to a
sister facility where an HP8410 network analyzer resided in a
temperature-controlled clean room.

Later I was able to purchase one of the first HP8510s ($250K) for my work lab.
It was rack-mounted and weighed a couple of hundred pounds. At that time NBS
(NIST) wouldn't even certify 3.5mm (SMA) standards.  BTW, a set of test cables
was >$3K.  Imagine trying to convince Management that these were throw away
items after so many connect-disconnect cycles.

Now I have the VNWA 3 analyzer in my home lab.  I can hold it in my hand and
within its frequency range, it is every bit as good as the HP and the software
is a whole lot more powerful.

Radio-wise, we live in magical times.

Wes  N7WS

On 8/21/2015 11:19 PM, Edward R Cole wrote:
>
> But for really precise SWR I use directional couplers and calibrated open,
> short and 50-ohm terms.  They are never subjected to over +10 dBm.  Return
> loss is what is actually measured and one can use a conversion chart to
> determine SWR.  If I had the money then a VNA is the optimum instrument.  But
> the average ham does not need that.

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OT Power Measurements

Bob McGraw - K4TAX
In reply to this post by Hank Garretson
Seems that I somewhat stirred the pot on this topic with my suggestion
of using a Bird 43P or LP-100a.    In this regard with a Bird 43
instrument, proper choice of a slug is necessary.  Thus if one wishes to
measure 10 watts or so then a slug of the proper full scale range, both
in power and frequency,  should be used.   In no way would I suggest or
imply a 100 watt slug be used to measure 10 watts.

We seem to overlook the point the Bird meter, as well as most other ham
type power meters, are voltage devices.  In this regard, the accurate
power measurement relies on the calibration at precisely 50 ohms.  Any
other Z, resistive or reactive basically negates the accuracy of these
devices.  Now used as a means to determine SWR, they work OK as one is
comparing two different power values obtained with the same instrument
at the same point in the feed line and using a calculator or nomograph
to determine actual SWR values.

One of the few instruments to calculate the true power is the LP-100a in
as much as it has two sensors which are used to  measure both voltage
and current.  At this point the Z component is insignificant to a larger
degree.

As to using an oscilloscope, again the calibration is a critical point
in accuracy plus the resolution accuracy or the ability of one to
determine the actual value of the trace as displayed.    And too, the
accuracy of the dummy load becomes a significant factor.    As a rule we
presume most dummy loads are 50 ohms, but are they?  I have four
different ones, all showing a difference in R value, yet are a
"supposed" to be 50 ohm loads.

As someone else stated, all of this is determined by the accuracy of the
items being used to measure power and the operator understanding and
knowing the limitations of the measurement system.

73
Bob, K4TAX
K3S s/n 10,163

On 8/22/2015 9:00 AM, Hank Garretson wrote:

> On Fri, Aug 21, 2015 at 11:19 PM, Edward R Cole <[hidden email]> wrote:
>
> When I need to know accurate power readings my best instrument is either
>> scope and good 50-ohm termination, or using my HP432A mw power meter.  Its
>> about 1/2 dB accurate.
>
> Isn't "1/2 dB accurate" the same as "12 percent accuracy"?
>
> 73,
>
> Hank, W6SX
> ______________________________________________________________
>


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Re: P3TXMON question?

Cortland Richmond-2
In reply to this post by Bill Breeden
On 8/21/2015 9:03 PM, Ken Kopp - K0PP wrote:
> Bird accuracy is specified to be ± 5% of meter full scale ... a 100W
> element would be a poor choice to measure a 100W output level.  Take a look
> at any Bird's meter scale.  It's not linear and can be read with the most
> accuracy to the left of center scale.  A 250W element is much better for
> measuring 100W.

I've a few wattmeters myself, of various makes and accuracy -- no Birds
--but if I want ACCURACY I use 40dB directional couplers with additional
attenuation into  a spectrum analyzer or a 'scope.  I generally leave a
scope and counter on line for the two main radios in use, with two
directional couplers feeding a 2-way hybrid, which lets me monitor
power, flat-topping and frequency all at once. Still need to get the GPS
disciplined oscillator running, and as I get my brain back (don't ask)
I'll get that done.

Note on 'scopes: If all you need one for is setting output safely below
distortion level, you don't need  $$; the cracked-graticule 15 MHz,  
flea-market, Leader scope I left at the Lowell (MI) ARC station is good
enough reading across a Cantenna.

Cortland Richmond
KA5S
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Re: P3TXMON question?

Bob McGraw - K4TAX
In reply to this post by Wes (N7WS)

This seems to have things really screwed up.   Yes, the Bird 43 is a 5%
of F.S. accuracy instrument.   The Bird 43P is somewhat less accurate,
although 5% F S with carrier, and more like 8% F S or so in peak mode.
    In measuring a 100 watt radio with a 100 watt F S slug would seem to
be most accurate.    Total accuracy decreases as the indicated value
approaches the left side of the scale.   Now using a 250 watt slug to
measure a 100 watt radio,  the earlier states that most accuracy is to
the left of center, which by the way, is the compressed side of the
scale.  This makes no sense as the scale markings are much more
difficult to approximate.    In fact the most accurate area is to the
right of center toward full scale is the expanded scale  which is where
the highest accuracy actually occurs.   With a 100 watt radio and a 100
watt F S  slug the error is +/- 5 watts at 100 watts.  Using a 250 watt
element and measuring 100 watts near center scale the error is more like
+/- 12.5 watts or 5% of the  F S value.

If one measures the same power source with identical elements and gets
different results, they should refrain from buying ham fest elements for
indeed the elements are not identical.  To wit, I purchased 3 new 100
watt elements and 3 new 2500 watt elements. They all give identical
results +/- the width of the pointer.  I don't buy ham fest Bird
elements as I find they are junk and not worth the brass they contain.

And remember, Bird 43 instruments are calibrated for only a 50 resistive
load.  Any other load being used leaves one with a "best guess"
situation as to actual power.

73
Bob, K4TAX
K3S s/n 10,163

On 8/21/2015 11:48 PM, Wes (N7WS) wrote:

> So by your "logic" it would be best to measure one Watt using a 100W
> element.
>
> On 8/21/2015 8:03 PM, Ken G Kopp wrote:
>> Bird accuracy is specified to be +/- 5% of meter full scale ... a 100W
>> element would be a poor choice to measure a 100W output level. Take a
>> look
>> at any Bird's meter scale.  It's not linear and can be read with the
>> most
>> accuracy to the left of center scale.  A 250W element is much better for
>> measuring 100W.
>>
>> Wanna chase your tail?  Measure the same power source with identical
>> Bird
>> elements......
>>
>> Don's method is better, but all methods are obviously subject to the
>> accuracy of the final indicating instrument.
>>
>> FWIW .....
>>
>> 73l
>>
>>
>
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Re: P3TXMON question?

Ken G Kopp
Bob,

The scale calibration --is-- compressed to the right of center,
--not-- to the left as you state, making the left portion expanded
and easier to read.

73!

Ken - K0PP

On Sun, Aug 23, 2015 at 2:14 PM, Bob McGraw - K4TAX <[hidden email]>
wrote:

>
> This seems to have things really screwed up.   Yes, the Bird 43 is a 5% of
> F.S. accuracy instrument.   The Bird 43P is somewhat less accurate,
> although 5% F S with carrier, and more like 8% F S or so in peak mode.
> In measuring a 100 watt radio with a 100 watt F S slug would seem to be
> most accurate.    Total accuracy decreases as the indicated value
> approaches the left side of the scale.   Now using a 250 watt slug to
> measure a 100 watt radio,  the earlier states that most accuracy is to the
> left of center, which by the way, is the compressed side of the scale.
> This makes no sense as the scale markings are much more difficult to
> approximate.   In fact the most accurate area is to the right of center
> toward full scale is the expanded scale  which is where the highest
> accuracy actually occurs.   With a 100 watt radio and a 100 watt F S  slug
> the error is +/- 5 watts at 100 watts.  Using a 250 watt element and
> measuring 100 watts near center scale the error is more like +/- 12.5 watts
> or 5% of the  F S value.
>
> If one measures the same power source with identical elements and gets
> different results, they should refrain from buying ham fest elements for
> indeed the elements are not identical.  To wit, I purchased 3 new 100 watt
> elements and 3 new 2500 watt elements. They all give identical results +/-
> the width of the pointer.  I don't buy ham fest Bird elements as I find
> they are junk and not worth the brass they contain.
>
> And remember, Bird 43 instruments are calibrated for only a 50 resistive
> load.  Any other load being used leaves one with a "best guess" situation
> as to actual power.
>
> 73
> Bob, K4TAX
> K3S s/n 10,163
>
> On 8/21/2015 11:48 PM, Wes (N7WS) wrote:
>
So by your "logic" it would be best to measure one Watt using a 100W

>> element.
>>
>> On 8/21/2015 8:03 PM, Ken G Kopp wrote:
>>
>>> Bird accuracy is specified to be +/- 5% of meter full scale ... a 100W
>>> element would be a poor choice to measure a 100W output level. Take a
>>> look
>>> at any Bird's meter scale.  It's not linear and can be read with the most
>>> accuracy to the left of center scale.  A 250W element is much better for
>>> measuring 100W.
>>>
>>> Wanna chase your tail?  Measure the same power source with identical Bird
>>> elements......
>>>
>>> Don's method is better, but all methods are obviously subject to the
>>> accuracy of the final indicating instrument.
>>>
>>> FWIW .....
>>>
>>> 73l
>>>
>>>
>>>
>> ______________________________________________________________
>> 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
>> Message delivered to [hidden email]
>>
>>
>>
>>
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
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> Please help support this email list: http://www.qsl.net/donate.html
> Message delivered to [hidden email]
>
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Re: P3TXMON question?

George Dubovsky
On Sun, Aug 23, 2015 at 4:36 PM, Ken G Kopp <[hidden email]> wrote:

> Bob,
>
> The scale calibration --is-- compressed to the right of center,
> --not-- to the left as you state, making the left portion expanded
> and easier to read.
>
> 73!
>
> Ken - K0PP
>

​Easier to read, perhaps, but less accurate. To read 100 W with the highest
accuracy, you have to use a 100W slug. (period).

73,

geo - n4ua​


>
> On Sun, Aug 23, 2015 at 2:14 PM, Bob McGraw - K4TAX <[hidden email]>
> wrote:
>
> >
> > This seems to have things really screwed up.   Yes, the Bird 43 is a 5%
> of
> > F.S. accuracy instrument.   The Bird 43P is somewhat less accurate,
> > although 5% F S with carrier, and more like 8% F S or so in peak mode.
> > In measuring a 100 watt radio with a 100 watt F S slug would seem to be
> > most accurate.    Total accuracy decreases as the indicated value
> > approaches the left side of the scale.   Now using a 250 watt slug to
> > measure a 100 watt radio,  the earlier states that most accuracy is to
> the
> > left of center, which by the way, is the compressed side of the scale.
> > This makes no sense as the scale markings are much more difficult to
> > approximate.   In fact the most accurate area is to the right of center
> > toward full scale is the expanded scale  which is where the highest
> > accuracy actually occurs.   With a 100 watt radio and a 100 watt F S
> slug
> > the error is +/- 5 watts at 100 watts.  Using a 250 watt element and
> > measuring 100 watts near center scale the error is more like +/- 12.5
> watts
> > or 5% of the  F S value.
> >
> > If one measures the same power source with identical elements and gets
> > different results, they should refrain from buying ham fest elements for
> > indeed the elements are not identical.  To wit, I purchased 3 new 100
> watt
> > elements and 3 new 2500 watt elements. They all give identical results
> +/-
> > the width of the pointer.  I don't buy ham fest Bird elements as I find
> > they are junk and not worth the brass they contain.
> >
> > And remember, Bird 43 instruments are calibrated for only a 50 resistive
> > load.  Any other load being used leaves one with a "best guess" situation
> > as to actual power.
> >
> > 73
> > Bob, K4TAX
> > K3S s/n 10,163
> >
> > On 8/21/2015 11:48 PM, Wes (N7WS) wrote:
> >
> So by your "logic" it would be best to measure one Watt using a 100W
> >> element.
> >>
> >> On 8/21/2015 8:03 PM, Ken G Kopp wrote:
> >>
> >>> Bird accuracy is specified to be +/- 5% of meter full scale ... a 100W
> >>> element would be a poor choice to measure a 100W output level. Take a
> >>> look
> >>> at any Bird's meter scale.  It's not linear and can be read with the
> most
> >>> accuracy to the left of center scale.  A 250W element is much better
> for
> >>> measuring 100W.
> >>>
> >>> Wanna chase your tail?  Measure the same power source with identical
> Bird
> >>> elements......
> >>>
> >>> Don's method is better, but all methods are obviously subject to the
> >>> accuracy of the final indicating instrument.
> >>>
> >>> FWIW .....
> >>>
> >>> 73l
> >>>
> >>>
> >>>
> >> ______________________________________________________________
> >> 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
> >> Message delivered to [hidden email]
> >>
> >>
> >>
> >>
> >
> > ______________________________________________________________
> > Elecraft mailing list
> > Home: http://mailman.qth.net/mailman/listinfo/elecraft
> > Help: http://mailman.qth.net/mmfaq.htm
> > Post: mailto:[hidden email]
> >
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> > Please help support this email list: http://www.qsl.net/donate.html
> > Message delivered to [hidden email]
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Re: P3TXMON question?

Bob McGraw - K4TAX
In reply to this post by Ken G Kopp
Thank you.   I stand corrected on the point.  Not physically having it
in front of me, I was recalling another power meter I use more
frequently.  It is expanded up scale and compressed down scale.

73
Bob, K4TAX
K3S s/n 10,163

On 8/23/2015 3:36 PM, Ken G Kopp wrote:

> Bob,
>
> The scale calibration --is-- compressed to the right of center,
> --not-- to the left as you state, making the left portion expanded
> and easier to read.
>
> 73!
>
> Ken - K0PP
>
> On Sun, Aug 23, 2015 at 2:14 PM, Bob McGraw - K4TAX
> <[hidden email] <mailto:[hidden email]>> wrote:
>
>
>     This seems to have things really screwed up.   Yes, the Bird 43 is
>     a 5% of F.S. accuracy instrument.   The Bird 43P is somewhat less
>     accurate, although 5% F S with carrier, and more like 8% F S or so
>     in peak mode.    In measuring a 100 watt radio with a 100 watt F S
>     slug would seem to be most accurate.    Total accuracy decreases
>     as the indicated value approaches the left side of the scale.
>      Now using a 250 watt slug to measure a 100 watt radio,  the
>     earlier states that most accuracy is to the left of center, which
>     by the way, is the compressed side of the scale.  This makes no
>     sense as the scale markings are much more difficult to
>     approximate.   In fact the most accurate area is to the right of
>     center toward full scale is the expanded scale  which is where the
>     highest accuracy actually occurs.   With a 100 watt radio and a
>     100 watt F S  slug the error is +/- 5 watts at 100 watts.  Using a
>     250 watt element and measuring 100 watts near center scale the
>     error is more like +/- 12.5 watts or 5% of the  F S value.
>
>     If one measures the same power source with identical elements and
>     gets different results, they should refrain from buying ham fest
>     elements for indeed the elements are not identical.  To wit, I
>     purchased 3 new 100 watt elements and 3 new 2500 watt elements.
>     They all give identical results +/- the width of the pointer.  I
>     don't buy ham fest Bird elements as I find they are junk and not
>     worth the brass they contain.
>
>     And remember, Bird 43 instruments are calibrated for only a 50
>     resistive load.  Any other load being used leaves one with a "best
>     guess" situation as to actual power.
>
>     73
>     Bob, K4TAX
>     K3S s/n 10,163
>
>     On 8/21/2015 11:48 PM, Wes (N7WS) wrote:
>
>         So by your "logic" it would be best to measure one Watt using
>         a 100W element.
>
>         On 8/21/2015 8:03 PM, Ken G Kopp wrote:
>
>             Bird accuracy is specified to be +/- 5% of meter full
>             scale ... a 100W
>             element would be a poor choice to measure a 100W output
>             level. Take a look
>             at any Bird's meter scale.  It's not linear and can be
>             read with the most
>             accuracy to the left of center scale.  A 250W element is
>             much better for
>             measuring 100W.
>
>             Wanna chase your tail?  Measure the same power source with
>             identical Bird
>             elements......
>
>             Don's method is better, but all methods are obviously
>             subject to the
>             accuracy of the final indicating instrument.
>
>             FWIW .....
>
>             73l
>
>
>
>         ______________________________________________________________
>         Elecraft mailing list
>         Home: http://mailman.qth.net/mailman/listinfo/elecraft
>         Help: http://mailman.qth.net/mmfaq.htm
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>         <mailto:[hidden email]>
>
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>         Please help support this email list:
>         http://www.qsl.net/donate.html
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>
>
>
>
>
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>
>

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Re: P3TXMON question?

Wes (N7WS)
In reply to this post by Ken G Kopp
In other words. you can read a less accurate value with greater precision.

On 8/23/2015 1:36 PM, Ken G Kopp wrote:

> Bob,
>
> The scale calibration --is-- compressed to the right of center,
> --not-- to the left as you state, making the left portion expanded
> and easier to read.
>
> 73!
>
> Ken - K0PP
>

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