[Elecraft] P3TXMON question?

[Bob McGraw - K4TAX]

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 
> <rmcgraw at blomand.net <mailto:rmcgraw at blomand.net>> 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
>
>
>
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