[Elecraft] P3TXMON question?

[George Dubovsky]

On Sun, Aug 23, 2015 at 4:36 PM, Ken G Kopp <kengkopp at gmail.com> 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 <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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> >>
> >>
> >
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