[Elecraft] KX3 and Data modes

[Bill W4ZV]

KL7UW wrote:

> I think the wrong impression has been taken of Bird's statement of 
accuracy.  I doubt the inaccuracy is a fixed amount that is the same 
at any reading.  More likely Bird does its calibrations at full scale 
and this is the accuracy that they will warrantee.  Seem more 
reasonable that the error is relative to the level of the 
reading.  The actual adjustment is a variable cap inside the 
element.  That and a resistor determine the level the element functions at.

The manufacturer's accuracy specification is what it is...not what you might
think is "reasonable".  Most analog meters are calibrated in % full scale
due to the inherent error in visually interpreting a needle on an analog
scale.  This visual error is constant at all readings, hence the
specification is a percentage of full scale.  This is exactly why DMMs
replaced analog meters (e.g. Simpson, Triplett, etc) decades ago.  

> But that being said, I have no proof the element in question is any 
better than reading 25w +/- 1.25w.  Ideally, I would have sent the 
meter to Radiodan to be calibrated with the element.  Then he could 
have specified what the accuracy was for the calibration.

The LP-100A is factory calibrated (NIST traceable in 11 frequency bands) to
5% of reading (3% typical).  As stated before, the key difference with the
analog Bird is that accuracy is specified in % of reading...not % of full
scale.  

> There is only one way for me to determine what the accuracy 
is.   That is by observing the waveform across the dummy load with my 
scope, calculating Vrms from the peak-peak voltage and using that to 
determine power using V^2/R, assuming the load is not reactive.  Well 
I might do that out of curiosity.   That is probably the most 
accurate way for most hams to measure power (unless you are very rich 
and own a calorimeter).  I did power measurement at 500-KHz by using 
my scope since I have no elements that work below 2-MHz.  My 100w 
500-KHz transmitter is equipped with an RF ammeter for 
measuring/monitoring power.

This is essentially what the LP-100A does using an A/D converter and
microprocessor.  Besides being much more accurate, it provides many other
useful features such as Z, R, X, SWR, SWR and phase versus frequency, Smith
Chart output, translates coupler load Z to antenna load Z (for remote
measurements), peak-to-average (useful for measuring SSB compression), etc. 
Measurement range is 1-3000 Watts over 1.8-54 MHz with the standard coupler
(higher power available as options) at full rated accuracy.

> For normal daily ham measurements I am willing to assume that the new 
element is my most accurate.  Will it matter much if I am off 
1.25w?  BTW it could be better than that.  That is the worse-case 
specification.

I can understand being locked in to Bird because of your significant
investment in 16 slugs (typically $60-80 each on eBay not counting the Bird
43 itself).  However, for anyone considering a truly state-of-the art
Wattmeter, it's hard to beat N8LP's LP-100A because it does so much more
than simply measuring power.  If you add up the total cost of a Bird plus
multiple slugs to cover the same power ranges, the LP-100A is a steal.  Like
all of Larry's products (LP-PAN, LP-Bridge, etc) the engineering and support
for the LP-100A is first rate (e.g. providing a customer upgrade path from
the original LP-100 to the LP-100A).

http://www.telepostinc.com/  

I have no connection with Larry other than being a very satisfied customer
with several of his products.

73,  Bill  W4ZV


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