[Elecraft] W2 Questions

[Paul Christensen]

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" <k7peh at comcast.net>
To: "Elecraft" <elecraft at mailman.qth.net>
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
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