[Elecraft] W2 Questions

[Jack Smith]

Don:

All I've done is read the spec sheet, but Minicircuits has a relatively 
new sensitive termination wattmeter with USB interface for a quite 
reasonable price, at least by Agilent standards. 
http://www.minicircuits.com/pdfs/PWR-6G+.pdf -- it's a "virtual" 
instrument as it  consists of the sensor and a USB port to plug into 
your computer. At $700, it isn't much more than you might pay for a 
single used Agilent sensor in decent shape and calibration.

Depending on frequency and power range, the "typical" error runs from 
+/- 0.1 db to +/- 0.35 dB. power range from -30 to +20 dBm, frequency 
range 1 MHz - 6 GHz.

If I didn't already have a 437B and 8481A and 8482A sensors, I would 
give the Minicircuits product serious consideration.

Jack K8ZOA


Don Wilhelm wrote:
> Phil,
>
> The W2 wattmeter is similar in its detector accuracy to the Tandem Match 
> (by John Grebenkemper KI6WX) in that its accuracy depends on matching 
> the detector diodes with the compensation diodes.
> The "Gold Standard" of power measuring devices is the HP436A wattmeter, 
> and it has a stated accuracy of +/-0.05 dB.  That amounts to a +/-1.16% 
> accuracy - you are not going to get much better than that lab instrument 
> in an amateur grade instrument.
> The Tandem Match that KI6WX built tracks the HP436A within +/- 0.5 dB 
> over a range of 10 mW to 100W (your 11.2% error), and also tracks the 
> HP436A within +/-0.1 dB over a 1W to 100W range for a 2.33 % difference.
>
> Power measurement is tough on accuracy as expressed in percentage.  Most 
> ham grade wattmeters specify 20% of full scale.  The Tandem Match and 
> the W2 wattmeter are percentages of actual readings.
>
> Since power is normally best expressed in dB (because the apparent 
> signal strength is related in dB), a specification of 0.5 dB is not bad 
> at all.
> BTW - I believe that is the accuracy of the power reported using the PC 
> link.  The resolution of the LED scale is not adequate to indicate the 
> degree of precision available.
>
> The directional coupler will have frequency dependencies as well as 
> accuracy implications.
>
> 73,
> Don W3FPR
>
> Phil Hystad wrote:
>   
>> 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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