[Elecraft] Rescaling the W2?

Fri Nov 20 13:50:08 EST 2015

The inductors in a directional coupler are not linear. The response to the turns count is actually a squaring function, so it would be difficult to remove turns and have the effect you want. The other problem is that the W2 firmware has a lot of data tables that depend on the values that are set in the sensor - changing the sensors means changing the tables. I believe that using the scaling factor that is already built in to the W2 would be the best way to achieve what Scott wants. It does have a down side, though. If someone else were to look at the scaled W2 and see the 10 LED light up, we would naturally think it was indicating 10 (or 1 or 100 or 1000) watts instead of whatever value Scott has scaled for.

- Jack, W6FB

> On Nov 20, 2015, at 10:08 AM, Michael Blake <k9jri at mac.com> wrote:
> 
> Alan, while I do not own a W2 it would seem that the pickup coils in the sensor could be reduced in turns by the correct amount to lower the coupling loss loss by 3 dB.  Would not the rest of the W2 work correctly at the 3 dB (or whatever you choose) lower power level?
> 
> Michael Blake - K9JRI
> 
> 
> 
>> On Nov 20, 2015, at 12:07 PM, Alan <n1al at sonic.net> wrote:
>> 
>> I just tested it.  The maximum you can set the W2 calibration value to is 650.  (Using the ">" and "+" RS-232 commands)  That causes the wattmeter to read about 60% high on my W2.  So with the W2 set to read 2000W full scale, the actual full scale would be about 1250W.
>> 
>> Or you could go in the other direction.  The minimum calibration value is 350, which causes the power to read about 47% (on my unit).  With the W2 set to read 200W full scale it would actually be about 425W full scale.
>> 
>> Alan N1AL
>> 
>> 
>> On 11/20/2015 07:15 AM, Cliff Frescura wrote:
>>> I find the scaling awkward as well.  My W2 is placed on the input side of my
>>> KPA500 and it seems that dividing the scale by two might do the trick.  I've
>>> not looked at the schematic, but wonder if it could be tricked by a resistor
>>> divider in the sensor line.
>>> 
>>> 73,
>>> 
>>> Cliff K3LL
>>> 
>>> -----Original Message-----
>>> From: Elecraft [mailto:elecraft-bounces at mailman.qth.net] On Behalf Of Don
>>> Wilhelm
>>> Sent: Friday, November 20, 2015 5:55 AM
>>> To: Scott Townley; elecraft at mailman.qth.net
>>> Subject: Re: [Elecraft] Rescaling the W2?
>>> 
>>> Scott,
>>> 
>>> I believe that would require a new sensor and firmware to support it.
>>> Popular scales on wattmeters are 200 watts and 2000 watts full scale, so you
>>> are not going to get much better with another brand product.
>>> The W2 used with its utility program can give you more resolution, but then
>>> using the Utility when mobile would not be advisable.
>>> 
>>> 73,
>>> Don W3FPR
>>> 
>>> On 11/20/2015 8:32 AM, Scott Townley wrote:
>>>> I know the W2 can be "dialed in" to match one's personal standard,
>>>> but...can it be completely rescaled?
>>>> I use the K3/KPA500/W2 mobile, and the KPA500 is mounted in my pickup
>>>> bed so the W2 is the only system meter available at the operating
>>>> position.  However, the 2's scaling doesn't give me much display
>>>> dynamic range...the KPA500 will only light 5 of the 17 LEDs at full
>>>> power.
>>>> It would be far more useful for me to have the meter scaled to 600W
>>>> say...then the 15th LED would be 450W.  Even scaling it to 1000W would
>>>> give me more than half the display range.
>>>> 
>>>> 
>>> 
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