[Elecraft] New K3 built - can I reset the 5w calibration?

[Don Wilhelm]

Mike,

You read it right.  A newly calibrated Bird slug (how many hams have 
recently calibrated Bird wattmeters and slugs?) is specified to have an 
accuracy of 5% OF FULL SCALE.  So yes, a 100 watt slug can be in error 
by as much as 5 watts - anywhere on the scale.  A reading of 50 watts 
indicates a power somewhere between 45 and 55 watts. a reading of 25 
watts indicates a power somewhere between 20 and 30 watts, and a reading 
of 10 watts indicates a power somewhere between 5 watts and 15 watts.

In other words, use a Bird slug that is close to the power level that 
you are trying to measure, and consider how long it has been since that 
meter and slug have been calibrated before making any absolute 
statements about the power accuracy.

BTW, you can use the "RF voltage across a precision dummy load" to 
calibrate your wattmeter (at any power level).  Doing that on a periodic 
basis will give you faith in the integrity of your measurement tools.

73,
Don W3FPR

On 12/9/2011 9:08 AM, Mike wrote:
> Wait.
>
> Using a 100W slug, if you get a reading of 100 watts, the real power would be between
> 95 and 105 watts, right?
> If you get a reading of 50 watts the real power would fall in a range of less than 45
> to 55 watts?
>
> Not if the 5% at full scale is the best accuracy.  Or did I misunderstand what you said?
>
> 73, Mike NF4L
>
>
> On 12/8/2011 11:59 PM, Eugene Balinski wrote:
>> The accuracy of Bird elements is typically  +/- 5% of the
>> full scale value.  For a 100 W Slug, that is +/- 5 Watts.
>>     So theoretically speaking, with 5W in, and 0 registered
>> on the meter, the meter is still within its rated accuracy.
>>
>>
>> Additionally on the model 43 meter, there is meter scale
>> end compression.  To get the most accurate reading, one
>> would want to have the 5W reading at the middle of the
>> meter range, which means that one would want a 10W slug.
>>    Unfortunately I do not believe that Bird makes a 10W  HF
>> slug any more.  Perhaps they need an Elecraft W2 ??
>>
>> 73
>> K1NR
>>
>>
>> On Thu, 8 Dec 2011 16:47:27 -0600
>>    Nate Bargmann<n0nb at n0nb.us>   wrote:
>>>>  From my experience, trying to measure 5W with a 100W
>>> element leads to
>>> very inaccurate readings.  The Bird is most accurate when
>>> the reading is
>>> as near to full scale as possible.  That means a 5W HF
>>> element (is that
>>> even available?) would be ideal provided no more than 5W
>>> is put through
>>> the meter.  A 10W element would be less accurate but
>>> provide a safety
>>> margin for the meter.  Even better would be to have both
>>> elements and
>>> use the 10W one to get in the ballpark and the 5W one for
>>> a final check.
>>>
>>> 73, de Nate N0NB>>
>>>
>>> -- 
>>>
>>> "The optimist proclaims that we live in the best of all
>>> possible worlds.  The pessimist fears this is true."
>>>
>>> Ham radio, Linux, bikes, and more: http://www.n0nb.us
>>>
>
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