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

[Don Wilhelm-4]

Sorry I hit Send too soon --,the 5% error with a 250 watt slug is 12.5
watts - if the wattmeter has been recently calibrtrated.  So a reading
of 25 watts can have an actual; power between 12.5 and 37.5 watts!  This
is with one of the most highly respected wattmeters -- when the power is
lower than 50 watts, you can do better with simple measurement tools.
0
I prefer using the RF voltage developed across a 1% 50 ohm dummy load to
give me a more accurate power reading than any analog power meter I have
found.

Please take my comments in context - they are limited to a 50 ohm
environment and are quite dependent on the precision of the dummy load.  
If I want an approximation, I will use the words provided by my word
processor, but if I want to be exact, I will use the dictionary

73,
Don W3FPR

On 12/9/2011 8:15 PM, Don Wilhelm wrote:

> Mike. but 5% of full scale for a 100 watt slug is 5 watts.  That is
> exactly the point being made.  The error is a percentage of the Full
> scale reading, and not a percentage of the actual reading.
>
> A 250 watt slug can have an error of 37.5 watts - whether the power
> reading is at 10  watts or 50 watts
>    al that can be concluded it that there is some power output - the
> number displayed by the meter cannot be relied on if the power is
> significantly lower than the power ratting of the slug .
>
> 73,
> Don W3FPR
>
> On 12/9/2011 7:11 PM, Mike wrote:
>> 5% of 50 watts is not 5 watts.
>>
>> 73, Mike
>>
>> On 12/9/2011 10:32 AM, Eugene Balinski wrote:
>>>>    From what I understand, the meter is rated at 5% of the
>>> **full scale** rating according to Bird.  Full scale
>>> rating, is the rating on the slug.
>>>
>>> That would mean that for a meter with a 100W slug, your
>>> accuracy is +/- 5W (5%).   So, if your wattmeter is reading
>>> 50W, the actual RF power could actually be 45 or 55 W....
>>>
>>> 73
>>> K1NR
>>>
>>>
>>> On Fri, 09 Dec 2011 09:08:55 -0500
>>>     Mike<[hidden email]>    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<[hidden email]>     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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[Mike Reublin]

Okay gents. I'm convinced. I do like a good exchange.

73, Mike NF4L

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[Edward R Cole]

I've been reading the comments about Bird43 accuracy for awhile, but
the claim that the error is fixed amount for all levels of power
measured on a given element just does not agree with my
experience.  (Just about) ALL of my RF power measurements have been
using the Bird and what I see is a scaled error and not a fixed
one.  If the full scale reading is off 5% then the quarter power is
likewise 5% off.  In other words 100w measured with a 100E element at
432-MHz might actually  be 95w.  If I measure 50w with the same
element the actual power will be about 47.5w.  25w will be about
24w.  I'm not saying the accuracy tracts exactly linearly with power
level but it seems approximately so.

That being said, the accuracy for measurements at under 25% of the
full power rating of the element is not of much value except as a
relative number.  I try to chose an element so the meter reads >70%
full scale for best accuracy and resolution if I am trying to obtain
absolute power measurements.

If I want better accuracy I use calibrated attenuators with my HP432A
microwave power meter (10-MHz-18-GHz) which measures -20 to +10
dBm.  I have two high-power 20-dB coax attenuators: 100w NARDA (good
to 4-GHz) and 10w Bird (good to 1-GHz).  I measured the Bird on a
steady 2m signal yesterday and it is exactly 20 dB within the 0.2 dB
resolution of the HP meter.  For measuring 300w on 1296 I have some
40 and 50-dB directional couplers from the cellular industry (rated
for high power).  That permits power measurements to be made with the
HP power meter (300w = +55 dBm => -50 dB = +5 dBm)  2:1 SWR reflected
power would be 30w (+ 45 dBm +> -40dB = +5 dBm).  But this also
allows me to check the accuracy of the Bird power meter.  I suspect
this is "good enough" for ham radio purposes.


73, Ed - KL7UW, WD2XSH/45
======================================
BP40IQ   500 KHz - 10-GHz   www.kl7uw.com
EME: 50-1.1kw?, 144-1.4kw, 432-QRT, 1296-?, 3400-?
DUBUS Magazine USA Rep [hidden email]
======================================

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