[Amps] Time for New Power Meter

Sat May 2 22:06:02 EDT 2015

I have Bird slugs of different power levels thru 2304 mHz plus various 
attenuators and directional couplers good thru at least 3 gHz. Ive never let 
an accuracy percentage in any of the parts concern me as if I absolutely 
have to I can use a HP VNA and 437 power meter to get exact numbers.

OTOH the only numbers I really care about is attenuation in cables, 
connectors, power splitters since that is the only place it really counts.

Carl
KM1H
----- Original Message ----- 
From: "Roger (K8RI)" <k8ri at rogerhalstead.com>
To: <amps at contesting.com>
Sent: Saturday, May 02, 2015 9:39 PM
Subject: Re: [Amps] Time for New Power Meter

> Although the Bird is recognized as the standard, even the gold standard, 
> it is a very poor standard with the stock calibration being 5% of full 
> scale. (I have 2) That is only if the slug hasn't been dropped or abused. 
> You can have a slug, or slugs calibrated at specific power levels  and 
> frequencies with a specific sample line to +/- 3%.
>
> Yes that 5% is only 0.2 db, but on a stock slug at half scale is much more 
> than 0,2 db.
> For rough measurements and up on-the-tower they are handy as well as 
> staying legal.  As SWR is a measurement between two powers they are fine 
> for that although if you use two different slugs one may be  +5 % and the 
> other - 5% giving a 10% error at full scale although the extremes are 
> unlikely
>
> The nearest slug I can find to the legal limit is 2500 Watts. 5% is 125 
> watts,  125 watts is a bit over 8% (8.333%...)+/- 125 Watts, or 
> 1500-125=1375 to 1500+125= 1625
>
> A calorimeter is an "accurate" way of measuring power and thus calibrating 
> a meter at specific power levels and frequencies, but not convenient. 
> HOWEVER  you can't just use a calorimeter and say the result is traceable 
> to NBS.  That requires sending the calorimeter  in to a qualified lab, to 
> be calibrated periodically.  At that point your measurements are second 
> generation to NBS but kinda pricey for hams.
>
> OTOH those slugs are very expensive if you want to cover exciters and amps 
> from 160 through 440, or higher.
>
> NORMALLY as the old saying goes,  the Bird is "Good enough for who it's 
> for!", but for efficiency measurements its limitations need to be taken 
> into account.  I consider the Bird "good enough" for measuring power loss 
> in coax runs, SWR, and power out if not interested in absolutes, but 
> although the FCC and others may consider it a standard, I do not.  That 
> may be due to my background.   I base that on doing a wide range of 
> measurements traceable to the NBS in industry over roughly 23 years.  OTOH 
> the equipment I used would be considered almost antique today as I quit in 
> 87.
>
> 73
>
> Roger (K8RI)
>
>
> On 5/2/2015 6:44 AM, Jim Thomson wrote:
>> Date: Fri, 1 May 2015 11:16:58 -0400
>> From: Gerald Williamson via Amps <amps at contesting.com>
>> To: drkirkby at kirkbymicrowave.co.uk, k7fm at teleport.com
>> Cc: amps at contesting.com
>> Subject: Re: [Amps] Time for New Power Meter
>>
>> Hi All, I also use a Bird 43 as a gold standard. Why? Because I have it
>> already. A 5% error amounts to about .2 dB which is close enough for my
>> amateur  needs.
>>   The capability of easily changing connectors is a plus not available on
>> most if not all of the other meters.
>>   Maybe we should call the 43 a "Brown Standard"?
>>   73,
>> Gerald K5GW
>>
>> ##  What freq does bird /cd  calibrate their  slugs on ??  talking abt 
>> the typ 2-30 mhz slug.
>> On a side note, IF a CD pep board is installed, or the model 83000 is 
>> used, the accuracy is
>> +/- 7%.....when switched to pep mode.  When a bird  pep board is 
>> installed on a bird 43, the
>> accuracy is now +./- 8%...when switched to pep mode.   Both are +/- 5% in 
>> average mode.
>>
>> ##  The problem with the bird  /cd meters /slugs is... they are +/- 
>> 5/7/8 %  of full scale...any where on the scale.
>> IE: 5% of a 1 kw slug = 50 watts.   So if meter reads 800 watts....the 
>> true pwr could be  750w...and meter
>> is reading 50 watts high.    Or true pwr could be 850 watts..and meter is 
>> reading 50 watts low.
>>
>> ##  If meter reads 100 watts.... true power could be as little as 50 
>> watts......or as high as 150w.  In this
>> last case, the error could vary from  50-100%  outa whack. Bottom line 
>> is..u gotta use the smallest slug
>> for the job.
>>
>> ##  with a 5 kw slug, my L4B  reads 700w.    ( low power mode, 1900v). 
>> With a 2.5 kw slug, it then reads 650w.
>> With a 1 kw slug, it no reads 625 watts..which is very close to dead on.
>> Dunno if a bird slug is most accurate on the freq its calibrated for..vs 
>> extremes in freq.   IE:  IF they calibrate it
>> at say 16 mhz..... what is accuracy at 2 mhz + also 30 mhz.
>>
>> ##  IMO, the array solutions power master blows both the bird /cd slugs 
>> away..hands down.   If u don’t like their
>> NIST calibration, u are free to re-calibrate it urself.... since the 
>> calibration can be changed in 1% increments....
>> and with a +/- 15% range.   +/- 15%...in 1% increments is as good as is 
>> gets.    The calibration points are printed on each
>> individual coupler..for both frwd and rvs power...for  both HF...and 
>> again for 6m.   160-6m  on one coupler is pretty good.
>> Then they have couplers for 144/220/432 etc.
>>
>> ##  with no high swr alarm etc, etc, the bird doesnt cut it anymore. 
>> Bird doesn’t sell wattmeters...they sell slugs.
>> The only advantage the bird /cd has..is it reads average power if u want 
>> to.   the array solutions will only read pep.
>> U cant see the effects of increased average power when using processor on 
>> ssb mode.
>> Flip side is..the pep bargraph on the array solutions wattmeter is so 
>> sensitive, it will easily show..dithering
>> when 3 % ripple is present on a B+  supply..which is typ when 8  series 
>> 200 ufs cap are used.   Any RF scope
>> will also show that effect.
>>
>> ##  the only connectors I use are  SO-239  and also 7-16 DIN.  I don’t 
>> use Type N.... but can easily add an inter series
>> adaptor if needed.  My  3 kw coupler get the so-239....and my  10 kw 
>> coupler gets the 7-16 din.
>>
>> Jim  VE7RF
>>
>> adaptpr
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>> Amps at contesting.com
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>
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