[Amps] Time for New Power Meter

Sat May 2 21:39:04 EDT 2015

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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