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@rogerhalstead.com>
To: <amps@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@contesting.com>
To: drkirkby@kirkbymicrowave.co.uk, k7fm@teleport.com
Cc: amps@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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