The Bird 43 wattmeter is fine for trend observations, and as said
below, will last a long time.
However, do not see their display results as gospel. If you need
to know the actual power, use a digital RF Power Meter like
the kind that is discussed herein made by Array Solutions
(PowerMaster). That firm prides itself on calibration, and the
spin-off to the Amateur market of milspec-quality instruments
leaves the Bird meters far behind.
The Bird meters have two movements. One is a 30 microamp
movement and the other is a 100 microamp movement. The slugs
that drive each meter movement are different. For instance, the
50KW slug in my 3-1/8" line section is specifically made for the
Bird 375 wattmeter with a 100uA movement, and scales calibrated
for KW, not W.
If anyone needs a reliable source for slugs, please contact Jerry
at Economy Electronics, http://www.economyelectronics.com
at telno 501-676-3234. This business offers all sorts of high power
RF stuff and is also a certified supplier to our cellular projects
with heliax, coax, connectors, etc.
Hal
W4HBM
[snip]
All slugs will give 30uA at indicated power.
The slugs have a small variable potmeter that can be adjusted for
calibration. Then you need a good reference and gain access to the pot.
I check Bird meters as you explained with a 12V source connected to the
Slug connection via a 470k pot and a multimeter reading microamps.
I have many slugs where most are purchased seconhand. It is not unusual
that readings are off by as much as +-10%, comparing slugs or measuring
with a Narda coupler and HP435 powermeter. With a meter that reads full
scale with 30uA and new slugs, power is accurate within +-5%. The Bird
43 is a nice instrument that last for decades if it's cared for.
[snip]
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