I spoke to someone at Bird (when they were really Bird) years ago and I
was told that the Bird wattmeter is accurate to ±5% of top scale. This
means that a 100 watt slug can be off ±5 watts _anywhere_ on the meter.
So, a transmitter emitting 50 watts out, using the Bird and a 100 watt
slug, can read between 45 and 55 watts. That's why he said it was
important to keep the reading in the top 1/3 (highest) end of the
meter. This is where the error is less. When taking reflected power
readings the slug should be 1/10 of the forward slug value when testing
a reasonably good antenna. So, a 100 watt forward slug would require a
10 watt reverse slug for reasonable accuracy.
I retired my Bird 43 and the vast assortment of slugs for a Telewave
Model 44A wattmeter and never looked back. The drawback to the 44A is
it is limited to 20-1000MHz. The Bird would be good for HF use.
73, Joe, K1ike
Date: Mon, 19 Mar 2018 18:40:41 +0000
Always bear in mind that their odd meters (30 uA) are very non-linear and
measurements made using element ranges that fall in the bottom 1/3 or so of
the scale are the most accurate. Overall, they claim to be accurate to +/-
20 percent of full scale. HORRIBLE in
today's world!
FWIW ...
73!
K0PP
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