[Elecraft] OT: Bird Wattmeter "meter failures"

[Bob McGraw - K4TAX]

Ron mentions various well taken points regarding the Bird 43 meter 
series.  This also applies to almost all watt meters as well, and that 
is the power calibration is relative to a 50 ohm load only. Any other 
load Z will introduce errors in the meter accuracy and indication.

At the same time, the ratio measurement for forward power and reflected 
power will always be correct in that each value will be measured with 
the same degree of error.  Thus using this information,  one can 
accurately calculate the SWR using the forward power indicated and the 
reflected power indicated.   Where as, absolute values will not 
necessarily be accurate under these conditions.

73
Bob, K4TAX

On 11/22/2015 11:38 AM, Ron D'Eau Claire wrote:
> Bird instruments specs a Bird 43 at plus or minus 5% of full scale. If you have a calibrated 1000 watt slug and meter it will read within 100 watts of the real power. What many people miss is that the possible 100 watt error is constant over the range of the meter, so measuring 500 watts the meter will indicate something between 400 and 600 watts and at 100 watts the reading can be off by a full 100%!