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When the
FCC (Federal Communications Commission) inspector comes to visit, he
will ask how you determine the operating power of your FM transmitter.
If you answer by saying that you look at the output power meter on your
transmitter, you are wrong. He will want to look at the power
amplifier voltage and current on your transmitter. He will then
multiply those by each other and then multiply the total by the rated
efficiency of the transmitter. The result needs to be between 90%
to 105% of the station authorized TPO (Transmitter Power Output) as
listed on the station's FCC license.
In rare instances, the FM station may be
operating by the "direct" method, which requires a wattmeter be
calibrated at the station TPO and then read into a dummy load at least
every six months to verify the meter calibration. Almost no
stations do that.
The chart like the
one on the left is easy for to create on a computer with a spread sheet
application. It is easy for operators
to read and interpret. Upper and lower power limits are bracketed
for easy reference. It is hard to go wrong with this one.
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