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Technical Tips from Mark W. Persons

TPO (Transmitter Power Output)
Chart for FM Broadcast Stations

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.     

The stories go on and on.  Stop in again sometime.  I'll leave the soldering iron on for you. 
Mark W. Persons   ham W0MH      

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