[BC] 9th FM harmonic causing interference

[Dan Dickey]

> To insure compliance you need a calibrated line probe and compensation
> chart for the 9 octave frequency change.

Warren is exactly correct. But the measurement accuracy is not the main 
concern if genuine interference is present. No matter whether the 
transmitter complies with the FCC -80dB rule or not; if it is creating 
interference that prevents another licensed primary service from functioning 
then the two parties are required to resolve the issue. If the interfered 
with service cannot reasonably resolve it on their own then the licensee of 
the interference generator must attempt to resolve the problem. There are 
many cases where FM stations must specify 90dB or greater attenuation of 
certain harmonics due to cell or other services that are nearby.

I had an interesting case unrelated to commercial broadcast where the 
specified harmonic levels were -120dBc in specific bands due to the EIRP. 
Measuring that attenuation is a real challenge even if you have calibrated 
couplers. But when the TPO is almost 4MW and the EIRP is several hundred MW 
you do what you gotta do.

Best regards,
Dan