All FM transmitters produce harmonics at even multiplies of fundamental frequency. If your harmonics fall on or near TV channel, air service, army or maritime frequency you could cause severe interference on that channel.
The most common cause of fines from federal agencies is due to TVI or other interference from your transmitter which generates a complaint. Use of a low pass filter is the best method of eliminating this kind of interference.
Since the insertion loss of these filters is less than .2dB, these filters are well suited for use at power levels as low as 100 milliwatts or up to 800 watts.
