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Commentary: Adjust Rules for NRSC Measurements

Here’s something the FCC can do to help many AM stations

Mark Persons Part of a Radio World series in which we share industry opinions about AM revitalization.

Normally I offer tech tips but this time I want to express a personal opinion on a topic important to me.

If it is a goal of the Federal Communications Commission to reduce regulatory and financial burden on AM broadcasters, then here is one way to help: Modify FCC rule 73.1590(a)(6) requiring annual occupied bandwidth and RF harmonic radiation measurements on AM stations, known as AM NRSC measurements.

You might remember that NRSC is the National Radio Systems Committee, which created standards for occupied bandwidth on AM and FM stations. The FCC turned those standards into rules.

I propose to exempt AM stations that use solid-state transmitters from the existing requirement to make annual measurements.

The rules were written when vacuum tubes were often used in transmitter designs. Tube performance degrades with time. The result is that tubes must be replaced every year or two in order to maintain operating specifications. Beyond that time in service, an AM transmitter may not be able to comply with FCC rules for occupied bandwidth, which results in interference to other stations on the dial. In the case of FM transmitters, a weak/soft tube does not normally cause bandwidth issues.

For AM stations continuing to use tube transmitters, this annual requirement should still apply. The requirement that all AM and FM licensees keep their equipment in compliance with FCC rules should stay in place, regardless of which transmitter design they use.

Changes in any AM or FM equipment that could alter the occupied bandwidth should automatically trigger the requirement to do measurements to assure compliance with FCC rules. A 30-day window to make successful compliance measurements sounds appropriate to me. The equipment change could be as simple as replacing an audio processor with a different model number.

This rule revision would bring AM stations into the same level of scrutiny that FM stations should meet; I feel my suggested changes will also assure FM compliance.


Note that any change in equipment lineup could unwittingly cause bandwidth problems. The only way to be sure the station is FCC legal is to do spectral analysis.

Further, the procedure for AM and FM stations should be written to require listing model numbers of studio transmitter links, audio processors and transmitters. (Serial numbers are not important.) In the case of FM stations, audio processors, stereo generators, RDS/RBDS generators, studio transmitter links and transmitters should be listed.

In essence, anything capable of controlling or changing occupied bandwidth should be documented.

The report would not be placed in a public file. Instead it would go into the station’s engineering file, which is not seen by the public. No change there. In that way, a station’s “custom lineup” of audio processing would not be revealed to competitors.

FCC FM rule 73.1590(d) regarding measurement data needs to be modified to strike the words “for a period of 2 years, and on request must be made available during that time to duly authorized representatives of the FCC.” This re-written rule would require measurement data to be kept on hand until superseded by a newer report. It is documented proof of legal operation.

An FCC inspector or mock inspector would request this report when visiting a station. He or she would check to see if the same equipment is employed, even if it is years later. Any report that did not have this data would be invalid.

Practically speaking, my proposal would mean that all or most stations would need to perform a new set of measurements based on these criteria in the immediate future. Again, any changes in the equipment lineup should require a new set of measurements to assure FCC compliance.


On another note, station technical consultants need to be vigilant in watching for new transmitter sites or changes to existing transmitter sites within five miles or so of the transmitters they are watching after. A new onsite or offsite transmitter in the AM or FM band might create mixing products that could render the station illegal under FCC rules.

Mandatory annual measurements are not needed, in my opinion. Just watching after the store, so to speak, is what is necessary.

For perspective, technology has improved to make equipment more reliable and trouble-free. FCC rules have been modified in the past to keep up, even if they did lag a bit from reality. Stations were required to read and log all operating parameters every half hour up until about 40 years ago. Monthly carrier frequency measurements were required until about 30 years ago, as were annual audio proof of performance measurements.

We don’t even have operator licenses anymore. Now is the time for the FCC to make the changes I outlined. It is good for the radio broadcast industry and makes perfect sense.

Comment on this or any article. Write to [email protected].

Mark Persons, WØMH, is a Certified Professional Broadcast Engineer and has more than 30 years’ experience. His website is