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Part 15 Broadcasting Is Not Without Problems

Date:2020/5/23 17:29:18 Hits:




Newly minted amateur broadcasters may need a quick course in broadcast engineering

Tim EdwardsThe author is chief engineer for KOZY(AM), KMFY(FM) and KBAJ(FM).

As has been addressed in previous articles in Radio World, many churches and other groups are starting to broadcast “drive-in church” services and other events.

As a local contract broadcast engineer I have received several inquiries about how to do this. As Radio World has pointed out in your recent articles, the only option is under the FCC Part 15 rules, which allow for low-power signals in the AM or FM band. After explaining rules and limitations, those I’ve talked to have instead opted for live streaming services.

Clearly, most, however, don’t seek out advice of local radio professionals, and instead seem to simply be searching the internet for “Drive-in Church” etc. 


This is where the trouble lies, as this search brings up thousands of churches that are doing this, countless articles published in church and religious magazines and websites telling how easy it is, along with a raft of YouTube videos of pastors, ministers, church assistants, youth ministers and others showing how easy it is. Basically they tell you to order an FM transmitter from eBay, or Amazon, and plug it into the church’s audio board and you’re on!

One problem with this approach is the FCC’s lack of ability or desire to stop the sale of illegal FM transmitters in the USA via these sellers because so many of the transmitters being sold are illegal in the USA. Many use misleading advertising “Long Range FM Transmitters,” “No License Required,” “FCC Compliant,” “Perfect for Churches,” so forth and so on.

An FM Part 15 transmitter sold in the USA must be certified by the FCC. Most sold are not.

Over the years I have done testing on many of these transmitters and found that not only are they substantially over the legal limit (sometimes by a hundred times and more) but they also generate spurs and harmonics. 


This, of course, causes interference to other, licensed stations on the FM band, as well as into public service frequencies and most often into the aviation band causing interference with aircraft communications and navigation. In fact interference in the aviation band is one of the common ways these illegal transmissions are discovered and tagged by the FCC. Airport tower operators contact the FCC to complain!

I suggest that local engineers keep their eyes and ears open for churches and other organizations advertising drive-in broadcasts. We have a local arts center starting live broadcasts of concerts with no live audience in the theatre to an audience in cars in the parking lot.

If there are any, do a bit of legwork with a field intensity meter and spectrum analyzer and see if those broadcasts are legal. The Part 15 limit is 250 uV/m at 3 meters from the transmitting antenna. Basically if you can hear them more than 250–300 feet from the site they’re not legal.

Then look for harmonics, spurs and overmodulation. Usually these transmitters either have no modulation indicator, or it amounts to a blinking LED, and are horribly inaccurate. Operators with no experience tend to overmodulate substantially causing splatter to adjacent frequencies. Usually if they’re illegal it’s blatantly obvious. Then reach out politely and let them know they are violating FCC rules. If it’s in your ability and desire offer to help them make their broadcast legal.

Based on my observation there may be thousands of brand new illegal FM transmissions on the air over the past few weeks.




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