Part 15 Broadcasting, Transmitter Guidance (Radio World) May 22, 2020 10:07:11 GMT
Post by Boomer on May 22, 2020 10:07:11 GMT
Part 15 Broadcasting Is Not Without Problems
Newly minted amateur broadcasters may need a quick course in broadcast engineering
By Tim Edwards
The 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. ....
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!
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. .....
I wonder why all these Part-15 churches haven't joined up here, I think it's open to become a member and talk to real Part-15. Also, I heard about another Part-15 site closing, and they probably picked a bad time!
Low-Power Transmitter Guidance From Larry Wilkins
Legal, unlicensed broadcasts under Part 15 are a buzz topic right now about radio engineers.
Here’s what Larry Wilkins, director of engineering services for the Alabama Broadcasters Association, writes in his e-newsletter this week:
Broadcast engineers have been approached lately by churches and other organizations about setting up a low-power transmitter for use during COVID-19. The question of legal operation is covered in FCC Part 15.
The quick answer allowed coverage area is approximately 200 feet for an FM transmitter. The full answer is much more complicated than that: 250 µV/meter @ 3 meters (also measured as 48 dBuV/m). The same is true on the AM broadcast band, where devices are limited to an effective service range of approximately 200 feet (61 meters).
Right here on these Part-15 forums we've discovered that even with the most stringent setup, Part-15 AM will reach out more than 200 feet to an average radio! There's a saying that 'the grass is always greener in another person's yard' implying that you see how things are better at your neighbor's. Radio engineers seem to take it that the grass is browner.