Friday, March 28, 2014

Part 15 for Dummies - AM vs FM

I've been posting several miscellaneous things lately, and suppose I should focus specifically on Part 15 topics more, since after all the Part15LAB is a Part 15 blog..

So this morning I'm going to begin the first in a series of chapters of Part 15 for Dummies.. by a dummy. 

I'm not an engineer, nor have any background as a professional broadcaster, nor do I posses much knowledge concerning the mechanic of radio and radio wave propagation.. There certainly others more qualified than I to school on this topic.

However, over the numerous years, I have learned a thing or two about Part 15, and feel confident that the information I provide here is accurate and useful to anyone wishing to join in on this unique and satisfying hobby of Part 15 broadcasting.

So then, lets begin somewhere in the middle.. but we're still going to call this chapter 1.. 

Part 15 For Dummies - Chapter 1

A common question I get asked is..
Why not broadcast on FM instead of AM?
Good question. It's true that FM has a cleaner, clearer signal with better fidelity and it's in stereo. Whereas AM suffers more from interference, has a less favorable fidelity range, and it's only a mono signal. At first glance it certainly appears that choosing to broadcast on FM would have been the better choice, and in many cases it is, but in this situation it's not.

To explain why, let's take a look at the legal issues of Part 15 broadcasting..
The FCC's Part 15 Rules and Regulations allow and govern unlicensed broadcasting in both AM and FM. One common utilization of these allowances are use of the FM frequencies, due to the improved sound quality. Micro radio stations, cordless microphones, speaker systems, headphones, public address systems, and forms of wireless networking, make use of this legal unlicensed broadcasting in FM.

However, broadcasting on AM has definite advantages. 
First and foremost is the fact that with AM a considerably greater range can be legally achieved. That is, with AM, the signal is more likely to travel a greater distance. 
Also on a directly related matter; there are specific AM transmitters on the market specifically Certified by the FCC (as opposed to "type-accepted" or "compliant")  under sec.15.219, which eliminates the
limitations imposed on how far the signal can legally travel in an area, and under these circumstances, the primary concern is limiting power input to 0.1w, and the antenna system to 3 meters height. 
Transmitters such as these are highly efficient, and perceived as more FCC friendly, and though substantially more expensive, often considered essential to legally accomplish the establishment and growth of a community broadcast.

For this reason, FCC certified unlicensed AM transmitters seem to be the preferred choice to employ in the operations of a Community Broadcast.
However, truth is that is really no genuine advantage of broadcasting with a certified unit as opposed to using just a compliant one. Both are eligible for use under 15.219, and both can be comparably efficient. The FCC doesn't care if your transmitter is certified or not, as long as it is operating in compliance with the rules and regulations.
Nevertheless, there still is one major advantage to a certified unit; They are already built and ready to use.. Plug and play, as it were.

FM, on the other hand, (under Part 15) is severely limited and can not legally broadcast farther than a few hundred feet under any codes, under any circumstances, or in any situation. 
AM has much more freedom. That's the primary reason to choose to broadcast on the AM frequency!

That concludes this chapter, stay tuned for more....

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