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Transmission refers to the process of taking the sound you generate in the studio, turning it into radio waves, and sending it out into the air. On the other end, your listeners will use receivers to capture the radio waves and turn them back into sound. Transmission can be hard to understand because we can't see or hear the electromagnetic waves. It's also hard to predict how transmission will work - your signal will be affected by things like mountains, trees, buildings, rain, and the presence of other radio waves. No station knows exactly where their signal will go before they turn on their transmitter. However, with a basic understanding of the physics behind radio frequency transmission, you can make some fairly good predictions. The documents below are intended to demystify the science behind radio transmission, while also addressing common challenges and solutions in radio transmission.
- The Transmission Toolkit
- Mapping Your Ideal Area of Coverage and Antenna Location
- Hang 'em High: Options for Antennas, Masts and Towers
- Sound Around Town: Studio-to-Transmitter Links
- Low Power FM Equipment Guide
- Encroachment Explained
- Changing Your Low Power FM Studios, Transmission, or License
- Audio Processing and Compressors for your Station
- Basic Electronics for Radio
After community, the transmission site is the second most important component of a successful community radio station. This guide explains what makes a good LPFM transmission site, explores the merits of building your own verses sharing an existing tower, and provides tips and tools for finding a great site.
Before you begin searching for a location to put your LPFM antenna and transmitter, you need to identify the communities and neighborhoods you want to cover with your broadcast. Making visual maps is very useful for anyone helping you determine an ideal transmitter antenna site. Using Google Maps, it is easy to draw polygons around your ideal area of coverage. The guide below explains how to use this tool and share your maps
First, we should note the difference between antennas, masts and towers. A mast or tower is simply the thing that holds the antenna up off the ground. Masts are usually metal, but under unusual circumstances they might be made of wood or other substances. In FM broadcast, the antenna is usually mounted to the mast near the top. A mast is generally a single piece of pipe, while a tower is a set of interlocking pipes (typically in a triangular configuration) which can be much taller.
For whatever reason, you need to bring high quality audio from one place in town (where your studio is) to another place (where your transmitter is). Maybe this is because Congress forced you to locate your transmitter in a weird place to meet bizarre distance standards between radio stations. Or maybe because you got a nice site on top of the mountain, but you want your studio to be in the middle of town. Whatever your needs, you were probably surprised to discover that just moving a signal from one point to another can easily cost you twice what your broadcast transmitter (which will reach everybody in your town) is costing. Below is a compendium of the options we have found over the years, ranging from crackpot to industry standard.
This document discusses both the studio equipment (like CD players and mixers) and the transmission equipment (like transmitters and antennas) needed for Low Power FM.
When a full power radio station wants to move their signal, typically they cannot interfere with any other existing full power stations in their way. Unfortunately, this is not the case for existing LPFM stations. The full power station does not have to pay any attention to LPFM stations when they move. In fact, the FCC will order an LPFM station off the air if it's located where a full power station wants to move. This document explains encroachment and provides some resources where you can find more information.
There are many little things you can do to improve your LPFM. Improving your audio equipment—getting new microphones or a new audio processor, for example—can do wonders for the quality of your signal. However, if your station would like to increase the power of its broadcast or change the location of the transmitter and antenna, you might need to apply for permission from the FCC. This guide gives an overview of different changes you could make to your station and what it would take to get them done.
Why do I need audio processing for my station? Do I need a compressor? Or a limiter? Or a clipper? Or a Multiband audio processor? Or something with Automatic Gain Control? And does a $2000 audio processor sound 10 times better than a $200 compressor?
Do you ever wonder how sound that goes into a radio transmitter comes back out of a radio receiver as sound, when you can't hear any sound along the way? Sometimes it's easiest to pretend that everything that happens inside these devices is magic, and only the wizards and witches inside need to understand the magic. We can say that a transmitter is a "black box" that turns waves of sound into waves of electricity and a receiver is a black box that turns electricity back into sound. But if you ever need to build one of these devices, or fix one that breaks, then it helps to know a little about how the electronic stuff works. The electronics used in radio, known as radio frequency or RF electronics, is a vast subject with entire books devoted to it, and there's no way we can explain it all in one document. Instead, we'll try to explain some of the most fundamental theory and the most common components used in RF electronics, with the hope that it will be enough to get you started.