Equipment and stuff to get you going.
All you really need to get on the air is a couple hundred bucks worth of equipment that can be easily obtained from online sources. In its simplest form, your broadcast station need only comprise a transmitter, antenna, audio source and a cable. Here's what you need to get started.
Transmitter. There are many low-powered DIY FM and AM transmitters on the market. Some transmit only a few feet, while others can have an effective range of miles. Before selecting a transmitter, be sure you are aware of the FCC regulations governing unlicensed radio transmissions under Part 15. For AM the maximum legal limit is 100mW with certain restrictions on antennae. For FM, the max is measured in field strength: 250uV/m (48dBu), measured at a distance of 3m (about 10'). Since we will concentrate more on FM, due to its better audio fidelity than AM, it should be noted that the maximum range you will get for legal operation will be a few blocks or less, depending on terrain, receiver sensitivity, etc. For the more daring types, there are transmitters available for a couple hundred dollars, with power outputs ranging from a couple watts to 50 or more, yielding a signal good for several miles or more. Just remember: if the FCC sends you a Notice of Unlicensed Operation (NOUO) for your 10 or 20 watt operation, you're on your own. The penalties can range from a cease-and-desist notice, up to fines of thousands of dollars. If you live in a large city, your chances of getting caught are obviously much greater. If you live in the boonies, you just might get away with high-powered operation--for a while. The risk and liability is all yours. You decide if you want to pursue the high-power option.
A good, low-cost unit to consider for your FM transmitter is the Fail-Safe CZH-05B, which delivers a selectable 500mW and 100mW RF output. It comes with an attached "rubber duck" antenna, power supply and a 3.5mm male-to-male stereo cable. This unit costs around $100 on Amazon and is a rock-solid transmitter. You can select any frequency from 64-108MHz, in 0.1 MHz increments. Select an empty channel, plug in your audio source, and you're off and running. The high power (500mW) setting is likely well beyond FCC limits, so you may want to consider running this transmitter at the low (100mW) setting, and add a 50 ohm RF attenuator pad to drop the power even further. The sound output of this transmitter is fantastic and the signal will cover your home and neighborhood quite well. You get a lot of bang for the buck with the Fail-Safe unit.
Or you can build your own from a schematic if you have a bit of electronics skills.
If you do want to take the plunge and go full-pirate, Fail-Safe also makes more powerful, long-range FM transmitters: 1 watt, 5 watts, 10 watts--up to a 20 watt model. With the right antenna, you can broadcast up to 10 miles or more. HLLY also makes several low-cost models, ranging from below 1 watt, up to 50 watts. You'll want to be off-shore or way in the sticks to transmit with any high-power unit. Those transmitters operate well above Part 15 limits, and you must assume all risks when using them.
Antenna. Many low-power FM transmitters, including the previously-mentioned Fail-Safe unit, already come with an attached antenna, typically a "rubber duck" style, or small telescoping aerial. Since these stock antennas are designed to transmit over a wide range of frequencies (FM band), they tend to be poorly-tuned for any one frequency and are therefore not very efficient (low gain). You can build your own external antenna, tune it to the frequency of your choice, and yield better efficiency (higher gain!!!), and place it in a better (i.e., higher) location. A simple dipole antenna can be constructed for a few bucks, using some wire, and a length of coaxial cable for a transmission line. Here is another dipole plan to consider as well. If you don't want to build one, you can purchase a good, low cost indoor dipole antenna for around $20. This type of antenna can be mounted on a rooftop, balcony, in a tree, or hidden from view in an attic, etc., for better line-of-sight FM coverage. The higher the antenna is above the surrounding terrain and other obstacles, the farther your signal will reach. Just be sure to keep the length of your transmission line coax as short as possible, to minimize line losses.
One caveat: replacing your antenna with a higher-gain external one may increase your effective radiated power (and range), turning what was a not-so-noticeable broadcast into a more noticeable broadcast. So be careful--you don't want to get busted.
For further reading, the blog Low Power Radio has an excellent primer on selecting or constructing an antenna for FM transmissions.
Audio Sources. This is fairly straightforward, as all you need is an MP3 player, CD player, tape deck, or any other device with a 3.5mm stereo phono jack to connect with the Fail-Safe transmitter. Just connect from the player's headphone jack to the transmitter's audio input with the supplied double-end stereo miniplug cable. Alternatively, you can also get a cable from Rat Shack to connect from the RCA output jacks on a player to the input of your transmitter. You can also connect the output of your PC's sound card and broadcast music from your computer. Some transmitters, including the Fail-Safe, have a mic jack for those who want to provide voice-over of their programming (like we really want to hear your droning voice).
Additional gear. You can add on to your little broadcast system, by using a small mixing board, compressor/limiter, microphones, etc. Be your own DJ, annoy your neighbors, etc. The possibilities are endless. Good luck, and watch out for the FCC!
SOME NEW GEAR WE FOUND!
We just discovered a new vendor of FM transmitters and antennas. CZH Wholesale FM Transmitter. They offer transmitters ranging in power from 1mW, up to 5000W. Lots of fun toys!
For high power on a budget, we've just discovered this little gem on Amazon. The SainSonic CZH-7C FM Transmitter, with selectable 1W/7W output power. The unit comes complete with power supply, audio cable, and a nice telescoping antenna (which is much better than the rubber ducky antennas that usually come with these boxes). All for under $70...with FREE shipping! Transmitters in this power range usually cost upwards of $200 elsewhere, so this model is a real steal. With 7 watts of power, you should have no trouble getting a decent signal out several miles. Even at the 1 watt setting, you should get a mile or more. The reviews on Amazon for the SainSonic look promising.
Some more sources for gear:
Other things we like: