Many of the questions I receive deal with what it takes to begin a free radio station. The majority of these folks are looking to set up an FM operation.
While there's lots of how-to documents on the legality and general organization of an FM free radio station, none answer the most basic question of all.
The following is an answer I gave to a recent email, where the question was, "I don't know what goes between the outputs of my mixer and the inputs of the antenna, and in what order."
First of all, the MOST IMPORTANT knowledge you need is on radio frequency (RF) theory. You must understand how radio waves work and how the equipment makes the radio waves. If you go into this blind, you're absolutely looking for trouble. Nobody can explain it to you in an email - most websites out there are hopelessly incomplete on the subject, or are designed for those already RF-skilled. I'd recommend actually going out and buying a real paper book on the subject - there are some wonderful ones out there.
Electronics-skills wise, you don't have to be at more than the conceptual level, unless you want to make all your gear yourself. If so, better read some more books. However, there is good plug-and-play radio stuff out there, but the downside is its price. Sometimes it is worth paying more for the quality of professionally built and designed equipment.
Now, onto the gear itself: the general list of stuff you need for the "air chain" of your station, and its order, are as follows:
1) Sound source(s). Originates with CD, tape deck, mic, computer, turntables, etc. Your choice. Something to control what goes over the air and when.
2) Mixer. A simple word describing the most important piece of gear in regards to how your show will sound. This controls what sound sources you have, and their access to the airwaves at any given time. This doesn't have to be fancy, especially if you don't have a lot of sound sources. But without one, it's nearly impossible to broadcast coherently.
3) Audio processor. Equipment that "cleans up" your audio. There are different kinds and they do different things; the two most common are compressors and limiters. These two are often bundled together, and they prevent you from sending the next part of the air chain a signal that could cause you problems with the way your broadcast not only sounds, but also with interference.
4) Exciter. This is the transmitting stage, it includes the ability to generate the RF frequency desired and translate the audio input into RF. If the mixer's the brain, this is the heart of your air chain, and the other stuff are the other vital organs.
The trick here is to put out the cleanest RF signal possible, without spurious emissions which can interfere with everything from your neighbor's TV to the local air traffic control system. The cleaner the signal, the longer the station's lifespan. If you do this one up wrong, your time on air will be much shorter before tha Man comes knocking.
5) Amplifier. This is optional, but allows you to add more power at less expense. The amplifier takes the signal from the exciter, juices it up to a higher power level, and sends it to the antenna. It's cheaper to buy a small transmitter and add an amplifier to get to the desired wattage than it is to buy a transmitter outright at the desired wattage. And, I think, you'll want to start small, get all the bugs worked out of the station, then increase power (at your own risk).
6) Filter. This goes between the final output of your RF signal (either the exciter or amplifier, depending on your setup) and the cable feeding that signal to the antenna. Having a filter is essential to prevent unintentional interference to others - without one, you're signing your seizure (or arrest) warrant.
7) Coaxial cable. People blend this in with the antenna, but it really should be considered separate from that. A good quality cable can increase both your signal range and sound quality with no increase in power. And if you maintain it in good condition, it'll stay that way for years. Try to keep the cable length as short as possible for maximum power efficiency.
8) Antenna. Either a J-Pole or Comet antenna will do you well, most people go with the J-pole because it's the most widely understood to build, but the Comet is the easiest to tune to the proper frequency. The height of your antenna will make a big difference in how far your signal will travel: the general rule of thumb is the higher the antenna, the farther the range. Putting your antenna up higher is a less risky and less expensive way to increase signal range than upping your power.
That should about do it. Remember - this is only the basic equipment necessary to set up a station. For the most complete story, see the Beginner's Guide to Low Power Broadcasting, one of the most comprehensive introductory sources to the subject available online. Also good is the Technical Primer from Stephen Dunifer, which focuses more on the science behind radio. Think of these as the bare-bones checklists for the knowledge you'll need.