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A Street Tech How-To: WHOLE HOUSE AUDIO THE WIRELESS WAY 
I love music. Throughout the day, I pump an eclectic mix of sounds into my home office. At any given time, I might be listening to Jazz FM direct from London via an Intelsat satellite perched over the Atlantic, The BBC World Service via World Radio Network, CDs, or just a local radio station. What I really wanted was to be able to listen to music in the bedroom, living room, study, or even outside, without cluttering up the place with speaker wires running everywhere. The solution was a small battery-powered stereo FM transmitter which was actually designed to send music from a portable CD player to your car stereo. These transmitters have a short cable with a mini-phone plug attached that connects to the output of any audio source and a tunable frequency output that lets you transmit on an empty spot on the FM radio band. These transmitters are allowed by the FCC under Part 15 of FCC rules which governs unlicensed low-power transmissions. Your transmitter must be low-power enough so as not to cause harm to any licensed spectrum users, and if you experience interference with your transmissions, you just have to live with it.
 A typical battery-powered FM transmitter The power output of these little babies is enough to be heard within a 50-100' radius of the transmitter, depending on the material through which the signal must pass. This means that you should site the transmitter in the center of your home if you can. I have mine plugged into the headphone jack of the stereo in the office and have no trouble picking up a full-strength signal anywhere in the house. I can also pick it up on the outside deck or out in the yard. None of my neighbors receive the signal. If you live in an apartment complex or a neighborhood with close housing, the signal might be heard by the neighbors, so you should give some thought to what's being transmitted. You must also consider where you are on the FM band. If you're transmitting close to your neighbor's favorite station, you may be causing interference and creating unwelcome problems ("Jimmy, put the gun down. I'll re-tune my transmitter!"). These devices are found in virtually every big consumer electronics store and are all battery powered. That ends up being their biggest problem. Most operate on one or two AAA batteries (1.2 volts each) which, if used sparingly, will last a week or more. But if you use your transmitter like I do--24/7--they only last about two days. The biggest problem with weakening batteries, when used with a transmitter, is that they cause the transmit frequency to drift. The solution is to add a stable power supply which you can plug into house current. What you're looking for is a regulated 1.5 or 3 volt DC power supply. The "regulated" part reduces the hum which can occur if you use an unregulated supply. Radio Shack sells such a power supply (RS #273-1654) for $14. You can do a simple modification to run your transmitter on the adapter and make it possible to use batteries too if you want to make it portable. With your power supply unplugged from the wall, cut the connector with a pair of wire cutters (scissors will work too). You'll notice that the wire is actually two insulated wires. Separate the two by peeling them apart to about two inches from the end. Note that one of the wires has a white stripe along its edge. This is the positive or (+) wire which carries the voltage. The other wire is the negative or (-) wire and is the ground. Strip the insulation from about half an inch on each end. Buy a package of mini-alligator clips (RS #270-1545). The package will contain 12 clips with 6 red and 6 black plastic insulators. Take two clips and one red and one black plastic clip cover out of the package. First, place a red and black clip cover over the end of each wire. Now solder each bare wire lead to each alligator clip. Open each clip and stick a pencil into its jaws. This allows you to slip the insulator cover up over the clip with just the tip of the clip exposed. Do this to both wires. Remove the battery compartment cover and take out the batteries. You will have to cut a small notch out of the plastic housing where the wire enters the battery compartment to allow the device to set flat on a shelf. Clip the red to the positive (+) battery lead and the black to the negative (-) battery lead. Both clips must be firmly attached to the battery leads and not touching each other. Slide the battery compartment cover back over the clips. Set the power supply switch to 1.5 or 3 volts depending on the voltage requirement of the transmitter you're using and plug it in a wall outlet (the extra voltage will not hurt the transmitter). Plug the audio cable into your stereo and play a CD on it. With another radio, search the FM band for whatever's playing on your CD player. If it's too close to another station, turn the little setscrew on the bottom of the transmitter, as directed in the instructions, until you can locate your transmitter on an empty frequency. That's all there is to it!
 Converting the transmitter to a DC power supply.
Ordering Your Transmitter - Ken Reitz [3/1/98] Other wireless wonders reviewed on Street Tech:
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