No Static at All: A Review of Low-Power FM Transmitters
Have you ever had an excellent source of audio material that was in the wrong place in your home? Perhaps you would like to play your favorite Internet radio station or MP3 files from your personal computer's (PC's) hard drive on your back porch. Maybe you want to hear the television audio in your garage. Or perhaps you would like to hear your Talking Book player through the car's sound system on your next trip. For me, it was playing books from my Audible Otis through the car radio and other radios in my home. (For more information on Audible, see the web site <http://www.audible.com> or the article, "Books on Tape Without the Tape!" in the January 2003 issue of AccessWorld®.)
Making audio sources more portable within your home or car is easily accomplished with the use of a low-power FM transmitter. An FM radio transmitter can be connected to the audio-out or headphone jack of almost any device, including a PC sound card, Talking Book player, MP3 player, or tape recorder. The audio is transmitted to any nearby FM radio receiver, such as the car radio, a Walkman radio, or your stereo receiver. Note, however, that the range of a low-power, license-free FM transmitter is limited, so you will not be able to transmit from your home and receive the signal miles away while you walk around town. Nevertheless, many people who are visually impaired find limited-range portability of audio material to be convenient in their homes. In fact, these transmitters have been discussed extensively on the PC-Audio e-mail group. (To subscribe to the list, send a blank e-mail message to <email@example.com>.)
This article reviews two FM transmitters that are popular with audio enthusiasts who are blind or have low vision: the Arkon SF120 Sound Feeder and the C. Crane FMT Digital Wireless FM Transmitter. Two other transmitters are discussed for readers who want to explore the topic further. These units cover a range of price points and capabilities.
With any of these models, the transmitter needs to be connected to the audio source, typically by plugging an audio connecting cable into the headphone jack on the source. The transmitter must be tuned to a frequency on the FM radio band that is not in use in your area of the country. Finally, volume levels on the source or transmitter must be adjusted to provide an audio signal that is strong enough, yet not so loud that it overdrives the transmitter. A signal that is too loud will generate distortion of the audio as it is transmitted. After you finish these setup steps, your audio program is broadcast like any other radio station to a nearby FM radio receiver. Finally, the radio receiver you will be using needs to be tuned to the frequency that you selected when you set up your transmitter.
The Arkon SF120 Sound Feeder
The battery-powered Arkon SF120 Sound Feeder allows you to play your portable CD player, MP3 player, or MiniDisc player through your car's FM radio. It can also be used indoors with television, video games, keyboards, or computers.
The SF120 Sound Feeder is enclosed in a small plastic case, measuring 3 3/8 inches x 2 3/8 inches x 1 inch and weighs 2.6 ounces. It operates on one AA battery. A telescoping 3½-inch antenna is built into the top right of the case. Also on the top is a slide switch for power. Moving this switch to the right toward the antenna turns the unit on. At the top of the left side is the jack for the audio-input cable. Below this jack is a tuning knob that is used to select the SF120's transmit frequency. Below the tuning knob is a three-position switch that is used to select the portion of the 88-108 MHz FM band to be used. This frequency-range switch basically divides the FM band into thirds, allowing the frequency-tuning knob to offer finer tuning than would be possible if it were covering the entire range in one rotation. The battery compartment is located near the bottom of the back of the unit. It is opened by sliding the compartment's cover to the left.
All the controls of the SF120 are accessible. Operating the unit is fairly simple; all you need to do is to find an unused frequency on an FM radio, connect the SF120 to an audio source, turn it on, and tune the SF120 until you hear your audio source in the radio. There is no audio-level adjustment on the SF120, so the volume control on your audio source is used to control the transmitted audio volume.
Advantages and Disadvantages
The SF120 is an inexpensive choice to begin experimenting with audio broadcasting.
However, the transmission range on the unit I evaluated was limited. The unit worked well transmitting to a car radio from anywhere within the car, so it was excellent for sharing Talking Books or the contents of an MP3 player with others on a road trip. But I found that the limited range made it impractical for transmitting farther than within one room at home. The audio cable that was provided was short, so that the SF120 had to be within a foot of the source. Also, tuning the transmit frequency was a bit of a problem. Although it was easy to accomplish without sighted assistance, even a slight movement of the tuning dial caused a fairly large movement in the frequency. Even after I set the transmitter on the open frequency I chose on my FM radio, it was easy to accidentally bump the transmitter frequency control and have to retune.
The C. Crane FMT Digital Wireless FM Transmitter
The C. Crane FMT Digital Wireless FM Transmitter is available directly from the C. Crane Company. With the FMT, you can listen to streaming or MP3 audio. Plug it into the headphone jack of your computer's speakers or sound card and listen on any FM radio anywhere in the house. The FMT does so by taking the audio and turning it into an FM radio broadcast. It has an approximate line-of-sight range of 70 feet. Walls and metal objects will reduce this range.
The FMT is enclosed in a small plastic case measuring 3.1 inches x 3.5 inches x 1 inch and weighs 5.8 ounces. It operates on two AA batteries or an included alternating-current power adapter. The case has rubber feet on both the back and the bottom sides, so it can be positioned flat or vertically on a desk or shelf. A telescoping 11-inch antenna is located on the top left of the unit. In addition to telescoping, this antenna has a swivel base, so that it can be adjusted to a vertical position, regardless of how the FMT is oriented.
With the FMT lying flat, the on-off button is just slightly above the center on the top surface. It is a wide oval-shaped button. Pressing it quickly turns the unit on. If the button is held down for more than a few seconds, it activates an automatic power-off feature. The FMT cycles through 1-, 2-, 4-, or 8-hour timer choices. To the right of the power button is a small red LED (light-emitting diode) that indicates that the input audio is too loud. Below the power button is a digital frequency display. To the lower right of this display are two buttons that are situated on a diagonal. The upper right of these two buttons increases the broadcast frequency, and the bottom one lowers the frequency. Each time these buttons are pushed, the frequency changes by 0.05 MHz. There is a transmit-volume control on the right side of the case. The built-in audio cable is attached on the lower left side of the case; it is a coiled cord that can be extended to about three feet. Below this cable is the jack for the included 110V power adaptor. The battery compartment is on the lower half of the back of the unit; the cover slides off to the left to allow the installation of two AA batteries.
Not all the FMT's controls and features are fully accessible to a user who is blind, but the unit is still easy to operate. The frequency can be set by pushing the frequency-increase buttons while listening for the signal on your FM radio tuned to an unused frequency. The transmit-audio level can be set by ear, again listening to the volume and quality of the signal in the radio.
Advantages and Disadvantages
The FMT is easy to tune. Once set, it is not easily bumped off the selected frequency. The stereo audio quality is excellent, and the range is good. The manual states that a range of 70 feet in an unobstructed area should be expected. I did not attain this range, but I was using the FMT in my home, so the signal was obstructed by walls and electrical systems. The included 110V power adapter is a handy feature when you use the FMT in a fixed location, such as when it is connected to a computer's sound board output.
However, I found that it was easy to turn on the FMT accidentally while I was carrying it in my briefcase. The power button was probably pressed by something while in transit. Without a radio to hear the signal, there is no way for a blind user to know if the FMT is on or off.
Two FM transmitters by two other manufacturers deserve a quick mention. Although I have not evaluated either of them, these transmitters from Veronica and from Ramsey Electronics have been discussed extensively by contributors on the PC-audio e-mail group. Veronica is a European provider of transmitters in both kit and assembled versions for professional applications. Many of its products exceed the U.S. power limits for license-free operation (see Veronica's home page at <www.veronica.co.uk>). Ramsey Electronics offers several AM and FM transmitters (see its home page at <www.ramseyelectronics.com>). Note that the Ramsey Electronics transmitters and some Veronica models are kits that require assembly by someone who is experienced in building electronic kits.
Rules and Regulations
In the United States, RF (radio frequency) devices are regulated by the Federal Communications Commission (FCC). The FM transmitters that have been discussed in this article fall under these regulations. Anyone who operates such a device is responsible for understanding and complying with the appropriate regulations. A good introductory discussion of the FCC rules regarding low-power, license-free FM broadcasting can be found on the Ramsey Electronics web site at <www.ramseyelectronics.com/resource/default.asp?page=fcc>. If you buy a kit that requires adjustment to comply with regulations or a device that is not designed to be used in the United States, you are still responsible for operating it in compliance with the FCC rules.
Product: SF120 Sound Feeder
Manufacturer: Arkon Resources; 20 La Porte Street, Arcadia, CA 91006; phone: 800-841-0884 or 626-254-9005; web site: <www.arkon.com>. Price: $24.95.
Product: FMT Digital Wireless FM Transmitter
Manufacturer: C. Crane Company; 1001 Main Street, Fortuna, CA 95540; phone: 800-522-8863; web site: <www.ccrane.com>. Price: $79.
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