
Low Power Broadcasting FAQ
(Frequently Asked Questions)

   Revised 1997.01.04
   
  What is low power broadcasting?
  
   Some individuals and small groups operate low power radio stations as
   a hobby, or as a way of spreading some commercial, religious or
   political message. These stations are often short-lived, sometimes
   portable, and generally unpredictable.
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  Is low power broadcasting legal?
  
   This depends on what country you are in. The situation varies from
   place to place, so you should check with a lawyer or with the agency
   that regulates broadcasting in your part of the world before turning
   on any transmitter. Don't rely on web pages or usenet newsgroups for
   such critical information.
   
   Here in the United States, legal unlicensed broadcasting is limited to
   microscopic power levels, and it must be done on a frequency that does
   not interfere with reception of licensed stations. The power limit for
   unlicensed FM transmissions is 250 microvolts per meter, measured 3
   meters from the transmitting antenna; at this power level, stereo
   reception with a good signal to noise ratio is only possible within a
   100 foot radius, and an average car radio can barely detect the signal
   at a distance of 200 meters. On the AM band, the limit is 0.1 watt and
   an antenna system no more than 3 meters long; with an optimized
   antenna, this provides a range of 3 or 4 city blocks for cheap
   receivers, farther for high-quality radios. Obviously a network of
   such low-power stations would be needed if you wanted to legally cover
   any significant amount of territory.
   
   Other legal options include carrier current transmission (using the
   power lines as an antenna system, legal only on educational campuses);
   cable FM broadcasting (working in conjunction with your local cable TV
   system); and burying special "leaky" coaxial cable to use as a
   transmitting antenna on a piece of private property such as a tourist
   attraction. The booklets available from Panaxis cover these options in
   greater detail. (You can look up the rules in title 47 of the Code of
   Federal Regulations, Part 15.) The US regulations also allow
   microscopic power levels on the shortwave broadcast bands, but they do
   not allow any unlicensed emissions on television broadcast
   frequencies.
   
   It is a good idea to obey the rules, give or take a fraction of a
   watt. People who seriously break the rules often have to pay large
   fines and their equipment is sometimes confiscated. Many people feel
   that the rules are too restrictive, and a court battle against the
   federal government is underway; see the freeradio.org site for more
   information about this.
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  What equipment do I need to start a station?
  
   You will need audio sources (tape players, CD players, microphones,
   etc.), an audio mixer, a transmitter, a coaxial cable (usually RG-8 or
   RG-58/U) to carry the signal from your transmitter to your antenna,
   and an antenna.
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  How much territory can my signal cover?
  
   If you are in the USA and you obey the signal strength limitations
   imposed by the federal government, your range will normally be limited
   to a radius of 1/4 mile or less. However, people who make a hobby of
   listening to low power signals have sometimes heard 0.1 watt AM
   signals at distances of several hundred miles. They accomplish this by
   using sensitive (expensive) receivers and large antennas located in
   rural areas away from urban static, and they listen when atmospheric
   conditions are good.
   
   On FM broadcast frequencies, antenna height puts an upper limit on
   your range, regardless of power levels. The distance from your antenna
   to the radio horizon is determined by this formula:
   
   distance_in_miles = 1.415 * square_root_of_(antenna_height_in_feet)
   
   You can add the transmit antenna's range to the receive antenna's
   range to predict whether reception will be possible. Example: a
   transmit antenna is 25 feet high; the square root of 25 is 5; 1.415 *
   5 = 7.075 miles to the radio horizon. If the receive antenna is also
   25 feet high, if there are no major obstructions between antennas, and
   if power is high enough (or receiver sensitivity is high enough), then
   reception at a distance of 14 miles could be achieved.
   
   In summary, the range you can reach depends on your transmitter power,
   antenna height and effectiveness, and the sensitivity of the
   listener's receiver.
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  Where can I get a transmitter?
  
   Below is a brief list of companies selling low power transmitters and
   transmitter kits.
   
   Note to newcomers: to assemble these kits, you must be able to solder
   components onto a circuit board, and it helps if you know the
   difference between a resistor and a capacitor. If you haven't reached
   this stage of electronic know-how yet, consider buying some of the
   educational kits available from C & S Sales, 1245 Rosewood, Deerfield
   IL 60015, telephone 800-292-7711. Their electronic components course
   (item #ECK-10) might be especially helpful to newbies.
   
   sources of transmitters: 
   
   DC Electronics
   P O Box 3203
   Scottsdale AZ 85271
   phone 800-423-0070
   
   The Improved Stereocaster is an FM stereo transmitter based on the
   BA1404 chip with a few milliwatts of output power ($29.95 plus $3.50 S
   & H). It has a smooth fine-tuning control which makes it easy to get
   on the exact frequency you want, and a voltage regulator which
   improves stability. It has been reported that the power output can be
   increased by replacing the supplied output transistor with an MRF581.
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   Free Radio Berkeley
   1442 A Walnut St., #406
   Berkeley, CA 94709
   phone 510-464-3041
   e-mail frbspd@crl.com
   
   Items listed in their ads include a 1/2 watt stereo FM transmitter kit
   ($50), an FM transmitter with phase locked loop (PLL) frequency
   control ($95), plus kits for output filters, dummy loads, RF
   amplifiers, and antennas.
   
   Some people have posted messages in alt.radio.pirate indicating that
   FRB sometimes takes several weeks or months to respond to orders. Some
   have said that the instructions are not very helpful.
   _________________
   
   
   Panaxis Productions
   P O Box 130
   Paradise CA 95967-0130
   (send $1 for catalog, or $2 if you're in a hurry)
   
   This company offers many interesting books and kits. The FMO kit ($75)
   is a high fidelity stereo FM transmitter kit with 2 to 20 milliwatts
   of output power. The FME-500, a half-watt mono FM transmitter with
   excellent technical specs, can be combined with their stereo generator
   to build a high-quality low power station (more than $200 for the two
   kits). Panaxis kits might not be suitable for absolute beginners; you
   should have some experience in circuit assembly before you tackle
   these.
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   Progressive Concepts
   phone 708-736-9822
   fax 708-736-0353
   
   RF amplifiers, FM transmitters and stereo generators, components for
   RF circuits, high-quality antennas for low-power FM broadcasters, and
   more.
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   Ramsey Electronics
   793 Canning Pkwy
   Victor NY 14564
   phone 716-924-4560
   
   Ramsey kits have well-written instruction manuals, and most of the
   circuit boards have lots of wide-open space which makes modifications
   easy. The company also has a good reputation for service. On the
   negative side, they only offer plastic cases for their broadcasting
   kits (transmitter circuits generally perform better in metal cases).
   
   The FM-10A is an FM stereo transmitter kit ($34.95 plus shipping) with
   a few milliwatts of output power; it is based on the BA1404 integrated
   circuit. The FM-25 kit, which has PLL tuning for greater frequency
   stability, costs about $129.
   
   Ramsey also offers a low-budget AM transmitter and a more expensive AM
   transmitter that has PLL frequency control.
   
   Check out the Ramsey web site for more information.
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   Scott Communications
   6974 Larkspur Rd. RR-3
   Sooke, B.C., Canada VOS-1NO
   phone 604-642-2859
   e-mail: kscott@pinc.com
   
   This company offers a 3-watt mono FM transmitter which they say has
   good sound quality and frequency stability. Kits cost $90 plus $5
   shipping; fully assembled and tested $129 + $7. They have recently
   added a stereo FM transmitter with PLL frequency control to their
   product line; contact them for details.
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   Veronica FM
   18 Victoria Street
   Bradford
   West Yorkshire BD13 1AR
   United Kingdom
   phone 01274 816200
   
   Antennas, audio processors, and transmitters (fully assembled; no
   kits).
   _________________
   
   
   The L D Brewer company sells transmitter kits, antennas and supplies
   from a variety of companies, and will assemble a kit for you if you
   don't know how to do it.
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  How do I select a frequency?
  
   Receivers with digital tuning will only lock onto signals that are on
   standard broadcast frequencies. In the US, AM stations are at 10 kHz
   intervals, ranging from 540, 550, 560 ... to 1700. FM stations are
   spaced at 0.2 MHz intervals, ranging from 88.1, 88.3 ... to 107.9 MHz.
   
   Do not use an out-of-band frequency; they are reserved for other
   services. (For example, the frequencies just below 88 MHz are used for
   TV broadcasts, and the frequencies just above 108 MHz are used for
   aircraft communication.)
   
   Make a survey of the band you are planning to use. Get some graph
   paper or notebook paper and make a list of all the channels. Listen
   during the day and at night, making a note of what station(s) you can
   hear on each channel. Use a good receiver with digital tuning and a
   decent antenna, not some cheap piece of junk clock-radio or dime-store
   pocket radio. Repeat this band-scanning process several times during
   the course of a couple of weeks. (If you really want to be thorough,
   get a list of all the licensed stations in a 150-mile radius. You can
   extract this data from the Broadcasting Yearbook [a trade publication]
   or the FCC database [available on computer disks from several
   vendors]). If you know any DXers (people who make a hobby of listening
   to distant and unusual signals), ask them for a copy of their "log."
   
   Now, sit down with your data and search for an appropriate channel.
   Don't start with any prejudices or pre-conceived notions: don't plunk
   your signal onto 99.9 MHz just because you think it's cute ("666"
   upside down) or onto 1000 kHz because you think it's an easy number to
   remember. Don't try to wedge your signal into the non-commercial part
   of the FM band (88 to 92 MHz) if there isn't an appropriate opening.
   
   An appropriate channel for low power broadcasting is one that is not
   occupied by a local station, or by an often-audible distant station.
   The adjacent channels -- the next channel above and the next channel
   below the one you're considering -- also must not be occupied by local
   stations, because they will "splatter" onto your signal (and they will
   claim that you are splattering onto them).
   
   There are a couple of other things you must keep in mind when
   selecting an FM broadcast frequency. First, if there is a TV station
   broadcasting on channel 6 in your area, it is unwise to operate on
   88.1, 88.3, or 88.5 MHz. TV receivers have broadband tuning circuits
   (a TV channel is 6 MHz wide, enough spectrum to hold 30 FM stations),
   so broadcasts at the "low edge" of the FM band can easily interfere
   with reception of channel 6.
   
   Another thing for FMers to consider is the mixing of signals that can
   occur in a listener's receiver. Most FM radios use an intermediate
   frequency of 10.7 MHz; in other words, whatever frequency you're tuned
   to is converted down to 10.7 MHz before the sound waves are extracted
   from the radio waves. As a result, a strong signal can interfere with
   reception of stations that are on a frequency 10.6 or 10.8 MHz above
   or below it. For example, if you transmit on 92.3 MHz, some listeners
   who are located near your transmitter will have trouble hearing a
   station on 102.9 or 103.1 MHz (92.3 + 10.7 = 103.0). The interference
   might take the form of an "image" of your signal being heard on the
   other frequency, or vice versa; or a mixture of the two signals might
   be heard on blank spots and on top of weak signals all over the band.
   So, do the math and avoid picking a channel that is 10.6 or 10.8 MHz
   away from a strong local signal.
   
   In some major cities, there is no room in the FM band for any more
   signals.
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  Where can I get more information?
  
   Introductory electronics textbooks are available at most bookstores
   and libraries. Magazines such as Electronics Now, Popular Electronics,
   and Nuts & Volts sometimes have articles and advertisements of
   interest to low power broadcasters. Monitoring Times and Popular
   Communications carry relevant news items from time to time.
   
   Keep an eye on these Usenet newsgroups:
   alt.radio.pirate
   rec.radio.amateur.antenna
   rec.radio.broadcasting
   alt.radio.broadcasting
   
   Relevant world wide web sites:
   
   http://www.clandjop.com/~jcruzan/frn.html (FRN)
   http://www.rootsworld.com/rw/feature/rrb.html 
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   This text is copyright 1994-96 by Rick Harrison. Permission is hereby
   granted for unlimited distribution of this text via Usenet newsgroups,
   Internet file servers, and computer bulletin boards. Any publication
   of this text in semi-permanent form (such as hardcopy or CD-ROM)
   requires the author's prior permission.
   
