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Subject: Low Power Broadcasting FAQ (Frequently Asked Questions)
This article was archived around: 23 Jun 1998 12:08:48 GMT
Low Power Broadcasting FAQ (Frequently Asked Questions)
copyright 1994-1997 by Rick Harrison
NOTICE: It is not the author's intention to advocate unlawful
activity. If the broadcasting regulations in your country are too
restrictive for your liking, you should try to get them changed
or move to a less repressive environment. If you choose to disobey
the regulations, you must be willing to face the consequences.
The web version of this document contains more information, is updated
more often, and is illustrated with graphics and tables. Its URL is
What is low power broadcasting?
Some individuals and small groups operate low power radio or
TV stations as a hobby, or as a way of spreading some commercial,
religious or political message. Some volunteer groups operate
unlicensed stations with a "public access" format, allowing
virtually anyone to get on the air for an hour or two each week
and broadcast any sort of material that they feel passionate about.
Unlicensed stations are known by such terms as "free radio" and
"micropower broadcasting." Some of them operate within the legal
guidelines for unlicensed stations, while others use a bit more
power than the rules allow.
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 entirely on web pages or usenet
newsgroups for such critical information.
In some European countries (e.g. the Netherlands), you can be arrested
for merely possessing an unlicensed transmitter. In Ireland,
unlicensed broadcasting is unlawful but stations that don't cause
interference are seldom prosecuted. In Taiwan, the authorities have
recently threatened to imprison unlicensed broadcasters. Indonesia
generally tolerates unlicensed broadcasts on shortwave. Canada and
Japan have made it possible for people to get licenses for very low
power FM stations if the licensees promise to provide programming that
is not available from mainstream outlets.
In the United States, Title 47 of the Code of Federal Regulations
(Part 15, subpart C) indicates that unlicensed broadcasting is limited
to microscopic power levels. The power limit for unlicensed FM
transmissions is a signal strength of 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 100 meters. On the AM band, the limit is
0.1 watt and an antenna system no more than 3 meters long; this
provides a range of 2 or 3 city blocks for cheap receivers, farther
for high-quality radios.
Some have argued that the strictness of these regulations violates the
US Constitution (footnote 1) and the UN Declaration of Human
Rights.(footnote 2) Others have said that the federal government does
not (or should not) have jurisdiction over low-power transmissions
that do not cross state lines. There have been many court battles over
the FCC's regulations, and no doubt there will be many more.
Apart from the Part 15 rules mentioned above, legal unlicensed options
include carrier current transmission (using the power lines as an
antenna system); cable FM broadcasting (working in conjunction with
your local cable TV system); and burying special "leaky" coaxial cable
to use as an AM transmitting antenna on privately owned land. Panaxis
and LPB can provide more information about legal options.
1. From the Bill of Rights: "Congress shall make no law respecting
an establishment of religion, or prohibiting the free exercise
thereof; or abridging the freedom of speech, or of the press..."
2. Article 19: "Everyone has the right to freedom of opinion and
expression; this right includes freedom to hold opinions without
interference and to seek, receive and impart information and ideas
through any media and regardless of frontiers."
What equipment do I need to start a station?
For a radio 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.
A piece of equipment called a compressor/limiter is also very
important. It reduces the level of sudden loud sounds so that they
don't over-drive the transmitter, and brings up the volume of quiet
sounds so that people riding in cars and listening in other noisy
environments can hear them. Radio stations that operate without a
compressor/limiter sound very amateurish and run a higher risk of
interfering with stations on nearby frequencies.
For television, you also will need video sources (cameras, videotape
players, character generators, etc.) and a video switcher.
How much power should I use to get a range of X miles?
This is the most frequent question, and many newbies want a simple
answer. There is no simple answer. The distance at which your signal
can be heard will vary from listener to listener, depending on their
equipment and location. In fact, many elements affect your range:
* the transmitter power
* the transmit antenna's height and effectiveness
* local terrain (hills, large buildings, etc.)
* interference from distant stations on the same channel
* splatter from local stations on adjacent channels
* the height and effectiveness of the listener's antenna
* the sensitivity of the listener's receiver
* amount of "static" at the listener's location
predicting the range of an FM or TV signal
On FM and TV broadcast frequencies, antenna height puts an upper limit
on your range, regardless of power levels. (It is true that
diffraction can extend your range slightly, and signals sometimes
travel greater distances when atmospheric conditions are just right,
but we will ignore these factors for the time being.) The distance
from your antenna to the radio horizon is determined by this formula:
distance in miles = 1.415 times the square root of the antenna height
Now you see why FM and TV stations go to the expense of building
antenna towers that are hundreds of feet high, or locate their
antennas on mountain-sides that overlook the cities they want to
Of course, the formula assumes that the terrain is relatively flat.
If the transmitting antenna is located at the top of a hill, its
range might be better, but this depends on the direction in which the
antenna radiates its energy (i.e. its vertical radiation angle). If the
antenna shoots a lot of energy up into the sky (as some types of antennas
tend to do), placing it in a higher location will not help much. You
can see the effect of terrain on coverage by following this link to some
low-power FM coverage maps ( http://www.bcradio.net/fmsrmap.htm ).
[The web version of this FAQ contains more information on this topic.]
Where can I get a transmitter?
Below is a brief list of companies selling low power transmitters and
Note to newbies: 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.
Several web pages that will teach you how to solder are available:
* sources of transmitters:
web page: http://indigo.ie/~alinton/rigindex.htm
This company sells low power FM exciters, stereo coders, and
RF amps. Apparently located in Ireland.
P O Box 3203
Scottsdale AZ 85271
The Stereocaster is an FM stereo transmitter kit based on the BA1404
chip with a few milliwatts of output power ($29.95 plus $4 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 signal strength can be
increased by replacing the supplied output transistor with an MRF581.
The Stereocaster is more stable than Ramsey's famous FM-10.
New items: a stereo transmitter kit with PLL tuning, and some FM
191 Madera Ave
Ventura, CA 93003
web page: http://www.silcom.com/~dschmidt
Offers a digital frequency readout for FM transmitters, and two low
power Panaxis transmitters, plus assorted parts and gadgets. The
DTMF-activated relay could be used for remote control of transmitters
in various locations by sending tones to them via telephone lines or
10740 N. 56th St., Suite 186
Tampa FL 33617
phone 1-800-886-8023 or 1-813-960-8023
web page: www.ldbrewer.com
The L D Brewer company sells FM transmitter kits, antennas and supplies
from a variety of companies, and will assemble and repair kits.
28 Bacton Hill Road
Frazer PA 19355
web page: members.aol.com/lpbinc/
Since 1960, LPB Inc. has been a source of legal low power broadcast
equipment, including carrier-current transmitters, radiating coaxial
cable equipment, and other such gear. They ask their customers a lot of
questions and clearly want to avoid selling equipment to rule-breakers.
North Country Radio
PO Box 53
New Rochelle, NY 10804-0053
web page: www.northcountryradio.com
Items offered include a low power FM transmitter that (thankfully) does
not use the BA1404 chip, and some TV transmitters for use by licensed
amateur radio operators. New item: an AM transmitter kit.
P O Box 130
Paradise CA 95967-0130
(send $2 for catalog)
web site: www.panaxis.com
This company provides many interesting books and kits. They offer a
half-watt mono FM transmitter with excellent technical specs, which can
be combined with their stereo generator to build a high-quality low power
station (more than $200 for the two kits). They also have some AM gear.
Panaxis kits might not be suitable for absolute beginners; you should
have some experience in circuit assembly before you tackle these.
P.O. Box 586
Streamwood, IL 60107
web page: http://home1.gte.net/dgagl/progressive/
FM transmitters, antennas, low-pass filters, microphones and audio
mixers, SWR meters, studio to transmitter links, etc.
793 Canning Pkwy
Victor NY 14564
web site: http://www.ramseyelectronics.com
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 enclosures).
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. Several people have posted messages in alt.radio.pirate
indicating that the FM-10A has a problem with frequency drift and must
be adjusted frequently; others have said they do not have this problem.
The FM-25 kit, which has PLL tuning for greater stability, costs about
Ramsey also offers a low-budget AM transmitter and a more expensive
AM transmitter that has PLL frequency control. The cheaper AM-1 kit is
not very good, in my opinion; it tends to drift and the audio quality is
R. Scott Communications
6972 Larkspur Road
web page: http://www.sasquatch.com/~zane/catalog.txt
A source of fully assembled FM transmitters with PLL frequency control
that (according to their catalog) meet FCC and Canadian government
standards, from 20 millwatts to 110 watts. Antennas too. Tech support
by phone; one year parts and labor guarantee.
18 Victoria Street
West Yorkshire BD13 1AR
phone 01274 816200
web site: http://www.legend.co.uk/~veronica/
Antennas, audio processors, and FM transmitters (kits and assembled).
People who've experimented with several brands have reported on the 'net
that Veronica equipment is very well designed.
How do I select a frequency?
Most 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, and FM
stations are spaced at 0.2 MHz intervals, ranging from 88.1, 88.3 ...
to 107.9 MHz. (In Europe, AM stations are spaced at 9 kHz intervals.)
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 navigation and communications.)
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 100-mile radius. You can
get this data from trade publications, or on the web from the
Station Location Page: http://www5.jagunet.com/~kodis/station.html )
Now, sit down with your data and search for an appropriate channel.
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 "first 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 your signal will splatter onto theirs. (An
explanation of splatter is coming up later in this document.)
If there is a TV station broadcasting on channel 6 in your area, it is
unwise to operate on 88.1 or 88.3 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.
What kind of antenna should I use?
The antenna is the most important part of a broadcast station; it has
more effect on signal strength and station safety than any other
Remember that YOUR ANTENNA CAN KILL YOU. Don't put up an antenna in a
place where it could fall onto a power line, or a place where a power
line could fall onto the antenna. Make sure your antenna mast is
properly grounded so that if lightning strikes, the lightning will be
conducted into the ground instead of into you. Falling off of roofs
and ladders can result in injury.
Factory-made antennas are available for the FM band; the 5/8-wave
vertical antenna made by Comet has gotten good reviews on the 'net. If
you need to build an antenna, the J-pole and the half-wave dipole are
good choices, and lots of FM antenna plans are available on the
If you are broadcasting on AM or shortwave, you will probably end up
building your own antenna system. If so, you would be well advised to
get a copy of The ARRL Antenna Book, which is published by the
Amateur Radio Relay League and available from ham radio supply dealers
and Amazon (www.amazon.com).
* quick and dirty antennas
The following types of antennas can be built quickly and cheaply, and
will serve to get you on the air when you first start out. As you
learn more, you will want to upgrade to better antennas.
For shortwave broadcasting, a horizontal dipole works well enough. Cut
two pieces of un-insulated copper wire; the length of each piece will
be 234 feet divided by your frequency in MHz. Example: for 6950 kHz,
each element will be (234/6.950=) 33.7 feet long, and you will need
two trees or other support structures about 67 feet apart. Solder one
element to the center conductor of your coaxial feedline, and solder
the other element to the outer conductor (shield) of the co-ax. (Note:
the solder joints cannot bear the weight of the cable; loop the cable
once over an insulator and provide some "strain relief".) Make a
little loop at the free end of one element, and tie a long piece of
string to that loop. Tie a small, heavy object (such as a lead fishing
weight) to the other end of the string. Throw the weight or use a
slingshot to launch it up into the branches of a tree so that it goes
over a branch and comes back down to earth; then hoist up that half of
your antenna. (Suggestion: don't hit yourself in the head with the
weight.) Repeat the process for the other element.
In AM broadcasting, a vertical section of TV antenna mast, 10 or 20
feet tall, provides a quick antenna.
The center conductor of the coaxial cable from your transmitter is
connected to the bottom of this vertical mast; the base of the mast
sits on an insulator which sits on the ground. If the vertical
radiator is made of several sections of antenna mast, make sure the
sections are electrically connected -- try screwing some self-tapping
sheet metal screws into the joints. Obviously the mast will not stand
up by itself; use nylon rope or other non-metallic materials to
support it. The outer conductor (shield) of the coaxial cable is
connected to a set of "ground radials," which are pieces of copper
wire radiating out from the base of the antenna like spokes from the
hub of a wheel. (The radials are not connected to the vertical
radiator.) The radials can be buried a few inches below the surface
for a permanent installation. "Beware the lawnmower."
This antenna is only a tiny fraction a wavelength high, therefore it
will not be a very efficient radiator. There are ways to improve the
efficiency slightly (loading coils, capacitance hats, etc.) -- study
the ARRL Antenna Book and visit the Medium Wave Alliance web site
( http://www.geocities.com/ResearchTriangle/Lab/1635/equip.html ) for
[For those who use 1 watt or less, the web version of this FAQ
contains a section called "getting every milliwatt to radiate."]
How can I avoid interfering with other signals?
No transmitter puts out a pure signal. In addition to the main
signal, there will be harmonics and spurs. These impurities really
can interfere with other signals. So please, do yourself and your
colleagues a favor and make your signal as clean as possible!
Harmonics are found at multiples of the main frequency. For example,
an FM transmitter tuned to 100.1 MHz will also be emitting weaker
signals at 200.2 MHz, 300.3 MHz, and so forth.
Spurs (called "sprogs" in Britain) occur at unpredictable frequencies.
For example, if your transmitter has PLL tuning and uses a 4 MHz
crystal reference oscillator in the circuit, there might be some
mixing of signals in the circuit and you might find a spur at 4 MHz
above and/or below your main frequency. Spurs are especially
dangerous because it is hard to predict what frequency they will be on
or how powerful they will be. The only way to "see" them is with an
expensive piece of test equipment called a spectrum analyzer. (In
major cities, you may be able to rent a spectrum analyzer, but it
might be better to spend the money on a filter; see below. You can
see spectrum analyzer displays of some low power FM transmitters'
spurs and harmonics on the DSchmidt Technologies web pages.)
There is no way to completely eliminate spurs and harmonics; they are
a fact of life in radio-frequency circuits. Broadcasters have an
obligation to reduce the intensity of these "spectral impurities" so
that they do not have any effect on the rest of the world.
One step you can take is to install an external lowpass filter or
bandpass filter between your transmitter and antenna. If you're
transmitting with more than half a watt of power, you should do this.
A lowpass filter allows signals below a certain frequency to pass
through, but frequencies above that cutoff point are reduced in
intensity; the amount of reduction increases as the frequency gets
farther from the cutoff point. A bandpass filter reduces the
intensity of signals above and below its frequency range.
Splatter is another form of interference. When you try to tune in a
station and you hear some hissing and harsh sputtery noises from
another station on a near-by frequency, that's splatter. Splatter has
a variety of causes including excessively high level of audio fed to
the transmitter (over-modulation) and poor choice of operating
Splatter is also more of a problem in areas close to one of the
transmitters, where that rig's signal is much stronger than the one
being splattered on (the splatter-ee). This is why it's not a good
idea to operate a pirate station with more than 1 or 2 watts of power
in the middle of a densely populated neighborhood. Many of the
complaints that caused the authorities to attack free radio stations
in 1997 were inspired by splatter onto second adjacent channels. For
example, an unlicensed station on 99.1 in Tampa, Florida splattered
onto a licensed station on 99.5 MHz. Several people in the
neighborhood of the unlicensed station's transmitter complained when
they were unable to hear coverage of a football game on 99.5 one
[The web version of this FAQ also discusses images, co-channel
interference, and RF feedback in audio gear.]
How can I take phone calls on the air?
The question of getting phone audio on the air was raised in
alt.radio.pirate in September, 1997. The following suggestions
DJ Bryce wrote: "Your best bet is the Radio Shack speaker-phone box.
Its easy to use, simple to install and is a good cheap interface.
Just tap off the speaker leads... and if you want to, pick up their
1:1 transformer for a buck or two, and that will clean up any hum or
buzz. It works for many a commercial station that can't afford a
Gentner or Telos."
Bungalow Bill wrote: "My scanner will scan the 49 MHz range, where
cordless phones operate. It has a headphone jack in the back of it,
so I bought a simple patch cable that just takes 1/8 inch to 1/4 inch.
Then I plug in the cordless phone, and tune the scanner to its
frequency. When someone calls in, just up the volume on the mixer,
and they're on! Simple, and elegant."
How can I avoid getting `busted'?
The easiest way to avoid a clash with the authorities is to stay under
the power limit for unlicensed broadcasts. If you exceed that limit
for some reason, you will probably get busted sooner or later, unless
you lose interest and quit broadcasting first.
* the hunter's tools
When the authorities get around to sending one of their direction-
finding (DF) vehicles into your area, it's easy for them to find your
transmitter. Disguising your antenna or telling lies about your
location on the air will not help you. Modern DF equipment quickly
and efficiently leads the authorities directly to the source of your
signal. Many broadcast engineers, ham radio operators, and avid radio
listeners are also equipped with DF gear or have figured out ways to
find transmitters by using receivers that have fairly directional
antennas on them. For less than $400, you too can buy your very own
DF equipment. ( http://www.agrelo.com/dfjr.html )
* guerilla tactics
Many people in the new microbroadcasting movement in the US frown on
guerilla broadcasting tactics. They advocate broadcasting 24 hours a
day with relatively high power levels from publicized locations, as a
form of civil disobedience and a way to give legitimacy to the
movement. They hope that a growing number of stations operating in
this manner will inspire public support for microbroadcasting and will
pressure the government into changing the regulations. So far, the
government has responded to this "pressure" by forcibly confiscating
transmitters from several of the more defiant stations. I think the
microbroadcasting movement has over-estimated the amount of pressure a
small group of people can put on a large government. Broadcasters who
want to remain on the air rather than becoming martyrs for the
movement might be well-advised to consider some guerilla tactics.
Some "pirates" in Europe have used the following approach to avoiding
the authorities: they put a battery pack, a transmitter, and a taped
program on a roof-top or hill-top and leave it unattended during the
broadcast. If the authorities find the transmitter, they cannot jail
or fine the broadcaster -- unless they catch him when he comes back to
retrieve his equipment, or find his fingerprints on the gear.
Technically adept broadcasters have used timers to turn the
transmitters on and off when the station personnel are at a safe
distance, and have wired up motion detectors to turn off the
transmitters when people get near them.
Transmitting from locations that cannot easily be reached by the DF
vehicles (islands, boats, forests, etc.) may also hold some promise.
People have experimented with broadcasting from moving vehicles.
Transmitting from a location where nobody can approach you without
being seen will work, but the broadcaster must constantly keep a
In major US cities where the broadcast bands are very crowded,
unlicensed stations have set up informal agreements by which they
share the few available channels. One station will operate on a
channel on Friday nights, another will take it on Sunday afternoons,
and so forth. This strategy has the side-effect of giving a little
protection to the stations involved. The authorities would have to
keep a DF vehicle in the area for an entire week or two if they wanted
to track down all the stations using a frequency. Depending on what
else they have on their agenda, they might not be able to invest that
* being busted
So, what happens if the authorities catch an unlawful broadcaster?
Like everything, it varies from country to country. In China, they
probably shoot the broadcaster and bill his family for the bullet.
In the US, the process normally (but not always) goes like this: The
FCC becomes aware of a station. Two or three agents in a DF vehicle
track down the station and measure the signal strength near the
transmit antenna. Then they knock on the door and ask to inspect the
station. If allowed in, they will attempt to get the station
operator's identity, they will demand that the station be turned off,
and they will ask that the transmitter be surrendered. (Often they
will claim that no further action will be taken if the transmitter is
handed over, but actually the field agents do not make that decision,
and people who have given up their transmitters have sometimes been
fined and prosecuted later.) If not allowed entry, the agents will
angrily storm off, threatening to come back with a warrant. It might
take them several hours or even several weeks to get the warrant, but
they will be back.
It is very important to the FCC that they get the operator's identity.
Their entire legal strategy depends on having a person's name so that
they can extract a fine from him and request a permanent injunction
against him, and they usually assume that a station is operated by a
single person. They will use any means they can to get a name:
license plates on vehicles, property ownership records, receipts in
the trash can, whatever.
A station that is actually being operated by several people can
survive a bust simply by moving to another site and being run by the
surviving (non-busted) members of the group. When that happens, the
FCC has to start its investigation all over again. Unfortunately many
stations that claim to be operated by community groups are actually
dependant on one pivotal person. If the authorities manage to
neutralize that person the station will go silent forever.
After "inspecting" a station, the FCC usually mails the operator a
Notice of Apparent Liability indicating how large a fine is owed
(usually $750 to $11,000). In many cases the FCC will also go to
court and get a permanent injunction against the station operator,
which can lead to draconian enforcement measures against him if he
continues to broadcast. And frequently they come back later with
federal marshals or local cops and forcibly confiscate the transmitter
and other equipment.
Where can I get more information?
Introductory electronics textbooks are available at most bookstores
and libraries. Magazines such as Popular Electronics
( http://www.gernsback.com/pe/pe-index.html ) and Monitoring Times
( http://www.grove.net/ ) sometimes carry relevant articles and
http://burn.ucsd.edu/~mai/pirate_kiosk.html contains a bit of
philosophy and a list of links. The FRN web site (www.frn.net) contains
a wealth of articles plus a message board, real-time chat, and several
large lists of web links. Andrew Yoder's books and magazine are
advertised on the Radio Free Internet pages ( http://www.frn.net/rfi )
An interesting college thesis about unlicensed broadcasting is
at http://www.cruzio.com/~rogue/thesis.html It contains a detailed
analysis of the FCC's procedures of enforcement and identifies some
potential weak links in their legal chain. It also gives great
perspective on the 70-year history of the struggle between free radio
and the authorities.
The following Usenet newsgroups contain useful data once in a while:
= end =