diy
Low Power Broadcasting FAQ (Frequently Asked Questions)
---
From: raredata@geocities.com (R. Harrison)
Newsgroups: alt.radio.pirate,alt.answers,news.answers
Subject: Low Power Broadcasting FAQ (Frequently Asked Questions)
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Followup-To: poster
Date: 23 Jun 1998 12:08:48 GMT
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Expires: 21 Jul 1998 11:49:30 GMT
Message-ID:
X-Last-Updated: 1997/12/31
Archive-name: radio/broadcasting/low-power-faq
Posting-frequency: biweekly
Last-modified: 1997.12.31
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
http://www.geocities.com/Athens/5383/lowpower.html
-------------------------------
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.
* footnotes
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
in feet.
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
serve.
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
transmitter kits.
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:
http://www.epemag.wimborne.co.uk/solderfaq.htm
http://surf.pangea.ca/~rmiller/solder.html
http://www-sgc.colorado.edu/itll/uvsoder.html
* sources of transmitters:
ABC FM
web page: http://indigo.ie/~alinton/rigindex.htm
e-mail: ndls@bigfoot.com
This company sells low power FM exciters, stereo coders, and
RF amps. Apparently located in Ireland.
---
DC Electronics
P O Box 3203
Scottsdale AZ 85271
phone 800-423-0070
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
antenna kits.
---
DSchmidt Technologies
191 Madera Ave
Ventura, CA 93003
fax 805-676-1092
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
radio links.
---
L.D. Brewer
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.
---
LPB Inc.
28 Bacton Hill Road
Frazer PA 19355
phone 610-644-1123
fax 610-644-8651
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
Wykagyl Station
New Rochelle, NY 10804-0053
phone 914-235-6611
fax 914-576-6051
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.
---
Panaxis Productions
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.
---
Progressive Concepts
P.O. Box 586
Streamwood, IL 60107
phone 630-736-9822
fax 630-736-0353
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.
---
Ramsey Electronics
793 Canning Pkwy
Victor NY 14564
phone 716-924-4560
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
$130.
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
poor.
---
R. Scott Communications
6972 Larkspur Road
Sooke, B.C.
Canada, VOS-1NO
phone 250-642-2859
fax 250-642-7742
e-mail: kscott@pinc.com
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.
---
Veronica FM
18 Victoria Street
Bradford
West Yorkshire BD13 1AR
United Kingdom
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
component.
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
world-wide web.
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.
shortwave
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.
AM
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
more information.
[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
frequency.
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
weekend.
[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
were given:
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
lookout.
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
much time.
* 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
interesting advertisements.
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:
alt.radio.pirate
rec.radio.amateur.antenna
rec.radio.broadcasting
= end =
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From: hrick@gate.net (Rick Harrison)
Newsgroups: alt.radio.pirate
Subject: Low Power Broadcasting FAQ
Date: 3 Jan 1996 02:09:24 -0500
Organization: CyberGate, Inc.
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Archive-name: radio/broadcasting/low-power-faq
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Last-modified: 1995.12.05
Low Power Broadcasting FAQ (Frequently Asked Questions)
contents:
[1] What equipment do I need to start a station?
[2] Is low power broadcasting legal?
[3] How much power do I need?
[4] Where can I get a transmitter?
[5] What kind of antenna should I use?
[6] How do I select a frequency?
[7] Where can I get more information?
----------------------------------------------------------------------
[1] 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.
When you are selecting audio equipment, try to get items that have
metal cases (not plastic or wood) and three-prong grounded electrical
plugs. This will reduce your chances of having problems with radio
energy from your transmitter getting into your audio gear and causing
interference.
The most important item for a low power broadcaster is the _raison_
_d'etre_, the reason for existing. You won't have a high power
signal, and you won't have billboards and TV commercials announcing
the existence of your station, so listeners will have to put some
effort into finding and receiving your signal. They probably won't
make the effort unless you are offering something unique and
interesting.
------------------------------
[2] Is low power broadcasting legal?
This depends on what country you are in. Here in the United States,
legal unlicensed broadcasting is limited to microscopic power levels.
For example, the 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.
Violators who get caught are usually given a monetary fine, and
sometimes their equipment is confiscated. The situation varies from
country to country.
------------------------------
[3] How much power do I need?
There is no simple answer to this question. For starters, it depends
on whether you are broadcasting on the AM (medium wave) band, the FM
band, the international shortwave bands, or TV. In order to reduce
interference to other radio services, it is always a good idea to use
the lowest amount of power that will serve your target audience.
Newbies often want to know how much territory they can cover with a given
antenna configuration and amount of power. I have added this section on
predicting coverage in response to their shrill, strident queries...
On FM and TV 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. (It is possible for FM and TV signals to
travel greater distances by means of phenomena such as sporadic E-layer
skip and tropospheric ducting; however, these propagation modes are
intermittent, and are more likely to work for higher-power signals than
for relatively low power broadcasters.)
If you know the amount of power being accepted by your antenna (i.e. the
transmitter output power, minus losses due to attenuation in the feedline,
minus losses due to impedance mis-matches), then you can use the following
BASIC program to calculate what the "free space" field strength would be
at any given distance from your antenna (the program assumes you are using
a half-wave dipole). "Real world" field strengths are likely to be lower
than "free space" (theoretical) calculations...
100 INPUT "power accepted by antenna (in watts)"; PT
110 INPUT "distance (in miles)"; M
120 R = M * 1609
130 E = (30 * PT) ^ .5
140 E = E / R * 1000
150 D = E * 1.28
160 IF D < 100 THEN D = INT(D * 1000) / 1000
170 PRINT "free space field strength" D "millivolts per meter"
180 END
What's a useful field strength? In the US, FM stations must provide at
least 3 millivolts per meter in their primary coverage area. Even the
cheapest receivers will pick up a signal having 1 millivolt per meter of
intensity. A fancy receiver with a good antenna can pick up a signal as
weak as .001 millivolt per meter, but reception will be noisy; and very
few listeners will tolerate any kind of static or fuzzy reception.
Okay, so much for FM. Signals in the AM broadcast band generally travel
by ground-wave (following the surface of the earth) in the daytime; at
night, the signals can also reflect from a layer of the upper atmosphere
and travel great distances. The range of your ground-wave signal will
depend on your power level, the effectiveness of your antenna system, and
the moisture and mineral content of the soil in your part of the world, as
well as the frequency you have chosen -- lower frequencies have better
ground-wave propagation.
On the shortwave broadcast bands, propagation is usually accomplished by
skipping the signal off the ionosphere; the angle at which the power
radiates from your antenna will determine how far away the first "hop"
will be. A dipole antenna's height above electrical ground will influence
its angle of radiation; see the _ARRL_Antenna_Book_ for more info.
------------------------------
[4] Where can I get a transmitter?
Below is a brief list of companies selling low power transmitter kits.
Please send me information about any companies not listed, so that I
can include them in future versions of this list.
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, $14.95) might be especially helpful to newbies.
When assembling radio circuit kits, I prefer to use narrow-diameter
silver-bearing solder (Radio Shack #64-013) and a 15 watt soldering
iron. You will need a more powerful soldering tool for making
antennas out of large-diameter wire, soldering really large connectors
to a printed circuit board, etc., but the 15 watt iron works fine for
assembling most kits and reduces the chances of over-heating
transistors and other heat-sensitive components.
a word about the BA1404 chip:
Many of the FM kits listed below use Rohm's BA1404 integrated circuit,
which is esentially an FM transmitter in a single 18-pin chip. The
BA1404 has some limitations in sound quality. The separation between
the left and right channels and the overall audio distortion are not
up to "broadcast standards." To get a clear idea of how bad it is,
obtain a studio reference CD (a.k.a. audio system test CD) that has a
"sweep" on it -- a sweep is a tone that steadily rises in pitch from
very low to very high -- and play the sweep through any BA1404-based
transmitter, while listening on a high-quality receiver. Blecccch!
------ sources of AM, FM, and TV 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 for the
BA1404 which improves stability.
Compared to Ramsey's FM-10A, the Stereocaster doesn't drift as much,
and I think the audio quality is slightly better; however the assembly
instructions are not as clear as Ramsey's, the PC board layout is not
as elegant, and Ramsey's circuit puts out a little more power.
-----
Free Radio Berkeley
1442 A Walnut St., #406
Berkeley, CA 94709
phone 510-464-3041
Items listed in their ads include a 5 watt mono FM transmitter kit
($55 plus shipping), a 1/2 to 1 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.
FRB is spear-heading an organized challenge to the FCC's regulations
and is trying to foster a low power broadcasting movement. Contact
them for more info. (Internet: frbspd@crl.com)
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.
-----
North Country Radio
PO Box 53, Wykagyl Station
New Rochelle NY 10804-0053
phone 914-235-6611
(send $1 for catalog)
Many TV-related items: a 50 milliwatt UHF transmitter with crystal
controlled frequency ($78); a "video pallete" to create special
effects; a switcher that does cross-fades and wipes; and upconverters
that will take channel 3 video from a VCR and shift its frequency up
to any UHF channel 25 thru 70. For licensed radio amateurs, they have
a line of more powerful UHF TV transmitters.
With a 100-foot range and a price of $62.50, their FM stereo trans-
mitter is not exactly competitive, but it is interesting from a
technical point of view. Their stereo infrared transmitter and
receiver could be used to build a difficult-to-trace studio-to-
transmitter link.
-----
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 REB-1 kit is
a 100 milliwatt transmitter for the upper end of the AM band ($34.95
plus shipping). 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 (> $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.
-----
Progressive Concepts
1434 N. Mills Ave.
Claremont CA 91711
RF amplifiers, FM transmitters and stereo generators, components for RF
circuits, high-quality antennas for low-power FM broadcasters, and more.
-----
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 company has just introduced the FM-25 kit, which has PLL
tuning for greater frequency stability; the cost is about $129.
Unfortunately, the audio section of the FM-25 is identical to the
FM-10A; it uses a BA1404 with inadequate RF bypassing.
In a message dated 19 May 1995 15:46:14 GMT, William Conkright suggested
the following modifications for the FM25 circuit:
> First replace the .01 bypass caps with .001 's . The .01s cause
> unstability and are too high in value for this frequency. 2) carefully
> check the 2sc xstr for the first rf buffer. I have found that I needed
> to use a 47k resis vs 10k res here. The 10K saturated, turned on the
> xstr too hard. [...] Replace the 2 47 pf caps used around the 4 Mhz
> ref osc, with mini ceramic pc mount 2-50 pf trimmers avail from DC
> Electronics, Scottsdale AZ. They enable one to fine tune the ref osc, so
> that you can get an exact (down to the 10 hz) range setting for your freq.
Their AM transmitter kit (item #AM-1, $29.95) and their TV transmitter
kit (item #TV-6, $27.95) might also be of interest; however, there is
much room for improvement in the design of these two circuits.
(Robert Myers of Ramsey Electronics tells me they do intend to release
an improved version of the AM-1 kit at some point in the future.)
-----
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.
-----
Supercircuits
13552 Research Blvd
Austin TX 78750
A source of low-power TV transmitter kits and miniature cameras.
-----
Veronica FM
18 Victoria Street
Bradford
West Yorkshire BD13 1AR
United Kingdom
phone 01274 816200
Antennas, audio processors, and transmitters (fully assembled; no kits).
-----
Xandi Electronics
Box 25647
Tempe AZ 85285
phone 800-336-7389 / 602-894-0992
The XFS108 kit ($41.95) is an FM stereo transmitter, probably based on
the BA1404. Their advertisements give no specifics.
-----
In a message dated Nov 08 06:01:55 EST 1994, an22190@anon.penet.fi wrote:
>There is a company called "Spectrum Communications" in Dorchester England
>that sells fm transmitters and associated gear. A transmitter tunable from
>88-108Mhz (part CTX100V) with output of 0.5Watt is available for 135 pounds.
>This unit is synthesised. ... The phone number is 0305-262250.
-----
sources of shortwave transmitters:
Shortwave pirates generally use "ham" radio gear that was designed for
licensed radio amateurs. Used vacuum-tube transmitters from the 1945
to 1975 era are sold at swapmeets and hamfests; certain types are
suitable for broadcasting music and speech. (The Viking Challenger is
especially popular for this purpose.)
------------------------------
[5] What kind of antenna should I use?
Antenna theory, design and construction is a very complex topic. If
you really want to understand antennas, I recommend that you buy a
copy of _The_ARRL_Antenna_Book_ (published by ARRL, 225 Main St.,
Newington CT 06111 USA). It is a large book and you might have to
spend several weeks studying it before it all begins to make sense.
Assuming you want to get on the air in a hurry, and then build a
better antenna system later on, I will describe the quickest and
simplest options available. The systems described here are all less
than optimum, but they will get you on the air pronto.
WARNING: There are several ways you can get killed or injured while
putting up an antenna. Never get within 10 feet of a power line, and
never mount an antenna where it could possibly fall onto a power line,
or where a power line could fall onto the antenna. Avoid falling off
of roofs and ladders. Permanent outdoor antennas must be provided with
a ground rod so that lightning, if it happens to strike, will go into
the ground instead of into your equipment and your body.
For FM broadcasting, try Radio Shack's omni-directional FM antenna
(catalog #15-2164, price $12.99). Don't forget the 75-to-300 ohm
impedance matching transformer (#15-1140 or 15-1143). (A 50-to-300
ohm transformer would be better, but you won't find those at Radio
Shack.) This antenna can be mounted on a typical TV antenna mast, or
a chimney, or hidden in the attic. Best results will be obtained when
it's outdoors, away from trees and other objects, and mounted several
feet higher than the rooftops in your neighborhood.
In AM broadcasting, a vertical section of TV antenna mast, 10 or 20
feet long/high, makes a decent 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. 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."
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 7385
kHz, each element will be (234/7.385 =) 31.7 feet long, and you will
need two trees or other support structures about 63 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 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.
Repeat the process for the other element.
------------------------------
[6] 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 1600. (Some Travellers
Information Stations are licensed on 530, 1610, and 1620. The
channels 1610 through 1700 may soon be allocated to broadcast
stations.) In some other countries, AM stations are spaced at 9 kHz
intervals. 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 allocated to 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
there.
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. In some areas where the authorities have
foolishly licensed both a channel 6 and a low-edge FM station, the
stations often have to go to great lengths to deal with interference
complaints.
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.
Any other transmitter in your immediate neighborhood, whether it's a
cellular telephone system, an AM or FM broadcaster, or any other
service, might interact with your transmitter in unexpected,
interference-causing ways. So, do some testing with a variety of
receivers (including cheap junk) before you make a final decision on
your frequency. In many major cities where the FM band is quite
crowded, you will find a few conspicuous empty channels; in some
cases, these channels have been kept unused (or had to be evacuated)
because of interference problems caused by signals mixing together at
the transmitters or in people's receivers.
*How to define "often audible" is a matter of debate; opponents of
radio freedom say that _every_ channel is occupied by a distant
station that some DXer might be able to hear with his 50-foot
antenna tower and $1,000 radio.
------------------------------
[7] Where can I get more information?
Introductory electronics textbooks are available at most bookstores
and libraries. Magazines such as Electronics Now, Popular
Electronics, 73, QST, Communications Quarterly, 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. The ACE, a monthly newsletter,
covers shortwave pirates well and occasionally contains data useful to
AM and FM broadcasters (send $2 for a sample copy to Box 11201,
Shawnee Mission KS 66207).
Keep an eye on these Usenet newsgroups:
alt.radio.pirate
rec.radio.broadcasting
rec.radio.amateur.antenna
Files of some relevance are available for ftp from these sites:
site directory filename
==== ========= ========
crl.com /users/ro/frbspd (several)
dg-rtp.dg.com /fm10 FM10-FAQ (& others)
world wide web --> http://www.crl.com/~clark/mycal/
----------------------------------------------------------------------
This text is copyright 1994-95 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.
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