Internet Info 1997 December/Internet_Info_CD-ROM_Walnut_Creek_December_1997.iso/faqs/alt/radio/pirate/low_power_broadcasting_FAQ

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From: [e-mail] (Rick Harrison)
Newsgroups: alt.radio.pirate,alt.answers
Subject: low power broadcasting FAQ
Date: Wed, 24 Sep 1997 21:59:29 -0500
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Last-modified: 1997.09.24

Low Power Broadcasting FAQ (Frequently Asked Questions)

A longer, illustrated version of this document is available on the
web at http://www.geocities.com/Athens/5383/lowpower.html
Those of you who still have the old (magicnet.net) URL on your web
pages, please update your links!
á
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[1] 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. These stations are often short-lived, sometimes
portable, and often unpredictable.
á
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[2] 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.

Here 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 200 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.

-----------------------------------


[3] 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. For television, you will
need video sources (cameras, videotape players, character generators,
etc.), a video switcher, plus a transmitter and an antenna system.
á
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[4] How much territory can my signal cover?

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 sensitivity of the listener's receiver

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.

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.

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.

Now that you know the upper limit on your range resulting from your
antenna height, can you calculate how strong your signal will be at a
certain distance from the antenna? Not very easily. The following
formula predicts the strength of a signal in free space at a given
distance from an isotropic transmitting antenna. "Free space" is a
theoretical world in which nothing exists except for the transmit
antenna and the receive antenna. An "isotropic" antenna is one that
radiates equal amounts of power in all directions; in other words, it
has a spherical radiation pattern, kind of like the sun radiating light
into space in all directions. The formula is:

E=((30*Pt)^0.5)/R
where E = field strength (in volts per meter),
Pt = power accepted by the transmit antenna (in watts),
R = distance (in meters)

Let's put the formula to work for us. The table below gives free space
field strengths for various power levels at a distance of 1 mile and 5
miles. Signal field strength is expressed in units called millivolts per
meter (mV/m).
á
power           field strength (mV/m)
(in watts)     at 1 mile    at 5 miles
  ---          ---------    ----------
  100            34.0          6.8
   50            24.1          4.8
   10            10.8          2.2
    5             7.6          1.5
    1             3.4          0.68
    0.5           2.4          0.48

Typical car radios and home stereos need a signal strength of about 1
mV/m to give good reception with an acceptable signal-to-noise ratio.
Cheap portable radios require a much stronger signal. Judging by the
table above, a 1/2 watt transmitter connected to an isotropic antenna
would provide a range of more than 1 mile for typical receivers; we
would have to increase the power to 10 watts if we wanted to have a
similar field strength at a distance of 5 miles.

Fortunately, antennas designed for broadcasting use the transmitter
power more efficiently than an isotropic antenna. An isotropic radiator
would send equal amounts of power up into the sky, down into the ground,
and out toward the horizon. A good FM or TV broadcasting antenna focuses
the energy toward the horizon and does not shoot a lot of energy up into
space. As a result, you can get better results than the formula
predicts, depending on the quality of your antenna system.

If your transmitter is located in an area where people live, improving
your antenna system is always a better idea than increasing your power.
Using a high power transmitter in a residential neighborhood is likely
to interfere with radio and TV receivers in the area. Even if your
signal is technically "clean" (minimal spurs and harmonics), it can
overwhelm receivers in the vicinity (through front-end overload). If you
interfere with people's radio and TV reception, some of them will
complain to the authorities.

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[5] Where can I get a transmitter?

Below is a brief list of companies selling low power transmitters and
transmitter kits.

***

DC Electronics
P O Box 3203
Scottsdale AZ 85271
phone [phone]

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.

***

The L D Brewer company (http://www.ldbrewer.com) 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. (L D Brewer is the best
source of the Free Radio Berkeley kits; many people who have ordered
directly from Free Radio Berkeley have waited a very long time for their
orders to arrive.)  FM only; nothing for low power AM, SW, or TV
broadcasters.

***

Since 1960, LPB Inc. (http://members.aol.com/lpbinc/) 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 law-breakers; in fact, they have supported the
NAB's campaign to persecute unlicensed broadcasters.

***

Panaxis Productions
P O Box 130
Paradise CA 95967-0130
(send $2 for catalog)
web site: www.panaxis.com

This company offers 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). Panaxis kits might not
be suitable for absolute beginners; you should have some experience in
circuit assembly before you tackle these.

***

Progressive Concepts
phone [phone]
fax [phone]
web site: http://home1.gte.net/dgagl/progressive/

RF amplifiers, FM transmitters and stereo generators, components for RF
circuits, high-quality antennas for low-power FM broadcasters, and more.
FM only; nothing for low power AM, SW, or TV broadcasters.

***

Ramsey Electronics
793 Canning Pkwy
Victor NY 14564
phone [phone]
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 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 $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, IMHO; it tends to drift and the audio quality is mediocre.

***

Scott Communications
6974 Larkspur Rd. RR-3
Sooke, B.C., Canada VOS-1NO
phone [phone]
e-mail: [e-mail]

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.

***

Veronica FM
18 Victoria Street
Bradford
West Yorkshire BD13 1AR
United Kingdom
phone [phone]
web site: http://www.legend.co.uk/~veronica/

Antennas, audio processors, and FM transmitters (kits and assembled).
FM only; nothing for low power AM, SW, or TV broadcasters.
á
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[6] 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. FM stations are
spaced at 0.2 MHz intervals, ranging from 88.1, 88.3 ... to 107.9 MHz.

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 get this data from
trade publications such as the Broadcasting Yearbook or on the web from
the Broadcast Station Location Page.)

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).

In some major cities, there is no room in the FM band for any more
signals. In this situation, you might find that a low-budget station in
the area goes off the air between midnight and 6 a.m. and you can use
their channel during those hours. (Many college stations sign off early
during major holidays and the summer months.) Otherwise, you might
consider broadcasting in the AM band, even though it is not as trendy
and fashionable as FM.
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[7] 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 try to 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 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 is a good choice, and lots of
FM J-pole plans are available on the 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.
á
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[8] How can I avoid getting `busted'?

The easiest way to avoid a clash with the authorities is to obey the
rules. If you are not able to do so for some reason, it is likely that
you will eventually get busted, unless you lose interest and quit
broadcasting first. When the authorities get around to sending one of
their direction-finding vehicles into your area, it is a simple matter
for them to find your transmitter, especially if you are operating from
a fixed location. Just to give you a hint of how easy it is, I myself
have located the home bases of two low-power stations in my town using
only a hand-held radio that has a signal strength meter on it.

Some "pirates" in Europe have used the following approach: 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. Some observers believe
that operating a mobile station (in a car or van that is on the move
during the entire broadcast) would make matters more difficult for
the authorities, but few (if any) low power broadcasters have done this.

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[9] Where can I get more information?

Relevant world wide web sites:

http://www.frn.net contains a wealth of articles plus a message board
and real-time chat.

http://www.rootsworld.com/rw/feature/rrb.html is the home of the Free
Radio Press.

The following Usenet newsgroups contain useful data once in a while:

alt.radio.pirate
rec.radio.amateur.antenna
rec.radio.broadcasting

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This document is copyright 1994-97 by Rick Harrison.