From: fybush@world.std.com (Scott Fybush)
Subject: Welcome to AM/FM DXing (FAQ - File)
Originator: wdp@gagme
Organization: Internet Radio Journal
Date: Mon, 11 Jan 1993 08:58:52 GMT


INTRODUCTION TO AM/FM DXing

By Scott Fybush

One of the easiest parts of the radio spectrum to explore is the
broadcast bands.  This posting will attempt to offer some hints to
make your exploration of the medium wave and VHF-FM bands more
enjoyable.

I. WHAT ARE THE AM/FM BROADCAST BANDS?

The medium wave (commonly referred to as AM) broadcast band currently
extends from 525 to 1605 kilohertz.  Channels are spaced in even 10
kHz increments; i.e.: 530, 540, 550, ... , 1600 kHz in the United
States and Canada.  Elsewhere, channels are generally spaced in 9 kHz
increments, i.e.: 531, 540, 549, etc.  In the United States, plans are
underway to expand the band to 1705 kHz.  Within a few years, stations
will begin appearing on the 1610-1700 kHz frequencies.

The FM broadcast band in the United States extends from 88 to 108
megahertz.  Channels are assigned at 200 kHz increments; i.e.: 88.1,
88.3, 88.5, ... , 107.9.  The channels from 88.1 to 91.9 are reserved
for noncommercial educational stations.  Outside the United States and
Canada, the boundaries and channel spacing vary.  In Japan, the band
starts at 76 MHz.  In Western Europe, the band runs from 88-108 MHz,
but channels can be irregularly spaced, i.e.: 101.25 MHz.

II. SIGNAL PROPAGATION

The distant stations you are able to receive will depend largely upon
signal propagation.  This varies depending upon the time of day, the
season, and other factors.  For medium-wave, the single most important
factor for good DX is the time of day.  Medium-wave signals pass
through the ionosphere during daylight hours and are lost to space.
As a result, all medium-wave signals received during daylight hours
will arrive by ground wave.  Reception of signals over a few hundred
miles away is generally impossible in daylight.  At night, however,
the ionosphere reflects medium-wave signals, making it possible for
signals to be heard at much greater distances, up to a few thousand
miles.  Reception also tends to be better in winter than in summer.
Many smaller medium-wave stations are required to sign off or reduce
power sharply at sunset so as to reduce interference to distant
stations.

For FM, daylight is unimportant.  FM signals generally carry no more
than 150-200 miles even under the best conditions.  Since the
ionosphere generally does not reflect VHF FM signals, such signals
must travel line-of-sight to reach the receiving antenna.  FM
transmitting antennas are thus usually located as high as possible.
Tall towers, high buildings, and mountaintops are common FM
transmission sites.  Under certain conditions, the E layer of the
ionosphere will reflect VHF FM signals, thus making it possible to
receive extremely long-distance FM reception.  This is almost
impossible to predict, however.

III. RECEIVERS

Almost any radio is capable of some broadcast-band DXing, especially
long-distance medium-wave reception.  However, most recent radios,
even those designed for quality shortwave reception, do not have
outstanding broadcast band reception.  One exception is the General
Electric SuperRadio II (Model No. 7-2885F.)  The SR II is designed for
optimum AM/FM broadcast performance, incorporating:

* RF amplifiers on both bands
* Ceramic filters and Automatic Frequency Control on FM
* An analog tuner with an IC-type receiver chip and air-variable
capacitors.
* No PLLs or digital displays for less electronic noise.
* A 2-way speaker system with 1 watt of audio power.

The SR II is a bulky (4" x 10" x 12") portable radio which can be run
off 120V AC or 6 "D" batteries, providinover 400 hours of battery
life.  The styling is cheap silver and black plastic, and has been
described as ugly.  Nevertheless, this radio has become popular among
the DX community for its exceptional performance.

It costs between thirty and sixty dollars in the US, and may be found
at many discount outlets.  It is generally back-ordered by mail, but
can be obtained from Bennett Brothers (Order #R8883) at 1-800-621-2626
or 1-800-631-3838, or from Best Products (Order # 140457) at
1-800-950-2398.

With the sale of GE's consumer electronics division to Thomson, this
product's future remains in the air.

If you don't have a SuperRadio, some important things to seek out in a
receiver are:

* External antenna connections.  These make it easier to use a better
antenna than the one supplied with the radio.

* High selectivity.  This refers to the receiver's ability to reject
strong signals on adjacent frequencies, and is more important to good
reception than is sensitivity, since a good antenna will provide
more-than-adequate signal strengths.

* Digital frequency display.  While the circuitry involved does add to
the level of internal electronic noise in the radio, digital display
makes it possible to more easily determine what station is being
heard.

IV. ANTENNAS

For medium-wave reception, most receivers have a short internal
ferrite rod.  This will provide acceptable signals for high-powered
distant stations.  The ferrite rod tends to be quite directional, and
the radio can thus be turned to null out strong interfering signals,
or to improve reception of the desired signal.

For more advanced DXing, an external antenna is a must.  The easiest
external antenna is a simple longwire, 50 feet or more run out the
window and then as high as possible (up in a tree, for example.)  The
wire can be connected to the external antenna terminal.  If none
exists, you can open up the radio and wrap the wire a few turns around
the ferrite rod inside.  It is also possible, although less desirable,
to simply wrap the wire around the entire radio.  If the radio has a
terminal marked "ground" or "GND," another wire can be run from this
terminal to a copper rod driven a few feet into the earth.

A more advanced antenna is the "beverage" antenna.  This is a length
of wire 1000 feet or more.  It is terminated at the far end with a 450
ohm resistor connected to a metal stake driven into the ground.  It
should be pointed in the direction of the desired station.  The
beverage antenna can, under good conditions, be used for transatlantic
and transpacific DX.  Another more advanced antenna is the loop, a
four-foot wooden frame with about 20 turns of wire run around it.  It
is connected to the radio with a 365 pF variable capacitor for tuning.
The loop is extremely directional.

For FM, the important factor is height.  The higher one can place an
antenna, the better reception will be.  A multielement Yagi antenna,
which can be found in Radio Shack or similar stores, will often
produce excellent reception.  Since a yagi is quite directional, the
use of a rotor is essential for reception of stations in different
directions. 

V. WHAT'S OUT THERE TO LISTEN TO?

There are over 10,000 radio stations in the United States alone.  It's
important to have some idea of what to expect to hear.  A good
directory is important (see STATION LISTINGS below), but it's
essential to know what the station information means.

For medium-wave, US frequencies fall into three basic classes:

* CLEAR CHANNEL: These frequencies are 540, 640, 650, 660, 670, 680, 690,
700, 710, 720, 730, 740, 750, 760, 770, 780, 800, 810, 820, 830, 840,
850, 860, 870, 880, 890, 900, 940, 990, 1000, 1010, 1020, 1030, 1040,
1050, 1060, 1070, 1080, 1090, 1100, 1110, 1120, 1130, 1140, 1160,
1170, 1180, 1190, 1200, 1210, 1220, 1500, 1510, 1520, 1530, 1540,
1550, 1560, 1570, and 1580 kHz.  Clear channels are home to one or two
50,000 watt powerhouse signals which can be heard reliably in half the
country or more.  Other stations on clear channels usually sign off at
sunset or reduce their power considerably.   In recent years, the FCC
has added many new stations to the clear channels, making reception of
some stations more difficult than it once was.

* LOCAL: These frequencies are 1230, 1240, 1340, 1400, 1450, and 1490
kHz.  Stations on local channels can use a maximum of 1000 watts.  At
night, these six frequencies tend to become chaotic, as the
hundred-plus stations on each channel cause each other tremendous
interference.  Identifying distant stations on these channels requires
a directional antenna, a good ear, and plenty of patience.

* REGIONAL: These are all the remaining channels.  U.S. stations on
these frequencies are restricted to 5000 watts.  While not as noisy as
the locals, reception on regional channels can be difficult.  Most
regional, or class III stations, use directional antennas to reduce
interference with distant stations.

On FM, the American FCC has reduced its restrictions on power and
antenna height considerably.  Today, FM stations are allowed up to
50,000 watts from a 150 meter antenna in the Northeast and California;
100,000 watts from a 610 meter antenna elsewhere.  Many stations,
however, serve much smaller areas.  These "Class A" stations use only
6000 watts or less.  They were formerly restricted to just a few
frequencies: 92.1, 92.7, 93.5, 94.3, 95.3, 95.9, 96.7, 97.7, 98.3,
99.3, 100.1, 100.9, 101.7, 102.3, 103.1, 103.9, 104.9, 105.5, 106.3,
and 107.1 MHz.  While the FCC no longer restricts class A stations to
those frequencies, most are still found there.  Likewise, only a few
of the high-power stations are found on the old class A channels.
For stations with extemely high antenna, the FCC mandates that
transmitter power be reduced proportionately; thus a station with only
430 watts from a 220 meter antenna will reach about as far as a 3000
watt signal from the usual 91 meter antenna will.

VI. STATION LISTINGS

An essential tool for any DXer is a good station listing.  This will
help identify what's being received, as well as provide a way to
contact the station being heard.

For North American stations, one concise and inexpensive directory is
the M Street Radio Directory, published annually.  The M Street
listing includes frequency, power, directionality, format, address,
phone number, and other listings less important to DXing.  M Street
also is indexed by call letter order and by frequency.  The M Street
directory costs $29.95 + p/h.  It can be purchased directly from M
Street at 800-248-4242 or +1 212 473 4668 voice, or +1 212 473 4626
fax.  The address is M Street Corp., 304 Park Ave S Floor 7, New
York, NY 10010 USA.  For FM DXers, the standard guide is Bruce Elving's
annual FM Atlas.  This includes maps showing every FM transmitter in
North America, plus listings by state and frequency indicating power,
stereo status, format, subcarriers, and slogans.  FM Atlas does not
include addresses or phone numbers.  It can be purchased directly
from Bruce Elving, PO Box 336, Esko MN 55733-0336.  It costs
$10.95 + $1.05 p/h.

Other listings include the NRC Log for AM stations and Broadcasting
Yearbook, which is available at some larger libraries.  The Canadian
Almanac and Directory includes call letters, frequency, and addresses
for Canadian stations.

For listings outside North America, consult the World Radio TV
handbook, published annually and available at bookstores or through
radio specialty mail order outlets such as the Radio Collection and
CRB Publishing.

VII. TIPS FOR BEGINNING

The most important element for beginning DXers is to get to know the
dial.  Spend a few hours scanning up and down the dial both during the
day and at night.  At night, the clear-channel 50kw stations should be
easy to hear.  Learn all the local stations.  Find out which ones sign
off at sunset and which stay on all night.  This will affect which
distant stations can be received.  If you have a local station on all
night, you shouldn't expect to hear another station on that frequency.
Experiment with radio placement.  As you turn the radio, observe its
directional characteristics.  

Prepare a log of the stations you've heard, arranged by frequency.
The better you know whatthe dial usually sounds like, the more
prepared you'll be for that unusual catch.

VIII. SOME ADVANCED IDEAS

Once you've mastered the basics, here are some suggestions for areas
of specialty DX:

* QSLing.  Most AM/FM broadcasters aren't used to QSLing.  You'll
probably have to send a letter to the station's chief engineer.
Expect verification in letter form.  Small stations are often excited
to find out they've been heard thousands of miles away.

* DX Tests.  A few stations still run special DX tests.  Some daytime
stations run experimental tests with their daytime power after dark.
Others will assemble special DX programs for distant listeners, often
late Sunday night/Monday morning, when some stations sign off for
maintenance (although not as many as used to do so.)

* Sunrise/sunset DXing.  Interesting medium-wave DX can be had when
your receiving station is in darkness, but a target transmitter is
still in daylight.  It's possible to hear distant daytime-only
stations this way.  This requires a lot of skill, since there may be
only ten or fifteen minutes in which to try.

* FM Subcarriers and Stereo.  FM stations are allowed to transmit
separate programming on a subcarrier.  This requires a special decoder
(the best source is Bruce Elving's FM Atlas; see address above.)
FM stations use their SCA (Secondary Communications Authority)
subcarriers for transmitting data, background music, ethnic
programming, and more.  Some AM stations now transmit in stereo.  With
an AM stereo receiver, you can hear stereo signals from thousands of
miles away.

* Transatlantic/Transpacific DX.  Some DXers in North America
specialize in trying to receive signals on the medium-wave band from
across the ocean.  This requires outstanding propagation
characteristics and plenty of patience.

* Meteor Scatter.  The most masochistic of all FM DXers attempt to hear
FM signals reflected from --yes, it's true-- meteors in the
atmosphere.  These DXers learn to identify stations on the basis of a
few seconds' listening.  

* Tropospheric Ducting.  Under certain atmospheric conditions (usually
very early mornings), FM signals will be carried long distances
through a "duct" in the atmosphere.  This is difficult to predict, but
can result in long-distance FM DX.
  
IX. IDENTIFYING YOUR CATCH

Radio stations in the United States are required to identify with
their full call letters and city of license once an hour, between 10
minutes before and 10 minutes after the top of the hour.  Canadian
stations are never required to identify, and many never use any
identifier other than "Q107" or "Toronto's 590 AM."  It's therefore
important to use other clues:

* Time announcements.  These can tell you at least what time zone a
station is in.  If there's only one or two stations on a frequency in
a given time zone, this makes identification easier.

* Format.  If you have a list of stations that includes formats, use
it.  That includes knowing what network a station uses, whether the
station uses a satellite-delivered music format, what slogans the
station might use, etc.

* Local color.  You might be able to hear names of cities or streets
or notable local personalities mentioned during commercials,
newscasts, talk shows, or weather forecasts.  If the announcer says,
"Here's the weather for the beaches today...", the station you're
hearing probably isn't in North Dakota.  Likewise, if the forecast is
snow flurries and six degrees, you're probably not hearing Miami.
These clues are among the most valuable.

X. CONCLUSION

Broadcast band DXing is an exciting way to hear the sounds of cities
and towns around the nation and even around the world.  It doesn't
necessarily require thousands of dollars of expensive equipment or
huge antennas on the roof.  All it asks of the would-be DXer is time,
patience, and knowledge.  Have fun!

THANKS TO...

Bob Foxworth, Garret W. Gengler (antenna ideas), Bob Parnass, Paul
Schleck (SuperRadio II information), and Bruce Werner, along with
anyone else I may have forgotten.

Scott Fybush -- ST901316@pip.cc.brandeis.edu

-- 
Ralph Brandi     ralph@mtunp.att.com     att!mtunp!ralph

"Dave / And if we were'nt good to you Dave / You shouldn't take it all the
way to your grave / We should all just learn how to behave" -Will Rigby


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