Internet Info 1994 March/Internet Info CD-ROM (Walnut Creek) (March 1994).iso/answers/rec/radio/monitoring/am-fm-dxing

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Summary: Answers to Frequently Asked Questions about long-distance
         reception of local AM (medium wave) and FM stations.
         This article is posted monthly.
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Archive-name: radio/monitoring/am-fm-dxing

[Last revised: Oct 3 1993]

AM/FM DXing

By Scott Fybush and Earl Higgins

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

I. WHAT ARE THE AM/FM BROADCAST BANDS?

The mediumwave (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 spaced in 9 kHz increments, i.e.: 531,
540, 549, etc.

In the United States, the band is being expanded to 1700 kHz.  Stations
which are currently experiencing high levels of interference will begin
appearing on the 1610-1700 kHz frequencies sometime in late 1993 or
1994. They will simulcast the new frequencies with the old for a period
of a few years, eventually dropping the `old' frequency. This opening up
of new channels presents some once-in a lifetime opportunities for the
alert mediumwave DXer.

The VHF-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 generally 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 mediumwave, the single most important
factor for good DX is the time of day.  Mediumwave signals almost always
get absorbed by the D Layer of the ionosphere during daylight hours. As
a result, all mediumwave signals received during midday hours will
arrive by ground wave, making reception of signals over a few hundred
km/miles away unusual in daylight.  At night, however, the ionosphere
reflects mediumwave signals, making it possible for signals to be heard
at much greater distances, up to a few thousand km/miles, via `skywave'.
To a lesser extent, the period up to two hours after local sunrise, and
two hours before local sunset, called "Critical Hours", have varying
levels of skywave, and also can provide some very unusual reception
opportunities for the mediumwave DXer. Reception also tends to be better
in winter than in summer, due to lower levels of atmospheric noise and
longer hours of darkness. In the United States, due to the large number
of stations, many smaller mediumwave stations are required to sign off
or reduce power sharply at sunset so as to reduce interference to
distant stations.

Whereas the mediumwave band can be counted on to provide distant
reception with much dependability, this is not the case at all on the
VHF-FM band. Under `normal' conditions, VHF-FM signals generally carry
no more than 150-250 km (100-150 miles), or `line of sight', since the
ionosphere generally does not reflect VHF-FM signals. VHF-FM
transmitting antennas are thus usually located as high as possible. Tall
towers, high buildings, and mountaintops are common VHF-FM transmitter
sites.

However, under certain rare conditions, the atmosphere will even reflect
VHF-FM signals, thus making it possible to receive these stations at
quite long distances. There are two major forms this distant reception
can take; the most common is Tropospheric Ducting, or tropo for short.
Typically, this occurs when a warm air mass forms on top of a cooler
mass closer to the ground. The area between these masses acts like a
pipe, `bending' the signals back to the earth well beyond the horizon.
This reception is most common in local late spring and summer months, in
the post-sunrise hours. It will enable the alert VHF-FM DXer to log
stations up to 800 km (500 miles) away in optimum conditions.

The other relatively widespread form of VHF-FM DX is called Sporadic E,
or E-skip, because it is the E Layer of the ionosphere which reflects
the signals. Like the name implies, this form of propogation is very
sporadic, yet very intense.  When it's in, it is VERY strong. Stations
from a relatively limited geographic area 1300-2000 km (800 to 1200
miles) away will suddenly boom in, strong, often in stereo but quite
fadey, even overpowering semilocals in many cases. It will start at the
bottom of the VHF-FM Band (actually TV channels 2-6 first) and work its
way up in frequency. The highest frequency at which signals are
reflected by the ionosphere is called the Maximum Usable Freqiuency
(MUF), just as it is in shortwave, and it can occassionally surpass the
top of the VHF-FM dial in an unusually good opening.


III. RECEIVERS

Almost any radio is capable of some broadcast-band DXing, especially
long-distance mediumwave 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
Superadio III (Model 7-2887.)  The SR III is designed for optimum AM/FM
broadcast performance, incorporating:

* RF amplifiers on both bands
* Ceramic filters and Automatic Frequency Control on FM
* No PLLs or digital displays for less electronic noise
* A 2-way speaker system with 1 watt of audio power

The SR III is a bulky (4" x 10" x 12") portable radio which can be run
off 120V AC or 6 "D" batteries, providing over 400 hours of battery
life.  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 can be obtained from Bennett Brothers (Order
#R3116) at 1-800-621-2626 or 1-800-631-3838, or from Best Products
(Order # 140457) at 1-800-950-2398.

If you don't have a Superadio, 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 can 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 mediumwave reception, most receivers have a short internal ferrite
rod.  This will provide acceptable signals for high-powered distant
stations.  Ferrite rods are 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, external antennas offer certain advantages. The
most common external antenna is a simple random wire, 15m (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 meter/a few feet into the
earth.

One problem with a random wire antenna for mediumwave work is it's
inability to reject strong local signals. Most receivers today lack the
dynamic range to effectively deal with the extremely strong signals from
a local mediumwave broadcaster as picked up by a random wire antenna.
Thus, some sort of tuned antenna is best for all but the most isolated,
rural locations.

The most popular antenna for mediumwave DX today is called a `loop'
antenna, and can be either of two types: ferrite rod or air-core wound
wire loop. These antennas are small, 25-100 cm (1-3 feet) in diameter,
and sit on the DXers desk or shack table where they can be easily turned
by hand for optimum peak or null of a signal. Each design works with a
tuned circuit before feeding the signal into your receiver, and usually
this circuit includes a small powered amplifier. Generally speaking, the
longer the ferrite rod, or the larger the diameter of the aircore loop,
(to a point), the sharper the null of the antenna.  45 to 55 cm (18 to
22 inches) would be optimum for a ferrite rod antenna.

Air-core loops need to be made by hand, as there are none on the market.
Ferrite loops, however, are available commercially from at least two
manufacturers; Palomar Engineers and Radio West. Unfortunately, these
two antennas do not have very long ferrite elements; and reviews of
their performance in the mediumwave press tends to be mixed. Ideally,
one would build their own antenna, or try to find either a used, older
Radio West loop or Space Magnet antenna, both pre-1980. Plans for
building all sorts of mediumwave loop antennas are available through
National Radio Club publications. The address is found later in this
FAQ.

A more advanced antenna is the "beverage" antenna.  This is a length of
wire 300 m (1000 feet) or more, with extremely high gain and narrow-beam
directional characteristics.  It is usually, but not always, 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.

For VHF-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 mediumwave, North American frequencies fall into three basic
classes:

* CLEAR CHANNEL: These frequencies are 540, 640-780, 800-900, 940,
990-1140, 1160-1220, and 1500-1580 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 also occupy the clear
channels, frequently using less than 1000 watts and very restrictive
antenna patterns.  In recent years, the US FCC has added many more low
power stations to the clear channels, making reception of the big,
primary, stations more inteference prone than it once was, but providing
excellent hunting for the serious mediumwave DXer. Also, the clear
channels are the primary hunting area for Latin American DX due to the
relatively small number of North American stations on them.

* LOCAL: These frequencies are 1230, 1240, 1340, 1400, 1450, and 1490
kHz, and are sometimes referred to as the 'graveyard' channels by DXers.
Stations on local channels can use a maximum of 1000 watts (somewhat
higher outside the US).  At night, these six frequencies tend to become
chaotic, as the hundred-plus stations on each channel cause each other
tremendous interference.  Although the primary service area of these
stations may be twenty miles or less, these stations have been known to
reach well over a thousand miles under good conditions. Identifying
distant stations on these channels requires a directional antenna, a
good ear, and plenty of patience. The National Radio Club keeps distance
records for all of the stations on these channels and publishes them in
their bulletin, _DX_News_, regularly.

* REGIONAL: These are all the remaining channels, including the expanded
band frequencies of 1610-1700 kHz.  U.S. stations on these frequencies
tend to be restricted to 5000 watts, although a recently signed
international treaty allows for the possibility of 10,000 or even 50,000
watt stations on these frequencies if they do not interfere with other
stations. In practice, only Canada has yet assigned high power stations
on these frequencies. While not as noisy as the locals, reception on
regional channels can be quite interference prone, with a listener able
to identify three or four stations coming in simultaneously on one
frequency.  Most regional, or class III stations, use directional
antennas to reduce interference with distant stations.

On VHF-FM, the American FCC has reduced its restrictions on power and
antenna height considerably.  Today, VHF-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 the following
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. 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, many of the clear-channel 50kw stations,
particularly the non-directional ones, should be easy to hear.  Learn
all the local stations.  Find out which ones sign off at sunset, which
ones go off late at night, 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 without some tedious nulling. Experiment with radio placement.
As you slowly turn the radio, observe its directional characteristics.
The Superadio III will receive signals coming from the front and back of
the set the best, and attenuate the signals coming in `off the side' of
the set. You can use this to your advantage and log several stations on
a single frequency.

By all means, keep a log of all new stations you hear; someday you'll be
glad you did! Better yet, keep it on the computer; that way you can
share it with others on the net. After a few months of listening; you
should have a list of 200-300 stations you've heard. Most of these will
be your `regulars', audible almost daily. Beyond that, you can hunt for
the rarer stuff. Try for all 50 US states (very, very difficult), or 20
countries (fairly easy in most locations). Within a few years, you'll
likely have heard a thousand or so stations and have a very interesting
logbook. Here's a `beginner's target list' of widely heard clear channel
AM stations to start you out; from most locations in North America you
should be able to hear all but four or five of these fairly easily.

 540 CBK   Canada SA Watrous          840 WHAS  USA    KY Louisville
 540 XEWA  Mexico SL Rio Verde        850 KOA   USA    CO Denver
 640 KFI   USA    CA Los Angeles      860 CJBC  Canada ON Toronto
 650 WSM   USA    TN Nashville        870 WWL   USA    LA New Orleans
 660 WFAN  USA    NY New York         880 WCBS  USA    NY New York
 670 WMAQ  USA    IL Chicago          890 WLS   USA    IL Chicago
 680 KNBR  USA    CA San Francisco    900 XEW   Mexico DF Mexico City
 700 WLW   USA    OH Cincinnati       990 CBW   Canada MB Winnipeg
 720 WGN   USA    IL Chicago         1020 KDKA  USA    PA Pittsburgh
 730 XEX   Mexico DF Mexico City     1030 WBZ   USA    MA Boston
 740 CBL   Canada ON Toronto         1040 WHO   USA    IA Des Moines
 750 WSB   USA    GA Atlanta         1070 CBA   Canada NB Moncton
 760 WJR   USA    MI Detroit         1070 KNX   USA    CA Los Angeles
 770 WABC  USA    NY New York        1100 WWWE  USA    OH Cleveland
 780 WBBM  USA    IL Chicago         1120 KMOX  USA    MO Saint Louis
 800 PJB   Neth Ant. Bonaire         1160 KSL   USA    UT Salt Lake City
 800 XEROK Mexico CH Juarez          1180 WHAM  USA    NY Rochester
 810 WGY   USA    NY Schenectady     1200 WOAI  USA    TX San Antonio
 820 WBAP  USA    TX Fort Worth      1210 WOGL  USA    PA Philadelphia
 830 WCCO  USA    MN Minneapolis


VII. SOME ADVANCED IDEAS

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

* QSLing:  Since broadcasters by and large don't use the "Q-codes" so
popular in Ham and shortwave DX, QSLs are called `veries' or
verification letters by mediumwave and VHF-FM DXers. You'll probably
have to send a letter to the station's chief engineer (names of actual
verification signers can be found in the NRC AM Log). Expect
verification in card form from the 50kw AM stations, and verification
letters from just about everybody else. Small stations are often excited
to find out they've been heard thousands of miles away, but you'll need
to take special care to explain to them exactly what you want as they
are likely to not know what a `verie' is. Also, remember to always
include return postage with your request.

* DX Tests.  A few stations still run special DX tests, usually arranged
for either The NRC or The IRCA (International Radio Club of America) and
published in advance in their respective bulletins (another reason to
join!).  In the past year alone, the following outstanding feats were
accomplished via DX Tests: Hawaii (KUAI-720) was heard as far away as
Ontario and Pennsylvania; New Jersey (via WJIC-1510) made it west of the
Mississippi; and New Mexico (KHAC-880) made it to the East Coast! These
are all fairly difficult states for most DXers (unless, of course, you
happen to live in or near them).

* Equipment Tests: Some stations run experimental tests with their
daytime power after local midnight, in accordance with US FCC and
Canadian CRTC rules. Often these will be late Sunday night/Monday
morning, when some stations sign off for maintenance (although not as
many as used to do so). For example, in Chicago Illinois, many DXers
have logged KOMO-1000 from Seattle Washington, testing when Chicago
local WLUP goes off on Monday mornings; thankfully Monday mornings just
happen to be the time when KOMO seems to like to test with their
non-directional day pattern. This makes an otherwise almost impossible
state relatively easy around the midwestern US.

* Sunrise/sunset DXing.  Lots of interesting mediumwave DX can be had
when your receiving station and/or the transmitter are in only partial
darkness.  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. In fact most mediumwave DXers log the greatest
number of stations in the hour or two right around local sunset,
especially in the Fall and Winter months. Don't be surprised if, say,
tiny KOKB in Blackwell, Oklahoma blasts right through CBJ and other East
Coast powerhouse stations on 1580, for a few minutes right around
Blackwell sunset! Anything can happen in the turbulent sunset and
sunrise hours.

* Transatlantic/Transpacific DX.  Some DXers in North America specialize
in trying to receive signals on the mediumwave band from across the
ocean.  This requires outstanding propagation characteristics and plenty
of patience (a nice, quiet coastal location can yield some amazing
results).

* FM Subcarriers and Stereo.  VHF-FM stations are allowed to transmit
separate programming on a subcarrier.  This requires a special decoder
(one source is Bruce Elving's FM Atlas; see address below.) 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.

* Meteor Scatter.  The most masochistic of all VHF-FM DXers attempt to
hear VHF-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.

VIII. 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 (although note, interestingly, there IS a TOWN
called Beach, North Dakota; go figure). Likewise, if the forecast is
snow flurries and six degrees, you're probably not hearing Miami. These
clues are among the most valuable.

IX. 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 AM stations, one essential tool is The NRC AM Radio
Logbook, now in its 13th Edition. It includes day and night antenna and
power information, format, hours of operation, address, verie signers,
network affiliations, etc. Price is $19.95 for US, $20.95 for Canadian,
three dollars cheaper for NRC Members. To order write NRC Publications,
Box 164, Mannsville NY 13661-0164 USA. NRC also publishes FM and TV
Logs. To become a member (highly recommended) and receive a year's worth
of `DX News', send $24.00 for US, $25.00 for Canadian to: NRC
Subscription Center, Box 118, Poquonock, CT 06064-0118 USA. All other
countries, write for price information.

Another 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 [phone]
voice, or [phone] fax.  The address is M Street Corp., 304 Park
Ave S Floor 7, New York, NY 10010 USA.

Another guide for VHF-FM DXers is Bruce Elving's annual FM Atlas.  This
includes maps showing every VHF-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.

Another listing is the 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 through your local bookstore or radio
specialty mail order outlets such as the Radio Collection and CRB
Publishing.

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 require
hundreds 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 (Superadio information), and Bruce Werner, along with anyone
else I may have forgotten.

Scott Fybush -- [e-mail]
Earl Higgins -- [e-mail]


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