18 What's out there to listen to? (AM/FM DXing)
Description
This article is from the Shortwave radio FAQ, by Ralph Brandi rbrandi@lucent.com with numerous contributions by others.
18 What's out there to listen to? (AM/FM DXing)
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.
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