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on a question below to be taken to the answer farther down this
page.
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Though the signal can usually be
"heard" 5-10 miles away over open country, the strongest signal area
is normally 3-5 miles in radius, regardless of the frequency being
used. Most operators position their "tune-to" signs within a 3-mile
distance. Signal distances can be less in areas with very hilly or
mountainous terrain or very poor soil. Distances can also appear to
be less in areas where interference is present from other radio
stations (especially at night) on or near the operating frequency or
where high voltage overhead power wires or AM-broadcast towers are
immediately present. Another factor that affects listeners' ability
to hear the signal at greater distances is the car radio.
Sensitivity of automobile radios vary, and different cars produce
different amounts of their own engine interference, which can affect
radio reception especially in areas where AM signals are not strong.
But in general, the AM car receiver is the best instrument for
reception.
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Most communities do
not promote this, because home reception varies widely with many
factors, including:
- Distance from the home to the AM transmitting antenna (AM signal
level);
- Quality of the AM receiver in the home;
- Presence of an AM receiver that will work on loss of power
(battery operated);
- Structure of the building and interference sources that it may
contain.
With a maximum of 10 watts of AM power, your transmitter is
optimized for in-vehicle listening.
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We don’t recommend it, though it can be done when
required. Your antenna is likely to work best on its own support
structure over open ground. If you do want to consider an existing
structure, the antenna-height restriction is 15 meters (49.2 feet)
from tip to ground. So don't select a structure that is too tall. To
function well, however, the antenna must be mounted at the top (not
side) of the structure you do choose and must have the opportunity
for a groundplane at the bottom.
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Generally speaking, this class of service is
voice only, noncommercial in nature. You are not allowed to transmit music,
mention commercial names (except in a noncommercial way, e.g., you
may use air carrier names to provide directions at airport facilities) or
provide any kind of commercial announcement. Although these radio stations
operate in the AM broadcast band, they are licensed under public safety
radio regulations; and decision about content must be made with that in
mind. The stations are not in any way meant to compete with full-power
broadcast services. Broadcast content should be targeted to people in their
vehicles and should comply with FCC Rules Part 90.242. For more on this
topic, please see our page “What May
Be Broadcast on AM Advisory Radio.”
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5.
Which frequency is the best to use at my AM
Information Station?
There is no single right answer
for everyone, partly because, in different areas of the country, all AM
frequencies are not available due to FCC separation regulations. Generally,
however, the conventional wisdom is as follows:
The favorite is 1610. Here's why:
▫ It is known by listeners as a common
information radio frequency.
▫ Its short antenna and smaller
groundplane are somewhat more convenient to locate and install.
▫ There are no radio stations in the US
on that frequency, which means that interference, especially at night, is
usually less.
▫ The short wavelength is interfered
with less by power lines.
The second favorite is 1620-1700.
▫ Very few commercial radio stations are
permitted on these frequencies, which lessens interference and produces good
signal range for information radio stations using them.
▫ Short antenna and smaller groundplane
are somewhat more convenient to locate and install.
▫ The short wavelength is interfered
with less by power lines.
The third favorite is 530.
▫ It is known by listeners as a common
information radio frequency.
▫ There are no commercial radio stations
in the US on 530 to cause interference, the only source of night
interference being Caribbean and Canadian stations in the eastern US after
dark.
▫ 530's long wavelength signal fades
slowly and can produce a large fringe coverage area.
The fourth favorite is 540-1600.
▫ Almost every car radio receives the
frequencies, but there is often more nighttime noise and interference in
this original AM frequency band.
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6.
May I use low-power FM instead?
At present, the FCC is not taking applications
for a low power FM service (LPFM), though it did as recently as 2001. At
that time, the Commission granted a handful of FM low power stations, each
with about 100 watts power (about 5 miles of range). The FCC has not
indicated that it will again offer the service for another round of
applications. Of special note: first-round grantees discovered that LPFM
stations are not ideal as pure information sources because of FCC-imposed
operating parameters, which, for example, mandated that LPFM station
operation be more like commercial FM stations in terms of hours of
operation, content restrictions and equipment requirements.
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7.
Can any field tests be done to see how well an AM Information Station
would perform at a given location?
Yes, but these tests are commonly done only
where the exact coverage pattern or range needs to be determined. They are
not often required, because transmitter power can be set anywhere in the
0-10 watt range to produce a standardized signal level at the FCC-mandated
1.5 km distance from the antenna. This means that unless there is severe
terrain, very poor soil or there is an interference potential, almost all
TIS stations will produce the same coverage pattern. As a result,
pre-testing isn't often required. If it is desired, however, ISS offers a
self-test service called Radio Express.
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10.
How can an AM Information Station tie in with our outdoor warning sirens?
The ALERT AM
system can. There are contacts on the ALERT AM system you can use to
make a specific pattern of pre-recorded messages trigger in conjunction with
a specific siren activation. Some communities simply assign a siren
controller to the ALERT AM system, and the radio system gets the same cue
that the sirens get when they are activated. Other communities put
pushbuttons in the EOC that the dispatcher can push, when certain situations
occur, to immediately broadcast messages pre-recorded for those situations.
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12.
What does an Information Station call sign mean and may I choose it? Why are
there seven characters, three of them numbers? How often must I broadcast
it?
Federal Communication Commission Rules (part
90) govern the licensing of Information Stations (TIS) issued to local
government entities such as states, cities and counties. The Commission
assigns 7-character call signs to all - 4 alpha letters, followed by 3
numbers.
Only the first character (the "W") has any particular significance,
however.* The next 3 letters and 3 numbers are sequential, based on when the
Commission grants each license.
Although the Commission does not permit applicants to request specific
call signs, in a few instances (when licensees indicated certain call signs
were objectionable), the FCC granted changes.
The FCC requires that the full 7-character call sign be broadcast every 30
minutes (or more) in English. Sometimes station operators inadvertently drop
off the three numbers of the call sign, probably because standard broadcast
stations (licensed under FCC Part 73 Rules) don't have numbers in their
call signs and have only three or four characters (WGN, WABC, etc.).
Information Stations operated by federal government agencies are licensed
through the NTIA (National Telecommunication Information Agency) rather than
the FCC and do not necessarily follow the same format. In some instances,
these call signs may begin with a "K," may have only three letters or may
have no numbers.
Information Stations authorized by branches of the military are not issued
call signs.
* Some older TIS call signs issued by the FCC begin with a "K".
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This page was last updated:
March 01, 2010. |
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