What is a table allocation system?


Tables are published for FM and TV, which allocate FM channels and TV channels
to specific cities.

Yes, FM has channels, starting with 200, although 201 is the lowest channel
actually allocated, while 200 is reserved for situations where 201 or higher
won't work.

The tables can be read on-line.

Modifications to the tables have been done from time to time.

"Matt Beckwith" wrote in message
...
The clarity of local AM radio stations is less at night. Is there
some sort of law that radio stations have to cut their output when it
gets dark? I've noticed that it's the amount of light outside, not
the time of day. That is, the lack of clarity occurs whenever it gets
dark, not at a certain time each day. I always presumed the stations
were cutting power to save money, but then why would it be based on
light vs dark, rather than on time of day?


Here is something the FCC prepared about AM radio at night:

Why AM Radio Stations Must Reduce Power, Change Operations, or Cease
Operations at Night
Most AM radio stations are required by the FCC's rules to reduce their power
or cease operating at night in order to avoid interference to other AM
stations. Our rules governing the daytime and nighttime operation of AM
radio stations are a consequence of the laws of physics. Because of the way
in which the relatively long wavelengths (see Footnote 1) of AM radio
signals interact with the ionized layers of the ionosphere several miles
above the earth's surface, the propagation of AM radio waves changes
drastically from daytime to nighttime. This change in AM radio propagation
occurs at sunset due to radical shifts in the ionosphere layers, which
persist throughout the night. During daytime hours when ionospheric
reflection does not occur to any great degree, AM signals travel principally
by conduction over the surface of the earth. This is known as "groundwave"
propagation. Useful daytime AM service is generally limited to a radius of
no more than about 100 miles (162 km), even for the most powerful stations.
However, during nighttime hours the AM signals can travel over hundreds of
miles by reflection from the ionosphere, a phenomenon called "skywave"
propagation. (Shortwave stations, which operate using AM modulation on
several bands between between 2.3 MHz and 26.1 MHz, also use this phenomenon
to broadcast still greater distances, up to thousands of miles). Because of
this change in signal propagation from daytime to nighttime, if every AM
station kept its daytime operating power at night, massive interference
would result. (See also Hours of Daytime-Only AM Broadcast Stations, First
Report and Order, BC Docket 82-538, 95 FCC 2d 1032 (1983) for a similar
description.)

The FCC was established by the Communications Act of 1934, and was given the
responsibility of making a "fair, efficient and equitible distribution of
radio service" to the various communities of the United States. In order to
meet this responsibility, and in recognition of the physical laws which
govern AM radio propagation, the FCC established three basic classes of AM
stations (Clear Channel, Regional, and Local), each of which operates on
specified frequencies, or channels There have been some changes since then,
but the main features of the plan have remained in place. Here is a quick
summary of the three types of AM stations:


a.. Clear channels. On these channels, only one station, called the
"dominant" station, was permitted to operate during nighttime hours in order
to provide service to a wide area. Footnote 2. A typical clear channel
station, transmitting with power of 50 kilowatts into an omnidirectional
antenna, provides nighttime skywave service to an area approximately 750
miles in radius. Some examples of clear channel stations are WCBS in New
York, WGN in Chicago, WHO in Des Moines and KFI in Los Angeles.

b.. Regional channels. On these channels several stations are permitted to
operate during nighttime hours, protecting each others' nighttime service
areas by use of directional antennas. As the name implies, stations on
regional channels provide nighttime service to moderately-sized or
"regional" areas.

c.. Local channels. Essentially, all stations on local channels are
permitted to operate during nighttime hours with the same facilities as
employed during the daytime. The nighttime service of such stations is
limited to very small "local" areas by massive interference from the
numerous other stations on the channel.
For the most part, the basic structure of the FCC's original frequency plan
has remained unchanged over the past several decades. Additional stations
gradually have been permitted to operate on the clear channels. In order to
preserve the wide-area nighttime service provided by the dominant clear
channel stations, when nighttime operation is permitted, many of these these
stations are required to use directional antennas in order to protect the
dominant clear channel station from interference to its nighttime skywave
service area. Most of these stations are also required to reduce power at
night, to avoid causing interference to the dominant stations and to each
other. Other stations, which cannot afford the necessary protection at night
to other AM stations, are presently licensed to operate during the daytime
hours only. (New daytime-only stations are no longer being authorized, since
December 1, 1987.)

To find out what daytime and nighttime operations are authorized for your
favorite AM broadcast station, you may use our AM Query. The Hours of
Operation for this Record field for the station will indicate what hours the
station may operate with the listed station parameters, either as Unlimited
hours operation, Daytime, or Nighttime. If the record shows the "Hours of
Operation" as "Daytime" or "Nighttime", then you can find the approximate
monthly times that the station will change from day to night operation (or
cease operation for the night in the case of a daytime-only station) by
entering the coordinates (latitude and longitude) into the the Sunrise /
Sunset Times Calculations program. Note that a station may have multiple
records, for different daytime and nighttime operations.

In article , "David Eduardo"
writes:

Useful daytime AM service is generally limited to a radius of
no more than about 100 miles (162 km), even for the most powerful stations.

The FCC apparently didn't take areas with high soil conductivity into
consideration when they wrote this.

Here in South Dakota, strong AM daytime signals propagate for 200 or more
miles. KFYR, WNAX, KSDN, KFGO, KSJB, etc. are all examples of this. And these
stations are only putting out 5,000 watts. Over in the Black Hills, KBHP runs
25,000 watts on 810 and can easily be heard up and down I-29 on the opposite
side of the state. That's 300-350 miles from the transmitter.

But that's okay. We're used to being ignored by the bureaucrats in Washington,
DC :-)

"SouthDakotaRadio" wrote in message
...
In article , "David Eduardo"

writes:

Useful daytime AM service is generally limited to a radius of
no more than about 100 miles (162 km), even for the most powerful
stations.

The FCC apparently didn't take areas with high soil conductivity into
consideration when they wrote this.

It's David who is oversimplifying. That statement couldn't have come from
anyone in the broadcast allocation part of the FCC.

The FCC rules definitely require consideration of ground conductivity. The
old printed rules contain a conductivity map and propagation curves for each
AM frequency for each conductivity. THAT is the basis upon which AM
stations are allocated and power and directional antennas specified.

Here in South Dakota, strong AM daytime signals propagate for 200 or more
miles. KFYR, WNAX, KSDN, KFGO, KSJB, etc. are all examples of this. And
these
stations are only putting out 5,000 watts. Over in the Black Hills, KBHP
runs
25,000 watts on 810 and can easily be heard up and down I-29 on the
opposite
side of the state. That's 300-350 miles from the transmitter.

But that's okay. We're used to being ignored by the bureaucrats in
Washington,
DC :-)

Your complaint is entirely unjustified.

I always presumed the stations were cutting power to save money, but then why
would it be based on light vs dark, rather than on time of day?


Power and/or pattern change is done to accommodate a station of lesser class
against a station of superior class; or a station of the same class, but one
which was authorized before the subject station.

AM is a "demand allocation" scheme, and the first station to be authorized is
usually the superior station, with respect to subsequently authorized stations.

Extreme example: 710 in L.A. and 1510 in Boston are protected by stations of
higher class (710 in Seattle and 1510 in Nashville) simply because these
stations were authorized before Seattle and Nashville were authorized. L.A. and
Boston remain Class B; Seattle and Nashville became Class A.

Power and/or pattern change is not always at local sunset or sunrise at the
affected station. It could be local sunset and/or sunrise at another station
(see 1110, 1530 and 1560 for examples). There are historical reasons for this.

So-called DA-3 operation is also possible, where a station has defined day and
night operating parameters, but during so-called critical hours it operates
differently, usually with parameters in between day and night, although not
always.

Matt Beckwith wrote:
The clarity of local AM radio stations is less at night.

This is because all of the other stations everywhere else in the world
are coming in through skip at night, and interfering with local stations.

Is there
some sort of law that radio stations have to cut their output when it
gets dark? I've noticed that it's the amount of light outside, not
the time of day.

Many smaller stations are forced to reduce power at night, or go off the
air altogether, to protect stations on the same frequency in other parts
of the country.

That is, the lack of clarity occurs whenever it gets
dark, not at a certain time each day. I always presumed the stations
were cutting power to save money, but then why would it be based on
light vs dark, rather than on time of day?

Because the ionosphere is denser and closer to the earth at night, which
is why you can get transatlantic AM stations at night and not in the daytime.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

All other channels are Regional channels.

If the expanded band is regional (these are local, I thought...) then there is
52.


Expanded band stations are Class B, for now, although I wouldn't put it past
some country to try to notify one of theirs as a Class A.


Again, the 60 clears are total for North & South America, or am I mistaken?


Total for this ITU region.


There is at least one Class I station (either Class I-A
or Class I-B) on every clear channel, and all such
clears are clearly identified in the NARBA and Rio
treaties as to power and antenna efficiency (although
for some Mexicans, the antenna efficiency may be
bogus).

Where would this listing be located on the web?


The FCC AM site.

List all stations on any clear channel (by specifying no call letters and
restricting the frequency range to any one specific clear channel) and observe
the class letter.

"A" is Class A, "B" is Class B, etcetera.

On a clear channel, you should find only As, Bs and Ds.

Central American stations will show up, too, and some of these are notified as
described, but many are not.

My assumption is if the FCC database has no class letter, then the United
States has not "accepted" the station's notification, or the class is
indeterminate.

It is common for any change to be submitted to Canada and Mexico for
acceptance, particularly in border areas, and vice versa.

This is one reason why almost all of L.A.'s FM's are operating way above Part
73 power ... because they started out that way, and when it came time to
formalize those existing operations, Mexico was requested to accept those
operations, which Mexico did, thereby "grandfathering" those stations with very
high (most) or even super power (KPFK).