Can you introduce North American frequencies

Date:2015/11/14 17:29:06 Hits:

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.

* LOCAL: These frequencies are 1230, 1240, 1340, 1400, 1450, and 1490 kHz, and are sometimes referred to as the 'graveyard' channels. 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.

* 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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