70-centimeter band

Posted by   relativity   |   Categories :   저소득층문제

The 70-centimeter amateur radio band is the 420 to 450 MHz portion of the UHF radio spectrum. This band is used by amateurs engaged in emergency communications where portable and mobile radios are frequently used. Many such radios have dual-band capabilities, operating on both the 70-centimeter and 2-meter bands.

Contents

1 History
2 Band allocation
3 Propagation characteristics
4 Comparison of the 2-meter and 70-centimeter bands
5 Use for the radio control hobbies
6 See also
7 References
8 External links

History[edit]

This section needs expansion with:

Origin
First use.
ITU allocation. You can help by adding to it. (January 2012)

Band allocation[edit]
The band’s allocation varies regionally. In the United States,[1] Australia and Trinidad and Tobago[2] the band ranges from 420 to 450 MHz with some geographical limitations; in Canada, the band is only 430–450 MHz; in the UK, amateurs are allocated 430–440 MHz. By international treaty between the US and Canada, operation in the portion of the band from 420 to 430 MHz is prohibited north of Line A,[3]which runs just south of the Canada–US border from Washington state to Maine, and east of Line C, which runs from northeast to southeast Alaska.
Propagation characteristics[edit]
70-centimeter propagation characteristics lie midway between 2-meter and 33-centimeter (~900 MHz) bands. Above 200 MHz, as frequency increases, building penetration is reduced.[4] However, smaller obstacles may also block or reflect the signal. Higher frequencies also present a lower noise floor, making it easier to overcome both natural and artificial interference, especially prevalent in urban environments.
Atmospheric thermal ducting is often more intense at UHF[citation needed], because shorter wavelengths have much greater refraction angles than longer ones. However, a much stronger thermal inversion is often required than is needed for ducting in the 2-meter band.
Comparison of the 2-meter and 70-centimeter bands[edit]
Propagation considerations often take a back seat to channel availability or economic concerns in system planning. One practical concern when comparing the 70-centimeter band to the 2-meter band is that a quarter-wavelength antenna is much less unwieldy at 70 centimeters than it is at 2 meters. Portable antennas for 2 meters are generally continuously loaded coil spring or “rubber duck” types, while on 70 centimeters they can be a full quarter wavelength. The diffe

2017년 2월 19일