Radios

Radios are communication systems that send and/or receive electromagnetic waves. Devices such as citizens’ band (CB) radios, walkie-talkies, and handie-talkies are two-way radios that can be used for interpersonal communications. Two-way radios consist of a transmitter, receiver, and antenna. They are available in mobile and base configurations. Unlike cellular phones, radios do not require a monthly contract or carry per-call charges. In the United States, two-way radios are regulated by the Federal Communications Commission (FCC) and use ultra high frequency (UHF) and very high frequency (VHF) bands. UHF radios use line-of-sight communications and repeaters. They provide better reception than CB radios, which can use either HF 27 MHz or UHF 477 MHz. VHF radios are used mainly in marine applications and by emergency personnel. VHF/UHF two-way radios are also available. Radio accessories include two-way antennas, UHF connectors, battery chargers, and external GPS receivers.

Two-way UHF radios use family radio service (FRS) and/or general mobile radio service (GMRS). In the United States, FRS radios use 14 channels (1 -14) and do not require an operator’s license. They have a maximum power level of 0.5 mW and a relatively short range. FCC regulations prevent users from modifying FRS radio transceivers and FRS antennas. GMRS radios use eight dedicated channels (15 - 22) and require an FCC operator’s license. They have a greater range than FRS radios and may be outfitted with antennas to extend their range. Most GMRS radios have power ratings of 1.0 to 5.0 W and a maximum allowable power level of 50W. FRS/GMRS hybrid or dual-service radios provide access to both the FRS and GMRS bands. They can be operated without an FCC license is only the FRS channels are used.

Radios differ in terms of performance specifications and features. CB radios have 40 channels, squelch or mute features, a public address (PA) switch, clarifier, and circuitry to reduce radio frequency (RF) gain. UHF radios differ in terms of range, which is usually measured in miles or kilometers. Features such as voice scrambling can help prevent the unauthorized monitoring of radio communications. Direct calling allows an operator to call one person in the group without contacting all of the group’s members. Privacy codes extend the number of available channels by adding 38 continuous tone coded squelch system (CTCSS) codes to each channel. For example, FRS radios with CTCSS codes have a total of 532 channels (14 x 38). Additional features for two-way radios include backlighting, adjustable squelch, auto-scan, out-of-range alert, keypad lock, selectable power level, and battery indicator. Some FRS radios and GMRS radios use AA or AAA batteries. Others use NiMH rechargeable batteries and may include a battery pack and charger.

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  Communications Receivers: DSP, Software Radios, and Design, 3rd Edition From reception basics to cutting-edge software radio design, this one-stop resource provides ready-to-use insights on the...
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  White noise on the plant floor can cause electrical interference that often affects the function of proximity sensors. This radio frequency (RF) "noise" is caused by the use of variable frequency...
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Part Numbers for Radios