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ISM Band Cordless Telephones
"Unlicensed Spread Spectrum"
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ISM stands for "Industrial, Scientific, Medical", the designation given to several radio frequency bands available for use without a license if certain conditions are met. Since in the US one of the requirements is the use of spread spectrum technology, this market segment is also referred to as "unlicensed spread spectrum". Parts 15 and 16 of the United States Federal Communications Commission (FCC) regulations allow for the use of three Industrial-Scientific-Medical frequency ranges: 902 to 928 MHz, 2400 to 2483 MHz and 5725 to 5850 MHz. Bands available for unlicensed use in other parts of the world are typically clustered near 2.4 GHz.
The use of ISM bands for cordless telephones is largely a US market. The simplest of these ISM phones broadcast at very low powers (<1 milliwatt) to avoid most of the FCC requirements placed on higher powered phones. The RF content is limited to a few discrete transistors that serve as LNA, PA, mixer, and modulated VCO. Tropez is a typical manufacturer. More complicated phones broadcasting at 1 watt (the FCC limit for such devices) may be either analog (looking like AMPS phones) or digital (looking like GSM, NADC-TDMA, or NADC-CDMA phones). To date nearly all ISM phones operate in the 900 MHz band, where designers have ready access to inexpensive and adaptable technology from either cordless or cellular systems. The consumer focus of ISM systems creates an emphasis on inexpensive SMT plastic-packaged devices.
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