Stevens Water Monitoring Systems, Inc.

FCC offers free VHF radio spectrum (MURS) for personal and business use

Radio communications is a growing, cost-effective solution for environmental monitoring applications. The International Telecommunication Union (ITU) governs the allocation of communications frequencies world-wide, with participation by each nation’s communications authority (The Federal Communications Commission (FCC) in the United States).

Radio modems are designed with specific frequency ranges for usage in the frequency band as defined by the ITU and FCC.

While most terrestrial radio frequencies are restricted or require a license from FCC, the FCC has set aside some frequencies for unlicensed, free usage by the user. For environmental data communications, the term “spread spectrum” is often associated with unlicensed frequencies.

The FCC allows the use of spread spectrum technology in three radio bands, 902-928 MHz, 2400-2483.5 MHz and 5752.5-5850 MHz for radio transmission under 1 Watt of power. This power limit prevents interference within the band over long distances.

However, one unlicensed frequency band often overlooked is known as MURS (Multi-Use Radio System), which includes five VHF frequencies (154.820, 151.880, 151.940, 154.570, 154.600 MHz). The FCC formally defines MURS as “a private, two-way, short-distance voice or data communications service for personal or business activities of the general public.”

MURS is different from other license-free radio spectrums that the FCC offers:

First, the radio may be of a higher power than other unlicensed spectrum. Under the MURS rules, a radio may have up to a maximum 2 watts of Transmitter Power Output.

Secondly, the FCC puts no restrictions on the amount of gain that a MURS antenna may have. The only restrictions are the antenna cannot be higher than 60 feet from the ground if free-standing or 20 feet higher than the structure it is mounted on.

The third advantage is that radios in a lower frequency range are less prone to having signals blocked by hills, foliage and other objects. However, the lower the frequency the larger the antenna must be to receive and transmit the signal.

As with all radio services, the environmental conditions and terrain can effect transmission distance but with a proper radio survey and antenna configuration, users of MURS should expect a distance of 3 to 15 miles.

Stevens currently offers the MURS-certified TS4000 radio modem that can be shipped with settings to facilitate the easy setup of a MURS radio network.

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