Multi Use Radio Service
MURS, VHF CB, also rendered as "Multi-Use Radio Service" - not to be confused with similar services such as FRS/GMRS, regular old 26-27 MHz CB, VHF marine or licensed land mobile (business radio) services.
Short distance voice and data service for use by the general public for personal and business communications. Included in Part 95 of the FCC rules (Personal Radio Services) along with the more familiar services such as CB, FRS, GMRS, etc. Since it is a VHF CB service, MURS fills the gap between the UHF FM services (FRS/GMRS) and the original "Class D" HF AM/SSB 26-27 MHz CB service.
MURS is similar in function and intended use to the Freenet 149 MHz VHF CB service available in Germany and the "VHF 245" 245 MHz VHF CB service in Thailand, among other similar CB-like services worldwide. Many MURS users are business, commercial or industrial users.
MURS Frequencies / Channels:
|MURS Channel||Identifier||Frequency||Maximum Bandwidth|
|MURS Channel 1||MURS-1||151.820 MHz||11.25 kHz (any mode - narrowband)|
|MURS Channel 2||MURS-2||151.880 MHz||11.25 kHz (any mode - narrowband)|
|MURS Channel 3||MURS-3||151.940 MHz||11.25 kHz (any mode - narrowband)|
|MURS Channel 4||Blue Dot MURS-4||154.570 MHz||20.00 kHz (any mode - wideband)|
|MURS Channel 5||Green Dot MURS-5||154.600 MHz||20.00 kHz (any mode - wideband)|
MURS regulations, restrictions and other information
Maximum transmitter output power is 2 watts. No limit on effective radiated power (ERP). Antenna height is limited in FCC rules and the highest point of the MURS antenna must not be more than 18.3 meters (60 feet) above the ground or 6.10 meters (20 feet) above the highest point of the structure on which it is mounted.
Maximum bandwidth on 151.8200 MHz, 151.8800 MHz and 151.9400 MHz is 11.25 kHz and maximum bandwidth on 154.5700 MHz and 154.6000 MHz is 20 kHz. No restriction on transmission mode as long as it meets the bandwidth requirement.
MURS is unique among the American (FCC Part 95) personal radio services (CB, FRS, GMRS, etc) in that AM, FM, CW, and data modes are allowed. F2D modulation and A2D modulation (digital using FM or digital using AM) are also permitted on the MURS frequencies. Voice inversion scrambling is permitted and offered as an option on radios such as the Motorola RMM2050 MURS portable radio. CTCSS and DCS are often used to facilitate frequency sharing. Because of the permissible data usage on the MURS frequencies, there are often data link networks heard on the MURS frequencies during VHF band openings.
Digital voice modulation (for example, DMR or MotoTRBO, Project 25 or APCO-25 P25, C4FM, D-STAR) or other digital voice modes may be used legally on the MURS frequencies - provided their emission bandwidth is less than or equal to the 11.25 kHz (for the 151 MHz frequencies) or the 20 kHz (for the 154 MHz frequencies) bandwidth restrictions. The 11.25 kHz narrowband is the same as the regular narrowband FM voice - known as NFM - required for frequencies above 150 MHz by the FCC since 2013.
Common MURS emission designators are 11K2F3E or 11K0F3E for 151.82 MHz, 151.88 MHz and 151.94 MHz and 20K0F3E for 154.57 MHz and 154.6 MHz. Many users simply use narrowband for all five channels to reduce confusion. However, popular portable handheld radios, including those manufactured by Motorola, automatically switch to wideband 20 kHz 20K0F3E emission on 154.570 MHz and 154.600 MHz and do not allow the end-user to switch back to narrowband on these frequencies.
Repeaters are not allowed on the MURS frequencies per FCC rules. This includes duplex and simplex repeaters, also known as "store-and-forward" repeaters. This rule is apparently often ignored by MURS users as evidenced by the existence of simplex repeaters operating on the MURS frequencies as well as cross-band repeater setups using MURS (on VHF) and FRS/GMRS channels (on UHF). There are several reports on various radio hobbyist Internet forums of MURS repeaters including wide-area simplex repeaters located on mountaintops or MURS simplex repeaters with antennas located on high-rise buildings in urban areas.
The 154 MHz frequencies were moved from the Business Radio Service (Part 90 of the FCC rules) and stations previously licensed to use these frequencies with higher power levels are considered grandfathered users and may legally transmit high power transmissions. Wal-Mart, Costco, Sam's Club and other retailers that started using 154.600 MHz and 154.570 MHz back when licenses were required have continued to use these frequencies after they were made license-free. Technically this means they're "grandfathered" users and enjoy primary status on the frequency - although this is murky in the FCC rules. Wal-Mart has a habit of using 154.57 and 154.6 with carrier squelch (CSQ), even in radio congested environments like large shopping malls and urban or suburban areas. This can lead to interference issues when multiple stores are using MURS frequencies in a small area.
CB networks on MURS, high power, militia groups, MURS repeaters, ham operators and other fun
Some CB and ham radio operators also use the MURS frequencies due to favorable propagation characteristics, often with high power. This is against the FCC regulations but is widespread in certain areas due to the availability of open-band VHF/UHF radios, easily modified ham radio equipment that can transmit on the MURS frequencies and the adoption of the MURS frequencies by militia and prepper groups. MURS-based VHF systems range from simple handheld radios programmed with the MURS and FRS frequencies (for example, the Baofeng UV-5R and UV-82 series) to high powered mobile and base station simplex networks to simplex and duplex repeater networks. There are reports of cross-band repeaters using the FRS frequencies and MURS, in addition to high powered MURS simplex repeaters located on mountaintops or tall buildings in urban areas. See also: CB repeaters.
There is an effort to standardize the use of "channel 3" as a general "prepper" or emergency preparedness "calling" channel across the three Part 95 services, MURS, CB and FRS (MURS channel 3 - 151.94 MHz, CB channel 3 - 26.985 MHz and FRS channel 3 - 462.6125 MHz) in conjunction with HF/VHF/UHF amateur frequencies.