The IEEE defines the UHF radar band as frequencies between 300 MHz and 1 GHz.[1] Two other IEEE radar bands overlap the ITU UHF band: the L band between 1 and 2 GHz and the S band between 2 and 4 GHz.
Radio waves in the UHF band travel almost entirely by line-of-sight propagation (LOS) and ground reflection; unlike in the HF band there is little to no reflection from the ionosphere (skywave propagation), or ground wave.[2] UHF radio waves are blocked by hills and cannot travel beyond the horizon, but can penetrate foliage and buildings for indoor reception. Since the wavelengths of UHF waves are comparable to the size of buildings, trees, vehicles and other common objects, reflection and diffraction from these objects can cause fading due to multipath propagation, especially in built-up urban areas. Atmospheric moisture reduces, or attenuates, the strength of UHF signals over long distances, and the attenuation increases with frequency. UHF TV signals are generally more degraded by moisture than lower bands, such as VHF TV signals.
Since UHF transmission is limited by the visual horizon to 30–40 miles (48–64 km) and usually to shorter distances by local terrain, it allows the same frequency channels to be reused by other users in neighboring geographic areas (frequency reuse). Radio repeaters are used to retransmit UHF signals when a distance greater than the line of sight is required.
Occasionally when conditions are right, UHF radio waves can travel long distances by tropospheric ducting as the atmosphere warms and cools throughout the day.
AntennasEdit
Retevis GMRStwo-way radios operating on 462 and 467 MHz in the UHF band, showing the short antennas usedCorner reflector UHF-TV antenna from 1950s
The short wavelengths also allow high gain antennas to be conveniently small. High gain antennas for point-to-point communication links and UHF television reception are usually Yagi, log periodic, corner reflectors, or reflective array antennas. At the top end of the band, slot antennas and parabolic dishes become practical. For satellite communication, helical and turnstile antennas are used since satellites typically employ circular polarization which is not sensitive to the relative orientation of the transmitting and receiving antennas. For television broadcasting specialized vertical radiators that are mostly modifications of the slot antenna or reflective array antenna are used: the slotted cylinder, zig-zag, and panel antennas.
Since at UHF frequencies transmitting antennas are small enough to install on portable devices, the UHF spectrum is used worldwide for land mobile radio systems, two-way radios used for voice communication for commercial, industrial, public safety, and military purposes. Examples of personal radio services are GMRS, PMR446, and UHF CB. Some wireless computer networks use UHF frequencies. The widely adopted GSM and UMTS cellular networks use UHF cellular frequencies.
Currently channels 21–37 and 39–48 are used for Freeview digital TV.[6] Channels 55–56 were previously used by temporary muxes COM7 and COM8, channel 38 was used for radio astronomy but has been cleared to allow PMSE users access on a licensed, shared basis.
694–790 MHz:[7] i.e. Channels 49–60 have been cleared, to allow these channels to be allocated for 5G cellular communication.
791–862 MHz,[8] i.e. channels 61–69 inclusive were previously used for licensed and shared wireless microphones (channel 69 only), has since been allocated to 4G cellular communications.
863–865 MHz: Used for licence-exempt wireless systems.
UHF channels are used for digital television broadcasting on both over the air channels and cable television channels. Since 1962, UHF channel tuners (at the time, channels 14–83) have been required in television receivers by the All-Channel Receiver Act. However, because of their more limited range, and because few sets could receive them until older sets were replaced, UHF channels were less desirable to broadcasters than VHF channels (and licenses sold for lower prices).
There is a considerable amount of lawful unlicensed activity (cordless phones, wireless networking) clustered around 900 MHz and 2.4 GHz, regulated under Title 47 CFR Part 15. These ISM bands – frequencies with a higher unlicensed power permitted for use originally by Industrial, Scientific, Medical apparatus – are now some of the most crowded in the spectrum because they are open to everyone. The 2.45 GHz frequency is the standard for use by microwave ovens, adjacent to the frequencies allocated for Bluetooth network devices.
The spectrum from 806 MHz to 890 MHz (UHF channels 70–83) was taken away from TV broadcast services in 1983, primarily for analog mobile telephony.
In 2009, as part of the transition from analog to digital over-the-air broadcast of television, the spectrum from 698 MHz to 806 MHz (UHF channels 52–69) was removed from TV broadcasting, making it available for other uses. Channel 55, for instance, was sold to Qualcomm for their MediaFLO service, which was later sold to AT&T, and discontinued in 2011. Some US broadcasters had been offered incentives to vacate this channel early, permitting its immediate mobile use. The FCC's scheduled auction for this newly available spectrum was completed in March 2008.[9]
225–420 MHz: Government use, including meteorology, military aviation, and federal two-way use[10]
470–512 MHz: Low-band TV channels 14–20 (shared with public safety land mobile 2-way radio in 12 major metropolitan areas scheduled to relocate to 700 MHz band by 2023[12])
698–806 MHz: Was auctioned in March 2008; bidders got full use after the transition to digital TV was completed on June 12, 2009 (formerly high-band UHF TV channels 52–69) and recently modified in 2021 for Next Generation 5G UHF transmission bandwidth for 'over the air' channels 2 thru 69 (virtual 1 thru 36).
806–816 MHz: Public safety and commercial 2-way (formerly TV channels 70–72)
817–824 MHz: ESMR band for wideband mobile services (mobile phone) (formerly public safety and commercial 2-way)
824–849 MHz: Cellular A & B franchises, terminal (mobile phone) (formerly TV channels 73–77)
849–851 MHz: Commercial aviation air-ground systems (Gogo)
851–861 MHz: Public safety and commercial 2-way (formerly TV channels 77–80)
862–869 MHz: ESMR band for wideband mobile services (base station) (formerly public safety and commercial 2-way)
869–894 MHz: Cellular A & B franchises, base station (formerly TV channels 80–83)
894–896 MHz: Commercial aviation air-ground systems (Gogo)
896–901 MHz: Commercial 2-way radio
901–902 MHz: Narrowband PCS: commercial narrowband mobile services
^"Federal Government Spectrum Use Reports 225 MHz – 7.125 GHz". NTIA. Dec 2015 – Aug 2017. Retrieved October 21, 2019.
^"T-Band Report" (PDF). Npstc.org. March 15, 2013. Retrieved 17 December 2017.
^"Wireless Medical Telemetry Service (WMTS)". Fcc.gov. 3 November 2011. Retrieved 17 December 2017.
^ ab"TerreStar Corporation Request for Temporary Waiver of Substantial Service Requirements for 1.4 GHz Licenses" (PDF). the FCC. 2017-10-10. Retrieved 2017-10-11.
^ abc"Ligado Ex Parte re Iridium Analysis (PUBLIC 11-2-2016)" (PDF). Ecfsapi.fcc.gov. Retrieved 17 December 2017.
^"Galileo Signal Plan". Navipedia.net. Retrieved 17 December 2017.
^"Request for waiver and public interest statement". FCC. 2016-06-04. Retrieved 2018-04-02.
^"AWS-3 Transition". Ntia.doc.gov. January 29, 2015. Retrieved 17 December 2017.
^ ab"AT&T Mobility Petition for Limited Waiver of Interim Performance Requirement for 2.3 GHz WCS C and D Block Licenses" (PDF). Ecfsapi.fcc.gov. Retrieved 17 December 2017.
^"Globalstar Overview" (PDF). Globalstar.com. 2017. Archived (PDF) from the original on August 2, 2017. Retrieved 17 December 2017.
^"Broadband Radio Service & Education Broadband Service". The FCC. February 2016. Retrieved 2018-06-05.
External linksEdit
U.S. cable television channel frequencies
Tomislav Stimac, "Definition of frequency bands (VLF, ELF... etc.)". IK1QFK Home Page (vlf.it).