VHF highband: Mobile radio’s muscle
Under the spreading F-C-C The allocation stands; The choice, a mighty frequency For work and safety land; And the coverage of its brawny waves Makes strong this iron band.
As we poise on the advent of a new millennium, when all anyone wants to talk about is Internet Protocol, digital anything and communications “solutions,” it’s time for an ode to the last band standing.
It’s not new. It’s not sexy. Heck-it’s still calling itself radio instead of wireless. The Quasimodo of telecommunications is VHF highband, hiding in the towers and doing all the work. MRT readers deal with more than a dozen different, high-profile, mobile communications bands, ranging from trunked SMR and ESMR at 800MHz and 900MHz to paging frequencies to UHF-TV to PCS. Despite their individual business and agency plans, the one band with which most of them (over 80%) still dance is good ol’ VHF highband.
Busting the bad boys Several estimates still put three-quarters of law enforcement communications in VHF highband. (That would be about 1.2 million transmitters, give or take a base or two, using FCC licensing figures.) Most agencies have conventional analog systems, and although nearly half will replace and upgrade over the next 10 years, most will stay at VHF highband. Use of 800MHz and digital systems will probably double from their current rate of deployment; about 30% of agencies will be trunking by 2010. These changes, however, tend to take place in large agencies.
Despite high-profile, national efforts, a large majority of agencies prefer local interoperability planning, and most agencies still use VHF highband for interoperability with other law enforcement entities. Only about 5% of state and local law enforcement agencies employ 100 or more full-time sworn personnel. Granted, that small percentage accounts for two-thirds of people in blue-which is multitudinous mobiles and plentiful portables-but the remaining third scatters across 17,000 small departments (read: customers) from Key West to Nome. It’s a substantial market, but the city council members and county commissioners are not going to pony up for sexy radio systems. (They’re still paying the bills for Y2K and ADA compliance.) Highband users tend to be on a tight budget (or, people on tight budgets tend to be highband users-take your pick), and there are equipment and construction savings in single-site buildouts. These small agencies do not attract direct sales from Schaumburg, IL, Lynchburg, VA or Long Beach, CA. Their equipment will come from those places, but it will come through local dealers, and they know VHF highband.
Universal workhorse Interoperability needs are not limited to law enforcement. Fire protection, EMS, and forestry services lean on VHF highband for that function as well. Likewise, VHF “high-life” has been the band of choice for auto emergency response, railroads, highway maintenance, taxicabs, utilities, manufacturing and energy production. These users are not on the band because the FCC said “Sit here.” They use it because the radios work for the jobs they have to do.
The characteristics of VHF highband make it suitable to these professions. Two-way mobile radio operates in a small world-maybe one to 20 miles. For mobiles to keep in touch with base-and each other-transmitters have to have sufficient signal strength to cover that whole world. Propagation characteristics have to be suitable. Operating frequencies have to be in a part of the spectrum where antennas are efficient, omnidirectional and can be conveniently placed on masts, vehicles and portables (read: short). It has to be easy (and inexpensive) to generate adequate RF power. Vertical polarization is necessary to keep the radios robust and to gain a higher field strength near the ground. Short-range propagation also means the capability to assign the same frequency to a similar entity 50 clicks down the road.
VHF highband propagation characteristics are more suitable for affordable, wide-area coverage than higher frequencies. Antennas are short; range is good to excellent in urban and suburban locales; there is medium susceptibility to interference and foliage path loss is low. Okay, urban building fill-in coverage isn’t so hot-but no band is perfect.
Gilding the lily Imperfect or not, there has been a lot of upgrading of VHF equipment in the last 50 years, but the old indulgent highband continues to accommodate us with each new twist. The post-World War II appearance of the transistor made mobile radio a reality by creating something you could more easily put in a vehicle. Integrated circuits 20 years later made it something you could wear. Modulation schemes keep changing. Amplitude-companded single-sideband for spectrum conservation was the rage 15 years ago; now add to that “linear modulation” (LM; which some may argue is essentially the same thing).
Radios got smaller, data baud rates got faster, trunking protocols were created, continuous tone-controlled and digitally controlled squelch systems were added. Filters have been improved, and receiver chains have been refined. Multimode radios became available, and there are more than a few competing technologies now for modulating signals and accessing channels.
The overriding concern, however, is not improving technology to make VHF highband work better; it’s how to get more people on less of it.
The ‘Incredible Shrinking Bandwidth’ After W.W.II, there was a brief, shining moment in the land of VHF highband, when channel spacing was 100kHz. Then, thanks to the previously mentioned refinements in radio equipment, everyone wanted to use it. Then for years channels were 30kHz wide and spacing shrank to 15kHz. In the 1980s, private user groups became advisory committees one morning to handle frequency assignments because the FCC had other. It was staging rehearsals for its refarming initiative (which has had nearly as long a run as “Cats”).
Suddenly we were talking about 12.5kHz, 7.5kHz and (with LM) 5kHz channelization. “Thin” is “in.” Federal agencies, like the FBI, INS and U.S. Marshals Service, must halve their bandwidth allocations for VHF by 2005, and federally regulated commercial entities are following suit. MRT will examine some band plans for narrowbanding VHF highband in the future.
And the band played on Still, one 10-channel, trunked, narrowband repeater site is a lot of bang for the buck-so is a plain vanilla conventional system. Analog voice transmission techniques are still healthy. VHF highband may not get the publicity afforded other frequencies these days, but it’s still out there every day, doing good work. If you operate it, say it loudly and proudly: “I love VHF HB.”
References Bayly, Michael R. J., “Six into One Will Go,” Mobile Radio Technology, January 1999.
Bishop, Don, “Radio Communications Improve Service on Forest Lands,” Mobile Radio Technology, July 1996.
Kinley, Harold, “Using Crystal Filters at VHF Highband,” Mobile Radio Technology, June 1998.
Parsons, J. D. The Mobile Radio Propagation Channel, Pentech Press, London, 1992.
Reaves, Brian A. and Andrew L. Goldberg, “Census of State and Local Law Enforcement Agencies, 1996,” NCJ-164618, U.S. Department of Justice Office of Justice Programs, June 1998.
Shirley, Norman R. and J. Fred Cleveland, “VHF Highband Offers Narrowband Opportunities,” Mobile Radio Technology, May 1987. Singer, Edward, Land Mobile Radio Systems, Prentice Hall, Englewood Cliffs, NJ, 1989.
Taylor, Mary, R. C. Epper and Thomas K. Tolman. “Wireless Communications and Interoperability Among State and Local Law Enforcement Agencies,” NIJ Research in Brief, January 1998.
Zhao, Yilin, Vehicle Location and Navigation Systems, Artech House, Boston, 1997.