welcome to the vhf rebanding subcommittee of npstc s

Welcome to the VHF Rebanding subcommittee of NPSTCs Spectrum - PDF document

Welcome to the VHF Rebanding subcommittee of NPSTCs Spectrum subcommittee. The VHF rebanding subcommittee will be looking at the possibility, desirability and feasibility of realigning some or all of the VHF High band spectrum from 150 to 174

  1. Welcome to the VHF Rebanding subcommittee of NPSTC’s Spectrum subcommittee. The VHF rebanding subcommittee will be looking at the possibility, desirability and feasibility of realigning some or all of the VHF High band spectrum from 150 to 174 megahertz. This paper is an introduction to the Rebanding subcommittee. Background The use of radio to dispatch mobile units began back in the 1920’s and 1930’s. The radio link was one-way initially, using transmissions from broadcast stations and later from private stations. Among the first to try 2-way radio for answerback from the mobile was the Detroit Police Department, among others. This use soon became known as land mobile radio, to differentiate it from marine mobile and aeronautical mobile. Land mobile radio use ramped up significantly after World War II. By the early 1950’s the original AM signals had given way to the new FM system. Land mobile was also moving up in the spectrum, as the late 40’s use of the VHF 30-50 low band migrated up to the VHF high band 150-174 in the 50’s. During this time, the limitations of the simplex systems of the day were beginning to be overcome through the use of remotely-located base stations, strategically placed on high points to maximize radio coverage. At first, these remote stations were controlled by leased phone wire lines, which would later be augmented or replaced by dedicated radio control links. It wasn’t long before someone realized the radio control link could also be used by the mobile units. This configuration became known as the mobile relay station. The advantages of the mobile relay station, soon referred to as a repeater, lead to such wide-spread adoption that when the UHF 450-470 band was laid out in the 60’s, it was organized specifically to support the repeater configuration. Meanwhile, the VHF high-band, and to a lesser extent the VHF low-band, both continued to see the introduction of repeater operations. Both VHF bands are fragmented and, with limited exceptions, did not plan for repeater operations. A standardized transmit-receive frequency split was not part of the early organization of these bands. Present-Day Today, VHF low-band use is slowly being phased out overall. Equipment manufacturers have not developed much in the way of new products, resulting in limited choices for the low-band user. The VHF high-band continues to be heavily used, and equipment is more available with a wider choice. Repeaters are widely used in VHF high-band. Repeater frequency splits are non- standard, and there is sometimes a mindset of “fit ‘em in anywhere”. This has lead to cross-border and cross-discipline coordination difficulties, where one area has adopted a repeater frequency plan of low-input high-output only to find that its neighbor has adopted the reverse plan of high-input and low-output.

  2. Informal discussions have been going on in the communications industry for years on these issues. The upcoming FCC Narrow-Banding mandate is one of the items that has focused attention on the rebanding topic. Over time, a massive effort will be needed to convert to narrow band operations. It makes sense to make use of this effort to simultaneously convert to a new band-plan that recognizes and supports today’s repeater operations. The other item focusing attention on rebanding is the idea of wide-area VHF trunking systems. VHF trunking is evolving and is being implemented in several areas. The efficiencies of trunking are the topic for another paper. It is sufficient to point out here that trunking involves the use of repeater stations that the existing VHF band-plans do not readily support. VHF Trunking Today The continued use of the VHF spectrum makes sense for large, mostly-rural States that need wide coverage. Often with a relatively low population density over wide areas, these States find it cost-prohibitive to achieve the same coverage on higher frequency bands that would require many additional sites. At the same time, the advantages of trunking, especially digital with its added features, provides real improvements to public safety communications. The combination of VHF and trunking can offer large rural users the genuine advantages of trunking at a reasonable affordable cost. It should be no surprise that the VHF trunking systems being implemented, in Alaska and South Dakota so far, are in large rural states. A large trunking system on any band is fairly frequency-intensive, in that it will be using a lot of frequencies. Fortunately, the sparsely-populated rural states are the best candidates for VHF frequency availability for a trunking system. The Alaska frequency plan is a bit unusual. Alaska makes extensive use of Federal NTIA frequencies in the 137-144 range as repeater inputs, which are paired with FCC frequencies in the 153-158 range used as repeater outputs. Cccasioned by the strong partnership between Federal and State user agencies to build a joint system, this plan required a number of FCC rule waiver requests which were ultimately granted for the system. Montana is getting started on a VHF trunking system. A single-county system is being built, with the controller equipment, which is planned for later expansion along the northern border. The specifics of the channel plan layout is nor known. North Dakota has looked at VHF trunking in detail. They have decided to stay on VHF, but have put trunking on hold for the time being due primarily to fiscal constraints. South Dakota also has chosen VHF for its statewide trunking system, but staying in the FCC bands. This system started in east end with purchased VHF Public Correspondence (VPC) spectrum channels, using 156/157 mobile frequencies paired with 160/161 base frequencies. As the system has migrated west, the system has expanded to include PS 155 channels as inputs and PS 159 channels as outputs. Wyoming looked at the VPC spectrum but concluded that it would not be workable. We decided to stay within the FCC Public Safety land mobile allocations, and began looking for a usable frequency plan for our statewide WyoLink VHF trunking system.

  3. Floyd Ritter Plan About the time Wyoming was looking for a frequency plan, Floyd Ritter of Utah proposed a VHF rebanding plan to better support repeater operations. The Ritter Plan, to give Floyd the credit, also would support VHF trunking well, because trunking uses repeaters. Floyd’s draft plan needs a little work, but overall is pretty well thought out. The Ritter Plan pairs Low repeater inputs and High repeater inputs with Middle repeater outputs. The Low inputs at 150-152 and the High inputs at 158-159 are paired with Middle outputs at 154-156. Floyd and I met at Park City in July 2004 to work on the draft plan. I made some suggestions on some changes, and Floyd graciously agreed to allow me to do some work on it. Although the Ritter Plan can use some work and refinement, we considered it to have the characteristics needed for a successful VHF trunking system frequency plan. The basic Ritter Plan layout was adopted for the Wyoming WyoLink VHF trunking system. WyoLink System The new Wyoming Wyolink system will be a statewide VHF P25 digital trunking system open to all public safety users in the state, including Federal agencies. The acquisition and implementation of a 5-site Pilot phase in Cheyenne and Laramie County is currently under way. The system will ultimately be built out to include 57 high- level mountain top sites and 24 low-level County Seat town sites. Each site is planned to have 1 control channel and 6 voice channels, for a total of 7 VHF trunking channel pairs. There has been a lot of interest in how we are planning to build our system, including the aspects of frequency coordination and FCC licensing. A White Paper on the Wyolink System was written and submitted to NPSTC to answer the inquiries. The White Paper was initially published on the NPSTC website under What’s New. Today, it can be found in Archives section of the NPSTC site. NPSTC Involvement The final section of the WyoLink White Paper suggested that NPSTC would be a good choice to take the lead in a VHF rebanding effort. I attended the NPSTC meeting in Baltimore last September to present an introduction to the Paper. A new VHF Re-banding subcommittee was formed, under the Spectrum Committee, to examine the possibilities. Marilyn Ward asked if I would be available to assist the new Subcommittee. When I said yes, she named me Chairman.

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