The airtime operator’s Glass Slipper
FB8 is not a personalized license plate for you to decipher.
FB8 is a designation that comes with an FCC license stating that the licensed radio facility has a protected service area. That’s important because a trunked system with a protected service area can handle the most users — giving the operator more revenue for a given infrastructure cost.
Trunking means automatic channel selection from a pool of licensed channels. Channel selection can be controlled by software in the subscriber units (decentralized trunking) or by a repeater-based controller (centralized trunking).
Protection means that when FCC-certified frequency advisory committees (frequency coordinators) see the FB8 designation for a given frequency and location in their databases, they won’t forward any applications to the FCC to use the same frequency nearby in a way that would interfere.
On frequencies below 470MHz, most business and industrial two-way radio users share the frequencies with other users. Each user must monitor the frequency before transmitting and wait if the frequency is busy.
With decentralized trunking, the subscriber units send data to one another to identify an open channel and to gather the units in their working group on that channel. The subscriber units scan and monitor the trunked channels, any one of which might be occupied by users foreign to their airtime radio system, reducing the system’s capacity.
With centralized trunking, the protected control channel is always accessible for channel assignments. If one or more of the other trunked channels are FB8, too, it just gets better — no electronic monitoring is necessary and system capacity can reach a maximum.
OK, how do you get these valuable FB8s?
It takes computer-assisted frequency searches, some engineering, an application blessed by a frequency coordinator and a license grant from the FCC.
Frequency coordinators can find which frequencies qualify as FB8 based on site location, transmitter power and antenna height, among the most important system characteristics.
Engineering companies offer similar services. A license applicant with specific frequencies in mind might work with an engineering company to see how a system could be configured with site location, transmitter power, antenna height, antenna directionality and channel bandwidth to make a given frequency work in a given area. Applicants for narrowband channels have a better chance of obtaining FB8s because the frequency coordinator has to check fewer adjacent channels than when coordinating wideband systems.
Want to do it yourself? Some engineering companies make Web-based software tools available on a subscription basis.
With enough FB8s in enough locations, an airtime system operator can cover a wide area. Then, with the use of a networking protocol, such as PassPort (Trident Micro Systems), LTR-Net (E. F. Johnson) or ESAS (Relm Wireless), you can link the sites together.
Linked sites allow dispatch customers to communicate over wide areas, typically for much less cost than dispatch service offered by Nextel Communications. It makes independent airtime system operators highly competitive with the big boys.
Although it’s virtually impossible to obtain new FB8s in metropolitan areas with reasonable coverage areas, the farther from population centers, the more likely they are available. The trick is to find FB8s where enough population can be covered for a successful business.
Resourceful airtime system operators can draw upon the services of frequency coordinators and engineering companies to help them find those valuable FB8s.
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How ITA finds 450MHz FB8s
Frequency-by-frequency, in the entire 450MHz band, the Industrial Telecommunications Association’s software downloads all incumbents within a 100-mile radius and calculates the 39dbu service and 21dbu interference contours for the proposed and incumbent sites.
For F1 (first frequency), the software looks for a negative overlap of the proposed site’s interference contour with the incumbent sites’ service contours, and the incumbent sites’ interference contour with the proposed site’s service contour. Negative overlap is a “pass.”
If the analysis of the first or a subsequent incumbent on F1 is positive (a “fail”), analysis of F1 stops — there is no reason to analyze other incumbents. The analysis moves to F2, and so on. Once all frequencies in the band are analyzed, the system lists all “passing” and “failing” frequencies, based on contour overlap.
If no FB8s are found with a given transmitter power and antenna height, another analysis with reductions may succeed. Even if only a limited service area can be fit, it can be a good strategy to apply for it. That prevents any other facilities that would conflict from being licensed.
Then, you can ask for letters of consent from incumbents or see about changing the frequency to increase the coverage. But until you have your FB8, there is no limit on the number of shared users that may be added to the frequency.
— Andre F. Cote
Senior Vice President
Industrial Telecommunications Association
An up-to-date list of frequency coordinators can be found on the FCC Web site at http://wireless.fcc.gov/plmrs/coord.html.
Frequency coordinators that maintain their own databases of current FCC licenses and pending applications include ITA, PCIA and APCO. Some coordinators subcontract with ITA for coordination services, including database access. Others use one of two independent database providers.
Engineering companies that maintain their own databases include RadioSoft and SiteSafe.
“Our customers include some frequency coordinators that use our database and software tools on a daily basis to support their coordination work and to file applications directly with the FCC. A second group includes manufacturers and consultants who use the engineering tools available on our SpectrumWatch.com Web site to look up license information and to run studies to choose the best frequency for various applications,” said SiteSafe’s chief information officer, Winston Smith.
Peter Nordby, SiteSafe’s data services manager, added that the world in SiteSafe operates has two business models:
- coordinators that maintain their own databases and engineering tools. “A customer signs up for the package deal. You pay for the engineering services and have to file applications through them,” he said.
- other coordinators that use independent data providers, such SpectrumWatch.com or RadioSoft’s software packages.
“Our model is to provide basic engineering services that anyone can subscribe to. Customers do their own research and choose their coordinator. We support their engineering, and then load in the results for the coordinator. Then, as we generally are the database provider for that coordinator, we transmit the application directly to the FCC,” Nordby said.