Are you ready for narrowbanding? Understanding the details

The Federal Communications Commission (FCC) has rewritten Part 90 of the rules governing the operations of land mobile radio systems. The Commission has also set deadlines for radio equipment manufacturers to develop equipment that is capable of operating...


  • Any equipment certified for manufacture or import since Feb. 1, 1997, must be able to be retuned to narrow bandwidth. Some VHF equipment, however, has been found not to be programmable on every 7.5 kHz-spaced frequency. Your narrowband consultant, dealer or equipment supplier can help determine if your equipment is capable of narrowband channel spacing and operation.
  • Many vendors’ narrowband equipment includes a “companding” or compression and expansion software feature (Motorola X-Pand and others). This software is designed to improve the quality of the received audio in narrowband operation. If companding is desired, make sure all radios in your fleet are companding-capable. If companded and non-companded radios are mixed, recovered audio will be distorted and unacceptable. If you use multiple vendors and wish to use companding, make sure the companding algorithms are compatible between vendor equipment. Test before you buy.
  • Financial considerations
  • Reach out to local, state and federal legislators to explore budget allocations for equipment updates or replacements. Because 2012 is the latest implementation year, allocations must be budgeted in 2011 or earlier. Grant funding is currently not available for this mandate.
  • Determine costs for upgrade, reprogramming or replacements.
  • Logistical implementation
  • Determine the logistics for touching every radio and how many touches are required.
  • Determine the timing.
  • Establish how the transition from wideband to narrowband will take place.
  • Verify how the quality of service will be maintained.
  • Identify interoperability considerations with mutual aid partners and local jurisdiction departments.
  • Evaluate the possibility of using this opportunity to implement improvements that had been postponed.
  • Review your FCC license(s) to ensure that you are authorized to use the narrowband emissions.
  • VHF interoperability channels

If you are licensed for channels on or adjacent to any of the new VHF interoperability frequencies, consider relocating to avoid interference to and from these frequencies.

Considering non-equipment

In addition to equipment, finance and logistic issues, organizations preparing for narrowbanding are taking a close look at several other factors.

  • System coverage

Contract with a qualified engineering and consulting firm to review coverage of your system at more narrow bandwidths compared to your current wideband system. Coverage may be reduced, especially at the edges, in current weak spots and in-building. Ensure that current tower sites will provide the needed coverage. If you employ a simulcast system, review the overlap coverage and system timing to ensure no new “holes” are created.

Paging and volunteer alerting must be considered. Pagers by nature often operate at the edge of coverage for the system, including in buildings, plants or mobile homes. Transmitter sites may need to be upgraded, relocated or added to maintain the desired coverage.

  • Paging

The Report and Order exempts paging-only channels from the narrowbanding requirement. These frequencies are designated as paging-only frequencies by Part 90.

If you provide alerting or paging on any other frequencies, your paging frequency must be narrowbanded.

Per 90.20(C), Limitations 13 & 30, the public safety pool paging-only frequencies are:

  • VHF — 152.0075 and 157.450MHz
  • UHF — None

Per 90.35(B)(3), Limitations 29 and 36, the industrial/business pool paging-only frequencies are:

  • VHF (in MHz) — 152.480, 157.740 and 158.460
  • UHF (in MHz) — 462.750, 462.775, 462.800, 462.825, 462.850, 462.875 462.900, 462.925, and 465.000
  • First responder paging and alerting

Fire/EMS/EMA alerting and paging is normally on dispatch channels, which must be narrowbanded. Plan to replace wideband monitor receivers, siren, house alerting receivers and monitor pagers, with current narrowband-capable equipment. Digital paging systems for station alerting and siren activation can also be considered.

  • Eliminating interference

Narrowbanding creates more frequencies at UHF and VHF. In the VHF bands, the narrower bandwidth will tend to reduce adjacent channel interference. However, in the UHF bands, the new 12.5 kHz channel spacing has potential to increase adjacent channel interference as additional 12.5 kHz systems are licensed in between existing 25 kHz systems.

Due to the widening receiver bandwidth of the 25 kHz systems, there will be interference generated to the 25 kHz systems by the 12.5 kHz systems. Likewise, the wider modulation emission mask of the 25 kHz system, typically 16 to 20 kHz wide, will “slop over” into the 12.5 channel. This situation will only be resolved by the current 25 kHz licensees migrating to narrowband 12.5 kHz emission mode.

Coordinating services with adjacent channel licensees will help minimize interference.

  • Migration to 6.25 kHz

In 2007, the FCC mandated that, by January 1, 2011, any equipment submitted for certification and sale must incorporate 6.25 kHz technology. This will set the stage for future FCC plans to split the 12.5 kHz bandwidth channels again to a bandwidth of 6.25 kHz per talk path, and list those channels in the Part 90 rules. Organizations planning a complete system replacement should consider migrating directly to technologies that meet the 6.25 kHz requirement. Equipment that meets the letter and intent of the FCC recommendations to bypass 12.5 kHz rebanding and move directly to 6.25 kHz equivalent will soon be available.

  • Public safety applications available

Current Project 25 (P25) radio systems meet the functional and operational requirements of the public safety community. The P25 Phase 1 technology is narrowband compliant, utilizing a 9,600 bps data stream in a 12.5 kHz bandwidth channel.

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