In "narrow band" the signal occupies no more than 6.25 kHz on each side of the center frequency or a total of 12.5 kHz of bandwidth. This is half of the bandwidth the older 25 kHz signals occupied. In doing so 80 communications channels exist in every 1 MHz of bandwidth instead of the old 40. All new equipment is required for this change as the radio must transmit all of the information over a much narrower range of frequency. With the RF spectrum becoming crowded, doubling its capacity will allow for more efficient use of the spectrum and expansion of many radio systems.
This change is being made to the lower end of the UHF band and the VHF band only. Channel spacing for frequencies 470 MHz and up was already at 12.5 kHz. The so called UHF-T band, which was allocated in many large cities some 30 years ago using UHF TV channels 14-20 or 470-512 MHz, and the 800-900 MHz band were assigned from their inception at the narrower spacing.
Another development is the requirement for all TV broadcasting to be digital by next February, which will allow more TV channels to be broadcast in the same amount of bandwidth. At the same time TV stations at the upper end of the UHF TV allocations are being moved to lower frequencies, allowing the allocation of the new 700 MHz band to public safety and other users.
Narrowbanding and digital TV have the goal of squeezing more use out of the same fixed amount of radio frequency resource. Many areas in the country, mostly the major metro areas, that span many counties, had run out of radio frequency spectrum and some type of relieve was necessary.
Confused? Here is an example of the old spacing in the federal VHF band:
168.125, 168.150, 168.175, 168.200, 168.225, 168. 250 etc. which are spaced .025 MHz or 25 kHz apart.
The new narrow band spacing adds frequencies in between at .0125 MHz or 12.5 kHz apart and using our example above it would look like this:
168.1250, 168.1375, 168.1500, 168.1625, 168.1750, 168.1875, 168.200, 168..2125, 168.2250, 168.2375, etc.
Because FM is frequency modulation (Duh!) it modulates the signal by varying the frequency. Narrower signals must carry the same amount of information over a smaller range of frequencies so it is received at a lower volume on a scanner. The mix between narrow band and "wide band" radio reception is problematic with an older scanner, as the narrow band is so quiet the volume must be turned up to hear it. When the next reception involves an older "wide band" radio this same volume setting can blast you out of your seat. The new GRE-500 and 600 radios can be programmed to add an "audio boost" on the newer narrow band frequencies and the signals from a mix of narrow and wide band frequencies are now nearly equal at the same volume setting. This will become more important from now until 2013 when all public safety is required to transmit in narrow band, as there will increasingly be a mixture of narrow and wide band signals in every day listening.
Kern County happens to be on the leading edge of state and local agencies switching to narrow band. CDF began the process with the addition of two narrow band frequencies at 151 MHz for two new air to air tactics channels. All of the so called "federal interoperability" VHF channels were allocated in narrow band and these frequencies will see increased usage on incidents involving a mixture of federal, state, and local agency resources as more and more state and local agencies obtain narrow band radios. These frequencies are cleared for nationwide use and such frequencies are very much in short supply using existing "wide band" radios.
Bottom line, get used to narrow band, it is the future!
