Difference between revisions of "Narrowbanding"
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Revision as of 17:35, 17 November 2012
"Narrowbanding" and "refarming" are terms heard quite often but just as often misunderstood. Both refer to the FCC plan initiated in 1992 to increase the available spectrum in the VHF and UHF private land mobile bands. Narrowbanding should not be confused with 800 MHz rebanding.
After 15 years, numerous Petitions for Reconsideration and other challenges, the final FCC plan was decreed by the Commission early in 2007, with the setting of firm dates for the transition. The proceeding enacts a maximum 12.5 kHz bandwidth across the private land mobile bands between 150-174 and 421-512 MHz, and increases available channels by creating new ones between existing channels.
The official timetable is:
01/01/2011 - All new applications must have a maximum bandwidth of 12.5 kHz; no further modifications to existing wideband licenses after that date which will increase their broadcast footprint; all manufacturing of 25 kHz equipment to cease.
01/01/2013 - All current licensees must be fully operational on 12.5 kHz equipment.
While 12.5 kHz channel spacing is widely mentioned in communications media, there is usually no corresponding mention of the difference in channel spacing between VHF and UHF, which leads to the erroneous assumption that 12.5 kHz will be the standard channel spacing across the board. In truth, 12.5 kHz channel spacing (and eventually 6.25 kHz) only affects UHF between 420 and 512 MHz.
VHF private land mobile narrowband uses 7.5 kHz spacing. Existing VHF channels will remain, with new ones - already in use in some areas since the late 1990s - created between existing channels; for example, 160.230 and 160.245 remain, with 160.2375 created between them. This creates significant problems for many users of programmable radios and scanners, since nearly all are based on 5 or 6.25 kHz channel step size, and few of the designated 7.5 kHz channels in Part 90 can be reached with such channel steps. Makers responding to this challenge have found it necessary to implement 2.5 kHz channel steps to reach all of the defined channels in the allocation table. Buyers of new radios and scanners should check to determine whether they can tune to the new channels or not.
If your scanner only tunes 5 kHz steps you can still receive the 7.5 kHz spaced channels. Simply program the next higher or lower 5 kHz channel. If for example you want to listen to 155.7525 you would program 155.7500 or 155.7550. Most scanners automatically round off to the nearest acceptable frequency for their synthesizer step size and scanner selectivity is wide enough that you can receive frequencies 2.5 to 5 kHz off with little or no noticeable difference. Note that it is not legal to do this with radios used for transmitting on Part 90 frequencies as they must transmit on the exact assigned frequency.
In the UHF band, existing channels will remain as will existing low-power offset channels; the low-power offset channels will for the most part become normal channels like any other although some will become designated low-power channels. Between these frequencies will be created new channels with 6.25 kHz spacing.
If your scanner is limited to 12.5 kHz steps on UHF it will not be able to receive the new 6.25 kHz channels.
Examples of how frequencies will appear in the refarmed bands are:
* VHF (150 - 174 MHz) * 154.4000 - Existing frequency 154.4075 - New frequency 154.4150 - Existing frequency 154.4225 - New frequency 154.4300 - Existing frequency 154.4375 - New frequency 154.4450 - Existing frequency * UHF (420 - 512 MHz) * 453.30000 - Existing frequency 453.30625 - New 6.25 kHz frequency 453.31250 - Existing low-power offset frequency 453.31875 - New 6.25 kHz frequency 453.32500 - Existing frequency
While 12.5/6.25 kHz was originally considered "across the board", 7.5 kHz spacing was eventually chosen for VHF to minimize the impact on existing licensees; with the exception of eventually having to use narrowband-capable equipment after a certain date, existing licensees will not have to change frequencies. To keep it simple many users are simply retuning existing transmitters to a lower deviation setting so as not to go beyond the new channel limits until such time as they acquire new equipment. It is questionable whether this is legal, as stations are required to use equipment operating within an FCC grant of equipment authorization, and few older transmitters are certified for operation to narrow band specifications. It's hoped that FCC enforcement won't be called upon to shut down public safety and commercial operators whose emissions are within limits except that the transmitters aren't certified for the new emission type.
- On April 26, 2012 The FCC released DA-12-642 which waives the narrowbanding requirement in the 470-512 MHz UHF T-Band.
Answers to frequently asked questions
- The FCC private land mobile narrowbanding rule only affects Part 90 Public Safety Pool and Industrial/Business Pool frequencies in the 150-174 MHz, 421-430 MHz Canadian border area, and 450-470 MHz bands. It excludes frequencies used only for paging such as 152.0075, 154.625, 157.45, 157.74, 158.46 and 462.75-462.925 MHz.
- The FCC private land mobile narrowbanding rule does not affect the federal government land mobile bands (138-144, 148-150.75, 162-173.2, 173.4-174, and 406.1-420 MHz). They were nawrrowbanded years ago. Their deadline was in 2008.
- The FCC private land mobile narrowbanding rule does not affect VHF low band 30-50 MHz, mid band 72-76 MHz, the 216-222 MHz, 700 MHz, 800 MHz or 900 MHz bands.
- The FCC private land mobile narrowbanding rule does not affect 800 MHz and is not the same as rebanding.
- The FCC private land mobile narrowbanding rule does not mandate the use of P25 or any other digital mode. Some grant funding or interoperability plans may require public safety agencies in some areas to use P25 equipment.
- The FCC private land mobile narrowbanding rule does not require changing frequencies, only changing the emission mode of existing ones.
- The FCC private land mobile narrowbanding rule does not affect amateur radio.
- The FCC private land mobile narrowbanding rule does not affect CB.
- The FCC private land mobile narrowbanding rule does not affect GMRS.
- The FCC private land mobile narrowbanding rule does not affect FRS.
- The FCC private land mobile narrowbanding rule does not affect MURS.
- The FCC private land mobile narrowbanding rule does not affect the VHF marine band.
- The FCC private land mobile narrowbanding rule does not affect the VHF aircraft band.
- The FCC private land mobile narrowbanding rule does not affect the NOAA weather channels.
- The FCC private land mobile narrowbanding rule does not have anything to do with digital television.