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As part of the Refarming process most frequencies in Part 90 below 512 MHz were split into smaller band-width channels.  This is/was a multi-step process, but the two biggest changes were in authorizing and assigning "half-channels" of 12.5 kHz.  The next step is in authorizing and assigning 6.25 kHz bandwidth channels.

The problem is how "wide-band" (25 or 30 kHz) channels can co-exist with narrower band channels.  The short answer, is with great difficulty.

So in a separate, but related Docket, the FCC ordered a deadline for the switchover from "wide" (25 kHz) to "narrow" (12.5 kHz) channels.

In WTB Order FCC 04-292 (The Third Mo & O) it says:

• For licensees in the Industrial/Business Radio Pool operating in the 150-174 MHz and 421-512 MHz bands, we affirm the Second Report and Order’s January 1, 2013 deadline for migration to 12.5 kHz technology, or a technology that achieves the narrowband equivalent of one channel per 12.5 kHz of channel bandwidth (voice) or 4800 bits per second per 6.25 kHz (data) if the bandwidth for transmissions specified in the modification application is greater than 12.5 kHz.

• For Public Safety Radio Pool licensees operating PLMR services in the same bands, we also establish a January 1, 2013 deadline for migration to 12.5 kHz technology, or a technology that achieves the narrowband equivalent of one channel per 12.5 kHz of channel bandwidth (voice) or 4800 bits per second per 6.25 kHz (data) if the bandwidth for transmissions specified in the modification application is greater than 12.5 kHz.

You can download the entire order in pdf format.
 

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