Radio Bandwidth Frequency Offset
Notation
The new APCO standard for FM is Narrow Band +/-2.5 KHz. For amateur use set the radio to Wide Band +/- 5 KHz.
The new Land Mobile Radio standards of "wideband" vs "narrowband" refer to the bandwidth of the signal. Older analog wideband FM business band signals are 25 kHz wide. The new mandated narrowband signals are only 12.5 kHz wide.
- super or ultra narrow (2.5kHz deviation)
- narrow, and regular narrow (5kHz) wide.
- two way wide is 15kHz
- amateur wide is 15kHz
- amateur narrow is 5kHz
- commercial super FM narrow (2.5kHz) narrow and 5kHz standard narrow.
- normal 2 meter FM is considered wide band at about 5khz for amateur use.
- wide/narrow setting on newer ham radios: 25KHz (wide) or 12.5KHz (narrow).
- VHF private land mobile narrow band uses 7.5 kHz spacing.
- Old VHF radios are based on 5 or 6.25 kHz channel step size.
Narrowbanding
The FCC is trying to enact 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. As of 2013 the FCC mandated that 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.
- An old police scanner that tunes 5 kHz steps will still receive the 7.5 kHz spaced channels if you program the next higher or lower 5 kHz channel. If the older police scanner is limited to 12.5 kHz steps on UHF it will not be able to receive the new 6.25 kHz channels.
