The IRC is changing the way that we coordinate Narrowband Digital systems.
The IRC was assigning narrowband digital to the center of normal analog channels.
We are using a plan similar to one of the adjacent states.
We will offset the narrowband digital carriers either 5.0 KHz or 6.25 KHz.
Each analog channel will accommodate Two narrowband digital systems. Theoretically two
adjacent channels can be accommodated in the same location. This has
been tried yet, by another state. A different state has placed them
as close as 10 miles. We will not go that close,
For 2 meters, both the 15 KHz channels, and the 20 KHz channels will use plus or minus 5.0
KHz offsets from the analog channel center. The 15 KHz channels make
a tight fit, but is workable. We normally require more distance to
the adjacent channels for the 15 KHz channels, than we do for the 20
For 70 cm and other bands that use 25 KHz channels, we will use plus or minus 6.25 KHz.
Offsets. This is a good fit.
There are several benefits to use the offsets. First, we can accommodate more
narrowband digital systems, in that the channels can be shared, and
it will minimize interference on the analog channels.
Some Coordination bodies have certain frequencies assigned only for narrowband digital
use. Indiana does not have any frequencies available over the
A plus or minus offset will be selected by the coordinator depending on how close the
adjacent channel is. This is especially important on the 15 KHz 2
Normal center channel repeater spacing will be used, for narrowband digital, as for Analog
channels. We may assign another narrowband digital system to the
other offset channels, depending on adjacent channels and other
A note. Narrowband digital and Analog cannot share the same channel at the same
location. If the channel/location is used for narrowband digital,
then normal mileage spacing is required to place an analog system on
that channel, per the chart that the IRC coordinators use.
Changed to Policy 12-7-11