Channel Spacing Calculator

Channel spacing is the frequency separation between adjacent channels in a radio band plan. When a coordination body assigns repeater pairs or simplex frequencies within a band, every channel is placed at a fixed interval from its neighbors so that stations on adjacent channels do not cause mutual interference. The spacing determines how many non-overlapping channels fit within a given band segment, and it must be matched to the occupied bandwidth of the emission type — a 25 kHz spacing makes no sense for a 2.5 kHz deviation FM signal, and 5 kHz spacing cannot accommodate 16 kHz deviation wideband FM.

For amateur radio VHF and UHF FM operation, the most common spacing values are 25 kHz (traditional standard), 12.5 kHz (narrowband, increasingly adopted for 2m and 70cm), and 5 kHz (used for CW and SSB sub-bands on 2m). Many US regional frequency coordinators use a 15 kHz or 20 kHz grid for legacy repeater pairs, but 25 kHz is dominant for new assignments. On 70cm, digital voice modes such as DMR, P25, and System Fusion often use 12.5 kHz spacing to maximize the number of available channels in the band.

The channel grid is defined by a first-channel frequency and a uniform spacing increment. The first channel may not start exactly at the band edge — coordinators often offset the grid by a fraction of the spacing to prevent the last channel from falling on or near the upper band limit. This grid offset is an important parameter when verifying that an existing or proposed frequency fits a recognized coordination plan rather than falling between grid positions, which would indicate a non-standard or potentially coordinated channel.

Understanding channel spacing matters for more than just repeater coordination. It determines adjacent-channel rejection requirements for a receiver, the filter bandwidth needed in a transmitter, and whether a digital voice system's 12.5 kHz equivalent bandwidth fits within an existing 25 kHz FM allocation. Regulatory bodies including the FCC and ITU have pushed commercial land-mobile services toward 12.5 kHz and even 6.25 kHz channels, and while amateurs are exempt from narrowband mandates, the trend directly affects the availability of equipment and filters that hams use.

When planning a new repeater output, first obtain the band plan and channel grid from your regional frequency coordinator before running this calculator. Many coordinators publish their grid in the form "channels start at X MHz, spaced Y kHz, with a Z kHz offset from the band edge." Entering those exact parameters will show you which grid position number corresponds to your proposed output, confirming it is a valid coordination candidate rather than falling between grid positions.

The grid offset field is easy to overlook but important for accuracy. A common 2m coordination grid in North America starts at 144.0125 MHz (12.5 kHz offset from the band edge), not 144.000 MHz. Entering 12.5 in the offset field correctly shifts all channel positions to match. Without the offset, every calculated frequency will be 12.5 kHz low, and a frequency that appears to be Channel 5 in the calculator will actually be halfway between Channels 4 and 5 on the actual plan.

For digital voice mode planning, note that DMR Tier II and P25 Phase 1 both occupy 12.5 kHz of bandwidth per channel (6.25 kHz equivalent with two-slot TDMA for DMR). YSF (Yaesu System Fusion) can operate in both 12.5 kHz narrowband and 25 kHz wideband modes. If you are planning a digital repeater pair, choose 12.5 kHz spacing to ensure compatibility with the narrowest standard channel allocation and future migration to 6.25 kHz equivalent bandwidth systems.