Radio data, delivered with unnecessary personality.
Bandwidth refers to how much radio spectrum a channel occupies. On GMRS, channels use either 25 kHz wideband or 12.5 kHz narrowband, and which one applies depends on the channel number. Getting this wrong can cause poor audio quality or interference with adjacent channels.
GMRS uses FM (frequency modulation), where audio is encoded by swinging the carrier frequency up and down. The amount of swing is called deviation. Wideband FM allows up to ±5 kHz of deviation; narrowband limits it to ±2.5 kHz. More deviation means louder, fuller audio - but it also occupies more spectrum. When you speak loudly into a wideband radio, the signal can swing across nearly the full 25 kHz channel. A narrowband radio on the same audio would clip or compress to stay within 12.5 kHz.
The FCC assigned narrowband to the 467 MHz interstitial channels (8–14) for spectrum efficiency. These channels are the lowest-power tier in GMRS (0.5W ERP, handheld only per 95.1767(c)), and limiting them to ±2.5 kHz deviation keeps their signals from splashing into adjacent channels. The 462 MHz channels (both main and interstitial) use wideband because they have more spacing headroom. This is part of a broader FCC push toward narrowbanding across land mobile radio services.
The difference is audible, especially on voice. Wideband sounds fuller, louder, and more natural - the higher deviation carries more of the audio signal's dynamic range. Narrowband sounds slightly compressed and quieter, as if the audio has been squeezed through a smaller pipe. For most GMRS use cases this is fine, but on channels 8–14 you'll notice the difference compared to a wideband channel. Neither is "bad" - they're just optimized for different tradeoffs between audio fidelity and spectrum use.
Wideband transmissions carry more audio information, resulting in louder, fuller sound. Narrowband uses less spectrum but the audio is quieter and slightly more compressed. The key issue is mismatch:
On most handheld radios, the bandwidth setting is buried in the channel programming menu rather than displayed on the main screen. Ways to check:
When programming with CHIRP, bandwidth errors are one of the most frequent problems:
If your radio is programmed with the standard GMRS channel plan (and most factory-programmed radios are), it already uses the correct bandwidth for each channel. The only time you need to worry about this is when programming with CHIRP or manually entering frequencies:
Tip: In CHIRP, the bandwidth column is labeled "Mode" - set it to "NFM" for narrowband or "FM" for wideband. If you see all channels set to the same mode, double-check channels 8–14 are set to NFM.
A wideband signal on a wideband channel fits neatly within its 25 kHz slot. But if a wideband transmission occurs on a narrowband channel, it can splash energy into adjacent channels - a phenomenon called adjacent channel interference. This is particularly problematic on channels 8–14 (the 467 MHz interstitial channels) because they are designated narrowband per 95.1775(c). A mis-programmed wideband radio transmitting on one of these channels causes interference to adjacent users. The FCC's narrowband requirement for these channels exists precisely to prevent this. See also: Interference for more on how to identify and avoid it.
When communicating with FRS radios on the shared channels (15–22), both sides use 25 kHz wideband, so there's no mismatch. FRS radios on channels 8–14 also use narrowband. The bandwidth settings are defined by the FCC in Part 95, so any properly type-accepted radio should already be configured correctly out of the box.
If you're hearing distorted or unusually quiet audio from another station, a bandwidth mismatch is one of the first things to check - especially if they're using a radio programmed manually or through software. See also: Channels and Frequencies for the full GMRS channel plan.