Analog FM (Frequency Modulation) is a widely used mode of communication in amateur radio, offering reliable voice communication with simple and cost-effective equipment. FM signals can be transmitted with different bandwidths, most commonly 25.0 kHz (wideband) or 12.5 kHz (narrowband).

Bandwidth in analog FM refers to the range of frequencies a signal occupies. This is determined by the modulation method and deviation of the carrier frequency. Bandwidth choice affects audio quality, spectrum efficiency, and compatibility with repeaters and radios.

The two most common bandwidths in analog FM are:

1. Wideband FM (25.0 kHz): Offers higher audio fidelity and greater deviation but uses more spectrum.
2. Narrowband FM (12.5 kHz): Reduces spectrum usage, allowing for more channels in a given frequency range, but with slightly reduced audio quality.

Wideband FM was the original standard for analog FM and remains widely used in amateur radio. Key characteristics include:

1. Audio Quality: Superior audio clarity due to larger frequency deviation (typically ±5 kHz).
2. Spectrum Usage: Occupies more bandwidth, which can limit the number of available channels in a given frequency range.
3. Compatibility: Still common in legacy systems and many repeaters.

Wideband FM is ideal for situations where spectrum availability is not a concern and higher audio fidelity is desired.

Narrowband FM was introduced to improve spectrum efficiency, particularly in crowded bands. Key characteristics include:

1. Audio Quality: Slightly reduced audio fidelity due to smaller frequency deviation (typically ±2.5 kHz).
2. Spectrum Usage: Uses half the bandwidth of wideband FM, allowing more channels in the same frequency range.
3. Regulations: Required in some regions for compliance with spectrum management policies.

Narrowband FM is commonly used in urban areas, where spectrum is congested, or for applications that prioritize efficiency over fidelity.

In recent years, many regions have mandated a transition from wideband to narrowband FM to accommodate increasing demands for spectrum. This shift is particularly evident in:

1. Public Safety Communications
2. Commercial and Business Radios
3. Amateur Radio Repeaters in crowded urban environments

Bandwidth choice in analog FM affects several aspects of amateur radio operations:

1. Repeater Compatibility: Repeaters may only support one bandwidth type, so users must configure their radios accordingly.
2. Audio Quality: Wideband FM offers better clarity, but narrowband FM remains acceptable for most voice communications.
3. Spectrum Efficiency: Narrowband FM allows more users to share the same band, which is beneficial in high-density areas.

Repeaters on RepeaterBook include bandwidth information in their details. This helps users configure their radios correctly for each repeater. The following details are typically provided:

1. Bandwidth: Indicates whether the repeater operates in wideband (25.0 kHz) or narrowband (12.5 kHz).
2. Mode Compatibility: Indicates whether the repeater supports mixed-mode analog and digital.

1. User Convenience: Ensures operators know the correct settings for their radios.
2. Improved Spectrum Management: Encourages efficient use of available frequencies.
3. Support for Transition: Helps users navigate the shift from wideband to narrowband systems.

• RepeaterBook Home
• ARRL: American Radio Relay League
• FCC Regulations on Bandwidth