FAA Radio Spectrum Overview

Training module for new employees – understanding the FAA spectrum chart, aviation bands, and channel spacing.

1. What Is the FAA Spectrum Chart?

The FAA spectrum chart shows how different portions of the radio frequency spectrum are allocated to aviation uses: navigation aids, communications, radar, satellite links, and more. Nearly all civil aviation radio spectrum is shared between the Federal Government and the private sector, with certain bands reserved exclusively for aeronautical services.

Understanding this chart helps you:

Recognize which bands support navigation vs. communication vs. surveillance.
Interpret frequency assignments in FAA documentation and system specs.
Avoid interference when planning or analyzing systems that operate near aviation bands.

2. Visual Spectrum Map (Simplified)

The diagram below is a simplified, conceptual view of key aviation bands from low frequencies (kHz) up through microwave (GHz). It is not to scale, but it highlights major functional regions.

190–535 kHz
NDB (Non-Directional Beacons)

Low/medium frequency beacons used for older navigation methods.

4–30 MHz
HF Communications

Long-range communications (beyond line-of-sight) using ionospheric reflection, often for oceanic routes.

75 MHz
ILS Marker Beacon

Provides distance information along an instrument landing system (ILS) approach path.

108–118 MHz
VOR / ILS Localizer

VHF navigation aids: VOR and localizer signals for lateral guidance on approaches.

118–137 MHz
VHF Air/Ground Communications

Primary voice communication band between aircraft and air traffic control (ATC), towers, and other services.

225–400 MHz
UHF Air/Ground (Military)

Military air-ground communications and some glide slope allocations around 328.6–335.4 MHz.

960–1215 MHz
DME / TACAN / UAT / GPS (L5)

Distance Measuring Equipment, TACAN, Universal Access Transceiver, and some GPS signals.

2.7–3.0 GHz
Airport Radar & NEXRAD

Primary surveillance radar and weather radar bands.

5–5.25 GHz
MLS & Aeronautical Radionavigation

Microwave Landing System and related radionavigation services.

Note: This is a conceptual training graphic, not a precise engineering diagram. Always refer to official FAA spectrum charts and regulatory documents for exact allocations.

3. VHF Communications Band & Channel Separation

3.1 VHF Aviation Band (118.000–136.975 MHz)

The core aviation voice communications band spans approximately 118.000 MHz to 136.975 MHz. This band is internationally standardized and reserved for aeronautical mobile (route) services—air-ground voice communications.

Examples of uses within the VHF band:

Approach / Tower / Ground: Local control and ground movement frequencies.
CTAF / UNICOM: Common Traffic Advisory and airport advisory services at non-towered fields.
ATIS: Automatic Terminal Information Service broadcasts.
Emergency: 121.500 MHz – international emergency and distress frequency.

3.2 Channel Spacing: 25 kHz and 8.33 kHz

Within the VHF aviation band, frequencies are organized into channels separated by a fixed spacing. Historically, the standard spacing has been 25 kHz, meaning adjacent channels differ by 0.025 MHz (for example, 118.000 MHz, 118.025 MHz, 118.050 MHz, etc.).

In high-density airspace (especially in Europe), a narrower spacing of 8.33 kHz is used. Each 25 kHz “slot” can be divided into three 8.33 kHz channels, significantly increasing the number of available frequencies but requiring more selective radio equipment.

Channel Spacing Diagram (Conceptual)

25 kHz spacing (traditional):

118.000 MHz

118.025 MHz

118.050 MHz

118.075 MHz

Each block is separated by 25 kHz. Radios built for 25 kHz spacing can tune these discrete channels.

8.33 kHz spacing (high-density):

118.000 MHz

118.00833 MHz

118.01667 MHz

Three 8.33 kHz channels fit into one 25 kHz slot. Older 25 kHz radios cannot reliably use the intermediate 8.33 kHz channels without causing interference.

Key takeaway for new employees:
When you see references to “channel spacing” in FAA or ICAO documents, they are almost always referring to 25 kHz or 8.33 kHz separation between adjacent VHF communication channels—not 25 MHz. This spacing is critical for avoiding interference and maximizing the number of usable frequencies.

4. Regulatory Context & Frequency Tables

Frequency assignments and channel spacing rules are defined in multiple regulatory documents, including:

FAA Spectrum Management Charts: Show band allocations for navigation, communications, radar, and satellite services.
FCC 47 CFR Part 87 (Subpart E – Frequencies): Lists assignable frequencies and class-of-station symbols for aviation services.
ICAO and regional guidance (e.g., EUROCONTROL): Define implementation of 8.33 kHz spacing in high-density airspace.

For engineering work, spectrum planning, or system certification, always consult the latest official documents. This training page is intended as a conceptual overview, not a substitute for regulatory text.

5. Quick Reference – VHF Band Cheat Sheet

VHF Aviation Band

Range: 118.000–136.975 MHz

Primary air-ground voice communications worldwide.

Channel Spacing

Standard: 25 kHz (0.025 MHz) separation.

High-density: 8.33 kHz spacing (three channels per 25 kHz slot).

Spacing prevents interference and increases channel capacity.

Key VHF Frequencies

121.500 MHz: Emergency & distress.
CTAF / UNICOM: Common advisory at non-towered airports.
ATIS: Automated airport information (locally assigned).

6. Learning Check – Questions for New Employees

What is the frequency range of the VHF aviation communications band?
What is the standard channel spacing used in that band, and why is it important?
How does 8.33 kHz spacing differ from 25 kHz spacing in terms of channel capacity?
Which frequency is reserved for emergency and distress communications?
Why must older 25 kHz radios be considered when deploying 8.33 kHz channels?

Use these questions in onboarding sessions or as a short quiz to confirm understanding of the spectrum chart.