Radio Navigation Aids Frequency Bands

Electromagnetic Spectrum Bands

Aviation radio navigation aids use distinct frequency bands within the electromagnetic spectrum, classified as VLF, LF, MF, HF, VHF, UHF, SHF, and EHF. Each band covers a specific frequency range:

• VLF: 3–30 kHz
• LF: 30–300 kHz
• MF: 300–3,000 kHz
• HF: 3–30 MHz
• VHF: 30–300 MHz
• UHF: 300–3,000 MHz
• SHF: 3–30 GHz
• EHF: 30–300 GHz

Key Navigation Aid Frequency Bands

• NDB (Non-Directional Beacon): Assigned 190–1750 kHz (LF and MF bands). Note that commercial radio stations may also operate in this range, which can cause interference and is a common exam topic.
• ADF (Automatic Direction Finder): Receives signals in the same 190–1750 kHz band as NDBs.
• VOR (VHF Omnidirectional Range): Operates from 108.00 to 117.95 MHz (VHF band). The lower part of this range (108–112 MHz) is shared with ILS localisers.
• ILS (Instrument Landing System): Localiser operates from 108.10 to 111.95 MHz (only odd tenths), and the glideslope operates in the UHF band (329–335 MHz).
• DME (Distance Measuring Equipment): Uses UHF, specifically 962–1213 MHz.

Modulation Types

• NDBs use carrier wave modulation types such as N0N, A1A, and A2A for identification.
• VHF-COM (communications) uses A3E, which is amplitude-modulated speech.

Operational Notes

• Interference from commercial and marine radio stations is possible in the NDB/ADF band, but only aeronautical NDBs are approved for navigation.
• Fading can occur due to interference between sky waves and ground waves, especially in LF/MF bands.