What is SNR (signal to noise ratio) and how does it affect a radio call?

SNR (Signal-to-Noise Ratio) is a measure of signal quality. It compares the level of the desired signal (your voice or data) to the level of background noise in the system.

Definition:

SNR = Signal Power / Noise Power

It’s typically expressed in decibels (dB):

• Higher SNR = better quality
• Lower SNR = more noise and degraded communication

How SNR Affects Radio Calls:

1. 

Voice Clarity

• High SNR (e.g. 25–40 dB): Clear, intelligible audio with minimal distortion.
• Low SNR (e.g. <10 dB): Scratchy, garbled, or unintelligible audio.

2. 

Digital Radios (e.g., MOTOTRBO, NXDN, P25)

• Digital systems have a “cliff effect” — when SNR is good, audio is crystal clear; but when it drops below a threshold, audio rapidly cuts out or fails altogether.
• Unlike analog, where poor SNR means “noisy but usable,” digital often means “perfect or nothing.”

3. 

Range

• As you move farther from the transmitter, signal weakens, noise becomes more dominant, and SNR drops.
• Radios may still show full bars (RSSI), but if SNR is low, audio quality can still suffer.

4. 

Interference

• Electrical noise, co-channel users, or adjacent-channel signals can raise the noise floor, reducing effective SNR.
• This can result in dropped calls or degraded voice quality even in otherwise strong signal areas.

Good SNR Values:

• Analog Voice: ≥ 12 dB is typically usable, ≥ 20 dB is clear.
• Digital Voice/Data: ≥ 18–20 dB usually needed for reliable operation.

Why It Matters in LMR:

• SNR directly impacts user experience, especially in noisy environments like construction, public safety, or transport.
• It’s also a key metric in coverage testing, antenna alignment, and site placement.

Summary:

SNR is a core indicator of communication quality in LMR. High SNR means clean audio and reliable data. Low SNR results in noisy, choppy, or failed calls—especially in digital systems. Maintaining good SNR is essential for dependable radio performance