Skip to content

Squelch Menu

Jump to bottom
nicsure edited this page Feb 20, 2026 · 3 revisions

Squelch Overview

Squelch is a system designed to mute the main speaker until a valid signal is received. nicFW’s squelch implementation is significantly more advanced than that of most radios and allows for fine-grained control over how and when audio is unmuted.

nicFW squelch operates based on two independent factors:

  • Signal strength (RSSI)
  • Received noise level (ExNoise)

For squelch to open, the signal strength must rise above a configured threshold and the noise level must fall below its threshold.
For squelch to close, the signal must drop back below its threshold and the noise level must rise again.

While the Squelch Menu is open, the menu’s Extra Info field displays real-time numerical values for the current channel or frequency’s RSSI and ExNoise levels. These live readings can be used to determine optimal values for several squelch parameters and Signal Floor calibration.

Squelch Menu Options

Level

  • Available Values: 0 (Off) to 9
  • Default Value: 2

Controls the primary signal-strength requirement for opening squelch.

  • 0 (Off)
    Disables squelch entirely; the speaker remains unmuted at all times.
  • 1
    Special noise-only mode. This is the most sensitive setting, but also the most prone to false openings and closings.
  • 2–9
    Correspond to S-levels:
    • 2 → Minimum of S1
    • 3 → Minimum of S2
    • 4 → Minimum of S3
    • and so on

Noise Trigger

  • Available Values: 0 to 127
  • Default Value: 48

Defines the maximum noise level that must be met for squelch to open. Noise must fall below this value before audio is unmuted.

Noise Hysteresis

  • Available Values: 0 to 20
  • Default Value: 4

Defines a buffer zone between squelch opening and closing based on noise level.

Example:

  • Noise Trigger = 48
  • Noise Hysteresis = 4

Squelch will:

  • Open when noise drops to 44
  • Close when noise rises to 52

This prevents rapid toggling in marginal conditions.

RSSI Hysteresis

  • Available Values: 0 to 20
  • Default Value: 4

Defines a buffer zone between squelch opening and closing based on signal strength.

  • Units are in ½ dBm
  • Example:
    • Level set to 3 (S2)
    • RSSI Hysteresis set to 4

Squelch will:

  • Open at S2 + 2 dBm
  • Close at S2 − 2 dBm

Throttle

  • Available Values: 0 to 9
  • Default Value: 2

Sets a minimum time, in tenths of a second, that must pass after a squelch state change before another change is allowed.

This prevents rapid squelch chatter in noisy environments.

Noise Ceiling

  • Available Values: 0 to 127
  • Default Value: 60

Defines an absolute maximum allowable noise level.

  • Any noise at or above this value will immediately close squelch
  • Overrides hysteresis and tail settings

This setting is the primary reason for nicFW’s exceptionally fast squelch cutoff behavior.

Squelch Tail Elimination

  • Available Values: Off, RX, TX, Both
  • Default Value: Off

Reduces squelch tail noise (static bursts) at the end of transmissions.

This system works by transmitting a special 55.0 Hz CTCSS tone at the end of a transmission. If the receiving radio detects this tone, it immediately mutes the speaker before the carrier drops.

Options:

  • RX – Respond to tail elimination tones
  • TX – Transmit tail elimination tones
  • Both – Enable both receive and transmit behaviour

This feature requires compatible settings on both stations.

Tail

  • Available Values: 0.0 to 5.0 seconds
  • Default Value: 0.5

Defines how long the speaker remains unmuted after a signal drops before squelch closes.

Although often overridden by Noise Ceiling, this setting can help prevent squelch chatter when signals hover near the threshold.

Home

Search

Patreon

Clone this wiki locally