Module 2 - VHF Radio Basics
Squelch, Volume, And Listening Watch
What you will learn
Maintain an audible listening watch and use dual watch or scanning as aids without losing track of the channel that actually received the call.
A radio only contributes to safety when someone can hear and interpret it. Volume, squelch and watch facilities must support attention rather than create a false sense of coverage.
The MCA's small-craft guidance says to maintain a listening watch on Channel 16 whenever practicable. Vessel requirements and local instructions can add other watch obligations, so use the current passage plan, notices and equipment guidance for the operating context.
Dual watch commonly monitors Channel 16 alongside a selected working channel. Scan checks a programmed list. These are receiving aids: device behaviour varies, a strong signal may stop the scan, and neither function proves that a call was heard or understood.
When a watch facility stops on a signal, identify the displayed channel before replying. Keep the volume usable and the squelch no tighter than necessary. Radio use must not distract the watchkeeper from navigation, visual lookout or collision avoidance.
Reply on the channel that actually called
The radio stops scanning and you hear the final words of a call, but you did not see which channel caused the stop.
1. Do not guess
Look at the display and identify the received channel before pressing PTT.
2. Recover context
Listen for identity and purpose; if uncertain, request a repeat using correct procedure.
3. Restore the watch
After the exchange, return the radio to the required listening arrangement.
Sense check: Dual watch listens on two relevant channels; it does not transmit on both or turn Channel 70 into a voice channel.
Common mistake or limitation
- Leaving volume too low after a call and assuming an active display equals an active watch.
- Replying without checking which channel stopped a scan.
- Treating dual watch or scan as a replacement for human attention and a proper navigational lookout.
Recap
- Maintain the required listening watch whenever practicable.
- Dual watch and scan are receiving aids with device-specific behaviour.
- Identify the received channel before replying.
- VHF operation must not distract from safe navigation.
Optional quick check
Section 5 of 9
A scan stops on a brief signal. What should happen before you reply?
Sources and factual review
Reviewed 20 August 2026 - Compass Revision editorial review.
Continue studying VHF Radio Basics
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