Why is my VHF radio not transmitting, and how can I troubleshoot it?
My fixed VHF switches on and receives other boats clearly, but nobody seems to hear my calls. How can I check whether the problem is the microphone, power supply or masthead aerial before replacing the radio?
Answer
A VHF that receives but cannot be heard usually has a channel-setting problem, a faulty microphone, a voltage drop during transmission or an antenna/coax fault. Check the channel and watch what happens when you press the microphone's push-to-talk button, then measure voltage at the radio while transmitting.
Check settings and symptoms
Arrange a brief radio check with a nearby boat on a locally permitted ship-to-ship working channel. Set both radios to the same channel and regional channel group. Avoid Channel 16 for routine checks and wait until the channel is clear.
- Channel group: check that INT, USA or CAN matches your location. Some channel assignments differ between groups.
- Channel type: use a suitable simplex channel for the check. Duplex channels use different transmitting and receiving frequencies, so two boats may not hear one another.
- Power: fixed sets commonly offer 1 W and 25 W; handheld output varies by model. Start on low power for a nearby check, then try high power if needed and permitted on that channel.
- Controls: release any keypad lock using the key-symbol button, following the manual. Some channels restrict transmission or power automatically.
Turn up the receiving radio's volume and reduce its squelch until you hear background noise, then increase it just enough to silence the hiss. Your own volume and squelch normally affect reception, not transmitted power. You may simply be missing the reply.
Check TX indication and microphone
Press push-to-talk briefly and look for the TX indicator. If it stays off, suspect the microphone switch, its cable or connector, an operating restriction or a radio fault. The TX indicator confirms that transmission has been commanded; it does not prove useful power is reaching the antenna.
Switch off before reseating a removable microphone connector. Check for loose locking rings, bent pins, green corrosion and cable damage where the lead enters the microphone. Do not force connectors: pin arrangements vary between brands and models.
If another boat hears a carrier or its squelch opens but your voice is absent, suspect the microphone or audio circuit. Hold the microphone roughly 5 to 10 cm from your mouth, speak normally across it and shield it from wind. Keep your fingers clear of the microphone opening.
A transmission timeout can stop a long call. Release push-to-talk and try a short call after the set resets. Check the manual for its timeout period.
Measure supply voltage under load
A bright screen and clear reception do not prove the supply is sound. A typical 25 W fixed VHF draws several amps while transmitting, considerably more than when receiving. A corroded connection may only reveal itself under load.