Radiotelephone Equipment

As with all modern electrical equipment, VHF radios come in many designs with many different features built into them by the manufacturer. All radio operators need to have a basic knowledge of how to use the facilities on offer.

All radios have similar basic functions. They may have slightly different labels but all function the same way. This page describes the basic functions of any VHF radio. This information will enable the use of any VHF radio on any vessel.

The SIMS Interface on newer Lifeboats is the join between the physical radio set up and the computer generated Graphic User Interface (GUI). The operator uses a tracker ball to move around the screen to select the radio control. The radio operation is now no longer tied to one position it can be moved around any of the boats crew positions

Squelch and Volume Controls:

The Squelch control fitted to all VHF radios controls the sensitivity of the receiver. It should be turned anti clockwise until a roaring noise is heard, at which point the volume control can be adjusted to a comfortable level. The squelch should then be turned back clockwise to the point when the noise just disappears. This position is known as the ‘squelch threshold’ and will vary depending upon the atmospheric conditions of the day. It should be adjusted each time the radio is switched on and will require adjustment after changing channels.

Channel Selection:

On most radios, channel selection is made by pressing the numbered buttons on the outside of the set or by turning a Channel Selection knob; the selected channel will be shown on a built-in display.Some VHF sets can transmit and receive on up to 67 channels. Although reception of all channels is permitted, you can only transmit on the channels covered by the Ship's License and their Operator's Certificate of Competence. Lifeboats have access to all channels, however boathouses are only permitted to transmit on Channels 16, 31 and 67 in ROI, and 0, 16 and 31 in UK. See Appendix. Channels

Dual Watch:

Most VHF radios have a dual watch facility allowing you to simultaneously monitor Channel 16, (which has priority), and any other channel. Once the second channel has been selected, the radio will rapidly switch back and forth between the two channels.If a transmission is received on the selected channel it will be heard fairly clearly, although the set will continue to scan Channel 16. If this continual scanning makes the transmission unintelligible, then the dual watch facility will have to be turned off. If a transmission is received on Channel 16 the set will lock onto Channel 16 for the entire duration of the transmission. Note that some sets will not transmit while they are in Dual Watch mode.

The Sailor RT 2048 VHF Radiotelephone

The Sailor RT 4822 VHF Radiotelephone


Scanning is similar to Dual Watch but the set can scan more, or sometimes all, of its available channels. The equipment fitted to Lifeboats will continue to monitor Channel 16 every 1.2 seconds regardless of the number of other channels it has been set to scan.

Power Output:

The maximum power output for a small craft VHF set is limited to 25 Watts. As VHF transmissions are limited to line-of-sight this is normally more than adequate. Antenna height has a far greater effect on range and increasing the power to a VHF transmitter will not significantly increase its range. All sets can transmit on reduced power, (1 Watt), and this low power setting should be used for all routine communications.

Handheld VHF Radios:

Handheld radios normally have the same controls as mounted sets but as they are limited to 5 watts maximum power and rely on their own short, helical aerial, their range is significantly less. Most handheld radios are vulnerable to water, ( although all the sets used by the RNLI are fully waterproof). They should be held as upright as possible to improve transmissions and reception.

A typical radio station fitter to an ALB

Tamar radio station and SIMS radio pages

Handheld VHF Radio