Marine VHF Antenna Selection for Workboats

The VHF radio is still the primary safety and working channel on most commercial vessels. The radio set gets chosen carefully, but the antenna is often whatever came with the boat. On a workboat that operates in all weathers, the antenna choice has a direct effect on how far the radio reaches and how reliably it holds a signal in a seaway.

Gain and the effect of roll

Antenna gain at VHF is achieved by flattening the radiation pattern, concentrating energy towards the horizon instead of upwards and downwards. On a stable vessel this extends range. On a vessel that rolls or pitches hard, a narrow beam can tilt away from the receiving station.

• 3 dB: broad pattern, tolerant of heavy roll. Suits small workboats, RIBs and sailing vessels.
• 4 dB: a good middle ground for pilot vessels and crew transfer vessels.
• 6 dB: maximum range on larger, more stable vessels and for shore stations.

Options in the Renair range

• VHF73: 3 dB, 1.26 m fibreglass. Also available as the VHF73N with an N-female connector.
• VHF74: 4 dB, 1.36 m glass fibre, a common choice for commercial craft.
• VHF96: 6 dB, 1.2 m fibreglass.
• VHF76: 6 dB, 2.6 m fibreglass for maximum range.

Height and position

VHF range is mostly line of sight, so mounting height has more effect than a few decibels of gain. Mount the antenna as high as practical, clear of the radar beam and away from other transmit antennas. Where a vessel carries more than one VHF radio, separate the antennas vertically if possible to reduce interference. If AIS is fitted, plan its antenna at the same time. Our AIS antenna guide covers the separation points.

Do not lose it in the cable

Coax loss at VHF is lower than at cellular frequencies, but on a long run up a mast it still adds up. Use a low-loss cable for runs over 10 to 15 m, keep connectors to a minimum and seal every outdoor joint. A higher-gain antenna on a poor cable run can perform worse than a lower-gain antenna on a good one. Our coaxial cable guide has more detail.

Mounts built for the job

Workboat antennas take knocks from lines, cranes and crew. Use stainless steel mounts such as the MAST/RAIL MOUNT SS 1"-14NF or a lay-down mount where the antenna must fold for bridges or lifting operations.

Frequently asked questions

Is a higher-gain VHF antenna always better?

No. Higher gain narrows the vertical beam. On a vessel that rolls hard, a 3 or 4 dB antenna often gives more consistent communications than a 6 dB model.

Should the VHF antenna be above or below the radar?

Keep it out of the radar beam. Mounting above the radar on its own pole, or well below the beam, both work. Avoid placing it level with the scanner.

How far should two VHF antennas be apart?

Vertical separation on the same mast is most effective. Where that is not possible, keep as much horizontal distance as the vessel allows and follow the radio manufacturer's guidance.

See the full maritime range, or contact sales@renair.co.uk to match antennas to a vessel or fleet.