I have seen antenna specifications which state a gain of 9dB. Does this have more range than an antenna with a gain of 6dBi?

No. That little “i” in “dBi” makes a lot of difference. If it’s not there, the antenna supplier is being creative by relating antenna gain to radome length. It’s sometimes called “Marine Gain” which is meaningless because it has no standard reference, but allows the marketing department to invent numbers so the specifications appear more impressive. “Marine Gain” is not used by marine electronics technicians. To compare apples with apples, our antennas have both dBi and “Marine Gain” figures listed.

Can I use the little HeliFlex antenna as a permanent installation?

VHF HeliFlex antennas are fine for short range communications. They are a compromise solution, ideal for RIBS, workboats and other small boats where a full length antenna can be impractical. Some racing yachts remove their Pro Series 1.8m antenna and replace it with the helical for the duration of the race. Where maximum range communications are needed, the HeliFlex can be simply unscrewed and replaced with a full length antenna.

Cellular Heliflex antennas are good performers. Cellular frequencies are high enough that a small antenna is not a compromise. If you want to go to the limits of your service provider’s coverage, the extra height of a 1.8m or 2.5m antenna will get you there.

The AM/FM Heliflex is fine for boats which are within normal broadcast station coverage. Boats going further out can fit a 1.8 metre or 2.5 metre UltraGlass antenna.

Is more gain better?

Not always. High gain antennas need a larger, stable vessel, because the extra gain has been achieved by flattening out the “lobe” of the antenna. Smaller boats which roll around more, or yachts that are heeled over, may find that stations they are calling fade in and out of the antenna’s lobe as the antenna moves away from vertical.


So how is “gain” measured?

Gain is measured in decibels (dB), related to a known standard reference, usually an ”isotropic” antenna. Gain figures which show the comparison with an isotropic antenna are written dBi. For example, a 2.5m VHF colinear antenna with two radiating elements has a gain rating of 6dBi.

So, 2.5 metre antennas are high gain, right?

Only if they have two or more radiating elements. A 2.5 metre halfwave antenna has one radiating element and a gain of 3dBi. Unfortunately, some suppliers find that too complicated and rate their short antennas at 3dB and all the longer ones at 6dB, which sounds simpler but is misleading.

Range Calculator

To calculate the range between two base stations, enter the height of the antenna at each station in metres for the range in nautical miles
nautical miles