How to Choose a VHF Antenna

By Capt. John N. Raguso

When you are out of cell phone range, your vessel’s VHF radio is your lifeline back to civilization, should you have any medical, mechanical or electrical hiccups and need help pronto. If you’re a fisherman, the VHF is also a useful tool to “eavesdrop” on the conversations of other anglers who are either slaying them or wasting gas, along with some clues as to where the action might be happening should you decide to investigate. But the best VHF radio is only as good as the antenna that transmits and receives those high-frequency signals, so let’s take a deeper dive on how to choose the right VHF antenna for your boat.

Antenna Construction

The external part of a fiberglass VHF antenna is called a “radome” and when you are shopping around, it’s hard to tell the difference between one and another. They can look extremely similar on the outside, but there’s often a world of difference inside where you can’t see the quality of the build. Some antennas offer plastic/nylon ferrules to attach it to a mount, while other connectors might be constructed from chrome plated zinc, chrome over brass, or stainless steel.

A popular budget marine VHF antenna is Shakespeare’s model 5101 Classic, an 8footer that features a fiberglass outer radome, 6dB gain, with brass and copper elements inside, a chrome-plated brass ferrule with standard 1x14 thread pattern, 15-feet of RG-58 cable and a PL-259 connector to plug into your VHF radio. The latest price from Amazon is just under $100. In contrast, Shakespeare’s 8-foot 5225-HT Galaxy 6dB gain marine VHF antenna is roughly double the cost of the more affordable Classic detailed above. However, it offers upgraded internal components that include collinear-phased wave elements, a higher grade of brass and copper fittings for maximum range and efficiency, Ethafoam spacers that protect the elements from vibration for greater durability, low-loss RG-8/X cable, plus a thicker radome that’s covered in a special urethane exterior finish to prevent yellowing, cracking and UV damage. Is it worth the extra cost? I think so and have been using the higher end Galaxy VHF antennas on all of my boats with excellent results.

Italian competitor Glomex recently introduced their version of the ideal marine VHF antenna in the form of the Model RA1225HP, which is constructed from double-thick fiberglass with a smooth, five-layer, UV-resistant, anti-yellowing polyurethane finish. Inside, spiral copper wires are set into brass tubes for superior range and performance. The RA1225HP has a frequency range of 156-162 MHz, a 6dB gain, maximum input power of 100W, with 50-ohm impedance. Installing the RA1225HP is fast and easy thanks to its 316 stainless steel ferrule with integrated feed-thru that threads onto a standard 1x14 mount. It’s about the same price as the Shakespeare Galaxy, but offers a lifetime warranty.

ANTENNA HEIGHT & GAIN

Your VHF antenna is basically a “line of sight” tool whose range is affected by the curvature of the earth and its height off the deck of your vessel. When choosing the right antenna, height is of paramount importance when seeking maximum transmit and receive distance…the higher an antenna is mounted, the greater your range. To give an example of how antenna height affects range, let’s assume that your antenna is 8-feet long and is mounted on top of your boat’s hardtop, which is 8-feet above sea level. That would make the tip of your antenna approximately 16-feet above sea level. You are trying to communicate with another boat that also had an 8-foot antenna, but its base is only mounted 4-feet above sea level, which puts the antenna tip 12-feet above sea level.

Based on this info, what’s the max range that these boats could communicate? According to the Shakespeare Marine website’s (https://shakespeare-marine.com/choosing-the-right-antenna/) antenna height distance calculator, you would take the 4.88 nautical mile effective range of your boat’s antenna and combine it with the 3.99 nautical mile effective range of the other boat, to get an overall line of sight between boat antenna tips of 8.87 N/M, which is the calculated communication range in nautical miles. Actual range may be less (or more) depending on antenna quality and efficiency, output power of the VHF radios and other environmental factors.

With this limited range being stated, there are times when I have spoken with boats fishing the canyon edges from my marina, a distance of over 70 N/M away. How is that even remotely possible? Certain atmospheric condition produce situations where VHF signals can get an additional bounce and greatly increases range. On the flip side, dozens of fisherman chatting on channel 68 at the same time will greatly reduce your VHF’s effective comms range.

According to the techs at Shakespeare, gain is the transmission pattern of your antenna, measured in decibels (dB). The higher the dB, the farther the range. But as gain increases, the beamwidth is correspondingly narrowed. For smaller boats under 21-feet, a 3dB/4-foot antenna is likely the most useful tool for short range communications due to its wider beamwidth. For boats in the 23-to-40 foot range, a 6dB/8-foot antenna is a great compromise, with a good balance between the shape of the beamwidth, the gain and the rolling effects of the vessel. For larger boats over 40-feet in length, the taller 9dB antennas would probably work best and offer the greatest reach.

Most VHF antennas with a frequency range of 158MHz-163MHz will work with AIS, VHF, AM/FM, SSB and CB units. My boat has separate antennas for my VHF and AIS receive functions, but in a pinch, I can run both operations via a splitter if an emergency dictated such. Once your antenna is installed, it’s a good idea to periodically check the connections for corrosion. Signs of wear that could affect system performance include large cracks or fractures on a fiberglass radome. Loose connectors or those with excessive corrosion can interfere with communications. Equally important, the entire length of coax cable between the radio and antenna should be examined to ensure it is not kinked, crushed or cut. Damaged cable should be replaced. More accurate and sophisticated testing comes with the help of a meter that measures system performance. The ART-3 Antenna Radio Tester from Shakespeare offers a cost-effective method of ensuring the radio and antenna are performing to their best efficiency. Simple to use, the Shakespeare ART-3 tests radio output power, antenna VSWR (efficiency) and receiver functionality. Designed with boat owners in mind, the ART-3 displays RF output power up to 30 watts on an easy-to-read, built-in scale. It has an internal battery or can be connected to the onboard 12V DC power supply. I use this at least once a month to check the health of my boat’s comms system, which is a critical component whenever you head offshore.