Does A VHF Antenna Need To Be Grounded?
I have used VHF radios for my entire career, but I have never had to install one myself. It turns out there is a lot more to it than I thought. My biggest stumbling block was working out whether I needed to ground my VHF antenna or not. This led me to do some research to get to the bottom of it.
VHF antennas that come with an integrated ground plane do not need to be grounded. VHF antennas that do not have an integrated ground plane must be grounded, and their instruction manual will tell you how.
Either way, you need to consult the installation instructions for the antenna that you buy. Some require grounding and others do not.
Why do you need to ground a VHF antenna?
VHF antennas are designed to radiate energy out in the direction of the horizon. To do this, they are mounted vertically, sticking straight up in the air. The length of the antenna is related to the wavelength of the transmission. Fortunately, when you can’t mount a huge antenna, you can use a shorter one and make use of “reflection” from the ground.
Normally, when you mount an antenna in the ground, it uses the earth to help radiate the signal. On a boat, where the antenna is at the top of the mast, you need to simulate the ground instead. You do this with a “ground plane”.
There are a few different ways that manufacturers can simulate the earth with a ground plane. Some methods require a physical connection to the earth, and some do not. You need to check with the manufacturer of your antenna as to whether your aerial requires a physical ground connection or not.
On most boats, the antenna comes with an integrated ground plane. These do not need anything special in terms of grounding. You usually get enough ground bonding just by connecting the antenna to your radio set, which in turn is grounded through your boat’s power supply. These antennas do not need to be grounded.
Less commonly, you get antennas that do not have an integrated ground plane. If you have one of these, the installation manual will tell you that you need to make a good connection between the antenna and the ground. These antennas do need to be grounded.
How to ground a VHF antenna
If you have an antenna that needs to be grounded, you need to take great care to ground it properly. It won’t be enough to just connect it to the ground of your boat’s power supply. You’ll need a better connection to the water.
The best connection to the water would be a metal hull. The entire surface of the hull is in contact with the water, providing the grounding surface.
Beyond a completely metal hull, you are just looking for the largest surface area in contact with the water that you can. Other examples of grounding possibilities include:
- Foil below the waterline
- Metal water tanks
- Metal keel
- Propeller (connected through the engine)
- Steering gear
Whatever method you choose, you just need to make sure you have the largest surface area you can in contact with the water. The water is the ultimate ground, so you want the best connection with it that you can.
Can I ground my antenna through the boat’s battery?
With an antenna with an integrated ground place, grounding through the boat’s power supply is sufficient. The grounding on this sort of antenna is just for the electrical performance of the system rather than to create the ground plane for the transmission itself. You only need enough of a ground connection to dissipate extra electrical signals.
If you have an antenna that requires a dedicated ground connection, your boat’s electrical ground is not going to be sufficient. You will need to install additional grounding as we have described above.
Does grounding a VHF antenna improve performance?
Grounding does improve the performance of a VHF. Even when you have an antenna that has an integrated ground plane, having an electrical connection to the earth will help. It won’t always be a noticeable improvement, but it should improve.
The reason for this is that the antenna will pick up any electrical signals and you will hear them as noise. Grounding the system helps to reduce this noise. Just imagine that you are giving the stray signal a way to escape. It can get out of your system by passing through the wires and into the water.
Additionally, just like any electrical system, grounding to earth makes it safer. Should electricity find its way into the system, it’s better if it can work its way to the ground rather than go into the next person that picks up the microphone.
How does grounding work on a Handheld VHF?
With handled VHF units, the antenna will have an integrated ground plane, so it does not need additional grounding to work.
Grounding does improve the efficiency of a handheld VHF, however. Unfortunately, connecting through a wire is not an option. You do not have an obvious way of making a metallic ground connection. Instead, the handheld VHF uses the person holding it as the ground. The operator is coupled with the radio, who in turn is coupled with the ground.
It is for this reason that you sometimes notice a handheld radio sounds clearer when you are holding it rather than when you sit it on a surface.
Pro Tip: Keep your handheld VHF in your hand to get a better signal
Does grounding a VHF antenna stop lightning strikes?
Lightning is caused when an electrical discharge in the atmosphere needs to come to earth. When it does so, it looks for the path of least resistance. This is why lightning is jagged, it changes direction when it finds a lower resistance path.
Any structure sticking up into the air is likely to create a path with less electrical resistance than the surrounding air. Things like church spires are a classic example. They are often the tallest structure in a small town, so are usually the first thing that gets struck by lightning. To avoid damage to the building itself, a metal “lighting rod” is installed to give the electricity an alternative path to the ground rather than going through the timbers of the building.
In the same way, a boat on the ocean is often the tallest structure around. At the highest point of the boat, you will have the antennas. The antennas are the most likely part to be struck by lightning. It would make sense that grounding the antenna reduces the damage caused by lightning. In theory, the lighting would pass down the grounding cable rather than damaging the boat.
Unfortunately, it is extremely unlikely that the grounding cable you have on your VHF antenna is sufficient to carry the power of a lightning strike. Ground your VHF antenna alone is not going to be enough to stop a lightning strike.