The power of the radio’s transmitter can range between 1 and 25 watts. A 25-watt transmitter has a range of roughly 54 Nautical Miles (100 km/62 miles).
Factors like antenna height and line-of-sight all play their part in reducing the real-world range. Each boat will experience differences in its available range of Very High-Frequency radio transmissions.
A VHF radio is a primary safety device on a boat. It can result in a positive outcome if you ever find yourself in a bad situation. Unfortunately, the opposite is also true.
At a Glance:
1️⃣ The factors that affect the range include the transmitter’s power, the receiver’s sensitivity, the distance to the horizon, the weather conditions, and the radio’s power source.
2️⃣ Always install a good quality antenna in as high a location as possible.
3️⃣ Always exercise good radio etiquette when transmitting.
📡 Range Of VHF Marine Radio
Marine VHF radios use frequencies between 156 and 174 MHz. This band is defined by the International Telecommunications Union (ITU) as the Mobile Very High Frequencies Band.
Frequencies are separated into bands of 25 kHz. The lowest frequency band is 156 MHz and is allocated as channel 60. The channel numbers increase incrementally to channel 88.
This information is carried digitally, and the receiving set will alert the operator of an incoming call once its own MMSI is detected.
Calls are set up on the dedicated VHF channel 70, which DSC equipment must listen to continuously. The actual voice communication then takes place on a different channel specified by the caller.
Understanding the range of your VHF marine radio can be complemented by knowing which VHF marine radio channels to use.
Factors Affecting Range
VHF transmission range is affected by the transmitter’s power, the receiver’s sensitivity, the distance to the horizon, the radio’s power supply, and the weather conditions.
Power Of The Transmitter
The power of the radio’s transmitter can range between 1 and 25 watts. Giving a maximum range between aerials mounted on tall ships and hills and 5NM (9 km) between aerials mounted on small boats at sea level.
Sensitivity Of The Receiver
The biggest factor affecting the sensitivity of a receiver is the antenna. The antenna parameters that affect the receiver’s performance are gain (decibel rating), height, and length.
The higher the gain and height, the better the transmission strength and ability to receive. The longer the aerial, the better the performance.
Frequency modulation is used, with vertical polarization, meaning that antennas have to be vertical to have good reception.
The Distance To The Horizon
VHF transmitters must be in the line of sight of the receiver. The earth’s curvature affects the signal distance. Because of this, the higher the aerial, the greater the range.
Weather conditions affect range. Weather conditions that can be seen (fog, heavy rain, and snow) reduce the transmitting distance.
The Radio’s Power Supply
A small handheld, battery-operated radio has a reduced range compared to a fixed installation that draws power from the vessel. As the portable radio’s batteries discharge, the range reduces.
Assuming optimal variables, the typical ranges that can be achieved by a VHF radio are determined by the transmitter power – watts.
Approximate ranges are as follows:
|Size Transmitter||Operating Range|
|1-watt||200 yards (100 meters)|
|5-watt||12 miles (20 kilometers)|
|6-watt||20 miles (32 kilometers)|
|25-watt||62 miles (100 kilometers)|
📶 Antenna Types And Installations
The antenna’s height, position, and length affect the transmitter and receiver’s power.
The transmitter’s ability to transfer energy (in the form of radio waves) to the atmosphere depends on the following:
- The antenna you choose.
- The coaxial cable that connects the transmitter to the antenna.
The frequency bands available for marine VHF traffic result in a substantial energy loss as it passes through the cable. Optimal antenna cable reduces the loss.
The difference in range between inadequate antennas and optimal units is up to 120%.
The main differences between antennae generally involve how the signal is transported within the aerial.
The different combinations between antennas are listed below.
- A single coaxial cable.
- A combination of coaxial cable, brass, and copper.
- All brass and copper (this is the best performing, most efficient combination.
Select a model that only uses brass and copper for the best-performing antenna.
Antenna Height And Location
Because VHF transmissions travel by line of site, the higher the aerial is mounted, the further it will transmit. Keep all the antennas separate and ensure they do not conflict.
📻 VHF Marine Radio Channels And Usage
In the States, it is required that anyone using a marine radio is correctly licensed to do so. Training to use a radio will include the following information.
When using a VHF Radio during an emergency, tune it to channel 16 and full power.
If your life is in danger, you can make a distress call by saying “Mayday Mayday Mayday,” the name of the vessel and call sign.
After the coast guard responds, reply with the position of the vessel, ideally with your latitude and longitude from the GPS.
Commonly Used Channels
As discussed earlier, the channels in use by marine VHF radios range from 66 to 88, and the frequencies range between 156.025 MHz and 157.425 MHz
The channels and assigned frequencies are listed below.
|Channel No||A Ship Transmitter (MHz)||A Shore Transmitter(MHz)||In Use By|
|70||156.525||156.525||Digital Selective Calling enables transmission to specific vessels|
|75||156.775||156.775||Omitted because it is so close to the international distress frequency|
|76||156.825||156.825||Omitted because it is so close to the international distress frequency|
|81||157.075||161.675||U.S. Government Use Only|
|82||157.125||161.725||U.S. Government Use Only|
|83||157.175||161.775||U.S. Coast Guard Use Only|
Proper Usage And Etiquette
The rules of marine radio use and etiquette are in place for several reasons.
Preserving channels for their intended use reduces misunderstandings, ensures availability during emergencies, and prevents offense by avoiding inappropriate messaging.
In short, it enhances effective communication and respect among mariners.
The following rules and etiquette are in place:
|❌ Don’t||Never use emergency channels for casual conversation.|
|Do not use obscene or objectionable language.|
|Do not transmit music.|
|Do not transmit subversive information.|
|✅ Do||Keep transmission concise.|
|Use your vessel’s name and station ID to identify yourself.|
|After transmitting, always release the transmission key so you don’t block the channel.|
|Always have one channel tuned to station 16 (156.800 MHz) to monitor for emergency transmissions.|
|Only use channel 9 for radio checks.|
|Only use a marine radio when on the water.|
🔑 Key Takeaways
VHF radios are a vital part of safety equipment on board your boat. If you travel offshore, they are a necessity.
1️⃣ The range of a VHF radio is approximately 54 Nautical Miles (100 km/62 miles).
2️⃣ Several factors affect the range and quality of the transmission, including power, sensitivity of the receiver, and weather conditions.
3️⃣ The higher the quality antenna and the higher the antenna itself, the longer the range of transmission.
Once you understand the range of a VHF marine radio, you might want to learn how to register a VHF marine radio to help you grasp the concept of Digital Selective Calling (DSC).
To take maximum advantage of DSC radio, one should have a Maritime Mobile Service Identity or MMSI number, which can help you to connect with other vessels in the vicinity.
When a DSC radio is bought new, the user will get the opportunity to program it with the MMSI number of the ship it is intended to be used on.
But to change the MMSI after the initial programming can be problematic and require special proprietary tools. This is done to prevent theft.