When choosing a VHF antenna you need a balance between size, profit and cost. The type of antenna depends on the desired distance, physical requirements and costs. An antenna is the key to a good VHF coverage. An expensive radio has no value if it is not connected to a good antenna. A major consideration is the height of the antenna over the water. The larger the antenna, the greater the range or the coverage. The FM radio goes straight and is called the line of sight.
The lid is influenced by the curvature of the earth and all obstacles between the two radios. Since the height is an important factor in the area, the sailboats can achieve a significantly better range with the correct antenna by mounting the antenna on the top of the mast. Small boats are a few meters away, usually by water and the installation of a high antenna is impractical.
|image from Boat-Project|
The range of an antenna can be calculated according to the following formula:
Range in mile = square root of height above water (in feet) times 1.42.
Look at one of the following antennas. Note that the range is additive and depends on the antenna height of the other station. A 3 foot antenna produces a range of about 2.5 miles. If the other station is a 3-foot antenna then it can also 2.5 miles and the whole of the communication would be about 5 miles.
3 meters 5 miles
5 feet 9.8 km
10 meters 9 miles
20 meters 13 miles
Height = Height above water + Antenna height
So far, the observation has been sent to the ship. Communication with a coastal station significantly improved, usually, the BoatUS coastal station, has an extremely high-level antenna. An antenna 1000 ft has a 45-mile free space next to the height of the barrel antenna.
An antenna can be designed to deliver profit for a radio. A mariner radio is legally limited to 25 watts of transmission power. The antenna can not increase the amount of power. An antenna manipulates power and focuses it. In reality, an antenna Marine receives the power in the sky and concentrates on the horizon. If you're kidding a balloon, expand yourself.
The profit is measured in decibels (db). For each 3db of the profit, the effective radiation power is doubled. 6db gain can increase the effective power by 4 times.
For each 3db, the force is doubled
25w on a 6db (100 watt) amplifier antenna:
First 3db: 25w * 2 = 50w
Second 3db: 50w * 2 = 100w
A 9dB acquisition antenna would have an effective radiation power eight times the power supply so that 25 watts on a 9 dB antenna amplifier effectively radiated power of 200 watts.
200 watts looks good, but to get this amount of profit, the energy is a very thin line that radiates horizontally. Which is the best antenna.
Small fishing boat - Lake 3 'or 6'
Small fishing boat - Sea 3 'or 6'
Motorboat - see 3 ', 6' or 9 '
Motorboat - Sea 3 'or 6'
Big boat - more 3 ', 6' or 9 '
Big Boat Ocean 3 'or 6'
Sailboat 3 '
Another consideration is the coaxial cable and the connectors. All coaxial and connectors have a certain loss. Compared to the effective antenna gain, the coax is measured in loss in db normally per 100 feet. 25 watts power, which was placed on a 100 foot piece of coax with loss of 3db per 100 feet, would have 12 watts at the antenna output.
However, a typical coax race is 10 to 20 feet in a boat, so the loss is not a big problem. Some typical coaxial values at 156mHz (Make sure you check the Mfg ratings):
RG-58 / U 6.0 db
RG-8X 4.0 db
RG-213 3.0 db
RG-6 2.0 db
Installation of the antenna must also be considered. There are typically three ways to mount an antenna:
* Rail mounting
* Mast assembly (sailboats)
* Surface mounting
Keep in mind that obstacles can affect coverage. The antenna can be four meters above the water, but if the boat's structure is larger, the range in this direction is reduced by blocking the boat in the signal. A short antenna may have less coverage, but if communication with other drives can be maintained based on their location, you will not need to install a bigger antenna if that problem is over. However, if possible, a 6-db antenna is a good antenna, except sailboats that offer a good range and are not too big for most boats.
Take a few moments to look at your boat and help cover the type of antenna and mount that best suits your situation.