Selection of marine VHF antenna

VHF antenna selection requires balance between size, profit, and cost. The type of antenna depends on the desired distance, physical requirements and costs. Antenna is the key to achieving good VHF coverage. An expensive radio is not valuable if it is not connected to a good antenna. The main consideration is the height of the antenna above the water. The larger the antenna, the greater the range or the coverage. VHF radio is in straight line and is called visibility. Coverage is affected by the barrier between the ground and the two radio channels. Two stations will be able to communicate with each other if both fall below the horizon and "do not see" each other. Thanks to the Earth's curvature, the best VHF communication is usually approx. It is limited to 40-50 miles.

Since altitude is one of the most important factors in the region, sailors can better investigate the better range if the antenna is fitted with the appropriate antenna at the top of the column. Small-scale boats are generally only a few feet above the water and the installation of the high antenna is not practical.

The antenna radius can be calculated using the following formula:

Range Miles = Root (feet) of the square height above the water 1.42.

Let's look at some of the following antennas. Note that the range is additive and depends on the antenna height of the other station. The 3-pin antenna provides a range of about 2.5 miles. However, if the other station also has a 3-foot antenna, then it also sees 2.5 miles and the total communication range is about 5 miles. Above

* Height Height Height Height Height Water + Antenna height

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The antenna can be designed to provide a profit in addition to the radio. Profits work for both broadcast and betting. The marine radio is limited to 25 watts transmit power by law. So how does profit increase? Antenna can not increase the amount of power it supplies. The antenna manipulates power and focuses it. In fact, a marine antenna is used, which goes straight into the air and sets it to the horizon. Like a balloon, if it breaks, the pages are widened.

The gain is measured in decibels (pcs). For every 3d of the gain, the actual radiation power is doubled. 6D gain 4 times increases the actual performance.

Each 3db power has doubled, so a [620db] amplifier antenna (100watts):
First 3db: 25w * 2 = 50w
Second 3db: 50w * 2 = 100w

Antenna will provide an efficient input power of 8 times the input power, so the 25 watts 9dB amplifier antenna has 200 watts of effective radiations.

Caution should be taken into account. 200 watts sound very good, but in order to get this amount, energy is a very thin line that radiates horizontally. Just think of a laser beam. Moves straight. This can cause disadvantages to seas, so that the cases roll and spin, this signal can easily enter the water rather than on the horizon and the result can not communicate as the signal enters and exits when the boat moves.

Which antenna is the best.

Boat Antenna
Small Fishing Boat – Lake 3 or 6 & # 39;
Small Fishing Boat – Ocean 3 or 6
Power Station – Lake 3, 6 & # 39; or 9 & # 39;
Power Boat – Ocean 3 or # 6;
Great Ship – 3, 6 & # 39; or 9 & # 39;
Great Boat – Ocean 3 or # 6;
Sailing 3 & # 39;

Another aspect of the coaxial cable and connectors. All coaxial and connectors have some loss. This loss lies in the coaxial specification and is decibels. Against the effective antenna ratio, coaxial loss was measured at a loss of normal at 100 feet. So with a 100-foot coaxial and 3db loss over the length of the cable would lose half a percent of the power placed on the line. 25 watts of power 100 feet coaxially, with 3db loss of 12 watts per 100 feet per antenna input.

However, a typical coaxial run of 10 to 20 feet in one boat, so the loss does not pose a big problem. However, sailing can work much longer and take into account the used coaxial types.

Some typical coaxial values ​​at 156 MHz (make sure you check the MFG values):

RG-58 / U 6.0 pcs
RG-8X 4.0 pcs
RG-213 3.0 pcs
RG-6 2.0 pcs

Installation of the antenna should also be considered. There are usually three ways to mount the antenna:

* Rail mounted
* Lifting device (sailboat)
* Surface mounting

Please note that obstacles may affect coverage. The antenna is four meters above the water, but if the ship's structure is higher, the signal will be reduced due to the blocking part of the boat. Always observe the following:

* Mount the other antennas
* Install large metal objects
* Mount as high as possible

Consent. It is almost always a compromise to obtain the best range that can best be fitted on a boat. Think about what the majority of the radio requirements will be. A short antenna may have a smaller coverage, but if communication is left with other stations, it is not necessary to install a larger antenna if it is a bigger problem. However, if possible, 6 antennas are used, except for sails that provide a good range and are not too large for most vessels.

Source by sbobet

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