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A common type of monopole antenna at these frequencies for mounting on masts or structures consists of a quarter-wave whip antenna with a ground plane consisting of 3 or 4 wires or rods a quarter-wave long radiating horizontally or diagonally from its base connected to the ground side of the feedline; this is called a ground-plane antenna.
A mast radiator or mast antenna is a radio tower or mast in which the whole structure is an antenna. Mast antennas are the transmitting antennas typical for long or medium wave broadcasting. Structurally, the only difference is that some mast radiators require the mast base to be insulated from the ground.
Usually a chain-link fence is used, but sometimes wooden fences are used to prevent currents induced in a metallic fence from distorting the radiation pattern of the antenna. An alternate design is to mount the mast on top of the antenna tuning hut, out of the reach of the public, eliminating the need for a fence.
They all have masts or towers to install antenna systems. In most cases, the mast is a passive structure to support the antennas. But in low frequency stations (such as AM radio), the mast itself may be the active antenna element. In such cases, the mast is isolated from the ground.(See Monopole antenna). If the mast itself is an active antenna ...
The folded unipole antenna is a type of monopole mast radiator antenna used as a transmitting antenna mainly in the medium wave band for AM radio broadcasting stations. It consists of a vertical metal rod or mast mounted over and connected at its base to a grounding system consisting of buried wires.
If the structure has an antenna at the top that is greater than 40 feet, a medium-intensity white strobe light must be placed above it rather than below. The common high white strobe flashes 40 times per minute, at an intensity of 270,000 candelas for daytime, 20,000 candelas at twilight, and 2,000 candelas at nighttime.
More common is electrical beam tilt, where the phasing between antenna elements is tweaked to make the signal go down (usually) in all directions. [1] This is extremely useful when the antenna is at a very high point, and the edge of the signal is likely to miss the target (broadcast audience, cellphone users, etc.) entirely.
Counterpoises are typically used in antenna systems for radio transmitters where a good earth ground connection cannot be constructed.. Monopole antennas used at low frequencies, below 3 MHz, such as the mast radiator antennas used for AM broadcasting, require the radio transmitter to be electrically connected to the Earth under the antenna; this is called a ground (or earth).
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