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A discone antenna is comprised of two sections, one shaped like a disc and the other like a cone. The disc is perpendicular to the axis of the cone, and the size of these two components must fall within a certain ratio for the device to work properly. These antennas are capable of receiving signals over a wide range of frequencies and from all directions.
The structure of the discone antenna allows it to function over a wide section of the electromagnetic spectrum. This type of antenna is omnidirectional, which means that it can receive electromagnetic waves from any direction. It does not need to be pointed toward the source of the signal. This antenna is also capable of working indoors, though it will lose some functionality because the electromagnetic signal is degraded when it passes through the materials of the house or building.
Most discone antennas are set up so that the cone section is at the bottom and the disc is on top. The height of the cone is equal to about one-quarter of the smallest frequency that the antenna can pick up, and the disc has a diameter equal to 0.7 of the length of the cone. Between the cone and the disk there is an insulator, which is necessary for the antenna to function properly. The highest frequency that can be received by a discone antenna is generally about ten times greater than the lowest frequency.
The discone antenna may be solid or may be made out of a series of rods. Either way, conductive metal, such as copper is an ideal material. If the antenna is made out of rods, these rods extend from the bottom of the antenna in a cone shape and in a perpendicular circle on top of the cone. Any number of rods can be used, though a number between eight and 16 is common.
The most common uses for a discone antenna are in radio devices, such as ham radios and radio scanners, which can be used to pick up distant radio signals. It is possible to transmit through a discone antenna, though the antenna has a tendency to generate harmonic signals, which can interfere with the quality of the transmission. It is not an ideal antenna for use as a transmitter, though the broad range of frequencies it can receive and its ability to receive signals from any direction makes it ideal as a receiving antenna.
You are right about using a discone antenna as a transmitter. It is not only not ideal, it is a bad idea because, as you say, there is a problem with harmonics.
Unlike a CB antenna, a discone antenna can cancel out the signals of other broadcasters near you: One frequency cancels the other. Broadcasters using discone antennas to transmit do not deliberately transmit them, but they happen, and they are not in the transmitter's assigned channel, so they interrupt other broadcasts.
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