# Discone antenna

### The discone antenna is able to provide a bandwidth of around 10:1 with an omnidirectional radiation characteristic, making it ideal for many uses in the VHF and UHF portion of the spectrum including as a scanner antenna.

Discone antenna includes:
Discone basics     Buy best discone antenna

the discone antenna is used for many radio communication applications from radio scanning and monitoring for the commercial or military services to the home scanner enthusiasts.

in view of their size, weight and windage or wind resistance, these antennas are normally used for frequencies above 30 mhz, but on occasions they can be designed for lower frequency usage although the space required can be large.

## Discone antenna basics

the disc and cone can be made from solid metal sheet, but this would increase the windage, i.e. wind resistance or wind loading and its weight. normally they are made from rods that are able to electrically simulate the disc and the cone. often between six and sixteen rods are used, with most designs being within the lower region of the number of rods.

the discone antenna can operate over frequency ranges of up to 10:1 dependent upon the particular design, and it also offers a relatively low angle of radiation (and reception). this makes it ideal for vhf / uhf applications as its greatest sensitivity is parallel or almost parallel to the earth. however towards the top of its frequency range it is found that the angle of radiation increases slightly.

although it is widely used for receiving applications, the discone antenna is less commonly used for transmitting. there are several reasons for this. although it offers a wide bandwidth, it is not optimised for a particular band of frequencies and is less efficient than many other types of rf antenna design that can be used.

additionally the wideband nature of the rf antenna means that spurious signals can be radiated more easily and the level of reflected power will vary over the operating range and may rise above acceptable limits in some areas. however with modern equipment, the filtering of the signal is normally very good, and this should not be too much of an issue.

## Physical aspects of the discone

the basic rf discone antenna or scanner antenna design consists of three main components: the insulator, the cone elements and the disc elements.

$A=\frac{75000}{f}$

Where:
A is the length of the cone elements in millimetres.
f is the frequency in MHz

$B=\frac{52550}{f}$

Where:
B is the length of the disc elements in millimetres.
f is the frequency in MHz

the diameter of the top of the cone is mainly dependent upon the diameter of the coaxial cable being used. this determines the upper frequency limit of the antenna. the smaller the diameter the higher the frequency. it is represented by the distance c on the diagram.

## Additional vertical element on discone

this additional vertical element on the discone helps to extend the lower frequency response for the overall antenna, giving improved performance at lower frequencies.

the downside to the addition of the vertical element is that it can reduce the efficiency at higher frequencies.

## Discone operation

in operation energy from the feeder meets the rf antenna and spreads over the surface of the cone from the apex towards the base until the vertical distance between the point on the cone and the disc is a quarter wavelength. in this way it is possible for the energy to be radiated or received efficiently.

with the feed point at the top of the rf antenna the current maximum point is also at the top. it is also found that below the minimum frequency the antenna presents a very bad mismatch to the feeder. however once the frequency rises above this point then a reasonable match to 50 ohm coax is maintained over virtually the whole of the band.

in terms of its operation requirements, the antenna is self contained. unlike various vertical antennas it does not require the use of any ground connection, etc. also the discone is an unbalanced antenna and can be fed directly from a coaxial feeder.

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