Antennas for radio receivers. The radiation principle of a transmitting antenna is based on the creation of an electromagnetic field around a conductive wire, which is fed with radio frequency energy. If we bring another conductor with the same characteristics to this conductor wire, the created magnetic field will act on it, inducing currents and voltages proportional to the radiofrequency energy supplied by the first one. This is the reception principle on which the receiving antennas are based.
Summary
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- 1 receiving antenna
- 1 Types of receiving antennas
- 2 Outdoor or aerial antenna
- 3 L-type or single-line antenna
- 4 T-type antenna
- 5 V-type antenna
- 6 Two-wire antenna
- 7 loop antenna
- 8 Ferrite antenna
- 9 Telescopic antenna
- 2 Related Links
- 3 Source
Receiving antenna
A receiving antenna has the same properties as the transmitting antenna, it must have the same polarization, directivity, bandwidth and have good gain. The type of receiving antenna to be used will depend on the local conditions where the receiver is located and the frequency of the radiofrequency signal to be captured.
Types of receiving antennas
- Outdoor or aerial antenna.
- Loop antenna.
- Ferrite antenna.
- Telescopic antenna
Outdoor or aerial antenna
This type of antenna consists of a conducting wire whose length is approximately equal to half the wavelength , isolated at its ends. According to the way of connection, there are different types of aerial antennas:
- L-type or single-line antenna.
- Antenna type T.
- V type antenna
- Two-wire antenna.
L-type or single-line antenna
It is based on an insulated conductor wire at its ends, but one of them takes the energy induced in the antenna towards the receiver.
T type antenna
It consists of a wire also insulated at its ends, but the induced energy intake is made from the middle point of the wire.
V type antenna
It consists of the installation of two V-shaped antenna wires, the angle is such that it will achieve the highest received energy, it can be from 30 to 60 degrees. The energy is taken from the junction point of V.
Two-wire antenna
It consists of the installation of two parallel wire strands, separated approximately 1 meter from each other.
In general, aerial antennas have good properties and gain, but require a terrain without any intermediate obstacle for their installation. On the other hand, the radio receiver must be located as close as possible to the antenna and in fact it cannot be portable anywhere.
Loop antenna
The creation of a loop antenna was a great step in eliminating the difficulties of outdoor aerial antennas. It consists of the winding of the antenna wire, in the form of a frame, which turns out to be a coil. This antenna coil is mounted inside the radio receiver , giving you the ability to transport it anywhere without difficulty. This antenna has directional characteristics, that is to say to obtain good reception, the receiver must be placed in such a position that it is oriented towards the transmitting antenna.
Ferrite antenna
Modern receivers use the so-called ferrite antenna , which replaces the loop antenna. Its name is due to the core used for the antenna coil. The ferrite core is made of an alloy of round or rectangular rod-shaped molded magnetic materials. on which the antenna wire is wound forming the coil .
The size of the ferrite core depends on the size or type of receiver for which the antenna is intended. Ferrite rods 6 mm in diameter and 50 to 100 mm long are used in small receivers. rods of 10 mm diameter and 125 mm length are also used. For larger receivers the length of the rod can reach lengths of up to 200 mm and its diameter ranges from 1 to 15 mm. The ferrite antenna is attached to the inside of the receiver with insulating clamps and is generally placed on top of the receiver.
The antenna coil wound on the ferrite core uses a type of conductive wire called Litz wire which is made up of numerous insulated braided wires. This type of conductor has very low resistance to radio frequency, so the quality of the coil expressed by the power factor (Q) is high.
The antenna coil is not wound directly on the core but on an insulating cardboard mold which is passed through the center of the ferrite core, in this way the coil can slide on the core to obtain good frequency response and tuning in the receptor. In the ferrite antenna there can be as many coils as there are bands to be captured, that is, there will be one coil for long wave (OL), one for medium wave (OM) and one for short wave (OC).
Telescopic antenna
This type of antenna is very simple and consists of a conductive rod that is placed vertically. Its size is not very large, since it is mainly used for the high frequency band (short wave) and in the modulated frequency band (FM). This antenna is placed on the outside of the radio .