Friend, you are also talking about a rod antenna. Any radio equipment that relies on electromagnetic waves to transmit information needs an antenna. An antenna is a sensor. When transmitting, it converts the high-frequency current of the transmitter into space electromagnetic waves. When receiving, it converts the electromagnetic waves intercepted from space into high-frequency current and sends it to the receiver. Whip antenna pocket ultrashort wave radio station, receiving and transmitting with a pair of antennas. However, considering the different use environment, the aircraft will generally be equipped with two different types of antennas to choose from. One is a quarter-wave whip antenna, and the other is a small spiral antenna. Quarter-wave whip antenna is a common rod antenna, which consists of many sections. When working, the cable resonates with the high-frequency current emitted by the transmitter. Theoretically, the length of the whip antenna at resonance should be a quarter of the wavelength corresponding to the resonance frequency. However, because the propagation speed of electromagnetic wave in metal rod is slightly lower than that in air, and the wavelength of electromagnetic wave propagation on metal rod is also slightly shorter, the length of actual whip antenna is slightly shorter than a quarter wavelength. This shortening factor is related to the working frequency and the diameter of the metal rod. When the working frequency is high and the diameter of the metal rod is large, the shortening value is also large. The average diameter of this rod antenna is 4.5 cm and the shortening factor is 0.97. Take a quarter wavelength of the center frequency of the radio station and multiply it by the shortening factor, which is the actual antenna length. Spiral antenna spiral antenna is a new type of miniaturized communication antenna, which is especially suitable for pocket radio stations used in mobile communication. Because the antenna with a length of 1 meter is really a little long for pocket computers, it brings inconvenience to users, especially it is not safe to use near high-voltage lines. For this reason, a small spiral antenna with a total length less than one third of the rod antenna is specially designed for this machine. At present, this kind of antenna has been applied in communication and television. This paper mainly introduces its structure, working principle, calculation formula and manufacturing method. Structure: the metal wire is wound into a spiral shape at a certain interval, and the coil is supported by an insulating material pillar along the spiral axis. One end of the spiral is connected with the output end of the transmitter, and the other end is open, thus forming a spiral antenna. The product is made of carbon steel wire with a diameter of 1.2 mm, which is wound into a spiral with an average diameter of 1 cm on a common lathe and supported by a hot-formed polypropylene mandrel with a plum-blossom cross section. The outer surface of the spiral is sealed with rubber tube to prevent rainwater flooding. Working principle: Small spiral antenna is a slow-wave system. The propagation redundancy u of electromagnetic wave in the axial direction of helix is much less than the speed in air (approximately the speed of light c), so the wavelength is much shorter. In order to distinguish it from the wavelength corresponding to the working frequency, the wavelength in the helix is called "guided wavelength". Its principle can be illustrated by figure 1 Now, it can be roughly considered that electromagnetic waves travel at an approximate speed of light C along the winding direction of the metal spiral. When the electromagnetic wave makes a circle along the helix from point A to point B, in fact, the electromagnetic wave only travels the distance of S (pitch) in the axial direction of the helix. If this spiral circle is unfolded into a right triangle on the plane, the hypotenuse represents the propagation speed c of electromagnetic wave along the spiral, and the short right angle side represents the propagation speed u of electromagnetic wave along the spiral axis. According to the geometric relationship of right triangle U = C sin ψ (angle ψ is the included angle between the tangent of the spiral and the horizontal line), because sin ψ < 1, there is always U less than the speed of light C, so the spiral is a slow-wave system, which can slow down the propagation speed of electromagnetic waves. If the spiral antenna is also made to resonate at a quarter wavelength, it should resonate at a quarter "guiding wavelength", so the geometric length of the spiral antenna can be much shorter than that of the rod antenna.

Calculation formula: the length of the spiral antenna is equal to a quarter of the "guided wavelength". The "guided wavelength" is related to the spiral diameter d, the pitch s and the working frequency f, and there is a complex mathematical relationship between them. If the spiral antennas H ″ d and D are much smaller than the working wavelength, they can be calculated according to the following approximate formula:

When calculating, the appropriate spiral diameter d and length h (in meters) should be selected according to the service conditions, and the working frequency f is determined by the central frequency (in megahertz). The corresponding number n of spiral turns can be calculated according to the above formula. Of course, the selected H is much larger than D( 10 times or more), and the length of the metal wire used for winding the spiral can be calculated according to the following formula: L = n π d (2), such as one. The diameter of the spiral cut is d = 1cm, and it is hoped that the antenna size will not exceed 25cm, so the total number of turns according to formula (1) is 79.2, and the length of the wire used according to formula (2) is about 2.5m. Amateur whip antenna for pocket radio stations can be made of thin copper tube with a wall thickness of 0.2 mm, with an outer diameter of 5 ~ 7 mm and a length of 1 m. If the outer diameter is thicker, its length can be slightly shorter by 2 ~ 3 cm. One end of the copper tube is connected with the output end of the transmitter, and a small hole with a diameter of 2mm can be drilled at this end, from which a welding wire can be drawn to connect with the transmitter. The other end of the copper tube can be sealed with plastic toothpaste with similar caliber, if there is a pull rod antenna with the same length, it can be replaced. If the outer diameter of the rod antenna is thick, the antenna length can be slightly shorter. If there are no conditions, the whip antenna can be replaced by a plastic sheath conductor with a length of 1.05 meters. Fabrication of spiral antenna: The spiral line can be wound with enameled wire with a diameter of 0.8 ~ 1.5 mm, and the thickness of enameled wire has little effect on the performance of spiral antenna. Because the voltage between spirals is not high, low-strength oil-based enameled wires can generally be used. It should be noted that the spacing between spirals should be consistent and equal to the design value. When the working frequency is 72.7 MHz, the pitch s is 3 mm, and * * * turns 80 times. When winding, the metal bar with a diameter of about 9 mm is wound 85 times with a spacing of 2.5 mm After winding, the spiral rebound can be considered, which can basically meet the requirement of 3 mm center distance, and then the redundant turns can be cut off. The wound spiral is driven out by an insulating support rod, such as an epoxy rod, a plexiglass rod, a hollow electric plastic pipe or a thin bamboo rod. Helical wire can also be wound with aluminum wire with similar diameter, but aluminum wire is harder than copper wire and has greater rebound. At the beginning of winding, the center distance should be smaller, for example, about 2.2 mm, and after winding, it will reach 3 mm through shaping. Turn the upper half of the spiral to the center of the circle, bend it and support it with a support rod, as shown in Figure 2. It is best to cover the antenna with thermoplastic plastic sleeve or thin rubber sleeve to prevent the helix from being deformed by external force. The spiral antenna should work with the whole machine, so as to emit all the energy or send all the received energy to the receiver.

Whip antenna and spiral antenna have certain directivity, that is, the energy is most concentrated in some directions, and the effect of receiving or transmitting is the best. Therefore, when in use, the antenna can be rotated to obtain the best communication effect. The actual communication effect shows that the machine is equipped with a whip antenna with a length of 1 meter, which can reliably communicate in a flat area of 5 kilometers, and the communication distance with a spiral antenna is 3 ~ 4 kilometers. According to the above principle and calculation formula, the antenna parameters of radio telemetry and telecontrol transceiver equipment working at other frequencies can also be drawn. In principle, it can also be used for radio equipment, such as TV and FM radio reception.