Common equipment for amateur radio communication includes transceivers, various antennas, computer equipment and special software, modem equipment and various commonly used measuring instruments. The antennas are the favorite toss of fans and the most hobby. The field of personal skill and hands-on ability.
The antenna is actually an LC series circuit. Since the antenna conductor itself has a certain amount of inductance, there is a capacitance between the earth and the earth. The geometry of the antenna conductor, the distance between the antenna and surrounding objects, the ground, the electrical parameters of the antenna, etc. all affect the inductance and capacitance parameters of the antenna. When receiving a signal, the antenna resonates at a certain frequency. The electromagnetic wave in this band can cause the antenna to generate a large induced current, so that the receiver can find a specific signal. When transmitting, the transmitter maximizes the current in the resonant antenna and the signal can be transmitted. The resonant antenna can be equivalently regarded as a pure resistor, which includes two parts, the radiation resistance and the loss resistance. According to the ohm theorem, when the current is constant, the radiation resistance is larger, the emission efficiency is higher, the loss resistance is smaller, and the efficiency of the entire antenna is higher.
According to the ITU regulations, there are also domestic related spectrum regulations. Although it enjoys a wide spectrum covering the medium to ultra short-wave band, the frequency band that can be used in each band is narrower than the whole band, suitable for amateurs. Antennas used in radio communications are mostly narrow and efficient antennas.
1. Horizontal half-wave dipole antenna (Dipole Antenna), also known as DP antennaA half-wave dipole antenna that is erected by two conductors of equal length and a total length of about half a wavelength. It is also the simplest and most basic antenna that is easy for HAM friends to make. Other antennas are variants of this type of antenna. The total length of the antenna is approximately equal to 94% to 96% of the half-wavelength of the desired center frequency. It is slightly adjusted according to the actual effect of the balun. Both vibrators are 95% of the 1/4 wavelength, which is performed by a 1:1 balun. Match the connection. Under normal circumstances, the maximum affordable radiation power can be made larger, such as 500W~1000W. The radiation directions are two circles with the antenna as the symmetry axis and the feed point as the tangent point.
DP antenna schematic
Since the antenna emits a horizontally polarized wave, the horizontally polarized wave electric field is greatly affected by the absorption of the ground, and is not suitable for short-range communication. However, since the elevation angle of the emission is low, the sky wave propagates well, and it is suitable for DX communication.
A common form of such an antenna, in addition to horizontal erection, is an inverted V (positive V) erection with an angle between 110 and 120 degrees, which coordinates the long range and close range by changing the elevation angle of the launch. Communication.
(The picture shows the DP inverted V antenna erection diagram)
In order to shorten the antenna geometry and facilitate the erection, the antenna is also equipped with an inductor, which is commonly known as a trap, but this will cause a certain degree of decrease in antenna efficiency.
In this type of antenna, sometimes in order to achieve multi-band communication, multiple pairs of vibrators are added to the balun to enable the antenna to operate in more bands. Common manufacturers such as diamonds, eagle, etc. have ready-made DP antennas for sale online, and many antennas produced by many enthusiasts can have better communication effects.
2, vertical monopole antenna (VerTIcal Antenna), also known as GP antennaThe antenna is a deformed antenna derived from a dipole antenna. The bottom end of the antenna is connected to the inner conductor of the feed line, and the outer conductor of the feed line is connected to the ground net. The radiation in the horizontal direction is a circle, so the reception in all directions is performed. It has the same transmitting capability and is suitable for omnidirectional receiving and transmitting. Mobile handheld devices are mostly antennas of this type. Sometimes short-wavelength bands use this type of antenna for DX communication.
(The picture shows a short-wave GP antenna set up in the field)
The efficiency of the vertical antenna is very much related to the ground network. In the absence of a good ground network system, the efficiency of the vertical antenna is hard to exceed 50%, especially for vertical antennas less than 1/4 wavelength. Many vertical antennas usually add inductance to the antenna in order to shorten the geometry, but this sacrifices the efficiency of the antenna and theoretically has the highest efficiency at the top of the antenna. The GP antenna of the portable handheld device of the U/V segment is basically full-sense. Some GP antennas of short-wave carrying equipment are generally added in the middle, which is mainly due to mechanical strength considerations.
Due to the radiation angle, the vertical monopole antenna can radiate electric waves in various directions as well as absorb electric waves in all directions. Therefore, in some cases where the electromagnetic environment is not ideal, the bottom noise is likely to be high.
The common U/V segment vertical antennas of HAM have FRP antennas, mainly because they are covered with a glass fiber reinforced plastic outer casing, which is aesthetically pleasing and weather resistant. It is also made of a U/V segment vertical antenna made of metal material for easy installation on a car. Common U/V vertical antennas, such as diamonds, eagle, Huahong, etc., are now easy to purchase through the Internet.
(The picture is a car UV antenna, commonly known as the seedling)
Common short-wave vertical antennas, such as diamond, MFJ, Huahong, etc., diamonds are mainly short-wave antennas for vehicles, MFJ is more focused on short-wave base stations, and most of them are 1/4-wave vertical antennas.
3, Winton antenna (Window Antenna), also known as bias feed half-wave antennaMostly, it is made of a single wire. The feeder is also a single wire, which is connected to the center point 14%. It is generally used as a receiving antenna and as a transmitting antenna. Because of its small footprint, Winton antenna is suitable for HAM erection with small roof space, and is also suitable for portable use in field communication. There are also many sellers on the network selling well-made Winton antennas.
(The picture shows the schematic diagram of the Winton antenna and the modification of the erection)
4. Yagi AntennaIn 1925, it was invented by Yasushi Hideo and Yuda Shintaro, who was then the minister of the Northeastern University of Japan. "Yagi" is the English spelling of Yagi. This antenna is composed of multiple units and has strong directionality. The more directors The stronger the directionality, the higher the gain, and it is usually used in conjunction with a 360-degree rotator, which points to the object that needs to be connected.
(The picture is a hand-held Yagi antenna of 430-440MHz)
Yagi antennas can operate on multiple bands, and some can communicate in four bands in shortwave. There are also U-band or V-segment Yagi antennas, mainly used in FMDX communication, or radio direction finding and satellite communication.
Yagi antenna is also the goal of many HAM pursuits. The tower and the huge antenna are also very professional. In many amateur radio competitions at home and abroad, Yagi antenna has achieved good communication results.
(The picture shows a large Yagi antenna set up by a foreign HAM on the waterfront)
5, box antenna (Quad Antenna)Invented in the 1940s by the W9LZX (Clarence Moore) of Quito, Ecuador, it is also a good long-distance communication antenna. The square antenna is generally composed of two units, an excitation unit and a reflection unit.
The block antenna can basically achieve the communication effect of the Yagi antenna. In the entire frequency band, the Uad can achieve a slightly higher gain than the Yagi antenna, and is slightly weaker than the Yagi antenna in the latter part of the frequency band. In the entire frequency band, the standing wave ratio of the square antenna changes before and after, instead of being able to achieve a lower degree in the whole section like the Yagi antenna, which needs attention. The frame antenna is usually weak in mechanical strength, and it is necessary to mainly strengthen the strength of the two antenna elements when erecting, otherwise it is easily broken in strong wind.
(The picture is a two-unit box antenna)
6. Long Wire AntennaThe long-line antenna is also a common form of antenna. It mainly consists of a wire that is erected in one direction, and a matching grounding grid and balun. It is used in places where the location is limited. In order to cover as many bands as possible, The short-wavelength band typically has a length of 22.5 meters or 39 meters and matches a 1:9 balun and grounded ground.
Long-line antennas are less efficient than half-wave dipole antennas because the fields radiated by the major lengths of long-line antennas cannot be used in the direction of a certain distance like half-wave dipole antennas for fields radiated in other types of directional arrays. That way, you can simply superimpose the overlay.
The longer the length of the long-line antenna, the sharper the lobes, and the fact that the radiation in the free space is a true hollow cone, it gradually becomes sharper on both planes. At the same time, the longer it is, the smaller the maximum radiation lobes appear. Due to the simplicity of the production, the long-line antenna has also been favored by the majority of HAM.
Long-line antenna schematic
7, loop antenna (Loop Antenna)The whole antenna is made up of round metal or tubular metal. It is a small, high-efficiency and directional antenna. It is usually used in places with large space constraints and can cover multiple bands.
The loop antenna is a closed loop antenna, that is, the root conductor is bent into one or more turns and the ends of the conductor are closed together.
(The picture shows a loop antenna erected between buildings, with a small footprint)
Loop antennas can be divided into two categories: one is that the total length of the conductor and the maximum linear dimension of one turn are very small relative to the working band; the other is that the total length of the conductor and the ring size are comparable to the operating wavelength. . Common is a loop antenna called a small loop antenna, that is, an antenna with a total conductor length of less than 1/10 wavelength, such as a ferrite rod antenna in an AM radio, and some small transmitting antennas. . Small-sized loop antennas for transmission are basically tunable, and by operating their resonance in the short-wavelength band required, such small-loop antennas usually have a high Q value.
8, cobweb antenna (Cobweb Antenna)It is also a common antenna, mainly used on short waves, has strong directivity, and requires less space than Yagi antenna, and has high efficiency.
The spider antenna is also composed of several excitation units and reflection units. Generally, the spider antenna is supported by a non-metallic material with high strength. The excitation unit and the reflection unit of the spider web are composed of ordinary wires. The mechanical strength of the spider antenna is lower than that of the whole. It is a Yagi antenna of a metal vibrator. A well-designed and well-studded spider antenna can work in 3 to 5 short-wavelength bands at the same time, and has a relatively high gain in the main direction.
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