Commonly used short-wave antennas are mainly divided into three categories. The first category is vertical antenna (GP), the second category is dual antenna (DP), and the third category is Yagi antenna (YAGI). In addition, there are frame-type, diamond-type, dish-type, etc., here we mainly discuss the first three types of antennas, including the dual-level antenna and its deformation. From the point of view of use, GP antennas are mainly used for short-range-medium-distance communication, especially short-range communication relying on ground wave transmission, and the effect is very good. But the short-range communication effect of DP antenna is very bad. Due to the height limitation, it is impossible to set up a very high antenna. Generally speaking, GP antennas with a height of 5-10 meters are suitable for their own installation.
Generally, GP antennas are commonly used in the 21-29M frequency band, and GP antennas are no longer used in lower frequency bands. In addition, lightning protection for GP antennas is also more difficult. It is impossible to build a lightning rod next to the antenna that is taller than the antenna, right?
This is a typical DP antenna structure, in which the red part is an insulator, which is separated from the traction rope at both ends. The length of the main vibrator is 1/2 wavelength * 0.95 shortening rate. Why use 1/2 wavelength? This is because both ends of the 1/2 wavelength center tap are 1/4 wavelength, so that the impedance of the antenna is 50 ohms to match the transmitter.
The DP antenna mainly uses sky wave communication, the effect of long-distance communication is very good, and the erection is simple, there is no need to erect a very high antenna, and the production cost is low, so it is used by most radio enthusiasts. There are many distortions in the DP antenna. Let me introduce you one by one.
figure 2
+This is a modification of the DP antenna. One way of doing this can save the antenna's floor space. On the other hand, it can improve the short-range ground wave communication effect of the original DP antenna. But after doing so, the antenna has directivity, see the maximum radiation direction in the figure.
image 3
Since the shortwave transmitter can work in various bands of 0-30M, a single-length antenna cannot meet our needs, and it is not practical to make an antenna for each band.
In this way, we need a multi-band inverted antenna. The advantage of this is that it saves floor space and does not require several antennas to switch back and forth. But the disadvantage of this is that the vibrators of each band influence each other, and the length of the vibrators need to be trimmed one by one to achieve the best matching state.
Figure 4
Even-level antennas need to make two identical oscillators. For an experienced HAM, a multi-band antenna can be made in one hour. So for novices, is there any good way to use the machine immediately? of course can! Let's talk about monopole antennas below.
Shown in the picture is a prototype of a monopole antenna. As long as the length of the vibrator is long enough, it can cover various frequency bands. A single-stage antenna has only one vibrator. If it is used as a multi-band antenna, an antenna tuner is required to suit different frequency bands.
Figure 5
This is also a kind of single-stage antenna: WINDOM, translated as Winton antenna, also known as offset-fed antenna. The length of the vibrator is 1/2 wavelength*0.95, the feeding point is 14% away from the midpoint, and the feeding line is a single wire.
Figure 6
The monopole antenna can also be made into a multi-band, this is a multi-band monopole antenna, the center needs to add a 1:5 balanced/unbalanced converter. It is worth noting that the monopole antenna may have high voltage, so the transmitter must be *grounded, and the antenna element must be placed in an inaccessible place to prevent electric shock.
In fact, the shortwave antenna is not mysterious, as long as it is adjusted, it can work well. For example, my self-made antenna is a deformation of the inverted antenna, and the effect is very satisfactory. Therefore, as long as you master the principles and use your brain to use your imagination, you can also design an excellent shortwave antenna!
Our other product:
