Production of 900MHz frequency band directional antenna

This is a simple and easy-to-make high-gain directional antenna with a classic Yagi antenna structure, as shown below:

Note: This kind of antenna was invented by the Japanese Yagi, so it is called Yagi antenna.

In the figure, the linear vibrator is made of Φ10mm aluminum tube, and the reduced vibrator is made of aluminum strips with a cross-section of 10×3mm. Among them, the reflector is 200mm, the director is 130mm, and the converted vibrator is 150mm.

This antenna works best between 800-900MHz. The upper limit can be extended to the mobile communication frequency band of mobile phones. The effect is acceptable. After 970MHz, the gain decreases sharply. The lower limit can be as high as 780MHz, and the gain decreases sharply below 750MHz.

The number of directors can be selected according to the actual situation. Although the more the directors are, the better. However, if there are too many directors, the gain will not increase much, and the total length of the antenna will increase a lot. According to actual measurements, the antenna gain is about 10dB with 7 directors, and it is about 15dB as shown in the figure.

Pictures of the finished antenna are as follows:

At that time, the purpose of making this antenna was to solve the problem of long-distance (tens of kilometers) directional transmission of low-power (milliwatt-level) TV signals. Later, it was discovered that this antenna also has excellent performance in the 900MHz frequency band for mobile phone transmission and reception. According to the performance, several usages have been tested and summarized, and it is still very effective to solve the problem of using mobile phones in weak signal areas. Please note: This is a weak signal area, not a no-signal area. No method will work in a no-signal area.

One of the usages

This is also the simplest and most convenient way to use it.

The first is location selection, which means taking your mobile phone to find the location with the best signal. If it is at home, you probably don’t have to look for it. You must already know where you can get the call. But this is likely to be a location that is inconvenient for you, often on the roof, the hillside outside the house, etc. You can set up the antenna here and run the coaxial cable into the room. Note: The cable cannot be too long and should be controlled within 20-30 meters.

The end of the cable introduced into the room does not need to be connected to a mobile phone. You can connect it to a transmitting ring and place the mobile phone next to the transmitting ring and you can use it. If you find it troublesome to make a transmitting ring, you can also peel off a 10 cm long outer conductor at the end of the cable. The remaining inner conductor becomes a quarter-wavelength transmitting antenna. Put the mobile phone close to the antenna, and the effect is also good. .

Usage 2

This method allows you to use your mobile phone within a certain range in the house, which is much more convenient, but it also requires some money, dozens of dollars. The installation and usage diagram is as follows:

　　The system in the picture is divided into indoor and outdoor parts. The installation and debugging of the outdoor part is relatively simple. Just point the antenna in the direction with the strongest signal. The quality of the system basically depends on the installation and debugging of the indoor part.

　　There are two main debugging tasks for the indoor part: the location of the transmitting and receiving antennas and the gains of the two amplifiers. Of course, the effect will be better if the gain of the two amplifiers is higher, but if it is too high, the system's large loop will self-excite. The total gain of the two amplifiers cannot be greater than the sum of the isolation of the distributor and the isolation of the transmitting and receiving antennas. The isolation of the distributor is related to its own quality and cannot be changed. Therefore, the total gain is mainly controlled by the isolation of the transmitting and receiving antennas. , that is to say, adjusting the relative position of the transmitting and receiving antennas is the main debugging content of this system.

　　Usage three

　　The two methods introduced above are relatively simple methods, and generally electronic enthusiasts with certain hands-on abilities can complete the experiment.

　　The following describes a device that is similar to a regular mobile phone signal amplification station. The difference is that the transmitting and receiving antennas are all separated in order to save the expensive duplexer, as shown in the figure below.

　　Since both amplifiers have strong frequency selection characteristics and sufficient out-of-band suppression, the gain of the amplifiers can be 40-50 decibels, which is enough for a room of tens of square meters.

　　Although the system uses an amplifier with sufficient out-of-band suppression and will not form a large loop self-excitation involving both the uplink and downlink channels, the coupling between the indoor and outdoor antennas will form due to the use of a higher-gain amplifier. The large loop within the channel is self-excited. Therefore, the installation location of indoor and outdoor antennas must ensure sufficient isolation between antennas.