The antenna is a tool for the receiver to capture signals. Most antennas used for remote FM broadcast reception use Yagi (YAGI) antennas.The number of Yagi antenna units affects the reception range.The more the number of units, the sharper the direction and the higher the gain. , The further the straight distance.
The frequency band of FM broadcasting in China is 87.5-108MHZ, and the center frequency of the five channels of the TV is 88MHZ, so the five-channel antenna is basically suitable for remote FM broadcast reception. Enthusiasts can buy a five-channel TV antenna instead, and high-demand enthusiasts can use five The channel TV antenna is slightly modified. I recommend using the five-unit antenna, which has higher gain and is not bulky. The ordinary five-channel five-unit Yagi antenna is only more than ten yuan, and the most cost-effective change after purchase.
Below I introduce some processing methods of my antenna:
1. The matching problem of the antenna, the output of the general antenna is 300 ohms, and the cable is mostly 75 ohms, and the impedance must be matched, otherwise the high-frequency signals are difficult to transmit. The antenna matchers are mostly transformer-type and U-shaped half Wave ring type, transformer type matcher is more complicated to manufacture, the selection of wire and magnetic ring directly affects the matching coefficient. U-shaped half-wave ring type only needs a 75-ohm cable. I think that U-shaped half-wave ring is applied The style is better.
2. The debugging problem of the antenna. After the antenna is installed, it does not have the effect of seeing a pole. It needs to be debugged to have an incredible effect. First, determine the direction of the receiving station (because the antenna is a directional antenna), Align the direction of the antenna lead with the direction of the radio station. Use the receiver to test the radio station, then find the weakest signal in the corresponding direction to adjust the height of the antenna, find a position with the strongest signal and fix the antenna.
3. The problems that should be paid attention to when using the antenna amplifier. Most of the antenna amplifiers currently on the market are composed of two 9018s. Due to the large working noise of the 9018, it is best to change the 9018 to C3358 or C3355 low-noise tubes if you have a fever. When using the amplifier, unidentified digital sounds (audio pulses) appear on multiple frequency points to interfere with the signals of other stations. This is caused by the harmonic regeneration of the paging transmitter. It is due to the filter problem of the antenna amplifier. Add a BPF (88-108MHZ filter), which can be removed from the old FM radio (shaped like a TV 6.5MHZ filter). You can also add a 5-45P capacitor to the ground before the coupling capacitor of the first-stage amplifier.
4. The joint between the antenna and the cable should be protected against rust. The antenna is generally installed on the roof. The antenna interface is easy to rust after the sun is blown, which will affect the signal transmission and the matching of the antenna, making the reception effect worse. If there is an antenna The antenna of the amplifier is very easy to make the amplifier self-excited.It is best to apply anti-rust paint to the interface when the antenna is installed.
5. When the cable is installed, try to straighten it and do not roll it together. It is best to install a socket after entering the house. It can be unplugged quickly when thunder.
6. Pay attention to lightning protection when installing the antenna. High-rise buildings generally have lightning rods. The lightning protection range is an umbrella-shaped space with the needle tip as the origin and the needle at a 45-degree angle. The antenna should be safe in this space.
7. The maintenance of the antenna, because the antenna is blown by the wind, the sun, and it will be oxidized soon after rain. There is time to wash the antenna once a year. I change the antenna once a year. All interfaces of the cable are the same. Clean with 95% alcohol.
8. The reflector, vibrator and director of the antenna cannot be connected to the bracket, and they must be separated by plastic!
9. Most radio heads are 300 Euro input, you can disconnect the 300-75 Euro match in the radio head into a 75 Euro interface.
A FM receiving system does not have a good antenna, high-grade cable has a good reception effect. It is only possible if the antenna, cable and receiver cooperate with each other. Just like our audio fever, sound source, power amplifier, wire The best results are achieved when the speakers are matched with each other. We should note that when choosing a receiver, many radios on the market are not suitable for remote FM reception. The ordinary miniature radio is mainly designed to receive local and neighboring stations. It takes less time to tune the process, the adjacent frequency processing is not good, it mainly spends on the shape design. I think that the ordinary radio head is better than the digital tuning, the current domestic common digital tuning head is mainly Designed for its function, not for its high sensitivity, the hand-tuned radio is a mature product of China's national industry. Obviously, the ordinary hand-tuned radio head is better than the digital tuning. However, some domestic digital tuning machines are still good. It can be compared with some imported products. In my use, I found that the car FM receiver is quite good. Whether it is hand-tuned or digital-tuned, its sensitivity and adjacent frequency processing are very good, and the medium-intensity signal is 0.2. The MHZ is completely separable, mainly because it uses an integrated tuner. The integrated tuner is not designed on the same board as the middle amplifier and stereo demodulation like ordinary tuning, but is produced separately by a professional manufacturer. The technology is better. When using WALKMEN, I think that the hand tuning is better than the digital tuning, such as Panasonic, Aiwa, and Sony's radio functions are excellent.

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[Photo] Yagi five-unit FM antenna

Posted at 2006-04-15 21:08 • 629 views