Antenna Selection For VHF/UHF Amateur Communication-Part 3 Base Station Antenna

Antenna Selection For VHF/UHF Amateur Communication-Part 3 Base Station Antenna


The base station antenna is not limited by the moving conditions, so the high-gain antenna can be used, which not only increases the coverage area of the transmission, but also increases the conversion efficiency of the reception, and can better receive the weak counterpart signal and improve the communication quality. In addition to the use of high-gain antennas, for the case of interference, it is also possible to add narrow-band filters or moving antenna positions to reduce the influence of interference. The commonly used base station antennas are FRP high-gain antennas, four-fold oscillator array antennas, and eight-fold Vibrator array antenna, directional antenna, etc.

The FRP high-gain antenna has a number of in-phase-emitting half-wavelength vibrators arranged in a linear array, which is an omnidirectional antenna, which is suitable for simultaneous contact with different parties. According to the difference of antenna gain, it is divided into high gain antenna (above 8dB) and medium gain antenna (below 6.5dB). In the same frequency band FRP high-gain antenna, the higher the gain, the longer the antenna length is. The antenna length of the 10dB gain in the 430MHz amateur band is about 4 meters, the antenna length of the 8iB gain is about 2.2 meters, and the antenna length of the 6.5dB gain is about 1 meter. FRP high-gain antenna is the most used antenna in China’s amateur relay station, and the price is relatively moderate.

The four-fold oscillator array antenna is characterized by high power, high gain, adjustable gain direction, and high withstand power. Such an antenna is generally mounted on an iron or iron tower, and has a certain directivity depending on the reflection of the tower rod, and the direction is adjustable. When the four vibrators are installed at intervals of 90 degrees, the antenna characteristics are basically omnidirectional, when all four vibrators are installed. The antenna characteristics point in the same direction to the side facing away from the tower. When used in amateur repeaters, the gain-adjustable nature of the amateur repeater can be better adapted to irregular coverage areas. If the gain of the four-vibrator is not high enough, consider an eight-vibrator antenna whose horizontal characteristics are similar to those of a four-vibrator array, but provide a higher gain in the near-earth direction in the vertical plane. The gain of a typical quad array is 8 dB (omnidirectional) / 10 dB (orientation), and the gain of the eight-array array is 12 dB (omnidirectional) / 15 dB (orientation).

The directional antenna has the characteristics of strong directivity and high radiation gain in the main direction. The more the number of cells of the directional antenna, the higher the gain and the sharper the directivity, which is more suitable for communication over longer distances. If the general gain omnidirectional antenna does not meet the communication requirements, consider using a directional antenna.

The 8-cell directional Yagi antenna can achieve a gain of 12dB. The price of the directional antenna is much cheaper than that of the FRP antenna of the same gain, and the direction is concentrated. It does not cause unnecessary interference to the non-contact direction when transmitting, and can effectively avoid the interference in the non-contact direction when receiving.

The base station antenna can generally be installed at a high place. It is not affected by the changes of the human body, surrounding objects and corresponding ground conditions as in the hand or the vehicle. It can be accurately adjusted to obtain a relatively stable optimal state, and the communication effect is of course much better.

Post time: Nov-07-2019