Tuning antennas with a frequency response meter. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / HF antennas
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When establishing short-wave antennas, you can use the frequency response meter (X1-19B, X1-7B). Its output is connected to the input through the RF head (Fig. 1), and an antenna is connected to the connection points.
Ris.1
Tuning begins with determining the resonant frequency of the antenna. Depending on the type of antenna, either a "hump" (wave vibrator and other antennas with high input impedance at the resonant frequency) or a "dip" (half-wave vibrator, antennas derived from it) will be observed on the screen. By adjusting the antenna, they ensure that the maximum (minimum) of the curve on the frequency response meter screen coincides with the middle of the operating range. Frequencies are controlled by labels on the screen. An approximate view of the frequency response of the "Ground PIane" antenna (without feeder) for the 14 MHz band is shown in Fig. 2.
Ris.2
When looking at the characteristics of multi-element antennas, the "responses" from each element are clearly visible, which greatly simplifies the tuning process.
In this way, it is possible to measure not only directly at the antenna input, but also through a connected feeder, for example, a coaxial cable. At the same time, the total frequency response of the feeder and antenna is observed on the screen, which makes it possible, in the case of using a resonant feeder, to select its electrical length.
Ris.3
On fig. 3 shows an exemplary view of the "Inverted Vee" frequency response for the 3,5 and 7 MHz bands with a coaxial cable connected with a characteristic impedance of 50 ohms.
Authors: I. Kavetsky (UQ2G1G), S. Gokhberg (UQ2MU); Publication: cxem.net
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