Antenna with omega matching. Scheme, description

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Antenna with omega matching. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / HF antennas

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Used by many shortwave whip antennas without the use of matching devices, as a rule, have a high SWR. This is due to the fact that the input impedance of the whip antenna is quite small (about 30 ohms), therefore, when powered by a cable with a wave impedance of 50-75 ohms, the SWR is about 2-3.

Sometimes, to increase the input impedance of the antenna, the counterweights are placed not horizontally, but at an angle of 30-45 "to the horizon. The input impedance in this case increases, but the antenna begins to radiate at large angles to the horizon, which is undesirable when making long-distance communications.

The proposed omega-match compares favorably with the common gamma-match in ease of adjustment, since it does not require movement during the adjustment of the short-circuited jumper.

The described antenna is a vertical quarter-wave vibrator with a grounded base and horizontal counterweights (see figure).

Antenna with omega matching

The geometric dimensions for various ranges are given in table. one.

Table 1
Range, m A (cm) B (cm) H (cm)
10
14
20 255
340
320 40
60
90 10
14
16

The diameter of the matching rod should be three to four times smaller than the diameter of the vibrator. A short-circuited jumper is attached permanently, and all antenna tuning is carried out using two variable capacitors located at the base of the vibrator. Capacitor C1 is used to compensate for the inductive component of impedance, and capacitor C2 allows you to quickly and accurately match the input impedance of the antenna with the wave impedance of the cable.

In this design, capacitors KPK-1 and KPK-2 were used. The maximum values of capacitances C1 and C2 are shown in Table. 2.

Table 2
Range, m Maximum capacitance C1, pf Maximum capacitance С2,pf
10 50 20
14 80 25
20 150 30

Antenna tuning is carried out using an SWR meter or a field indicator. After tuning, the capacitors are enclosed in a moisture-proof box.

Author: V. Postnikov (UA3ZD), Gubkin, Belgorod region; Publication: N. Bolshakov, rf.atnn.ru

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