Used by many Amateurs whip antennas without the use of matching devices, typically have a high SWR. This is because the input impedance of the whip antenna is quite small (about 30 ohms), so the power cable with a characteristic impedance of 50 - 75 Ohm SWR of the order of 2-3.
Sometimes, to increase the input impedance of the antenna balances have not horizontally, but at an angle of 30-45" to the horizon. The input resistance is increased, but the antenna begins to emit at large angles to the horizon, which is undesirable for long-haul communication.
We offer omega-coordination differs from the common gamma-matching easy set-up, since no movement in the process of setting up a short jumper.
The described antenna is a quarter-wave vertical dipole with a grounded base and horizontal balances (see the figure).
The geometrical sizes for different ranges given in table. 1.
Table 1
Range, m
A (cm)
B (cm)
In (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. Shorted the jumper is permanently attached, and the whole setup of the antenna is performed by using two variable capacitors located at the base of the vibrator. The capacitor C1 serves to compensate the inductive component of the impedance, and the capacitor C2 allows you to quickly and accurately align the input impedance of the antenna with a characteristic impedance of the cable.
In this design were applied to the capacitors of the CPC-1 and CPC-2. Maximum values of the capacitances C1 and C2 are listed in table. 2.
Table 2
Range, m
Maximum capacity C1, PF
Maximum capacity C2,PF
10
50
20
14
80
25
20
150
30
The antenna tuning is carried out by using an SWR meter or indicator field. After tuning capacitors are enclosed in a sealed box.
Author: V. Postnikov (UA3ZD), Gubkin, Belgorod region; Publication: N. Bolshakov, rf.atnn.ru