A simple dual band antenna for frequencies 260-390 MHz, the radiation pattern is ellipsoidal, the gain of the signal compared to a half wave dipole is at least 3 dB.
Vibrators made in the form of circles, length of conductors is equal to the length of the wave.
The length of the wires is calculated by the formula:
L = 300/F,
where L - length of conductor in metres;
F is the operating frequency of the antenna in MHz.
50 Ω cable connects to the antenna via a matching transformer resistances are made in the form of a segment of cable with a characteristic impedance of 75 Ohms, the length of this section is 150 mm.
Author: Vasily Vasilenko, Yakutsk; Publication: www.inspector_v.chat.ru, www.cxem.net