The antenna is a 10-element Log-yagi (Fig.1), calculated UA3THQ and modified by me.
Fig.1
Specifications:
Lбума = 7000 mm
G28=9 db F/b=30 db
G24=6 db F/b=20 db
G2l=8,l db F/b=24 db
Material: tube D16T with a diameter of 24 mm. Vibrators W1 - W7 are insulated from the boom, the distance between the two halves of the elements 80 mm (Fig.2).
Fig.2
The setting is the selection of the length of the plume to reach the minimum SWR on the 21 MHz band. It should not exceed 1.3 in the entire frequency range. At the point of supply X-X resistance 200 Ohms. To align with the coaxial cable of 50 Ohms is used matching balun SPTL with a conversion ratio of 1:4 on the ring N CHH. Winding 2x10 turns MGTF, one twist per centimeter. =
Collective line is made of a cable RK-75-74-15, is used only external braid. A loop made of copper wire with a diameter of 1.5 mm, the total length of cable 1.5 m
Author: C. Ershov (UW3TU), Nizhny Novgorod; Publication: N. Bolshakov, rf.atnn.ru