Design of the antenna is very simple. Personally
I have made the antenna in 40 minutes. Antenna consists from reflector
(length 1002-millimeters) and vibrator (length 972- millimeters,
gap for coaxial cable- 10-millimeters). Distance between reflector
and vibrator is approximately 204 – 210- millimeters. Antennas
parts are made from insulated wire in diameter 4 millimeters.
Place of vibrator, where a coax was installed, was protected with
a raw compound.
You may use another protector… SWR for
the antenna (measured by SWR-121) was (1.0-1.1):1.
Input resistance of the antenna is 12,5 –Ohm, for matching with 50-Ohm Coaxial I have used a transformer
made with two bridged length of 50-Ohms coaxial cable. The coax
must have the similar length near 370- 440- millimeters (should
be find at adjusting). Both pieces must be tied at all length
one to another.
I was asked how is it possible to improve
gain but save wide DD? To do this it
is impossible to add another director, but it is possible to use
two phase antennas. Picture below shows this way. Good chose to
phase 2 or 4 antennas. We get good DD,
good gain and the system can receive mobile stations
in very good way compare to collinear
antennas in 5- 7 meter long.