Home |
Search |
Today's Posts |
#1
![]() |
|||
|
|||
![]()
Jimmie D wrote:
"The book shows a .25wl of antenna and a .25wl of stub,---." The J antenna is often described as a half-wave of antenna with a quarter-wave matching stub. Function of the stub is to shunt the antenna at a point so that the parallel combination of antenna and stub equal Zo. If the antenna were only 1/4-wavelength, reflection from its open-circuit end at its drive point may yet be compensated by a .25wl stub. At the 1/4-wavelength stub`s short-circuit, phase of the reflected voltage is reversed. Voltage reflected from the open-circuit tip of the antenna is not reversed in phase by its reflection. Both waves travel the same distance to the point where they meet at the antenna drive point. These tend to offset each other. Terman describes impedance matching using stubs on page 109 of his 1955 opus: "Thus, although a reflected wave is present in the length l1 because of reflection from ZL, there is no reflected wave on the generator side of the stub line as a result of the cancellation of the two reflected waves." Best regards, Richard Harrison, KB5WZI |
Thread Tools | Search this Thread |
Display Modes | |
|
|
![]() |
||||
Thread | Forum | |||
Flagpole antenna - experiences | Antenna | |||
Flagpole verticals | Antenna | |||
Flagpole/Vertical Antenna | Antenna | |||
Flagpole antennas | Antenna |