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German physicist Heinrich Hertz first demonstrated the existence of radio waves in 1887 using what we now know as a dipole antenna (with capacitative end-loading). On the other hand, Guglielmo Marconi empirically found that he could just ground the transmitter (or one side of a transmission line, if used) dispensing with one half of the antenna, thus realizing the vertical or monopole antenna.
Tests done by J.S. Belrose (1994) [7] showed that though the conventional T²FD length is close to a full-size 80 meter (3.5–4.0 MHz) antenna, the antenna starts to suffer serious signal loss both on transmit and receive below 10 MHz (30 m), with the 80 meter band signals −10 dB down (90% power loss) from a reference dipole at 10 MHz. [7]
The most common form of log-periodic antenna is the log-periodic dipole array or LPDA, ... with both halves being roughly equal in size. ... [11] [12] Log-periodic ...
This simplified arrangement has several advantages, including a shorter ground distance between the ends. For example, a dipole antenna for the 80 meter band requires a ground length of about 140 feet (43 m) from end to end. An inverted vee with a 40-foot (12 m) apex elevation requires only 115 feet (35 m).
Due to the size required to create a far-field range for large antennas, near-field techniques were developed, which allow the measurement of the field on a distance close to the antenna (typically 3 to 10 times its wavelength). This measurement is then predicted to be the same at infinity.
A "folded dipole" type of halo, similar to the original halo patent. [1] Gain along Y axis 1.2 dBi , gain along Z axis −10 dBi , gain along X axis −1.7 dBi . Fed at the center of the bottom conductor (at the red mark; feed-line not shown), supported at the center of the top conductor which is at ground potential for RF.