Log Periodic Dipole Array
So what your seeing here is my recently completed Log Periodic antenna. covering the 144, 222, and 432 MHz bands.
There are various types of log periodics that one can build, however this one is the most common form of log-periodic antenna and is know as the log-periodic dipole array or LPDA,
My LPDA consists of 16 half-wave dipole driven elements of gradually increasing length, each consisting of a pair of 6061 aluminum alloy rods mounted on two 6063 aluminum alloy booms.
The elements are mounted close together in a line, connected in parallel to the feedline with alternating phase.
Electrically, it simulates a series of three-element Yagi antennas connected together, each set tuned to a different frequency, and in this case for the complete bands of.....2 meters.....1. 1/4 meters.....and 3/4 meters.
My LPDA looks somewhat similar to a Yagi antenna, in that they both consist of elements mounted in a line along a support boom, however they work in very different ways.
Adding elements to a Yagi increases its directionality, or gain, where as adding elements to a LPDA increases its frequency response, or bandwidth, although the log-periodic still has more gain on all the bands it covers than a 3 element yagi designed for the same bands.
Every element in my LPDA is active, that is, connected electrically to the feedline along with the other elements, although at any one frequency most of the elements draw little current from it.
Each successive element is connected in opposite phase to the active connection and in this case each boom
.The two booms are being feed with the coax connected at the front of the antenna, the center conductor is connected to the one boom, and the shield is connected to the second boom, therefore the two booms act as the transmission line.
It goes without saying that the two booms with their respective elements are insulated away from one another.
The coax that is attached at the front of the antenna, is terminated at a SO-239 connector mounted on the Lexan mounting plate that I made especially for mounting the antenna on the Max-Gains fiberglass push-up-mast assembly used in the receiver of my mobile.
If you expand the photo, you can see the clear Lexan mounting plate centered on the balancing center of the antenna. The antenna will be used when operating as a stationary mobile.
Did I say the Log Periodic is an interesting build, what with keeping track as too where all those alternating elements go!
Click on the photo for a close look.....
Log Periodic loaded in my mobile.....
Log Periodic mounted on the mast of my mobile.....