This is a 200 to 400 MHz Log Periodic Antenna designed to work with the PRC-41 radio. Although there is not a seperate manual for this antenna there is some information in the manuals for the PRC-41. Some of the elements can collapse to make the antenna smaller for transportation, but they are designed to be pulled all the way out. This is not an adjustment, just a packaging feature. The VSWR is below 1.7 across the 220 to 400 MHz band.
The antenna was made by the Collins Radio Company.
There are 9 dipoles with the distance from shortest to longest = 28.75" = L in the Amateur Radio Handbook.
The shortest dipole is 10.875" long and the longest is 27.5".
The seperation between the shortest dipole and the one next to it is about 2.5".
The seperation between the longest diploe and the one next to it is about 5.25".
An Ohm meter shows that every other opsite element has continuity, but there is no continuity across any one dipole.
The Type N center conductor is connedcted to one set of elements and the Type N shield is connected to the other set, this is classical LPA zig zag construction, but there does not appear to be an balun.
B = operating bandwidth = 400 / 200 = 2
Alpha (the 1/2 angle at the apex) = 16.13 deg. and tau should be about 0.82.
Sighting along the tips of the elements shows that the 8 shortest elements have their tips all in a straight line, but the longest element is about an inch longer that the extension of the tip line, why?
Note that the pattern in the horizontal plane is very good. That is to say that there is gain in the direction of the pointed end.
But there is very little gain in the vertical plane, that is to say if the antenna is pointed upward like at a satellite, the null is off the ends of the elements.
1.1 Photos - sorry, missing filesAS-1405/PRC-41 antenna
TM-03816A-12/1 Fig 2-6 - drawing showing the antenna on it's tripod.
The AS-1405 is one of 3 antennas in this photo.
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