Topband: Antenna Comarisons

[W5UN]

FWIW, on 160 meters I am using a 100' tower with a 4 element 40 meter beam
at 100', and a 7 element 6 meter beam at 115'. This towers sits directly
behind, and next to my 30'X50' metal building shop, with no other
obstructions in the area. On this tower I have a single 1/4 wl radial for
160 meters running away from the shop building. It is connected at the 26'
feet height, and is fed with the coax center conductor, with the coax
shield connected to the to tower leg. I tool no care in detuning the lower
part of the tower.

I recently installed a shortened 'T' top loaded, ground mounted vertical
for 160 meters that is 70 feet high. This antenna has a ground screen under
it, together with 32 radials, and is totally out in the clear, away from
obstructions by at least 1/2 wl.

My purpose was to compare this antenna against the loaded tower. I fully
expected this antenna to be a performer. To my surprise this vertical does
not even come close to performing as well as the loaded tower. Measurements
show that gain in all directions is approximately 2 db less than the loaded
tower. 

Comments are welcomed as to why this situation occurs. Perhaps that metal
building roof top is acting as a good ground? Perhaps the "T" top vertical
is just not the performer it is cracked up to be. Computer modeling of both
antennas show essentially identical results.

73, Dave - W5UN						w5un at wt.net

homepage: http://web.wt.net/~w5un    Grid: EM23mg

RR 10, Box 27
Mount Pleasant, TX 75455