Topband: Antenna Comarisons

[Richard (Rick) Karlquist (N6RK)]

The tower with 1 radial is probably not
omnidirectional.  It could easily favor
one direction 2 dB at the expense of other
directions.  Maybe you happened to measure
it in a direction where it has 2 dB of "gain".
We can reliably assume the T-vertical has
0 dB of gain in all directions.

Rick N6RK

> -----Original Message-----
> From: topband-bounces at contesting.com
> [mailto:topband-bounces at contesting.com]On Behalf Of W5UN
> Sent: Monday, October 11, 2004 4:47 AM
> To: topband at contesting.com
> Subject: Topband: Antenna Comarisons
>
>
> 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
>
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