|Subject:||Re: [TowerTalk] SteppIR 40/30 and loading|
|From:||Jim Lux <firstname.lastname@example.org>|
|Date:||Wed, 05 Nov 2003 10:36:38 -0800|
At 12:50 PM 11/5/2003 -0500, K3BU@aol.com wrote:
In a message dated 11/5/03 12:45:42 PM Eastern Standard Time, email@example.com writes: <<Interesting charts, but in the real world wouldn't one be comparing antennas to which equal power is delivered rather than antennas with equal currents at the current maximum?
If your goal is simply to radiate the power, then a uniform current would be the best (since power dissipation goes as I^2, anything other than uniform I will suffer), and all the interesting analysis is valid. (I haven't given it much thought, but there are other arrangements with varying currents that might be as effective.. think of 3 phase power transmission viz DC)
However, this seriously neglects an important issue: that of the pattern. An idealized dipole (or a monopole over ideal ground) with the classical cosine current distribution has 2.15 dBi of gain, presumably squirted in a desirable direction. Make the current uniform along that radiator and the gain starts to look different. Taken to an extreme with a physically small lossless radiator, and the pattern can be arbitrarily close to isotropic.
The monopole over ground has a pattern that has maximum gain at the horizon and radiates nothing directly vertically. Start shortening the monopole, and you start radiating power at higher angles above the horizon. Might be good, might be bad, depending on where you are and what sort of propagation you're looking for.
I think that the average ham might be willing to give up a few tenths of a dB in loss in exchange for a few dB of gain in a desired direction.
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions and ask for Sherman, W2FLA.
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