At 10:25 AM 6/30/2005, TexasRF@aol.com wrote:
>
>The likely thinking is that a full sized 40m antenna element also resonates
>on it's odd harmonic frequencies; third being at 15 meters.
>
>A loaded element is going to have different odd harmonic resonances due to
>the loading device being a different reactance on each of these harmonic
>frequencies.
>
>It is very unlikely that there will be a resonance near 15meters therefore
>the lowered influence on the 15meter antenna.
>
Good points on resonance, however interaction isn't much affected by
resonance per se(unless you're worried about the resonant frequency of the
antenna being interacted with.. the 3 band dipole tuning problem). All the
popular Method of Moment modeling codes (which produce very accurate
results, and have good theoretical validation) calculate by using the
interactions between very short, non-resonant, chunks of the antennas.
Obviously, the pattern effects will be affected by resonance (or, more
properly, being near resonance, but not quite, so there's a phase shift),
and, a non resonant device (the loaded 40m thing being non-resonant on 15m)
will tend to have less current (because the reactance will be very high, so
there will be less current).
However, it's hard to make a general statement. That's why I'd push the
mfr to provide substantiation for the claim of less interaction. At the
least, one would have to define what "less interaction" actually means (for
all we know, they're talking about aerodynamic drag <grin>). Or, it might
mean that "we resistively load our antennas so they're less efficient, and
therefore don't couple as strongly". Cynically, my dummy load has an
excellent match, and very little interaction with my other antennas.
>73/K5GW
_______________________________________________
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.
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|