[TowerTalk] Interaction and loaded elements

[Jim Lux]

At 10:25 AM 6/30/2005, TexasRF at 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