My 5 cents on antenna interaction:
>From my experience while plying with various real antennas, there appears to
be, for the lack of better term, an "aura" or envelope of antenna's function,
that is close to it's radiation (or "RF suction" on RX) pattern. The resonance
of the antenna has major effect on the aura, because that is when the effect
is most pronounced (pattern forming). Just like with parasitic antenna (Yagi,
Quad array) other elements or things that exhibit being close to resonance of
another antenna (element) start effecting each other and modifying the
resultant pattern of radiation (suction). If the other antenna is detuned
(opened feed, or resonant freq. shifted) then the effect is diminished or
changed. Effect gets "weaker" with increasing distance between involved
antennas of course. You get two or more "auras" involved and they interact and
produce interesting effects. They either pick on each other's properties
(signals) and the result is enhancement or suppression of signals (noise). So
Beverage can pick on vertical's, etc. To minimize the effect of auras, they
have to be eliminated or minimized or changed in shape, so they do not overlap
- interact with each other (antennas). This can be done by opening or detuning
the antenna/structure. (As some of the previously mentioned examples have
shown.)
One example of weird interaction I had between Eu Beverage (abt 800 ft. at
8 ft high) and small shielded loop: my Beverage was run out of the shack's
basement window (from antenna tuner in the shack) to a post on the fence (abt
30 ft away), then made 90 deg turn and continued straight to Eu. I had small
shielded loop (copper tubing es shield with tuned 3 turns and one turn
coupling) abt 4 ft off the ground and with rotator. Loop was abt 4 feet from
the "corner" of my Beverage and in the line with Beverage wire. My Beverage
had to be the "night type" I rolled it out after dark, it ran accross the
(public) park and hudlums would rip the wire if left over daytime. As the band
was starting to open to Eu at sundown, I would hear faint signals on the loop.
When I unrolled the Beverage, signals came up on the loop significantly.
Beverage alone would be quite noisy, (had nearby power line noise). But when
listening on the "enhanced" loop I could get much better signal to power line
noise discrimination. By turning the loop, I could position it so it brought
in signals (from the beverage) and minimized noise and static. That
combination gave me better results then each of them alone. So it appears that
loop was coupling to the Beverage and providing some discrimination from the
power line noise and static.
Another unusual effect was with my 15 m stacked Razor beams (Quad-Yagi, 62'
booms at 106 and 45 ft), when I had 3 el Yagi mounted between them
(unconnected to array) and in certain position it would boost the gain of
Razor array by 3 - 4 dB! (Yes it was a boost, it was verified by removing it,
not a question of detuning it in other postions). Pretty good gain for lousy 3
el Yagi, when normally you would need to double the size of the array to get
the same result. (No, I didn't use chart recorders, whatever NECs, and do not
own a white coat!) I think another example of "auras" interacting. How it
worked? When pileup of JAs disapeared into the noise, I would bring the 3 el.
into "position" and the pileup would come up about 1 S unit - and there would
be another layer of QRPers. (Normally I used the 3 el with second RX to
monitor other directions from Razors.)
I only wish I could see the aura, it would make antenna things so much
easier! Anybody got any solutions?
I might take my mobile 160m aura to the oceanfront and/or hilltop this
weekend and do some country hunting in ARRL test.
73 de Yuri Blanarovich
VE3BMV, K3BU/m
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