Ok, 40 foot circumference is bigger than most shielded loop designs out
there. Generally, bigger is better when it comes to loops -- or so I
figured.
I have a 41.5 foot circumference loop made from RG213 enclosed in some 1"
pvc pipe. I built a 36 : 1 transformer, which tests fine using a resistor
as a load. My autek VA-1 measured the feed point (after the transformer) as
follows:
1.8 14 -j482
1.9 0 -j444
2.0 0 -j409
3.5 11 -j207
3.6 11 -j201
3.7 9 -j196
3.8 7 -j189
3.9 9 -j183
4.0 10 -j175
7.0 14 -j63
7.1 35 -j32
7.2 124 -j22
7.3 84 -j169
With that being said, I was expecting to see an inductive reactance at the
loop. Instead I see a very low R and capacitive. What's up with that?
Most loops use a capacitor to "tune out" the inductive reactance -- or so I
thought.
Can anyone explain to me what it is that is being "matched" on a shielded
loop?
Can anyone explain to me why 20 feet appears to be the maximum allowable
loop size -- or so I've been told from several articles, none of which
explained why. Is the shielded loop a resonant or non-resonant antenna?
Any help in solving these (and no doubt other questions) would be
appreciated.
Ford - N0OQW
ford@cmgate.com
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