Topband: 40 foot diameter shielded loop

[Ford Peterson]

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





--
FAQ on WWW:               http://www.contesting.com/FAQ/topband
Submissions:              topband@contesting.com
Administrative requests:  topband-REQUEST@contesting.com
Problems:                 owner-topband@contesting.com