Topband: Split shield loop rx aerial question. . .

[Tom Rauch]

> I have a question about the split shield receiving loop antenna.
> Typical designs I have seen have been make with coax.  Is anything
> about the antenna improved if more than one conductor is contained
> within the shield, and is a 'continuous conductor', rather than
> just having the ends shorted at the feed point?  I'm asking here
> because I'd like to hear from someone with real experience with it,
> rather than theory.  Thanks!

I have some measurement experience since I designed (and patented) shielded
loops for medical systems that reduced unbalancing and detuning from body
effects and radiation on cables connected to the loops. I also used single
loops and arrays of phased loops as far back as the 70's in amateur
applications, and designed some commercially produced loops. The commercial
and medical applications required extensive documentation and testing.

You can have as many conductors as you like inside the loop, or as few as
one. Whatever you use, it will not modify the way the loop works except for
the feed impedance and loss inside the loop. The shield will always be the
actual antenna, the sensitivity will always be the same for a given net area
as long as you don't make a mistake with the matching or tuning.

If a loop is made from coax and the shield is non-symmetrical about the
ground point or if the feed wires exit the shield gap as they sometimes do
with coaxial loops, the loop will be unbalanced and will not have a
symmetrical pattern. The coax to the loop will also become part of the
"antenna". Balance would be better if the shield were actually omitted
rather than being installed incorrectly.

The only thing the shield does is change the balance, and it can make
balance worse if not implemented correctly. The shield won't alter the field
impedance surrounding the loop either, except as loop and feedline balance
is changed.

73 Tom