Small Shielded Loop Antenna-Matching to 50 ohms?

[Reg Edwards]

You will have to learn to live with a narrow bandwidth. Its a fundamental
property of >ALL< high-efficiency antennas which are very small in
comparison with the free-space wavelength.

Download programs RJELOOP1 and RJELOOP2 from my website to obtain an idea
of what happens inside tuned loops on both receive and transmit. In the
first instance, don't bother with screened loops. Use the outer coax
conductor for the loop conductor because it has a larger diameter. Use the
programs to investigate how efficiency varies with diameter. And how it
depends on loop diameter. It also depends on how far away a loop is from
other objects such as the soil in your back garden.

Download in a few seconds. Not zipped up. Can be run immediately.
--
Reg G4FGQ
http://www.btinternet.com/~g4fgq.regp

Chip Owens <ow...@ale.atd.ucar.edu> wrote in article
<6m6ard$cqj$1...@ncar.ucar.edu>...
> I constructed a small shielded loop from some aluminum-jacketed
> semi-rigid coaxial cable. The loop diameter is approximately 5ft.
> I'd like to use this for receive-only on 160 meters. The loop
> impedance is very low-about 0.6 ohms in series with 79 ohms of
> inductive reactance. A pi-network can match this to 50 ohms over
> a very narrow bandwidth and the network values are pretty touchy.
> I'm wondering if someone has some experience matching to small
> loops like this that could offer some practical advice on getting
> some reasonable bandwidth, say 50kHz, in this situation. The
> impedance measurement was made at 1830kHz.
>
> I've tried using a 7:1 turns-ratio transformer on a ferrite core
> to step up the impedance, but with the big inductive component of
> the antenna I still get a very poor match.
>
> Is there a tried & true method to getting a decent match in this kind
> of situation? Any constructive advice would be appreciated. Thanks!
>
> Chip, NW0O
> ow...@atd.ucar.edu
>
> --
> Chip Owens (ow...@atd.ucar.edu)
>