Going Magnetic Loop

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flintstone mop:
I have been reading a lot about magical antennas, like magnetic loops and find them quite fascinating.
I just installed a magnetic loop 3 foot diameter antenna for listening. Got it on a TV rotator and it is a pleasure to pick something out of the grass...the noise, local noise, ma nature. I can see the noise floor go up over 10dB by switching between the conventional dipole or vertical to the loop.

I'm looking at some designs for a transmitting loop.........12 foot square, using aluminum pipe....rotating might become a problem. BTW this is probably the one antenna that becomes directional for transmit. A dipole only 40 feet off the ground on 75 or 160 is not directional. But a magnetic loop antenna is. It may not be beamed like a Yagi and have gain, but it does exhibit direction.
They can take legal limit, but the vacuum variable needs to be 30kv. A lot of hype about a magnetic loop antenna being just as effective as a dipole 1/2 wave up in the air and more efficient.
QST has an article about a Ham who built a 2 loop antenna.
Fred

K5WLF:
Fred,

If you come up with what looks like a workable design for 160, I'd sure love to know about it. I live on a leetle, tiny city lot with not even enough room for a decent antenna garden, much less a farm. I'm using a coil-loaded dipole on 160 right now, but I need to improve the 160 antenna, so all ideas are welcome.

ldb
K5WLF

Ed/KB1HYS:
How big is your lot? Any trees or just the house/roof?  I have the same problem with our 100x100ft lot, But I have some very tall trees (65 ft or so white pine and a few oak) that make great ant supports.  One day I will mess around with actually using the Tree itself as a vertical ant on 160 meters.  It's been done and is supposed to work, tested by the Army. 

W0BTU:
If you are very careful to minimize I2R losses, an STL (Small Transmitting Loop) can actually outperform a dipole mounted higher than the loop. Using large diameter copper pipe and a special capacitor is a must.

There's some good links and references on STLs at the bottom of http://www.w0btu.com/magnetic_loops.html.

I just received my vacuum variable (eBay, Russian military surplus) last week for my own STL project.

As for the QST article, there's a typo: it says the loop can approach the performance of a vertical, but "dipole" (more gain) should have been there instead of "vertical". Or, they could have said exceeds the performance of a vertical.

W0BTU:
Quote from: K5WLF on October 18, 2011, 08:38:27 PM

If you come up with what looks like a workable design for 160, I'd sure love to know about it.

Here's one guy who did that: http://www.bulldogtrust.com/index12.htm

And I've seen others, I think they're in the links on my STL page I mentioned.

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