Magnetic Loop Antennas

[Greatvalue1]

I was wondering if anyone has used or built a Magnetic Loop Antenna for 11 meter base station?

I looking for an alternative to my stealthy 102" whip that works pretty well concerning its limitations.

I've seen on the Y-tube that an operator made one with only 6 feet of 3/8 copper tubing, and this seems right up my ally.

Home Owners Association is the problem.

Gain? Rejection? Direction? Just some of the questions I have.

 

[AudioShockwav]

I built one just for fun, it worked very well for the size it was.
They are easy to build.
I was living in a ground floor Apartment at the time and no place to put an antenna, I used it on a small table on the patio.
It worked well enough to get a signal on the air, as far as rejection and gain, if you have nothing ...well you get the idea
They do work, and it is surprising how well for the size.
If you like to build stuff i encourage you to give it a try just for the fun factor.

http://www.worldwidedx.com/amateur-radio-antennas/137947-home-brew-10-12-meter-portable-loop.html

http://www.worldwidedx.com/tuners-mics-meters-other-accessories/135805-capacitor.html

http://www.worldwidedx.com/amateur-radio-antennas/108446-magnetic-loop-antennas.html

And here is Just a Loop.
http://www.worldwidedx.com/cb-antennas/82386-11-meter-loop-antenna.html


73
Jeff

 

[Greatvalue1]

Sounds like a good next-project to start. I'll let you guys know how it turns out.

I have most of the stuff in my garage, do you have any recommendations for the capacitor?

 

[HomerBB]

So disturbing . . .

On the list:

Moxon
one of these loops
Redo V4k w/changes
All metal Astroplane

and more.

I am having a anxiety attack.

 

[AudioShockwav]

The best capacitor is what you can find, I used a tuning cap from a small antenna tuner i bought at a ham fest.
The larger the plate spacing the higher the voltage it will handle, that means it will handle more power.
I never ran more than 100 watts into the one i built.
One thing to think about is loss, you want every connection to be as low loss as possible.
If you search the net about Magnetic loops and read up on some of the antennas that have been built it will give you some Ideas, like the Coke Can cap that Alex, PY1AHD came up with:

73
Jeff

 

[Riverman]

Does a magnetic loop behave more like a horizontal or vertical antenna? Am trying to picture if it can be used for both DX and talking to locals. Thanks.

 

[Captain Kilowatt]

A magnetic loop antenna responds to the magnet component of an electromagnetic field commonly called a radio signal. That field may be vertical, horizontal, or anything in between just like the electrical component of a regular antenna. The magnetic component is less prone to noise which is why they make good receiving antennas.

 

[Riverman]

A magnetic loop antenna responds to the magnet component of an electromagnetic field commonly called a radio signal. That field may be vertical, horizontal, or anything in between just like the electrical component of a regular antenna. The magnetic component is less prone to noise which is why they make good receiving antennas.

Thanks, Captain. Nearly all pics show magnetic loops being used in a vertical orientation. Would they not work better for DX if positioned horizontally like is recommended for dipoles?

 

[Captain Kilowatt]

Positioning an antenna for horizontal polarity simply allows you to take advantage of what is known as "ground gain". This is an additional 5-8 dB of gain obtained by combining the direct wave and a reflected wave that bounces off the ground and combines somewhere far away. A vertical antenna does not have ground gain. Since a radio signal twists and turns many unpredictable times in it's journey from point A to point B it is impossible to predict what the polarity will be when the signal is received. It is for this reason that I do not believe the old idea that verticals are for local and horizontal is for DX. This seems to come mainly from the CB crowd just like a lot of other untrue yet universally accepted myths.Also having owned dual polarity antennas in the past I can attest that there are many times when one station has to be vertical while the other is horizontal in order to maintain contact. Sometimes you may have to switch polarity several times during a single contact in order to maximize the signal, either incoming or outgoing, because of the constantly shifting of polarity due to propagation.


Good magnetic loop info: http://www.google.ca/url?sa=t&rct=j...t2O-Q7Jag0-Mixg&bvm=bv.92291466,d.cWc&cad=rja

 

[StrangeBrew]

Since a radio signal twists and turns many unpredictable times in it's journey from point A to point B it is impossible to predict what the polarity will be when the signal is received. It is for this reason that I do not believe the old idea that verticals are for local and horizontal is for DX.

Back in the day the only reason that horizontal was recommended for DX was because most local sources of interference tended to be vertically oriented, thus horizontal usually resulted in less noise in your receive.

The only reason vertical was recommended for local was because most mobile antennas were vertical so your base antenna would also have to be vertical for local comms, but it didn't matter for DX due to the twisting you already described.

At least that's the way I remember it, the theory about one propagating better than the other came later. It seems as though much of the commonly accepted advice regarding CB was originally based on fact but has been distorted way beyond its original intent over the years.

 

[Captain Kilowatt]

Yes the old idea was that since MOST people had groundplanes that were vertical anybody wanting to use a beam would have to be vertical to talk to them locally and to mobiles. Horizontal antennas however take advantage of ground gain as I mentioned above and they are also easier to stack in the case of multiple antennas on a single mast.

 

[Riverman]

Thanks, guys. That's some good info.

 

[M0GVZ]

Back in the day the only reason that horizontal was recommended for DX was because most local sources of interference tended to be vertically oriented, thus horizontal usually resulted in less noise in your receive.

Nope. The reason to use horizontal is to take advantage of ground reflection gain. Its a few dBi of gain given for free.

 

[Captain Kilowatt]

Are you sure that is dBi gain and not just dB gain?

 

[StrangeBrew]

I know that hams use horizontal beams to take advantage of ground gain now, but was this something that was known to CBers 30+ years ago when the horizontal for DX recommendations were first made? I never heard anything about it back then.