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160 m elevated aluminum tubing magnetic loop




 
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Author Topic: 160 m elevated aluminum tubing magnetic loop  (Read 28398 times)
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k1qar
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« on: October 26, 2007, 10:18:17 PM »

This antenna is a 15 foot doughnut made from 3 inch aluminum tubing hung from  a tree on our city lot.  It is tuned as a magnetic loop by a pair of parallel vacuum variable capacitors, and fed through a 2 foot coupling loop tied directly to the coax, no tuner needed.  Seems to hold its own signal wise.

Magnetic loop antennas are critical, with large voltages, large currents, and tiny bandwidth.  With a 2:1 SWR bandwidth of 2kc, a motor drive on the tuning capacitor is a necessity.  In order to run a kilowatt, the capacitor needs to withstand 30kV or so, and 100 amps.  It is said to sound good on AM, and  can be rotated to null QRM.

 Details are at http://x44.cc


* kw160loop2.jpg (475.45 KB, 1072x1611 - viewed 1832 times.)
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WA1GFZ
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« Reply #1 on: October 27, 2007, 09:38:52 PM »

This antenna works I've heard it a number of times and puts out an impressive signal on 160.
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W1UJR
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« Reply #2 on: October 27, 2007, 09:55:40 PM »

Neat concept if you don't have space.

Found the following on the website mentioned, especially like the "Deathray" comments!


DEATHRAY

Work with the ARR's engineer in charge of public RF exposure revealed that this particular magnetic loop's danger zone is 30 times larger than a dipole's, or about 30 feet at legal limit power. A wrought iron table 60 feet from the antenna will pick up enough energy to make a visible arc to ground; At 200 feet, field strength spontaneously starts and runs our vacuum cleaner at a speed proportional to the carrier power. You don't want to even think about what it would do to a pacemaker. 
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WA1GFZ
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« Reply #3 on: October 28, 2007, 10:27:08 PM »

I think the vacuum cleaner part is BS. since it would need a RX antenna to abosrb enough energy and besides it has a 60 hz motor not a 3885 KHz motor.
 Besides I think they run at about 500 watts.

I would avoid standing next to it though.
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flintstone mop
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« Reply #4 on: November 21, 2007, 08:32:47 PM »

WOW
All I need is a recipe for the goodies needed and prolly try it out. This is what radio is all about. Arcs and sparks and glowing pubes

fred
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Fred KC4MOP
flintstone mop
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« Reply #5 on: November 26, 2007, 07:56:09 AM »

Hello
Looking over this again, seems to be better suited for folks with space limitations. Then you have to consider the very high voltages and currents.
There is a lot of AM on 160 and 80 this season. This is good
Fred
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Fred KC4MOP
flintstone mop
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« Reply #6 on: November 26, 2007, 08:14:15 AM »

Sorry for multiple posts BUTwith the very narrow bandwidth (Author mentions 800 hz), what happens to a nice modulated AM signal? Same problem as a BC station?? Distortion? High audio frequencies distorted?

Fred
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Fred KC4MOP
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« Reply #7 on: November 26, 2007, 03:50:59 PM »

I was wondering the same thing about the sidebands, but he addresses that at one point saying it didn't seem to have a noticeable impact. I think that may have been on a second web page linked from the first IIRC.

I've considered a much smaller version for 75 and 40 meter mobile. There is a commercially made mobile loop by QMAC that covers down that low that claims to be 10-15 db better than a whip antenna on the low bands. It avoids the 'lack of counterpoise' issue that a small car body presents to low HF operations, but demands extremely low resistance construction. Then there's the whole mobile death ray problem....

I may do some experiments in my 'copious free time' sometime using aluminum hard line as the radiating element and see how it compares to my screwdriver on 75.
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73 de Kevin, WB2EMS
k1qar
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« Reply #8 on: November 27, 2007, 06:58:19 PM »

Frank, I could never make up anything that good.
The vacuum cleaner in question is a high end  Electrolux (model c133A).   600 Watts  sets it off.
 
Its one of those electronically controlled appliances that lights a light as soon as you plug it in.   I suspect the RF is fooling the control circuitry somehow. 
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Bacon, WA3WDR
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« Reply #9 on: November 27, 2007, 07:32:56 PM »

Note that it is vertical.  I tried a small 160 meter loop horizontal once, and all I heard was lightning static with super-weak locals behind it.  But then I wondered how they were hearing each other, because I couldn't hear them through the static at all!  And then it dawned on me that the horizontal loop had a round lobe at a low angle, but a great big null straight up where the local reflections were coming from.  So I went outside and lifted the loop until it was close to vertical, and boom there they were, just fine.

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Truth can be stranger than fiction.  But fiction can be pretty strange, too!
AMroo
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« Reply #10 on: July 11, 2008, 06:25:39 AM »

Loops really rock. I have been using them from my apartment and work DX such as Russia, Norway etc  from Sydney, downunder with 15-20watts, at this stage of the sunspot cycle thats pretty good.
I am three floors up and the feedline from my tower height  loop is only 15 feet, not much loss in that.
I have posted this pic before on another thread. Its my loop made of half inch helix and a few bread slicers.Tunes 80 thru 10 meters, The sig/niose improvement over my center fed L was massive.
Running my Swan 500C into it.
I do want to look making a at a 160M loop so your info is interesting to me. I guess I would use  a multi turn loop.


* loop.JPG (880.95 KB, 1200x1600 - viewed 2047 times.)
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