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Author Topic: Magnetic loop antennas  (Read 937 times)
K6ICU
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Posts: 2




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« on: October 18, 2001, 04:45:28 PM »

Are magnetic loop antennas any good?
 
I live in a neighborhood with antenna restrictions and was considering getting either an AEA isoloop or a MFJ1786 loop antenna for the attic.  I would like to hear some opinions on which antenna would be the best way to go.
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K1TWH
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Posts: 104




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« Reply #1 on: October 18, 2001, 05:31:28 PM »

.......I've used the AEA Isoloop and one consideration is how big an entry you have into the attic.  The band around the AEA Isoloop is flexible and you can "squish" it past almost any entry a person could fit through and many only a child could fit past.  The MFJ units are tubular and not "squishable" so this could be a consideration.   Please don't be taken by MFJ's hype wherein they claim that the tubular shape results in less loss.  This would be true for a multi-turn loop, but the full story is that  "electron bunching" BETWEEN turns is responsible for the additional loss in a coil made with flat band material.  Since both antennas are single turn loops, this doesn't influence the efficiency at all.
......The MFJ units are still in production and judging by the few units of either brand to be found on the used market, I'd say they both work pretty well.   Don't go for MFJ's 40-15 unit.  The efficiency on 40M is not worth it.  If they made it a 2 or 3 turn loop, it could work pretty well, but they made the capacitor bigger and left the loop at the same size.  
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WB2WIK
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« Reply #2 on: October 18, 2001, 06:03:01 PM »

I've used both, and did not know the AEA was still available.

They've both worked well, exhibiting similar performance and "symptoms," which, unfortunately, aren't all good.  One symptom both the AEA and the MFJ loops I've owned exhibited is poor workmanship or materials...with both, I've had to rebuild the capacitors.

The MFJ-1786 surprised me by making 3000-mile+ contacts on 30m CW, on several occasions, while installed in a condo attic.  Then, I found its mounting location to be extremely uncritical, and it worked just as well hanging from a 6' wooden stepladder on the patio looking rather the ugly clothing hanger.  In the attic, it was up nearly 40 feet above ground with a "view" for miles.  On the stepladder, its "view" was limited to maybe 20 feet.  Just didn't seem to matter.

I still own the MFJ and use it on the occasional camping trip, while I use larger, more "permanent" antennas at home.  I had an Isoloop several years ago and it performed, to my recollection, in the same manner as the Hi-Q Loop products.  By design, they are extremely comparable.

73 de Steve WB2WIK/6
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WB6BYU
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Posts: 13578




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« Reply #3 on: October 19, 2001, 12:07:16 PM »

Here is one approach to building your own magnetic loop quite
inexpensively:

http://www.qsl.net/7n3wvm/mag-loop.html

(The English text is at the end of the article.)
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W0FM
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Posts: 2057




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« Reply #4 on: October 19, 2001, 03:55:03 PM »

I used an AEA Iso-Loop 10-30 in the attic of my former condo for years with good success.  Another poster made an important observation about the flexible flat band  being able to squish through small attic openings.  That was my experience.  The MFJ model would have had to have been disassembled to even have a chance to fit through the attic access opening I had.  The AEA Iso-Loop worked some surprising DX for me, but, obviously, had to be tweaked every time I moved a few kHz because of the high Q design.  I eventually built my own control box for the loop because of the wobbly little plastic UP/DOWN buttons on the AEA version.  AEA's fancy and expensive memory tuner box they offered as an option sure didn't improve things.  I sent mine back after two days of ineffective "memory" tuning.  Nonetheless, bottom line was, the Iso-Loop 10-30 fit into my available attic space, and, if I could hear 'em, I could work 'em.  73,  Terry, WØFM
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KD7HVL
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Posts: 66




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« Reply #5 on: October 20, 2001, 03:44:16 PM »

Hello
I have read your message with respect to the magnetic loop antenna.  I have the MFJ loop 40-15 and the one for 20-10.  They work.  I now have them up in my rafters.  I found the ISOTRON type antennas work at my QTH about as well, and they have a little better bandwidth.  They are also a lot cheaper.  I really do not consider either of these a good antenna but for lack oof any-other type I guess they have to do. At least you can get on and have some sort of a signal.  I wish you luck with your antenna hunt,  and should you come accross something that is small and really works please don't keep it to your self but let the rest of us know.

Frank
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