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Coupling loop advice

 

Hi all and thanks for accept me in the group.
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I'm building a magnetic loop antenna for TX and I slightly follow the instructions in https://www.nonstopsystems.com/radio/frank_radio_antenna_magloop.htm and another sources. I've finished the main loop with the capacitor and its rotator and now I have to choose a coupling loop configuration. There are basically 2 variants: unshielded and shielded (aka Faraday loops). According to the link I've wrote I'd like to use the shielded F variant because it seems to be better cancelling E-fields in horizontal and vertical polarization. But there are some people that think both variants work the same.
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I'm in doubt with this. Any advice or experience?
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Thanks in advance. Regards.
 

Hi

Unshielded..been there done it..dont waste time on shielded. Its not the antenna, its just the coupling to the antenna which has already received any noise. A common mode choke in coax by antenna would be good though.

See bottom of my qrz page..Simon g0zen
 

I would agree with Simon. Use an unshielded coupling loop and place an effective common mode choke on the feedline, and also on any control cables.
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Regards,
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Martin
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On Sat, Apr 26, 2025 at 09:48 AM, Simon wrote:

Unshielded..been there done it..dont waste time on shielded. Its not the antenna, its just the coupling to the antenna which has already received any noise. A common mode choke in coax by antenna would be good though.
 

If you look at the physics of the "shielded" loop, you will rapidly realize it is NOT SHIELDED from the induced currents!? That's the whole reason for the gap at the top high-Z point, opposite the feed point and according to the reference diagram: "This will not work".

The use of the term "shielded" certainly connotes the physical appearance of the loop, but from an EMAG standpoint, it is totally in error.

Dave - W?LEV

On Fri, Apr 25, 2025 at 11:25?PM V¨ªctor J. S¨¢nchez via <vjosesan=[email protected]> wrote:
Hi all and thanks for accept me in the group.
?
I'm building a magnetic loop antenna for TX and I slightly follow the instructions in and another sources. I've finished the main loop with the capacitor and its rotator and now I have to choose a coupling loop configuration. There are basically 2 variants: unshielded and shielded (aka Faraday loops). According to the link I've wrote I'd like to use the shielded F variant because it seems to be better cancelling E-fields in horizontal and vertical polarization. But there are some people that think both variants work the same.
?
I'm in doubt with this. Any advice or experience?
?
Thanks in advance. Regards.



--
Dave - W?LEV
 

Hi Dave

Snake oil..lol

Just dont make any improvement..good selling point though!

Simon g0zen, ex maker of 160/80m mag loops that can get into USA, Caribbean etc from UK ssb.. ( now live on Dartmoor.. as you know,( rsgb tech marconi T) no longer need a tx mag loop. Though I do still have it incase I end up end of life in a HOA.( put a bird box in it..its a modern art tree..!)

Regards.Simon
 

On Fri, Apr 25, 2025 at 07:25 PM, V¨ªctor J. S¨¢nchez wrote:
Hi, Victor.
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Not to derail the discussion too much, but the toroid coupling method shown in figure 32 of that link works very well indeed.
Not only is it mechanically very simple and robust, but you can also infer something about the parasitic resistance of your main loop and interconnect to the capacitor.? I.E. once you have the turns ratio for best SWR at resonance, you can calculate the total resistance loading the secondary side of the transformer and then subtract out the radiation resistance.
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Dan - K3GMQ

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