Question regarding loop designs

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JEL
Posts: 161
Joined: Wed Feb 07, 2018 2:08 am

Question regarding loop designs

Post by JEL » Sat Feb 08, 2020 11:47 am

Hi guys :)

I'm hoping somebody has some knowledge on loop-antenna designs.

I consider 4 different designs (In my case this is for reception only), but wonder which pros and cons each design may have.

For all designs the following is true:
It will be around a vertical square metal grid which is about 1x1 meter (3x3 feet) in size (So 1 square-meter (9 square-feet))

The 4 options I consider:

#1:
A single loop around the metal grid.
So this will be a wire that totals 4 meters in length.

#2:
Multiple windings/turns around the metal grid.
So this will be a wire that is 4 meters long for each wind/turn (So 2 turns will be an 8 meter long wire, 4 windings will be a 16 meter long wire, etc)

#3:
A single wind/turn around the metal grid, but with the wire spiralling around the metal grid (See picture)
So this will also be a wire longer than 4 meters. How long exactly, will be determined by how close each spiral sits.
large.jpg
large.jpg (47.94 KiB) Viewed 2359 times
#4:
A mix of option 2 and 3, so multiple windings/turns of the spiralling wire instead of a single wind/turn.
So this will also be a wire longer than 4 meters.

I don't know much about loops in antenna-design, but based on the info given here; is there one of these options that is generally recommended over the others?

VE3EAR
Posts: 25
Joined: Sat Oct 05, 2019 10:13 pm

Re: Question regarding loop designs

Post by VE3EAR » Sat Feb 08, 2020 2:44 pm

It will be around a vertical square metal grid which is about 1x1 meter (3x3 feet) in size (So 1 square-meter (9 square-feet))
Just what do you mean exactly about a metal grid? Having any metal close to an antenna is not a good idea, as it is very lossy. A few more details on what and why of the metal grid would be helpful.

73, Bruce, VE3EAR

hotpaw2
Posts: 128
Joined: Sat Jan 14, 2017 11:07 pm
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Re: Question regarding loop designs

Post by hotpaw2 » Sat Feb 08, 2020 5:57 pm

Any of your options as far away from the metal grid as possible would be best.

JEL
Posts: 161
Joined: Wed Feb 07, 2018 2:08 am

Re: Question regarding loop designs

Post by JEL » Sun Feb 09, 2020 12:04 am

It's a kind of french balcony grate (Without the balcony though. It's basically a metal-tube bent into a square, with an attached metal mesh in the middle)
The only structure outside I can mount the loop-wire on, unfortunately.

It looks a bit like the image, except the mesh in the middle is both horizontal and vertical (On the image it's only vertical)
images.jpg
images.jpg (8.1 KiB) Viewed 2320 times

VE3EAR
Posts: 25
Joined: Sat Oct 05, 2019 10:13 pm

Re: Question regarding loop designs

Post by VE3EAR » Sun Feb 09, 2020 12:41 am

What frequency or range of frequencies are you wanting to listen to? Perhaps an active antenna, like the PA0RDT mini whip would meet your needs. It could be extended away from the grate on a wooden or plastic rod, and use the grate as its "ground" reference. You can find details of it here: http://www.radiopassioni.it/pdf/pa0rdt-Mini-Whip.PDF

73, Bruce, VE3EAR

JEL
Posts: 161
Joined: Wed Feb 07, 2018 2:08 am

Re: Question regarding loop designs

Post by JEL » Sun Feb 09, 2020 1:17 am

An outside antenna is not allowed here, so that's why I thought of using the railing as a kind of camouflage (People around here use them to string Christmas-lights around and that's considered acceptable, so a wire around it would not be conspicuous)

I'm not exactly looking for a particular frequency for this, just what it would do best really (If anything)
(Basically just hunting for wherever I can find an extra dB :) )

JEL
Posts: 161
Joined: Wed Feb 07, 2018 2:08 am

Re: Question regarding loop designs

Post by JEL » Wed Feb 12, 2020 1:24 pm

To answer my own question, in case others may one day be in a similar situation; I did an experiment, using a loop of 4 turns.

Result was good, but did not appear to be better than putting the same antenna up indoors (Of course it's hard to compare directly when doing it over different days, but at least I got similar SNR on the few bench-mark stations I use to evaluate different antenna-setups)

So not really a success (Meaning; no significant improvement over indoor-placement), but also not really a failure (Meaning; there was plenty of signal)

snn47
Posts: 213
Joined: Tue Dec 27, 2016 11:00 pm

Re: Question regarding loop designs

Post by snn47 » Tue Feb 18, 2020 5:23 am

You did not specify the frequency range you want to use the loop and if you intend to use a untuned or a tuned (magnetic) loop.

The grid will do two things increase capacitance = detune it and shield electrical antennas.
Magnetic loops unless completely shielded in a metall cage will be detuned due to the capacitance due to lower frequencies but will work if not to close to the grid.

How did you intend to feed #3? While electrically #3 would be much longer, I would assume that it will not be too efficient the more windings you will use, since it would cancel part of the radition inside of coils.

JEL
Posts: 161
Joined: Wed Feb 07, 2018 2:08 am

Re: Question regarding loop designs

Post by JEL » Tue Feb 18, 2020 12:23 pm

snn47 wrote:
Tue Feb 18, 2020 5:23 am
You did not specify the frequency range you want to use the loop and if you intend to use a untuned or a tuned (magnetic) loop.

The grid will do two things increase capacitance = detune it and shield electrical antennas.
Magnetic loops unless completely shielded in a metall cage will be detuned due to the capacitance due to lower frequencies but will work if not to close to the grid.

How did you intend to feed #3? While electrically #3 would be much longer, I would assume that it will not be too efficient the more windings you will use, since it would cancel part of the radition inside of coils.
Hi Snn47 :)

In the post above yours I have posted my findings from a simple experiment I did :)

It turns out it works fine with the wire on the grate, but no better than if the wire is inside away from metal.

Maybe the antenna is better outside but being dampened by the metal, and therefore appears to be just as efficient indoors away from metal. I don't know if that is the case (I can't really take the grate inside to test :D ) but what I did learn is that I was not able to better my reception (On any frequency. I did not specify any frequency in the original post since I was interested in people's own experiences on any frequency and not any specific ranges.)

I did have the same thoughts as you about #3, but since loops can be directional in both planes (Depending on wavelength) I figured it could perhaps be an improvement on some frequencies (And also, the windings around the grate would still be much less than the total circumference of the main loop, so I'm not sure if the effect would be only nulling or perhaps a mix of nulling somewhere and gain elsewhere)
I have not tested that option though, so that is still an open question.

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