Loop on ground question

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JEL
Posts: 185
Joined: Wed Feb 07, 2018 2:08 am

Loop on ground question

Post by JEL » Mon Jan 25, 2021 2:01 pm

For receiving only! Not for transmitting.

Would you rather...

A:
1 loop of wire equivalent to 1 full wave-length at desired reception-frequency (So the wire has the length of 1 full wave-length)

B:
2 turns of wire, so the wire is technically double the wave-length (2 times longer than desired wave-length)

or

C:
3 turns of wire, so the wire is thrice the wave-length.

when

the loop-diameter is the same in all 3 cases (Same size antenna in terms of width and depth, but 3 different lengths of wire laid out in 1, 2 or 3 turns around the loop-circumference)

AND

the entire construct will be passive and directly connected to the feed-line without any type of impedance-matching devices or anything else at any point.


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I plan to experiment with laying out some cable in my garden, for a 'loop-on-ground' antenna, and I would like to avoid cutting the cable unless a single-turn loop is far superior to simply rolling out the entire cable in 3 turns.

The roll of cable is currently 3 times the full wave-length I'm going for (So basically there's enough cable for 3 full-wavelength antennas)

But I'm unsure if using it like that is much better or much worse, or not making much difference, compared to cutting off a third of the cable which would give me enough wire for a single turn loop at the full wave-length.

When I google I get different answers.
Some say 'longer is always better', others say multi-turns won't enhance anything but also won't be detrimental, others say 1 single turn will cause the directional-lobes to be more along the horizon rather than straight up (Though others dispute that by saying a loop-on-ground is always just straight up)

So I'm not sure what might be better here and can't really try all options without cutting the cable, and I would obviously prefer the final solution to not involve a cable having been cut unnecessarily.

I know there are no easy answers and other things, such as soil-composition and so on, play in on which may be the better approach.
But I'm just interested in what people speculate might be the better option here.

VE3EAR
Posts: 49
Joined: Sat Oct 05, 2019 10:13 pm

Re: Loop on ground question

Post by VE3EAR » Sat Jan 30, 2021 5:08 pm

The perimeter of a full-wave loop hanging in free air will be much different than one that is laying on the ground. The ground's proximity to the loop will have a varying effect, due to the composition of the ground....black soil, gravel, or sand, each will effect the loop differently.

Based on that, my instinct would be to go with the un-cut wire in the three turns style of loop. You will only know for sure by trying it. I also think that it would be a good idea to use a broadband transformer with a 1:1 ratio, so that the balanced loop is not upset by feeding it with an un-balanced feed line.

Try it, and let us know how it works!

73, Bruce, VE3EAR

hotpaw2
Posts: 172
Joined: Sat Jan 14, 2017 11:07 pm
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Re: Loop on ground question

Post by hotpaw2 » Sat Jan 30, 2021 7:37 pm

The answer (not that I know) likely depends on (1) the noise floor in your environment versus the sensitivity of your receiver, (2) the frequencies over which you wish to receive, and (3) whether you care about true omnidirectivity (versus directional lobes and nulls).

Too large a loop wire length in relation to the wavelengths of interests might end up producing a more distorted pattern, and won't really improve the S/N if your receiver is sensitive enough for a smaller loop length. The latter you might have to experimentally determine for your receiver and site.

I would cut the wire, and experiment with 3 segments in series vs. in 3 segments parallel (same layout and loop area).

JEL
Posts: 185
Joined: Wed Feb 07, 2018 2:08 am

Re: Loop on ground question

Post by JEL » Thu Feb 04, 2021 9:36 am

Thank you.

I'm still pondering this and receiving advice from various places, so no concrete build-plans (or experimental results) yet.

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