Loops Is my vertical loop-layout 'sane'? (Image included)

[JELAIR]

I have the coax-connection going from the radio to the lower left side of the image (The yellow circle), where I connect the antenna-wire physically.

I use a 1.5 mm^2 (~15.5 gauge) wire 100 meters (~333 feet) long, circled into a loop (The red circle)

From the coax connection at the bottom left (The yellow circle) I drew the wire along the red line in the grass (It's not buried but just pushed about 1 or 2 cm under the ground) and up to the center-pole at ground-level.

From there I drew several turns in the clockwise direction (Per the view-point of the image).
(The loop-size is about 1.6 meters high and about 5 meters wide, give or take. I did not attempt to match it to any specific frequency since I'm not targeting any specific band)

And then I drew the wire from the center-pole at ground-level back the same route as before to the bottom-left side.

So technically I assume the feed-point (From the antenna's physical properties perspective) is at the center-pole at ground-level (Although I get that 2 wires side-by-side is not the same config (In terms of being balanced vs un-balanced) as a coax-cable, so I'm not sure if that has any effects I'm not aware of)

The coax-cable then goes from the bottom-left (Yellow circle) to the radio via a dedicated flat window-cable.

At the window-cable I attached a simple Y-splitter, onto which I have a 'ground-wire' connected (Only to the shield part)

That is the blue line. It goes side-by-side with the coax-cable down to the bottom-left and then follows the garden-perimeter over to the bottom-right side of the image, where it is dug into the ground about 30 cm (~1 foot)

This means it goes along the loop-antenna's ground-part.

In the opinion of those with more experience than myself; does this layout make sense or is there something I ought to change about it?

It works very well from about 2 MHz to about 18-19 MHz.
It also works fairly well from 0 to 2 MHz and I can pull in strong signals at both 27 MHz and even at 120 MHz.

Without the ground-wire the noise-floor is significantly higher, so the groundwire really improves the SNR quite a lot (I have not tried to measure the exact dB level, since its different on various frequencies, but on some bands it lowered the noise-floor by as much as 20 dB)

So the ground-wire empirically works, but is the layout... where I have it go directly along part of the loop (The part at the ground-level)... a bad layout in theory?
I don't know enough about loop-designs to tell if some other layout would have been smarter.

Anyway, the antenna works extremely well (Compared to all others I have tried so far), but I'm sure we all are always searching for ways to further improve things



As a side-comment I can mentioned I got a small electro-shock while connecting the ground-wire to the Y-splitter.
I normally wear gloves when handling electrical things, but apart from TV-antennae I have never before experienced a passive antenna give me shock, so I was using a single bare hand (Not both hands, as I know you never want to do that since that would lead the flow past your heart and chest) for this and guess I turned into a part of the circuit for a while
Not a painful jolt, but enough to surprise the heck out of me

I suppose that is a good sign the ground-wire is leading away static charges?

Touching either the antenna-wire or the ground-wire on their own does not do anything. It was just the short moment where I had both in the fingers at the same time.

Thanks in advance for any insight you might have.
jacob.

 

[majoco]

Your key comment is;

It works very well from about 2 MHz to about 18-19 MHz.

..... but without a reference you can't say!

...and of course bearing in mind that there is not much above 20MHz these days until the sunspots come back!

I have a triangular loop of only one turn - the apex of the triangle is about 6 metres up on a TV antenna mast not connected to a TV, then the two sides are about 10 metres down to a fence and then about 15 metres along the top of a 2 metre high fence. A 1:4 un-un is right at the apex and RG6 quad shield down to 8 port multicoupler where it feeds a few HF receivers. A ground rod is directly under the mast and all grounds are joined to that - it keeps moist from a constantly dripping tap! It works reasonably well and is nicely quiet too, much better than the the OCFD I had before..

IMHO I would put up a wire from your radio connection to one of the trees at the far end with a un-un at the near end to a bit of coax to your receiver - I don't know how far it is but 20 metres or more would be good - then you will have a reference by which to judge the performance. Don't just pick a couple of frequencies in the daytime but go for a random sample over all the bands day and evening - say the 19m band during the day until mid-afternoon and right down to the 49m or lower bands in the evening - quickly change from one antenna to another and note the differences in signal strength and noise. Also note that your loop may be very directional so pick stations form various bearings if you can.

My first attempt at improving things would be a un-un transformer of say 1:4 ratio right at the bottom of the loop at the centre post and coax back to the radio - and dig in a proper ground rod at that point and join the coax braid to that. The jolt that you got may well be just a bit of earth leakage from the power bypass capacitors in your radio - is there a three wire power plug on your radio or just two? Ideally there should be a ground lug on the back of your radio which you should wire to another earth rod outside your window. I note that you give your dimensions in metres so I guess you're not in the US so pay no attention to the hoards who will now say that you must bond all grounds blah blah....

Above all - experiment, take notes and have fun. Let us know what receivers you have too - you can't do HF properly with a scanner or one of those so-called 'wide band receivers' unless it's a very expensive one! (Wait for the flame wars to start.....)

 

[JELAIR]

Thank you for your input, Martin

I have tested quite a few different antennae types, sizes and placements, and this one is the one that drags in the most signals yet (The best SNR I have obtained of any test so far)

I obviously don't know where I am relative to 'best-physically-possible-setup', but I am at the top of anything I have previously tried, so in that sense it's doing great.

I have actually also tested a delta-loop (A triangular loop), except I had the apex 3 feet above ground (Where the wooden center-post is in the image) and the 2 feet at 6 feet above ground (Just behind the camera-position in this image)

That one was the decider for me (Because it performed very well), in making me go ahead and build the rectangular one in the image.

As far as my theoretical knowledge goes, both the delta-loop and the current rectangle-loop are directional in pretty much the same direction (Not quite, but both more or less east-west)

The rectangle-loop is of course strictly vertical and the null-points fit the expectation (I have an NDB transmitter I can test loop-directionality on, and it behaves as expected with this setup)

You think a ground-rod closer to the antenna would be better?

I was thinking it should be as close to the house-entry point as possible, since it would then alleviate loads from both the antenna and the rest of the wiring.

I have tested connecting it to 2 different spots. One just before house-entry and one 30 feet from house-entry (The cable is 30 feet, but the direct-distance between house-entry and cable-end is 7 or 8 feet, since the cable is curled up), and the closer I put the connection to house-entry the more the noise-floor drops (And SNR increases)

I am going to try to connect the ground-wire to both places at the same time and see what that does (I'm waiting for some hardware-plugs before doing anymore testing though, as I was told a galvanic isolator should be mounted to protect the radio from static discharges. So until that arrives I have arrested further testing to be on the safe side)

I have also done some tests where I used an antenna-selector (You connect 2 antennae to it and it has a switch so you can select between either antenna) and all those tests are what have led me to this loop-setup.

The big vertical loop beat the horizontal loop-on-ground, which beat the long-wire (Random wire), which beat all the indoor-antennae I tried (Dipoles, long wires, loops) with the one caveat that all the indoor-loops I tried could get signals below 1 MHz where all others would just be drowned in noise.

About throwing a line up into a tree; I think I would get in trouble with the HOA if I did that :/
I did a short test one afternoon for a few hours, where I had a long-wire thrown up as high as I could into a tree. But not long enough time for the test to be really conclusive (Except it had tons of noise below 1 MHz still. I'm in the middle of a city, so surrounded by urban noise unfortunately)

A 1:4 un-un is something I have not tried. I'm doing reception only, at the moment, so I haven't actually paid too much attention to any such device (I keep reading they don't really do all that much for reception, but I don't know)

I have tried the difference between a 9:1 balun on a random long-wire, vs just connecting the wire directly, and I couldn't see or hear any difference.

But I don't know what difference it would make to the loop in my case, if any.
I will google some more on that topic though, so thanks for the suggestion

I have been at this for quite some time (Many listening hours 'under the belt' now, of both days, nights, summers and winters), so I feel I have a fairly good impression of HF and what to expect at my location (Well, most of that time has been indoor-testing when I lived in an apartment less than a mile away from where I live now. But at the current house I'm in I've been at it for a good half-year now. Still lots to learn of course )

But again; I don't know what the maximum-best possible here would be, or where I am relative to that (Maybe I'm at 20% of what a more skilled person could achieve or maybe I'm at 70%, I just don't know since there are no other radio-people near-by that I know of and could compare notes with), but I do make steady progress I think (At least I keep getting better SNR on the various stations I use for bench-marking on HF for every test)

I am using an SDR (Software Defined Radio).
An Airspy HF+ Discovery.
I don't have a 'real' radio, since I don't have a transmit-license yet (The test for a license is in a different part of the country from where I live, so I haven't figured out a way to attempt getting one yet (It will require about the same effort as going on a small holiday, so slightly out of my reach at the moment). And you can't do them online here, so for the time-being I'm a receiving station only)

Anyway, there is no dedicated ground-plug on that radio, just the shield on the antenna-plug.

I've used 'real' CB-radios though (27 MHz band), and compared to those the SDR is doing very well.
And judging from youtube-videos on 'real' radios, and what people seem able to get from those in urban environments, I don't think the radio is much of a weak-spot (The HOA does not allow putting up outside antennae, so I can't get anything up high, and being surrounded by urban-noise I think the noise-floor is the limiting factor more than any difference in radio. But I have not tested a 'real' HF radio here though, so I clearly can't say with certainty what difference that would make, if any)

Yes, I'm in Southern Scandinavia (Denmark, to be exact), so the metric-system is the official one here, but being on the internet and 'cross-talking' between US and Europe I can do the imperial system fairly well too (It's also still the main system in aviation, so that keeps me proficient at it as well)

Yes, I get nothing much above about 18-19 MHz here as well. A few broadcast-AM stations but that's it.

With the 'big' loop here (Before I halted testing) I picked up skipping signals mostly between 1000-2000 km (600-1300 miles), as well as some faint local signals. So it appears to have a relatively low take-off angle, but a blind-spot to anything closer but still below the horizon.

The biggest surprise so far was when it picked up a maritime radio on 13 MHz from Olympia, Greece, since that is almost to its broadside (Null-side).
The loop is a full-wave loop at ~21 MHz, so as far as my theoretical knowledge goes the null-sides should be the same below 21 MHz and only 'weird' above 21 MHz.

Apart from that the farthest away I have received from is the USAF (Their EAM broadcasts)

But no 'exotic' stations from places like Asia or Cuba.

The mains-plugs here are all AC 220 Volts with no ground-connection in them (2 prongs only), but the SDR is USB-powered so it already inherently gets its fair share of computer-noise and common-mode noise.





Anyway, very long story short (And I'm sure few will read all of the above ) I'm currently waiting for some hardware to put on the antenna-cable to secure the radio against static electricity.

When that arrives I will continue my testing with this antenna and study up on the un-un and ground-rod location you mention

So thank you for those suggestions (And I'm glad the setup wasn't shot down as completely useless, since it's likely the most extensive setup I can do without getting in trouble with the HOA here )

jacob.