I built a large magnetic loop antenna under funding from my employer. Plenty of money and lets do it right attitude. I used a copper pipe formed in a large loop with a tunable vacuum capacitor in series with the loop using flat copper straps brazed to the copper. I inductively coupled as you did. The antenna was used with an NMR spectrometer to detect explosives/illicit drugs. It worked splendidly, management was pleased, I got a pat on the back.

Your suggestions about the square coupler loop having "more proximity" to the main loop, match EXACTLY with somebody's advice to squash a circular coupling loop to an ovoid, in a circular mag loop, in order to increase the proximity to the main loop. Perhaps you should revisit your squashed, main loop experiment and squash the coupler loop as well. You didn't do it the first time and you obviously didn't hear me shouting at the screen..."Squash the coupler as well! Squash the coupler as well." I've done the coupler squashing on a round loop and there's no doubt about it. 73 de G3NBY

Kevin, a way to show where the most current flows in the loop is to use a string of Christmas tree lights as the outer loop. The radiation current will cause the lights to come on near the current max.

Very interesting. That's what makes this hobby so fascinating: the fact that there is so much still to discover and improve.

Hey Kevin, Love your videos. I have a handy hint. I call it a poor man's field strength tester. I use a cheep florescent light bulb which will light up when held very close to the mag loop. I would not suggest this on loops running high power. I uses this in videos as it's real easy to see the "hot" spots on a video as opposed to a f.s. meter. 73 and looking forward to more videos. John

I appreciate your honest discussion of your process and testing.

Your channel is becoming one of my favourites Kevin!

You are a good experimenter. Don't be fooled by strong points of RF voltage. I also see people saying the opposite and incorrect statement in this thread, noting the high current points are where max signal is transmitted. When an antenna operates at its resonant frequency, a standing wave of voltage and current is established along its length. It's the accelerating charges, not the absolute voltage or current, that create the electromagnetic waves. These accelerating charges occur due to the changing electric and magnetic fields within the antenna as the voltage and current oscillate. The high voltage points provide the "push" for the electrons to move, and the high current points represent the actual flow of electrons. This combined movement creates the oscillating electric and magnetic fields that radiate outwards as electromagnetic waves.

Spot on Kevin. The cap. at the bottom is best. Max current = max radiation. Also a tight coupling with the feed loop is good. I see so many feeder loops a distance from the main loop. They are throwing away signal. EDIT: it's transformer coupling.

Yeah, good video! I been fighting with a Chameleon F-Loop under a metal roof!!! Not having very good luck with it!!! I bought a nice capacitor to build another loop with. Adding the second one is sweet !!! You got the cap / coil positions right,,,

Hi Kevin.Good video about mag loop antenna's.I build one myself for the cb citizen band, and did a few rebuilds before it was working good. I have made my copy also with the tuning capacitor on the underside of the loop, and coupling loop on top...Swr measure is dead flat. The tuning capacitor is between approx 15-80 pf, and this is still too much to tune the loop. So i placed a second tuning capacitor in line, and now its very easy tunable! The loop i made from flat alluminium strip, and coupling loop is build with a piece of rg8 coax cable. Aboud the radiation patern of the antenna...If i take a fluoriscent light tube, and go around the loop, i noticed the tube burns max around the tuning capacitor, and goes dimm around the coupling loop position...I see some industrial made loops(chameleon etc.) also made with alluminium tube loops, and some with coax loop and alluminium coupling loop. I wonder what the best materials will be, to make the best magnetic loop antenna out there...Keep the good work up. Greetings from the Netherlands...

I had a loop that I used many years for receiving shortwave that was built with an unbalanced tuning-capacitor from an AM radio, with the two gangs in series. What I noticed (if I recall correctly) was that the side of the loop that had less capacitive reactance toward the chassis of the capacitor (in other words, the side that was closer to ground) received less signal. Consequently the nulls on that loop were about 120° instead of 180° apart. Your main tuning capacitors seems to be completely unbalanced, with the chassis connected to one side. That definitely will affect your radiation pattern. For a symmetrical pattern you need either a tuning capacitor that isn't connected to its chassis on either side, or a tuning capacitor with two gangs that you can put in series.

Hi Kevin Two very valuable tidbits of info from this vid. The secondary cap changes everything when it comes to the difficulties controlling a magloop. The apparent directivity of a square loop vs a round loop raises all kinds of ramifications. Would like to see field strength comparisons of a square vs round loop of otherwise identical constructions especially for 40M NVIS ops. IE, Will rotating your little toy square loop CCW 90deg result in highest field strength in the virtical? Good job Old Man! Your a valuable asset to HAMdom........ 73 OM

Thanks for your interesting experiments. I too am interested in loop antennas. I cannot claim to be an expert in the field or to have a good understanding of the physics. However, I have strong reservations that field strength measurements taken so close to the antenna actually predict its real world performance at a distance. Generally, radio is about communicating at several wavelengths away from the antenna. Even taking a measurement at 50 feet would place you well under a full wavelength for a 40m signal. In short, I am not sure that your measurments tell us about the actual radiation pattern of the antenna.

Hello there , i really realy love Ur Grt Innovation to the Tuning Method of adding a smaller Var. Cap ... U jst Helped me make tuning my home brew Loop projects a LOT easier, TYVM i really really Love Urr solution to this very simple tuning issue yet annoying at times, with Ur innovation tuning just Got easier... tyvm...73s de n6mmq. Ps. I live in a place where ppol absolutely knw NOTHING abt amateur radio and Loop antennas are my Last resort to enjoy our great Hobby.

What a cool antenna! I never thought to use a milk crate for a form. I immediately scaled that up to a big square bread delivery tray in my mind for lower frequencies. I wonder if the milk crate then is scaled properly for a coupling loop? Guess I have to go try and buy a tray from a bread guy next time I see one. LOL Food for thought at the very least! Thanks!

GREAT videos, well done. Try field strength measurements 3 to 4 wavelengths away and see what it looks like where the vectors are a point source. 73'

I love your videos as you are like minded .You adhere to the rules and then bend them a little.One thing that has crossed my mind is that if you treat a mag loop as a transformer.Surely the better the coupling the better the output.So what would happen if you passed a primary loop and secondary loop through a ferrite bead.i.e the coupling point was married together through the bead/barrel. Just a thought.I would experiment myself but have No space to do so these days.

Very cool video Kevin, thanks for sharing with us. Did you ever make a video detailing the construction of your larger loop?

Kevin, may I ask for some direction. I am revisiting DXing from many years ago. Space is a big factor so mag-loop antennas caught my attention. My thought was to build my own tunable unit from 3 khz to 30 meg for receiving only. The antenna would be outside mounted on the side of a low chimney. I would mount a rotor so the antenna could be swept. I have looked at the MFJ 1886 LN and Brookwood ANA 1530 LN designs. I think that approach would work, however, the antenna amplifier would also need to bee fabricated. This would be a nice project before winter sets in. Radios in use are Hallicrafters S-120, Tecsun PL-660 and Tecsun S-2000. Could you advise.

A couple of thoughts. You mention that even a tenth of an Ohm can depreciate efficiency. If you do the math and solve for the radiation resistance you will see your antenna is below 0.005 Ohms on 20M- so even a thousandth of an Ohm makes a difference. You mention connecting the center conductor and the shield for "more copper". Connecting the center conductor does absolutely nothing to enhance the loop efficiency. Skin effect tells us that there is no E field inside the copper shield- deeper than (3) skin depths= 0.002" at 20M, so the center conductor is invisible. Using a single gang capacitor introduces serious Ohmic losses between the rotor and its contact to the frame, lowering efficiency greatly. Because the current is constant around an STL- it radiates equally around the loop. You are probing in the near field with an E probe. Dale W4OP

I like the way you coupled the coils to get more coupling. Have you ever seen the outer loop wrapped all the way around the primary coil. I was thinking of it like a transformer with it's turns ratio. With a complete loop it would be 1 to 2 turns hence 1- 2 voltage boost but if you did 2 turns primary and 2 turns secondary with only 1 tightly coupled you would not get the voltage doubling. but get the benefit of the complete turn coupling. just thinking out loud???? would this make it impossible to tune VSWR?? what is the voltage in a series tank? I have no experience building loops. I want to build one. I am getting my first HF radio soon. I built a 5/8 wave plumbers J-pole with great success for 2 M.

what did the resonant freq of the first two 'distorted loops' end up at? Maybe just a case of changing dimensions to accommodate the change in geometry.

Since you like loops, I think a 8 element loop in a collinear setup would allow you to talk to africa on 1 uw :) The whip antenna coupler setup Theodore is referring to is most likely a military tuner not the whip.

Really good! ... I also can agree with you

In fact , when I saw your first 2 videos , due to ease of creating a square antena I wanted to build two square loops and watching the second video , I wanted to make them closer on longer distance , exacty that I saw here in the same configuration, so in fact , you answer my possible question , how will it work :), fine I will do it ...!

How much does the bigger mag-loop, (being in close proximity), influence the tuning of the small one?

Thanks for sharing! I think it is great to show others that you can build compact antennas with reasonable efficiency or actually very high efficiency in proportion to the space used for almost no money. I believe your major mistake when measuring is that you are creating an antenna that generates most of its energy into the magnetic domain within the near field. Trying to measure it with an electrical sensor within less than a wavelength of distance shows you all kinds of erratic field conversions caused by the nearby electric conducting/resonating components in your room. having a second loop "in parallel" so close by might also influence your measurements. So please build a magnetic sensor head for your field strength instrument and then you may detect more logical near field patterns. Holding your current voltage based instrument close the capacitors should show the most RF, because that is the high impedance/high voltage side of the loop. The other side is just as powerful but contains high currents inducing a powerful magnetic field which will be almost invisible to your "RF voltmeter". Only in the far field, which is a few lambda away from the antenna, the electrical and magnetic fields are balanced out again, which will vive your electrical meter a true relative reading. This is why measuring the e-field cose by a mainly magnetic antenna is almost like trying to measure the wind velocity with a thermometer :-). You can also homebrew a magnetic field probe for your instrument from a tube and some coax cable ... have a look www.eevblog.com/forum/projects/diy-magentic-field-probes/ This will show you the actual domain of RF power your antenna creates nearby. In today's age of extreme RF noise magnetic antennas and phase noise cancellation devices are the only answer to a reasonably good reception, while the TX antenna should simply highest gain for the needed sky wave elevation, the RX antenna should have the best directivity to null out noise and pick up energy from the wanted signal. Amplifying signals from the generally noisy HF bands if usually not a problem, but fighting for the best signal to noise on the RX is what counts the most. And here the mentioned effect is making all the difference, most RF noise is electrical in the near field, so a purely magnetic antenna is relatively immune to that and then on top of that having the extreme luxury be able to null out signals is making these types of antenna in most cases very advanced versus fixed long wires when using it just for receiving. SWLs or hams in suburbs will be impressed how much better they may hear stations with a simple small homemade magnetic loop antennas vs. a huge wire antenna. So grab some wood to create a frame, take some wires and a variable capacitor from your junk box and have fun experimenting!

Thank you so much. I was wondering it the mag loop could be multiband. You answered my question and have given me hope. I live in an HOA community that would not allow an outside antenna. I have room in my attic but no much. Most of my neighbors have cable so I hope not to interfere with their tv.

The donut comparison got me interested....

Hey, Kevin. Seems like you could almost eliminate a section on the trimmer variable cap and have an even slacker, easier to tune range on it. Have you tried that?

When you squashed the main loop did you squash the coupling loop to match?

Just watched a video from SignalSearch 's channel about the W4OP loop. He mentions moving the Faraday (drive) loop up or down to change swr.

Loops work well for their size. I also distorted my loop and found the same as you, Kevin. On one loop I tried and found a better SWR by distorting the coupling loop. On one loop I bought a small 3 Volt motor with gearbox, using two D cells with 3 Volt for fast tune, then 1.5 Volt for slow tune. On the new loop I use a twin variable cap., one having large vanes and one with smaller vanes, the smaller for h.f. and add the large one to get lower frequencies even to 5 MHz but I don't expect efficiency to be great. I have 19 foot of ⅜" coax and want to try a large loop for the lower frequencies. G4GHB

Could a change in the diameter of the coupling loop fix your SWR problem on your smushed loop?

Could the stuff to the left and the loop behind be absorbing the r.f. and making it appear directional?

Hi Kevin, could you show what wires go to the varable capacitor to what parts of the capacitor, groung lug or one of the other screws, Im confused, please help

Kevin, Really enjoy your videos and and have learned a lot. I've decided I'll be building a loop pretty soon. I'm still in the planning stage. Something I haven't seen addressed. I plan to make the loop a semi-permanent installation on my roof, mounted on a tripod and aimed with a rotator. Since it will be a copper pipe I'm concerned about corrosion. Will anything be affected if I paint the loop? I suspect it will not as you have used insulated wire in some of your experiments. Lookin forward to some rag chewing on 80 meters. 73s, WB9HNX

Was looking at loop antennas for swl and found your video. Near field far field aside, was curious about your radiation pattern not being symmetrical. I was wondering if you placed a 1:1 balun between the loop and the coax, if the radiation pattern would then become symmetrical? I know there would be some loss with the balun but it might explain the odd pattern.

Could it be unbalanced feed to the pickup. The loop should be balanced and symmetrical. Reverse and see if there is a changed effect. VA7WN

I have Qrm on My 11 meter transceiver. 4 watt citizen Band Radio. My thoughts it would be better for home base than my inverted V Dipole.

Very interesting video Kevin. I am curious to know if the WSPR results confirmed your measured directivity of the small loop. I am becoming interested in loop antenna's also. 73, Bill KC5SB.

That directional assymetry seems very strange. Have you confirmed it on receive by listening to a steady signal and rotating the antenna ? Reciprocity must apply ! The only possible cause of this that I can think of is that the inner conductor of the coax feed is connected to a "hot" side of the feed loop and the ground causes a "cold" side. How about you try flipping over the feed loop (or at least the connections to it) and seeing if the radiation pattern changes ? That might help to pin down what the cause is.

Good stuff especially the small loop. I can't fathom the asymmetrical E-field measurement either, but perhaps the non-symmetry of the caps may have some small part. As for radiation... you are using, I assume, an e-field measurement device to sample the induction fields of the antenna. What's missing is a measurement of the h-field generated by the current in the coil. Both contribute to the far-field resulting pattern. The key point is your experiments turning the loop to "DF" WSPR signals is more telling than the measurement of only the e-field. Thanks for the great video.

Did the squashed loop reactance become capacitive or inductive compared to your previously symetrical resonant loop? Where was the squashed loop resonant compared to its former resonance on 40m?

Try some romex house wiring. It has 2 or 3 wires in it. They can be shorted together or conect to one wire then connect it to the next wire. The house wiring doesn't cost much, easy to get, also is 14 or 12 gauge.

?? If the coupling polarity was flipped would the would the stronger lobe flip to the other side? k8clm

thoughts my friend how about the small coil being moved from dead in the corner move it small amount out of the corner leaving an air gap on one side to see if it affects the field strengh patten it may be the answer to focas it more in one direction. tiny bit as a time regards g0myd

I'm new to HF and will be moving soon from a house to an apartment. I can't find any general distance/safety guidance for magnetic loops. I got a KX3 to break into HF on. Do you have any advice RF safety with mag loops? I have children and want to make sure the RF exposure is safe in the apartment.

Have you tried a triangular loop? If all the sides are the same length it will be sort of symmetrical

Hi Kevin, I really enjoy your videos and I'm keen to build a loop for 40 metres, can you give dimensions that we can work to please. God bless, Bill.

Do you think there could be a difference between 'near field' and 'far field' antenna directional properties? Your measurements using the 'in antenna' and 'handheld' field strength meters are surely near field measurements.

hey Kevin how are you. I really enjoy your videos sincerely I learn a LOT about antennas and particularly I build my magsLoops. let me tell you my experience when I placed my two magsLoops the portable rg8 maiden and the copper pipe fix station facing each other I observed this situation you are descibing here and as you see you have two magLoops maybe in Fase. you can re do the field meter radiation and move the biger antenna off the way and see what happens. 73s de kk4nww

kEVIN: please show this video with subtittles, I would appreciate so much;thank You I have learn a lot about your experiments and radio,antennas, software lesons so all absoluty is brilliant,thanks again.(Sorry my English.-Receive 73 from León guanajuato, MEXICO.

Because of the phase shift between de voltage and current its normal that the most off the power is emmited at the top not the bottom where the voltage is high

I suspect a lot of the SWR issue was the change in impedance.

I always understood that tuned loops weren't any good at all for transmitting. That's what I read, and this is the first time that I have seen any elaboration on that point. My experience has been, also, that loops do not give good reception in horizontal polarization. A few days ago, however, i read that a pirate broadcaster called Radio Capital used a very large tuned loop, horizontally oriented, for omnidirectional broadcasting on mediumwave, and supposedly it worked very well. The motive for using a tuned loop, I read, was to avoid skywave reception of the station.

What is a length or diameter of connection loop?

Goodnight. The yaesu receiver of this video which model is it?

Nodes and loops from multiple waves?

only guessing here but could the directionality be due to the direction of current flow ?????(2e0fok)

Hi, despite your moving the loop about and still seeing a max off to one side, you can't expect to see the real lobe with your 1ft box loop in front of another loop antenna, vertical cables over to the left, house wiring, house plumbing, and you stood to one side.. I know you are measuring near field pattern and on low power but your results or observations are still tainted. You should for your own satisfaction, do these tests outside, at least 1/10 wavelength off the ground and with feed cables tested either side of the antenna and done with the antenna pointed in different magnetic directions to collect good unbiased data. Only with reliable prouven data can you make decisions relating to developing its performance. And accurately confirm the results. Any false data and guesswork can only fog your perception of what is really happening. If you are searching for improvements then all your data has to be exact and as informative as possible.

The measurements you have made will be impacted by the proximity of the other loop behind it. These measurements need to be made say on top of a 8 ft wooden step ladder outside.

yes, my personal experience showed me that by placing the capacitor on top gives much better results.

Great, thank you. As I understand it, the maximum radiation is where the current is highest i.e where the coupling is. No idea why it is directional :-/

Good job I am from Hong Kong CBer

I would very much like to see experimenting with these in a Horizontal position.

are the caps parallel or series?

I would like to see how to use magnetic loop antenna with small sw receiver with a whip antenna coupler.

I'd like to see an experiment with a loop mounted horizontally.

It's a pity you dind't put a reflector on the left side of that square loop, just to see the field strength on the right.

what's a reasonable price for these old table-top donor radios at garage sales?

Try phasing the loops with another loop. That way you can shape the field.

I just like to try to use a magnetic loop antenna for 11 meter to 120 meter. for swl.

Your measurements are near-field. That can be quite different from the behavior of the far-field. Far-field is what determines the communications over any real difference.

hmm maybe you could try a more 3 dimensional shape. something like an actual doughnut shape using two ovals or even more keeping all the angles the same between the loops.

Something to try is use a 3 inch wide strip of aluminum roof flashing for the the loop I mite have to try this Just what I need one more project HI HI

You know what would be interesting? Trying a pair of loops to increase your gain, like: OO

I wonder how much extra capacitance was added using the multi-wire ethernet cables.

Late to the party, but the squashed loop idea isn't a new discovery; it has featured in texts and discussions going back a very long time. The efficiency of the loop is not changed as you imply; it's the coupling and energy transfer that is achieved as it should. The logical extension is to have much closer coupling than even a squashed primary - which then becomes the twisted gamma match (which may be a wire twisted around the secondary, or one run parallel to it). So, nothing new, and no enhanced efficiency is achieved. You only discovered how to make loops properly, rather than badly. 👍

I need to retake the test to become a ham.

I would like to build this loop for Rx.

You are measuring in the near field. This does not provide any usable results in regards of antenna characteristics in the far field (which you are interested in). In the near field there can be a wild mixture of E and H fields with different phases and amplitudes - so you are not really "measuring" something there. Place the antenna at an open field and move a away 3-5*Lambda for ideal results (1*Lambda would be ok for this type of antenna) and measure the H and E fields. If you have a tall tower available (most preferable a wooden one), place it in front of it and turn the antenna by e.g. 5° or 10° steps. Measure also at different floor levels. With this method you would get a very good horizontal and vertical radiation pattern of your antenna.

the loading coil should be triangular maybe?

I think that due to asymetrical coupling you have one big lob

The diameter of the conductor wants to be over 0.5 inch. 1" is better. 2" is great

Kevin, just a comment. You are attempting to measure radiation strength when the loop is coupled to the other loop almost touching it - plus it is coupling to the wiring in the house walls, ceiling. floor, wherever. Middle of the backyard up on a wood support at head high will be more informative.

I built a loop made of 2 inch wide aluminum flashing material 20 feet long. I deployed the loop in a delta shape with the cap at the bottom and a gamma match with the ground at the apex and the tap feed at .17 of the loop diameter down the side of the loop. I could not match the loop with a loop feed. The gamma match worked! Swr was 1.1 at 80, 40 and 30 meters! The delta loop shape uses an fiberglass mast to hold the delta up and two ground rods to hold the corners of the loop out. I am going to use a 65' loop for 80 meters and a 100 foot loop for 160 meters so I can work portable 160! Jim kd6iwd

You could get a hard hat and mount it in the center and run a wire to your ears and maybe your brain can increase the reception.

it would like a loop for novice class ham.

it's been a few years sense I took my exam.

Peeeeeeko