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.
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
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
I already have a video on squashing the coupling loop. I think it's titled something like magloops a small modification that makes a big difference. Or something like that. :-)
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...
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.
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.
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.
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
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
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.
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?
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!
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.
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.
You might be better off with an end fed half wave. You can use fairly thin wire and run it up to a tree. It will be practically invisible to your neighbors and perform well.
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.
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.
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.
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.
I saw another guy who rotated it slightly out of plane to adjust swr. I'm going to revisit that aspect in a future experiment. I'm also curious about why the driven loop needs to be near the edge instead of in the very center. I'm going to build a loop where I can move it around freely and see what happens.
The coupling loop is near the low impedance edge of the main loop. The opposite edge is extremely high impedance. At center it would null. At other edges the resulting impedance would also be different.
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
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.
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.
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.
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.
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.
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.
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
About 20 years ago i put microbore copper in the attic on the roof trusses in the triangle shape, and tuned 80 and 160 mtrs with a vac variable, reached scotland on a watt cw. on 80 .. G4XRM
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.
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
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.
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 do plan on building another loop where I can move the coupled loop around easily. I want to study the changes when it's near the edge, along the edge, or more towards the center of the loop.
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!
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
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.
+sfcmmacro you should stay at least one diameter away from it and be sure not to touch it. At those low power levels, don't worry about rf. But there's high rf voltage on the loop, so touching it could burn .
Kevin Loughin I figured there was a lot of voltage being produced in the antenna considering the variable capacitor and the potential for arc over in the capacitor. The one thing I couldn't find was any reference of a safe distance from a radiating antenna in relation to RF radiation. Thanks for the advice.
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.
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 ...!
The most common is a 3 foot (1 meter) loop. The driven loop is always 1/5th the outer loop. If your cap can get up to around 180pf, you should get down to 40 meters ok.
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.
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.
Very slick. Yes no doubt this measures electric field predominately. An easy check with a 1/4 wave monopole antenna, such as the mag mount in your lab, should reveal strong e-field at the top and much less at the bottom.
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.
Their radiation pattern is not very much different from a vertical antenna when you rotate them to a horizontal plane. You lose one big feature of the loop in doing so. The null perpendicular to the plane of the loop is VERY handy at tuning out noise sources.
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.
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.
A magloop would be a lot of work for SWL since you tune around a lot. You be constantly tuning the loop along with your radio. And a whip would defeat the positives of the magloop.
so each group of ends are tied to another. There is a thing called interwinding capacitance. The parallel conductors do not have to be separated electrically. The opposing peaks and differences in phase along the conductor (spatially) is enough to create lines of force between them (like in a tesla coil secondary) Just trying to shed light on ALL the variables in your tuning calculation. BTW I love your videos man! Getting on for QRP night tonight for the FIRST TIME. (had my tech license for 4 years and my general for a month lol)
I doubt there's any appreciable effect. The wire would have to be longer than a wavelength, I think. Anyway, they're all at the same potential, so I just can't see any problem. How'd you do on QRP night? We had a great time here, and a few nice contacts. I'll have follow up videos soon, and a special guest video in a week or two.
QRP night was cool. Made first contact on 40 meters. (once I got FLDIGI and CW happening :) ) Love to see some SDR stuff. (even a simple homebrew receiver) 73
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
@@dzuyd That's not what my field strength meter says and what my observations showed me. Theory is one thing, real experiments show you a whole different result.
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 :-/
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.
It has a radiation pattern kind of like a donut shaped the same way as the loop. So it acts omni directional like a vertical. That's the only difference.
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.
Oh yeah, also wanted to comment - reverse the coax connections to the coupling loop and see if the field strength flips. If not, it then likely is unbalance in the tuning cap.
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. 👍
Just saw your comment. I have been playing with loops on 10/11/15m made from left over RG6. Using a scrap RFI toroid core for coupling. Three turns of the centre of the RG58 feed line and one pass trough of the RG6. Seems to work a treat. I’ll try the aluminium strips but as I have a roll of flashing I found. For capacitors I use a small coax stub and cut it to the centre of the band I want to use. It’s funny. 10 & 15 will be dead while the 11m _chook band_ as we call it here (chook is aussie for chicken) will be open with people talking across the country and across the Tasman. Around a third of the 11m contacts I have are with other hams Anyway, we have some sunspots coming up so hopefully we will see some more action on the upper HF bands
Novice hasn't been around for awhile. Technician is the current entry level license. Most people with Tech stick mostly to VHF. A loop at those freqs is possible, but also very narrow and fiddly. A 1/4 wave vertical will cover the whole 2 meter band without trouble.
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
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.
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
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
I already have a video on squashing the coupling loop. I think it's titled something like magloops a small modification that makes a big difference. Or something like that. :-)
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...
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.
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.
Could the stuff to the left and the loop behind be absorbing the r.f. and making it appear directional?
Your channel is becoming one of my favourites Kevin!
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.
Jeri Ellsworth did something along those lines already. As I recall from her video, the most radiation happens near the coupling loop.
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
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
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.
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?
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!
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.
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.
You might be better off with an end fed half wave. You can use fairly thin wire and run it up to a tree. It will be practically invisible to your neighbors and perform well.
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.
How much does the bigger mag-loop, (being in close proximity), influence the tuning of the small one?
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.
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.
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.
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
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.
I saw another guy who rotated it slightly out of plane to adjust swr. I'm going to revisit that aspect in a future experiment. I'm also curious about why the driven loop needs to be near the edge instead of in the very center. I'm going to build a loop where I can move it around freely and see what happens.
The coupling loop is near the low impedance edge of the main loop. The opposite edge is extremely high impedance. At center it would null. At other edges the resulting impedance would also be different.
Very cool video Kevin, thanks for sharing with us. Did you ever make a video detailing the construction of your larger loop?
Yes, back a few pages in my videos there's a closer look at the larger loop.
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'
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
Could a change in the diameter of the coupling loop fix your SWR problem on your smushed loop?
Nodes and loops from multiple waves?
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.
Far field should mirror near field as far as the radiation pattern goes.
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.
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.
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.
Really good! ... I also can agree with you
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.
That's an interesting idea, I might have to try that sometime.
When you squashed the main loop did you squash the coupling loop to match?
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.
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
Have you tried a triangular loop? If all the sides are the same length it will be sort of symmetrical
About 20 years ago i put microbore copper in the attic on the roof trusses in the triangle shape, and tuned 80 and 160 mtrs with a vac variable, reached scotland on a watt cw. on 80 .. G4XRM
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.
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
I suspect a lot of the SWR issue was the change in impedance.
What is a length or diameter of connection loop?
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.
Yeah, thought I mentioned that in the vid. The mapped footprint matched the directionality of the little loop.
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 do plan on building another loop where I can move the coupled loop around easily. I want to study the changes when it's near the edge, along the edge, or more towards the center of the loop.
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!
The donut comparison got me interested....
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
No problem painting it as long as it's not conductive paint. You'll probably get some interesting looks from your neighbors!
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.
+sfcmmacro you should stay at least one diameter away from it and be sure not to touch it. At those low power levels, don't worry about rf. But there's high rf voltage on the loop, so touching it could burn .
Kevin Loughin I figured there was a lot of voltage being produced in the antenna considering the variable capacitor and the potential for arc over in the capacitor. The one thing I couldn't find was any reference of a safe distance from a radiating antenna in relation to RF radiation. Thanks for the advice.
Kevin Loughin is that the same rough estimate for a 100 W amplifier? I don't expect to do that very soon but of course that's always a possibility.
+sfcmmacro no, it would take a very high voltage cap and you would have a very strong field. Not good in close quarters.
?? If the coupling polarity was flipped would the would the stronger lobe flip to the other side? k8clm
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.
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 ...!
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.
The most common is a 3 foot (1 meter) loop. The driven loop is always 1/5th the outer loop. If your cap can get up to around 180pf, you should get down to 40 meters ok.
Goodnight. The yaesu receiver of this video which model is it?
FT-817.
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.
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.
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.
Yes, this is what I used.
th-cam.com/video/8Dd0oEzDepA/w-d-xo.html
Very slick. Yes no doubt this measures electric field predominately. An easy check with a 1/4 wave monopole antenna, such as the mag mount in your lab, should reveal strong e-field at the top and much less at the bottom.
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.
I would very much like to see experimenting with these in a Horizontal position.
Their radiation pattern is not very much different from a vertical antenna when you rotate them to a horizontal plane. You lose one big feature of the loop in doing so. The null perpendicular to the plane of the loop is VERY handy at tuning out noise sources.
what's a reasonable price for these old table-top donor radios at garage sales?
+Craig Gilbreath I've seen them for 5$ , also at junk and thrift shops.
are the caps parallel or series?
Parallel. It would still work in series though.
only guessing here but could the directionality be due to the direction of current flow ?????(2e0fok)
Not sure. The circular loop does not display the same directional characteristic on the loops plane.
the loading coil should be triangular maybe?
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.
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.
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.
I would like to see how to use magnetic loop antenna with small sw receiver with a whip antenna coupler.
A magloop would be a lot of work for SWL since you tune around a lot. You be constantly tuning the loop along with your radio. And a whip would defeat the positives of the magloop.
I wonder how much extra capacitance was added using the multi-wire ethernet cables.
+Eric Harris none. The wires were all joined together, making them one conductor.
so each group of ends are tied to another. There is a thing called interwinding capacitance. The parallel conductors do not have to be separated electrically. The opposing peaks and differences in phase along the conductor (spatially) is enough to create lines of force between them (like in a tesla coil secondary) Just trying to shed light on ALL the variables in your tuning calculation. BTW I love your videos man! Getting on for QRP night tonight for the FIRST TIME. (had my tech license for 4 years and my general for a month lol)
I doubt there's any appreciable effect. The wire would have to be longer than a wavelength, I think. Anyway, they're all at the same potential, so I just can't see any problem.
How'd you do on QRP night? We had a great time here, and a few nice contacts. I'll have follow up videos soon, and a special guest video in a week or two.
QRP night was cool. Made first contact on 40 meters. (once I got FLDIGI and CW happening :) ) Love to see some SDR stuff. (even a simple homebrew receiver) 73
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
Yep, I've thought about interaction between the two. I'll be doing more measurements. Thanks for watching.
yes, my personal experience showed me that by placing the capacitor on top gives much better results.
that is not the case, due to big currents in the top near the coupling loop thats the best for transmit
@@dzuyd That's not what my field strength meter says and what my observations showed me. Theory is one thing, real experiments show you a whole different result.
I think that due to asymetrical coupling you have one big lob
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 :-/
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.
Try phasing the loops with another loop. That way you can shape the field.
I'd like to see an experiment with a loop mounted horizontally.
It has a radiation pattern kind of like a donut shaped the same way as the loop. So it acts omni directional like a vertical. That's the only difference.
I would like to build this loop for Rx.
You'll get better overall broadband RX performance from a simple end fed random wire.
I just like to try to use a magnetic loop antenna for 11 meter to 120 meter. for swl.
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.
Oh yeah, also wanted to comment - reverse the coax connections to the coupling loop and see if the field strength flips. If not, it then likely is unbalance in the tuning cap.
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. 👍
You know what would be interesting? Trying a pair of loops to increase your gain, like: OO
The diameter of the conductor wants to be over 0.5 inch. 1" is better. 2" is great
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
Just saw your comment. I have been playing with loops on 10/11/15m made from left over RG6. Using a scrap RFI toroid core for coupling. Three turns of the centre of the RG58 feed line and one pass trough of the RG6. Seems to work a treat. I’ll try the aluminium strips but as I have a roll of flashing I found.
For capacitors I use a small coax stub and cut it to the centre of the band I want to use.
It’s funny. 10 & 15 will be dead while the 11m _chook band_ as we call it here (chook is aussie for chicken) will be open with people talking across the country and across the Tasman.
Around a third of the 11m contacts I have are with other hams
Anyway, we have some sunspots coming up so hopefully we will see some more action on the upper HF bands
I need to retake the test to become a ham.
You should!
it would like a loop for novice class ham.
Novice hasn't been around for awhile. Technician is the current entry level license. Most people with Tech stick mostly to VHF. A loop at those freqs is possible, but also very narrow and fiddly. A 1/4 wave vertical will cover the whole 2 meter band without trouble.
Good job I am from Hong Kong CBer
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.
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
it's been a few years sense I took my exam.
Peeeeeeko