Hey Adam, very interresting and probably the best design of a mag loop for sota I have ever seen. I agree with some comments before, a build video would be much appreciated! 73 Patrick - OE8ACT
I'm just getting into loops and love your concertina fold design. That is a very good way to get a portable circle! Japan! I bet that made your day!! Thanks, Adam.
Dang it!!! You're killing me. Now I have to build another antenna!! Fabulous work as always. Maybe a follow-up tabletop video with details on the capacitor box would be nice. Keep up the stellar work.
I’ve built a few loops, from simple ones made from reclaimed RG6 and a toroid core ripped from a switch mode power supply, through to one made from 1” x 1/16” aluminium strap with a motorised tuning capacitor that handled 50-60W but caught fire when I gave it the full dollar :-) They are excellent and, elevated enough seemed to out perform my back yard verticals I have made from aluminium tube The narrow bandwidth keeps the noise levels down, and certainly removes broadcast band interference on the Pixie my son built :-)
I’ve been messing with mag loops the last few weeks with the intent to make a portable one. The accordion design + gamma match you used made my jaw drop at the simplicity and compactness after looking into using large bore coax for POTA/SOTA ops. Just curious was it your original idea or a remix? Would love a finer points build video and thanks for the video. 73
Always great to watch your videos and see your new antenna builds in action. Amazing workmanship. A video on how you have built this loop would be great. 👍🏻
I've been using magnetic loops vfir more than 20 years. They are great. Especially 20m up to 10m I will not be without my copper frames 😂. Don't need a tuner. The vary cap is the tuner itself. Good job Adam.
Adam, I realize that this is an old video, but it is very much still relevant. Is there a chance that you can re-visit the build, and give us some "how to" pointers? Thanks for all you do!
For the wingnut - get some brightly-colored nylon "mason line" at a hardware store and CA glue+tie a length to one of the wings. You can hold the line or loop the end around a finger while you screw it on/off to save it if you fumble your grip. It also gives you a fighting chance to find it if you drop it in the brush/gravel. Can also screw+CA tack a few spares onto some of the other bolt stubs if there's room. Good to have a fix right at hand when you need it. Learned this trick the hard way with some adjustable garden antennas...
Hello Adam Mike VE2TH here, I'm doing QRP for 58 years now, Fantastic, I love it, Congrats on getting Japan on 40 meters, It sure make your day or your week Hi! It would be fun, if one of these day, you try it on the beach, very near to the " salt water amplifier" I'm sure it should be much better, what do you think about that ? I also like your loop, it is very compact, simple to build and it works!! Keep on the good work, and a BIG THANK YOU for sharing with us. 72/73 Mike, The QRP'er didit...
Excellent design ! Using fixed capacitors plus low value variable probably makes it easier to fine tune as on my loop the peak is very sharp and narrow and hard to find. I will give your idea a go.
Great job Adam !! Another Informative video !! Already built the micro-trapped EFHW. Was considering this type of loop but using a continuous piece of aluminum stock that I could roll up in a tighter coil to transport without all the mechanical connections of the sissor folding. Food for thought. Look forward to your video on the capacitor box. 73 Terry W4ZQ
I never really liked the idea of magnetic loops because they are so narrow banded. However, this video made me realize that for something like SOTA, that basically doesn't matter because you spot yourself on a frequency and stay there. So it looks like I have a new antenna to research...
Yes! For SOTA and POTA activating, most operating involves just selecting a frequency and calling CQ. I don't often use a mag loop on summits, but they are very convenient when space is limited for setting up a more efficient and broad-banded wire antenna.
Please help us learn about the components of your band switching box with the small air gap variable capacitor for tuning. Looking forward to seeing you share this information with us. 73's
Beautiful Job, Adam no doubt about it. This Mag Loop is definitly a burner. But If I tell you this true Story happened 2 weeks ago when I was portable out in the Fields. I was ear witness of a friend up in North Carolina talked to a QRP Station (0,5W) from England on 20m SSB. My friend up in NC State got the Big Ears with his beam antenna and the British Guy had a dipole antenna which I believe of a G5RV. Around this time it rarely happens that I hear UK Stations with even 400W of power. This Contact was phenomenal and my friend in NC was happy like a mike foxtrott. All I am saying is..."there's so much positive stuff and beautiful things out in this World no matter where you live or where you temporary are. People just need to keep their eyes and ears open to explore / experience them." Amen de DK5ONV
Very cool bagging Japan! As a newly minted ham I was stoked to bag Japan and Australia on FT8 last week on 40m. That loop antenna looks like a super interesting build, I'll add it to my long list of projects :) 73, Vince KC1PAN.
They are fun, unique antennas. One like this is no replacement for a full size antenna, but as you can see, they do work. And they are a lot of fun to build too.
Great job! I’m wondering about the joints between the bars and the resistance caused by not being a continuous piece. I had thought that was the reason people made them out of copper tubes and whatnot, but have not read up on them in ages.
That's an amazing result, I'd love to see more vids about its design and build. I know a lot of the information on the 'net insists that you need solid copper to deal with the high current at the feed point, but there's no denying a contact to Japan. Great stuff :)
I'm certain good propagation conditions were in my favor and it was largely a matter of luck, but the antenna does radiate. It will never be as efficient as a dipole or EFHW, but sometimes the compromise of a very small antenna is worth it.
The high current exists everywhere in the loop; the actual feed is much lower in current. Of greater concern is the capacitor that sees the high current and thus also high voltage, but not so much at 5 watts. Also, "skin effect" is such that the current only flows on the surface of the conductor; that's why I and other use hollow copper tubing. it wouldn't use the inside anyway.
@@ahbushnell1 "It's hard to fold up copper tubing." That it is which makes portability an issue particularly at lower frequencies (larger loops). RG-8 and similar coax works pretty well to provide large diameter outer conductor and some flexibility. Naturally the inner conductor is completely unused in that configuration. I might try some tinned copper braid to achieve the same result at less weight and increased flexibility.
man Oh man, I first of all loved that loop ANT, very creative indeed. Second Did I jump of my seat when u worked Japan HI HI Great DX there my friend 73 from Amman JY
Very Cool! For us instruction followers, (vs experimenters and innovators), what goes into "the box", and how is the Gamma match made? A video detailing the construction of "the matching box" and the gamma match components would be awesome. The remainder of the project seems very straightforward from a mechanical standpoint.
The idea is relatively simple. The capacitor tunes the loop BUT at that tuning, impedance increases as you work your way up either way from the feed point. So you want a 50 ohm point and it varies by frequency. That's why the alligator clip. Tune the loop for minimum SWR (maximum received audio noise) then move the clip for 1:1 SWR. Once you have found the sweet spot, put a mark on the antenna with a Sharpie or similar so you can find it again.
@@thomasmaughan4798 Thanks. Yeah, I get the alligator clip concept. Where I run into a wall is the "box". As I mentioned, I'm a good instruction follower, but my electronics technical skills are deficient, hence my plea for detailed construction directions. I like the ,"The idea is relatively simple." So am I ;-)
I found this thread on another method of marching that looks enticing - Thomas mentioned this in another comment thread as well. forums.qrz.com/index.php?threads/want-to-homebrew-a-loop-tuner-box.522931/ Might have to try that out as well.
@@Brewerbill Ah, careful reading, I see. Yes, the exact nature of the tuning capacitor is crucial. It is common to use a "butterfly capacitor" because the relatively high RF current does not then cross a "wiper" or rotating contact. What happens is each side of the loop has its own stator plates and *between* them pivots the rotor plates and acts as the capacitance between the stators. Consequently a high RF current never crosses a wiping contact. There's a hidden benefit to butterfly capacitor; the rotor can be grounded! That means it can be used as part of the feed circuit. The shield of the coax goes to the rotor of the butterfly, and the center conductor goes *through* a smaller variable capacitor to one of the stators. Electrically it resembles a gamma match; but instead of an auto-transformer action, this works on the difference in capacitance which thus divides the capacitive reactance between the main butterfly and the matching capacitor and the whole thing can be at the low end of the loop. This is how the MFJ portable loop tuners work. You can see the schematic online for the MFJ 936B for instance. Conventional magnetic loops with a little induction coil can be difficult to achieve a perfect match. You can tune the loop easily enough but you cannot ensure a 50 ohm impedance. To achieve the 50 ohm impedance you have to tinker with the spacing and size of the induction or exciter loop and if it is high in the air, a bit difficult to reach! Capacitive matching eliminates that complexity, but at the cost of another variable capacitor.
@@K6ARK The purpose of the matching capacitor is not immediately obvious since it *seems* to be in parallel with one of the main tuning capacitor sections, but in fact is is in series with the radio transmitter. When everything is in tune, the radio presents a 50 ohm resistive source without reactance; the matching capacitor is effectively in series with one of the sections of the main butterfly tuning capacitor. This creates a "voltage divider" exactly the function of a gamma match; but the gamma match relies upon inductive reactance and the capacitor match relies upon capacitive reactance. AT resonance it doesn't really matter! Initial tuning is NOT entirely obvious. You start with LESS matching capacitor and then find the strongest receive signal by tuning the main butterfly capacitor. When you have it, transmit a very low power continuous wave (I use "FM" mode on my transmitter) and adjust match for lowest SWR. Doing that changes the main tuning slightly, so you have to retune the main. With a bit of practice the procedure takes only a few seconds and the matching capacitor usually does not require adjusting within the band; only the main tuning capacitor. Being able to have the entire electronics of a loop antenna in a single box is hugely convenient. It means you can have as large a loop as you like and it can be highly irregular in shape if that's what it takes to make it fit. It makes it almost convenient to have several loops each optimized for a band, which is to say, the largest that you can make and still tune it. 20 feet of 3/8 or 1/2 inch copper tubing makes a great 40 meter antenna. Occasionally you'll encounter an amateur radio operator that thinks it isn't a magnetic loop antenna unless it is magnetically (inductively) coupled; but that is not the reason for the name. Magnetic loop antennas are named because they couple to the magnetic field of an incoming radio wave (or excite the magnetic field of an outgoing radio wave). Gamma matching and capacitor matching do create a DC electrical connection to the loop from the radio which in rare circumstances might be a safety consideration.
Loops are amazingly good considering their small size. I've used one indoors and got into a lot of Europe with it, 5 Watts or less. I used a coupling loop which is not perfectly circular to get a better match. I want to try the gamma match sometime. I got an FT817ND to go portable and a loop built for it using ½" coax so it can be coiled up to fit in my motorcycle panniers or rucksack. H/B radio too big. G4GHB
Indeed... photos.app.goo.gl/vvxfF9YWXS3D2kKK8 Fixed capacitors on a 3 position switch in parallel with a small air variable cap. The switch swaps in the fixed capacitance required to get the antenna resonant within each band and the variable cap tunes across each band.
@@K6ARK TNX - I worked on a similar project some months ago and had trouble getting suitable results with switching the capacitors so I've abandoned it. Perhaps I'll go back to it and try reworking it. I purchased a high voltage capacitor kit from Amazon for about $9 and have been using them with good luck on other antenna projects. They're very tiny and should work on this loop project.
@@glevideo cool. Feel free to email me direct for any questions/discussion on how I make it work. Also, if I remember correctly, some of the ceramic caps I used drifted too much with 5w of RF going through them, so I switched to silver mica. Class 1 caps should work too though (C0G or NP0). I believe I was using class 2 not knowing what impact that might have, and the result was drifting tuning in a very high Q circuit.
@@glevideo Sounds interesting, I must leave in my home in Caracas Venezuela all my junk boxes of many years as a ham, and here in USA the pandemic situation doesn't permit me to assist the hamfest usually happens here. Could you share the specs of the cap on Amazon? Many tks from YV5FCK Armando in MI.
got to be the best loop design so far! Are you about ready to show us how you build it would love to get some additional information how to build a magic box and the size of capacitors
@@K6ARK I was wondering if you have ever used an auto tuner to tune a magnetic loop directly ,- I have the MFJ 939 auto tuner and was wondering if it would work on a magnetic loop that I made mounted to a hula hoop, would not be using any other tuning circuitry other than this automatic container what are your thoughts o
I would love to see a build video for this! I would be curious to know how the use of an aluminum bar compares to using a piece of coax for the loop? I imagine both would weigh about the same as well as pack down easily. My concern with the aluminum is that it will oxidize with time and the DC resistance between segments may increase. Did you put anything on the segment joints to prevent oxidation or fo you clean them perioditly?
The aluminum is much lighter. Measure the weight of about 10 feet of coax, and a frame to hold it up. I used stainless hardware to connect the aluminum bars and a little wiggling back and forth as I straighten the segments seems to make the contacts clean enough to prevent issues. Even after not using the antenna for an extended amount of time. I suspect you could also use some dielectric grease but I didn't want the sticky dirt collection involved with that. Minimizing resistance is key in magnetic loops, and I have no illusions that this loop is very efficient. But it's light, packs small, and it certainly seems to work well enough. There seems to be a good amount of interest in a build video, so it sounds like I need to order up some more material and make another. 😁
@@K6ARK YV5FCK ARMANDO We will wait for the building video I will see in Lowes or ome Depot to find the Aluminum bar, please put in the video the mesures and the part for folding the elements Tks Adam
Very cool. My mcHF rig will be here next week. I should build the loop to use this summer in the Appalachians. Build info? Mostly interested in the matching device
Awesome antenna. I thought a loop antenna needs an inner loop? How did you get around today? Also are loop antennas less sensitive to proximity to ground?
It's how much power is coming out of the antenna compared to how much your radio is putting into it. Different antennas have different efficiencies depending on what kind of metal it's made of, the way the metal is shaped, how much metal you're using, and a whole bunch of different factors. This antenna is a lot smaller than most antennas but what you gain from it being so small you lose in how well it transmits that power. This answer is not the most technical but I hope it at least answers your question well enough to understand.
Yes, thanks Greg, that's a good simple description... The links in the description will give some approximations of efficiency for different size and dimensions of loops. Additional losses are incurred in points of electrical resistance like the joints in my accordion folds. With antennas everything is a trade-off. Size, bandwidth, and efficiency are 3 primary competing factors. Small transmitting loops (aka mag loops) are very small for the frequency of operation, and are actually relatively efficient radiators, but as a trade-off, they have very narrow bandwidth (high Q). And despite that relative efficiency, there comes a point of pushing too small of a loop too far, and losses grow.
Love your little loop antenna. I just got my general and am getting into building some loop antennas. Can you point me at more information on your little three band tuner box?
No 1/16 stock at my local HD but 1/4 worked ok. Cut it into 2 foot lengths since I am not likely to be doing much backpacking I used six feet and it came out to just a shade over a meter in diameter. I still have another four foot piece. I bet if I stuck that in there it would be more efficient on 40 m. Just thinking out loud. I have a couple of 2-20 pf air variables ordered. Now I need to figure out the fixed caps
Ran the calculator and it confirms my thoughts about the size. Going to add another 4 feet. something like 95% efficient on 10 meters. Pretty good on 20. Not real happy on 30 and 40 but it looks like it will work at a low efficiency
Wow! Great 40M JA contact. Very interesting construction. I'm amazed you can resonate on 40m wirh such a small circumference. Great idea of using a small variable cap to fine tune the large fixed caps. I've been suprised that other builders don't also do that and then complain about critical tuning. Seems like a 'No Brainer' to me. Should be standard practice. I'm curious. What is your Transmitting Band Width on 20M/40M. I assume wirh such a small loop that SSB TX would be very distorted. Regards/73 OM ..
Hi Adam, that’s a pretty neat way of assembling the loop and still packing it down. Maintaining good conductivity at the joints is the main thing in these loops, which are a really low impedance and have high currents in them. Any ideas about the power limit forced by the capacitors? I know lots of designs for higher power use vacuum capacitors to get the voltage rating needed. Even 5 watts produces several hundred volts at a high impedance point. P=E**2/R so E**2 can be 50k, E=223 if the impedance is 1000 ohms at the junction where the caps are. I guess an A/B comparison against a full size dipole is in order? Would not be surprised if the loop was 20 db down on a dipole. In good conditions, tolerable. Darkness across the Pacific on 40m helping with the JA contact, around midnight or 2AM local time in JA if it’s early morning in sunny California! 73 Andrew vk1da
Based on some calculators I've tinkered with, the capacitor voltage at 5w should be close to 500v. The silver mica 500v caps I have in the match box have held up this far. 😬 I really think opening and closing the segments (pivoting the joints) goes a long way to clean up the contact points and ensure decent conductivity, but I'm sure there is some loss there. I don't know how to measure the amount. I am fairly certain the loop is 10% or less efficient on 40m which basically means JG0AWE was able make that contact with a very marginal signal. The propagation gods were definitely in our favor. There's good reason this antenna isn't my usual SOTA choice, but it's unique and very useful when it's not possible to set up a longer wire. The packability and weight are awesome too.
The mini air variable was from eBay and I don't know what it can take as a max, but similar models I've seen for sale are rated to 1250v. I should look for a part number on it and see if I can find its max voltage.
@@K6ARK ok so that suggests the impedance may be higher yet than my guess, no surprises there! Agree re contact cleaning. Very neat idea, I think you’ll trigger a wave of folding loops now! As you say, not the best antenna but for those really difficult tight summits with no space for wire antennas or radials, a great backup option! 73 Andrew VK1DA/VK2UH
A well formed loop has about 50 percent efficiency, perhaps 3 db less than a perfect dipole placed suitably high in the air. Where that's not practical or possible the loop can greatly outperform a poor dipole.
yv5fck Armando It's very nice and knowing that works are important. I can't see what do you used to folding the antenna. Many tks for share your experience.
Theory says, all those connecting pieces in your loop means high resistance and lossy. But you just debunked that theory with your QSO with Japan. FB Adam, good video
Brilliant and well done on the 40 m QRP contact to Japan, been messing with loops for a long while so like the idea of switching in fixed value caps, do you have a circuit you used ???, also where did you get that lovely little paddle from???, just set up a 705 to start doing portable activations and trying to get the kit down in size so many thanks for your time and sharing, 73 de G0VCW.
Do you notice any improvement changing the direction of the loop? Has anyone compared this to a budpole, or any home brewing of 2 hamsticks configured at a dipole at about 6-10feet off the ground? I can see this antenna as designed easier to transport. Just curious how it compares performance wise to other portable antennas.
Jeff, it's a homebrew key made out of a sheet of acrylic with a slot cut in it. The paddles are pieces of shim stock material, and a small screw provides the ground contact.
@@K6ARK yv5fck Armando very difficult to see the electrical connections and the contact points, I think there are in the acrylic parts that form the box
I have heard some consider it a language, but I think technically speaking it is probably not. That said, learning Morse has a lot of similarities to learning languages.
The primarily limiting factor for loops is the capacitor which experiences very high voltages. Because mine is built with 500v fixed value caps and a small air variable cap, 5 W is pretty much the limit. To push it up to 100 W, I would need a much larger, more expensive vacuum variable capacitor or a very large air variable with big spacing between the plates.
![รีวิวการใช้งาน Module Analog output [SA01] input Thermocouple,PT100 Output 4~20 mA,0~20 mA](http://i.ytimg.com/vi/8a31vXzcZQE/mqdefault.jpg)
A build video would be awesome.
Yes, I'd like to see the inside of that little box!
Good one, Adam! Yes please, a build video would be very much appreciated! 73, Jan M7HNK
Hey Adam, very interresting and probably the best design of a mag loop for sota I have ever seen. I agree with some comments before, a build video would be much appreciated! 73 Patrick - OE8ACT
I'm just getting into loops and love your concertina fold design. That is a very good way to get a portable circle! Japan! I bet that made your day!! Thanks, Adam.
Awesome build Adam. I'd very much like to see a build video! Thanks.
What a great idea for the Mag Loop. Talk about thinking outside the box, or loop in this case!
Dang it!!! You're killing me. Now I have to build another antenna!! Fabulous work as always. Maybe a follow-up tabletop video with details on the capacitor box would be nice. Keep up the stellar work.
Yes, definitely coming... Thanks Steve!
Mooore please! Lotttts more!
@@K6ARK can't wait
Did Adam ever do a build video for this loop ?
Hi Adam, videos that cover your strategy for building and matching loops would be excellent.
I’ve built a few loops, from simple ones made from reclaimed RG6 and a toroid core ripped from a switch mode power supply, through to one made from 1” x 1/16” aluminium strap with a motorised tuning capacitor that handled 50-60W but caught fire when I gave it the full dollar :-)
They are excellent and, elevated enough seemed to out perform my back yard verticals I have made from aluminium tube
The narrow bandwidth keeps the noise levels down, and certainly removes broadcast band interference on the Pixie my son built :-)
That big loop was 3m wide as well. Killer on 40m
I’ve been messing with mag loops the last few weeks with the intent to make a portable one. The accordion design + gamma match you used made my jaw drop at the simplicity and compactness after looking into using large bore coax for POTA/SOTA ops. Just curious was it your original idea or a remix? Would love a finer points build video and thanks for the video. 73
You are a clever HAM Adam who graciously shares your technical expertise.
Thank you kindly
Sweet contacts with that cool antenna. First time I've seen a mag loop that folds up like that. Liked the cap switching and tuning too.
Always great to watch your videos and see your new antenna builds in action. Amazing workmanship. A video on how you have built this loop would be great. 👍🏻
That's an impressive antenna! Gamma matched, scissors folding.
I've been using magnetic loops vfir more than 20 years. They are great. Especially 20m up to 10m I will not be without my copper frames 😂. Don't need a tuner. The vary cap is the tuner itself. Good job Adam.
Adam, I realize that this is an old video, but it is very much still relevant. Is there a chance that you can re-visit the build, and give us some "how to" pointers? Thanks for all you do!
despite it not being required in Canada to obtain your license, there is something cool about morse code.. I love it.
Great innovation on your mechanical design for the loop, I haven’t seen one built like that before. Clearly it works 😀
For the wingnut - get some brightly-colored nylon "mason line" at a hardware store and CA glue+tie a length to one of the wings. You can hold the line or loop the end around a finger while you screw it on/off to save it if you fumble your grip. It also gives you a fighting chance to find it if you drop it in the brush/gravel. Can also screw+CA tack a few spares onto some of the other bolt stubs if there's room. Good to have a fix right at hand when you need it.
Learned this trick the hard way with some adjustable garden antennas...
Very cool construction!
Bravo Adam! Another super interesting antenna build you got here! Please do share the strategy for building and matching this compact magloop.
Hello Adam
Mike VE2TH here, I'm doing QRP for 58 years now,
Fantastic, I love it, Congrats on getting Japan on 40 meters, It sure make your day or your week Hi!
It would be fun, if one of these day, you try it on the beach, very near to the " salt water amplifier"
I'm sure it should be much better, what do you think about that ?
I also like your loop, it is very compact, simple to build and it works!!
Keep on the good work, and a BIG THANK YOU for sharing with us.
72/73 Mike, The QRP'er didit...
Hello, Adam! I enjoy Mag Loop too. I`m glad for you and your experiments! 73, Toly UN9PI
Thank you Toly, I appreciate your feedback 😀👍
Nice build. I've always been fascinated by loop antennas.
Congrats on getting Japan on 40 with the loop!
Excellent design ! Using fixed capacitors plus low value variable probably makes it easier to fine tune as on my loop the peak is very sharp and narrow and hard to find. I will give your idea a go.
Great activation. Great antenna. Great video. thanks for putting up the Morse code translation.
Really dig the way it folds up! Nice!
Such a cool antenna, and it looks like it can handle some abuse. Your ability with CW inspires me to get going with that again. Happy trails!
Build video FTW! Amazing design. Loved the concept and the portability of it.
Great job Adam !! Another Informative video !! Already built the micro-trapped EFHW. Was considering this type of loop but using a continuous piece of aluminum stock that I could roll up in a tighter coil to transport without all the mechanical connections of the sissor folding. Food for thought. Look forward to your video on the capacitor box. 73 Terry W4ZQ
Great video. I love how that loop packs up. I need to learn how to make these loops. All the best!
Wow! Amazing way to fold the antenna!
Pretty amazing loop QSO!! TU!
Great video!! Thanks so much! Here's another vote for build video, or two!!
I never really liked the idea of magnetic loops because they are so narrow banded. However, this video made me realize that for something like SOTA, that basically doesn't matter because you spot yourself on a frequency and stay there. So it looks like I have a new antenna to research...
Yes! For SOTA and POTA activating, most operating involves just selecting a frequency and calling CQ. I don't often use a mag loop on summits, but they are very convenient when space is limited for setting up a more efficient and broad-banded wire antenna.
I really enjoyed your EFHW videos, would be great if you could do a similar thing for a portable magnetic loop antenna.
I plan to, at least for the key elements of the matching capacitor and feed. Just need to find the free time to do it! 😜
Amazing!!! Keep experimenting and inspiring the rest of us! 73! Ed, N9EDL
Thanks Ed. Sometimes you can do some impressive stuff even with a compromise antenna. It's always an adventure.
Please help us learn about the components of your band switching box with the small air gap variable capacitor for tuning.
Looking forward to seeing you share this information with us.
73's
Thanks Adam. Great video. Your enthusiasm is infectious :-) Great QSO with Japan with only 5W and a mag loop. 73 de OK8MSW
I’ve had great success with building the bnc/transformer EFHW videos you made, I would love a video on this loop!
Beautiful Job, Adam no doubt about it. This Mag Loop is definitly a burner. But If I tell you this true Story happened 2 weeks ago when I was portable out in the Fields. I was ear witness of a friend up in North Carolina talked to a QRP Station (0,5W) from England on 20m SSB. My friend up in NC State got the Big Ears with his beam antenna and the British Guy had a dipole antenna which I believe of a G5RV. Around this time it rarely happens that I hear UK Stations with even 400W of power. This Contact was phenomenal and my friend in NC was happy like a mike foxtrott. All I am saying is..."there's so much positive stuff and beautiful things out in this World no matter where you live or where you temporary are. People just need to keep their eyes and ears open to explore / experience them." Amen de DK5ONV
Build video for this awesome SOTA loop!
Excellent Video Adam
Very cool bagging Japan! As a newly minted ham I was stoked to bag Japan and Australia on FT8 last week on 40m. That loop antenna looks like a super interesting build, I'll add it to my long list of projects :) 73, Vince KC1PAN.
They are fun, unique antennas. One like this is no replacement for a full size antenna, but as you can see, they do work. And they are a lot of fun to build too.
Love the channel, and all the crazy experiments. Hopefully i'll catch you on a peak someday.
I ran a FEM simulation. Since the antenna is
Sorry I came in late for this Adam... I always enjoy your videos. Good stuff!
Great job!
I’m wondering about the joints between the bars and the resistance caused by not being a continuous piece. I had thought that was the reason people made them out of copper tubes and whatnot, but have not read up on them in ages.
That's an amazing result, I'd love to see more vids about its design and build. I know a lot of the information on the 'net insists that you need solid copper to deal with the high current at the feed point, but there's no denying a contact to Japan. Great stuff :)
I'm certain good propagation conditions were in my favor and it was largely a matter of luck, but the antenna does radiate. It will never be as efficient as a dipole or EFHW, but sometimes the compromise of a very small antenna is worth it.
The high current exists everywhere in the loop; the actual feed is much lower in current. Of greater concern is the capacitor that sees the high current and thus also high voltage, but not so much at 5 watts. Also, "skin effect" is such that the current only flows on the surface of the conductor; that's why I and other use hollow copper tubing. it wouldn't use the inside anyway.
@@thomasmaughan4798It's hard to fold up copper tubing.
@@ahbushnell1 "It's hard to fold up copper tubing."
That it is which makes portability an issue particularly at lower frequencies (larger loops). RG-8 and similar coax works pretty well to provide large diameter outer conductor and some flexibility. Naturally the inner conductor is completely unused in that configuration. I might try some tinned copper braid to achieve the same result at less weight and increased flexibility.
Waiting for the video about your new 6m yagi!
Got old bicycle aluminum rims, wheels spinning how I can re-purpose into an antenna ; )
Here you go!
content://com.amazon.cloud9.FileProvider/images/screenshot/1620769332965-980462730.jpg
Wheels in head spin round and round
Great stuff Adam, well done.
Thanks for the video, Adam! I would also be interested in a build video, especially the capacitors/switch box. Thank you, 73 de KO4AYC
very nice design, close to my project, a would try to make the variable capacitor with the aluminum itself, sliding it close to each terminal
#MNHR #TeamReplay for the win!
That's super cool!
man Oh man, I first of all loved that loop ANT, very creative indeed.
Second Did I jump of my seat when u worked Japan HI HI Great DX there my friend
73 from Amman JY
Very Cool! For us instruction followers, (vs experimenters and innovators), what goes into "the box", and how is the Gamma match made? A video detailing the construction of "the matching box" and the gamma match components would be awesome. The remainder of the project seems very straightforward from a mechanical standpoint.
The idea is relatively simple. The capacitor tunes the loop BUT at that tuning, impedance increases as you work your way up either way from the feed point. So you want a 50 ohm point and it varies by frequency. That's why the alligator clip. Tune the loop for minimum SWR (maximum received audio noise) then move the clip for 1:1 SWR. Once you have found the sweet spot, put a mark on the antenna with a Sharpie or similar so you can find it again.
@@thomasmaughan4798 Thanks. Yeah, I get the alligator clip concept. Where I run into a wall is the "box". As I mentioned, I'm a good instruction follower, but my electronics technical skills are deficient, hence my plea for detailed construction directions. I like the ,"The idea is relatively simple." So am I ;-)
I found this thread on another method of marching that looks enticing - Thomas mentioned this in another comment thread as well. forums.qrz.com/index.php?threads/want-to-homebrew-a-loop-tuner-box.522931/
Might have to try that out as well.
@@Brewerbill Ah, careful reading, I see. Yes, the exact nature of the tuning capacitor is crucial. It is common to use a "butterfly capacitor" because the relatively high RF current does not then cross a "wiper" or rotating contact. What happens is each side of the loop has its own stator plates and *between* them pivots the rotor plates and acts as the capacitance between the stators. Consequently a high RF current never crosses a wiping contact.
There's a hidden benefit to butterfly capacitor; the rotor can be grounded! That means it can be used as part of the feed circuit. The shield of the coax goes to the rotor of the butterfly, and the center conductor goes *through* a smaller variable capacitor to one of the stators. Electrically it resembles a gamma match; but instead of an auto-transformer action, this works on the difference in capacitance which thus divides the capacitive reactance between the main butterfly and the matching capacitor and the whole thing can be at the low end of the loop. This is how the MFJ portable loop tuners work. You can see the schematic online for the MFJ 936B for instance.
Conventional magnetic loops with a little induction coil can be difficult to achieve a perfect match. You can tune the loop easily enough but you cannot ensure a 50 ohm impedance. To achieve the 50 ohm impedance you have to tinker with the spacing and size of the induction or exciter loop and if it is high in the air, a bit difficult to reach! Capacitive matching eliminates that complexity, but at the cost of another variable capacitor.
@@K6ARK The purpose of the matching capacitor is not immediately obvious since it *seems* to be in parallel with one of the main tuning capacitor sections, but in fact is is in series with the radio transmitter. When everything is in tune, the radio presents a 50 ohm resistive source without reactance; the matching capacitor is effectively in series with one of the sections of the main butterfly tuning capacitor. This creates a "voltage divider" exactly the function of a gamma match; but the gamma match relies upon inductive reactance and the capacitor match relies upon capacitive reactance. AT resonance it doesn't really matter!
Initial tuning is NOT entirely obvious. You start with LESS matching capacitor and then find the strongest receive signal by tuning the main butterfly capacitor. When you have it, transmit a very low power continuous wave (I use "FM" mode on my transmitter) and adjust match for lowest SWR. Doing that changes the main tuning slightly, so you have to retune the main. With a bit of practice the procedure takes only a few seconds and the matching capacitor usually does not require adjusting within the band; only the main tuning capacitor.
Being able to have the entire electronics of a loop antenna in a single box is hugely convenient. It means you can have as large a loop as you like and it can be highly irregular in shape if that's what it takes to make it fit. It makes it almost convenient to have several loops each optimized for a band, which is to say, the largest that you can make and still tune it. 20 feet of 3/8 or 1/2 inch copper tubing makes a great 40 meter antenna.
Occasionally you'll encounter an amateur radio operator that thinks it isn't a magnetic loop antenna unless it is magnetically (inductively) coupled; but that is not the reason for the name. Magnetic loop antennas are named because they couple to the magnetic field of an incoming radio wave (or excite the magnetic field of an outgoing radio wave).
Gamma matching and capacitor matching do create a DC electrical connection to the loop from the radio which in rare circumstances might be a safety consideration.
Loops are amazingly good considering their small size. I've used one indoors and got into a lot of Europe with it, 5 Watts or less. I used a coupling loop which is not perfectly circular to get a better match. I want to try the gamma match sometime. I got an FT817ND to go portable and a loop built for it using ½" coax so it can be coiled up to fit in my motorcycle panniers or rucksack. H/B radio too big.
G4GHB
Would love to see inside the capacitor box.
Indeed... photos.app.goo.gl/vvxfF9YWXS3D2kKK8
Fixed capacitors on a 3 position switch in parallel with a small air variable cap. The switch swaps in the fixed capacitance required to get the antenna resonant within each band and the variable cap tunes across each band.
@@K6ARK TNX - I worked on a similar project some months ago and had trouble getting suitable results with switching the capacitors so I've abandoned it. Perhaps I'll go back to it and try reworking it. I purchased a high voltage capacitor kit from Amazon for about $9 and have been using them with good luck on other antenna projects. They're very tiny and should work on this loop project.
@@glevideo cool. Feel free to email me direct for any questions/discussion on how I make it work. Also, if I remember correctly, some of the ceramic caps I used drifted too much with 5w of RF going through them, so I switched to silver mica. Class 1 caps should work too though (C0G or NP0). I believe I was using class 2 not knowing what impact that might have, and the result was drifting tuning in a very high Q circuit.
@@glevideo Sounds interesting, I must leave in my home in Caracas Venezuela all my junk boxes of many years as a ham, and here in USA the pandemic situation doesn't permit me to assist the hamfest usually happens here. Could you share the specs of the cap on Amazon? Many tks from YV5FCK Armando in MI.
ıf ı were you Adam i should get trade mark of the desıgn of the loop..perfectly easy to carry and activate...
Congratulations on the J call DX! Great video, thanks fer sharing ur ant 73 de VK2AOE
got to be the best loop design so far! Are you about ready to show us how you build it would love to get some additional information how to build a magic box and the size of capacitors
Yes, I just need the free time to make a build video. Been working hard on antenna kits, winders, and new 3d printed paddles. Hopefully soon?
@@K6ARK Isn’t it great to be busy!
@@PatAutrey I need to retire! This dang work thing is cutting into my fun time.
@@K6ARK I was wondering if you have ever used an auto tuner to tune a magnetic loop directly ,- I have the MFJ 939 auto tuner and was wondering if it would work on a magnetic loop that I made mounted to a hula hoop, would not be using any other tuning circuitry other than this automatic container what are your thoughts o
I would love to see a build video for this! I would be curious to know how the use of an aluminum bar compares to using a piece of coax for the loop? I imagine both would weigh about the same as well as pack down easily. My concern with the aluminum is that it will oxidize with time and the DC resistance between segments may increase. Did you put anything on the segment joints to prevent oxidation or fo you clean them perioditly?
The aluminum is much lighter. Measure the weight of about 10 feet of coax, and a frame to hold it up.
I used stainless hardware to connect the aluminum bars and a little wiggling back and forth as I straighten the segments seems to make the contacts clean enough to prevent issues. Even after not using the antenna for an extended amount of time. I suspect you could also use some dielectric grease but I didn't want the sticky dirt collection involved with that.
Minimizing resistance is key in magnetic loops, and I have no illusions that this loop is very efficient. But it's light, packs small, and it certainly seems to work well enough. There seems to be a good amount of interest in a build video, so it sounds like I need to order up some more material and make another. 😁
@@K6ARK YV5FCK ARMANDO We will wait for the building video I will see in Lowes or ome Depot to find the Aluminum bar, please put in the video the mesures and the part for folding the elements
Tks Adam
Really enjoyed this video, congrats on Japan! 73 de GM0WDD
Nice Vid!
Strong video, tnx DK5NQ
Very cool. My mcHF rig will be here next week. I should build the loop to use this summer in the Appalachians. Build info? Mostly interested in the matching device
Nice job, cool antenna 73's didier F4CPY
Awesome antenna.
I thought a loop antenna needs an inner loop? How did you get around today?
Also are loop antennas less sensitive to proximity to ground?
Brileant design ! I will copy it .
I would love to see more about how you go about building this type of antenna. I'm new to ham radio. Can you explain what you mean by efficiency?
It's how much power is coming out of the antenna compared to how much your radio is putting into it.
Different antennas have different efficiencies depending on what kind of metal it's made of, the way the metal is shaped, how much metal you're using, and a whole bunch of different factors.
This antenna is a lot smaller than most antennas but what you gain from it being so small you lose in how well it transmits that power.
This answer is not the most technical but I hope it at least answers your question well enough to understand.
Yes, thanks Greg, that's a good simple description...
The links in the description will give some approximations of efficiency for different size and dimensions of loops. Additional losses are incurred in points of electrical resistance like the joints in my accordion folds. With antennas everything is a trade-off. Size, bandwidth, and efficiency are 3 primary competing factors. Small transmitting loops (aka mag loops) are very small for the frequency of operation, and are actually relatively efficient radiators, but as a trade-off, they have very narrow bandwidth (high Q). And despite that relative efficiency, there comes a point of pushing too small of a loop too far, and losses grow.
Maravillado con tan magnífico ingenio 👏👏👏👏
Cool video, Adam! 72 de CT7/K9PM
Love your little loop antenna. I just got my general and am getting into building some loop antennas.
Can you point me at more information on your little three band tuner box?
Very interesting stuff Adam... way to go :)
Thanks Anton, it's a quirky antenna that actually works. A fun build, for sure.
Well, the noise floor at the upper west corner of the San Fernando Valley is pretty high.
Congrats from SV2YJ
Nice would like to see more of these de N0HIU
No 1/16 stock at my local HD but 1/4 worked ok. Cut it into 2 foot lengths since I am not likely to be doing much backpacking I used six feet and it came out to just a shade over a meter in diameter. I still have another four foot piece. I bet if I stuck that in there it would be more efficient on 40 m. Just thinking out loud. I have a couple of 2-20 pf air variables ordered. Now I need to figure out the fixed caps
Ran the calculator and it confirms my thoughts about the size. Going to add another 4 feet. something like 95% efficient on 10 meters. Pretty good on 20. Not real happy on 30 and 40 but it looks like it will work at a low efficiency
Awesome, John! Would love to see pictures when you're done.
awesome...
Wow! Great 40M JA contact.
Very interesting construction. I'm amazed you can resonate on 40m wirh such a small circumference. Great idea of using a small variable cap to fine tune the large fixed caps. I've been suprised that other builders don't also do that and then complain about critical tuning. Seems like a 'No Brainer' to me. Should be standard practice.
I'm curious. What is your Transmitting Band Width on 20M/40M. I assume wirh such a small loop that SSB TX would be very distorted.
Regards/73 OM ..
Would love to see a build video! Thanks! 73, KJ7YBY
Again, Adam, aka Inspector Gadget, awesome video... what key are you using?
Hi Adam, that’s a pretty neat way of assembling the loop and still packing it down. Maintaining good conductivity at the joints is the main thing in these loops, which are a really low impedance and have high currents in them. Any ideas about the power limit forced by the capacitors? I know lots of designs for higher power use vacuum capacitors to get the voltage rating needed. Even 5 watts produces several hundred volts at a high impedance point. P=E**2/R so E**2 can be 50k, E=223 if the impedance is 1000 ohms at the junction where the caps are. I guess an A/B comparison against a full size dipole is in order? Would not be surprised if the loop was 20 db down on a dipole. In good conditions, tolerable. Darkness across the Pacific on 40m helping with the JA contact, around midnight or 2AM local time in JA if it’s early morning in sunny California! 73 Andrew vk1da
Based on some calculators I've tinkered with, the capacitor voltage at 5w should be close to 500v. The silver mica 500v caps I have in the match box have held up this far. 😬
I really think opening and closing the segments (pivoting the joints) goes a long way to clean up the contact points and ensure decent conductivity, but I'm sure there is some loss there. I don't know how to measure the amount.
I am fairly certain the loop is 10% or less efficient on 40m which basically means JG0AWE was able make that contact with a very marginal signal. The propagation gods were definitely in our favor.
There's good reason this antenna isn't my usual SOTA choice, but it's unique and very useful when it's not possible to set up a longer wire. The packability and weight are awesome too.
The mini air variable was from eBay and I don't know what it can take as a max, but similar models I've seen for sale are rated to 1250v. I should look for a part number on it and see if I can find its max voltage.
@@K6ARK ok so that suggests the impedance may be higher yet than my guess, no surprises there! Agree re contact cleaning. Very neat idea, I think you’ll trigger a wave of folding loops now! As you say, not the best antenna but for those really difficult tight summits with no space for wire antennas or radials, a great backup option! 73 Andrew VK1DA/VK2UH
A well formed loop has about 50 percent efficiency, perhaps 3 db less than a perfect dipole placed suitably high in the air. Where that's not practical or possible the loop can greatly outperform a poor dipole.
Thomas, thanks for sharing your wisdom on the subject in all of your comments here. I really appreciate it!
yv5fck Armando It's very nice and knowing that works are important. I can't see what do you used to folding the antenna. Many tks for share your experience.
Great presentation. Where can I find the details for the timing box?
Theory says, all those connecting pieces in your loop means high resistance and lossy. But you just debunked that theory with your QSO with Japan. FB Adam, good video
Brilliant and well done on the 40 m QRP contact to Japan, been messing with loops for a long while so like the idea of switching in fixed value caps, do you have a circuit you used ???, also where did you get that lovely little paddle from???, just set up a 705 to start doing portable activations and trying to get the kit down in size so many thanks for your time and sharing, 73 de G0VCW.
It's looks like a bit smaller than 1m in diameter, isn't it?
Do you notice any improvement changing the direction of the loop?
Has anyone compared this to a budpole, or any home brewing of 2 hamsticks configured at a dipole at about
6-10feet off the ground? I can see this antenna as designed easier to transport. Just curious how it compares
performance wise to other portable antennas.
I would love to see inside the cap box
Here you go... photos.app.goo.gl/vyJRVBGFBP7FMgbR8
Great video please tell us about the key you are using.
Thanks your efforts are much appreciated.
Jeff, it's a homebrew key made out of a sheet of acrylic with a slot cut in it. The paddles are pieces of shim stock material, and a small screw provides the ground contact.
photos.app.goo.gl/D7EqdfsHLjLyBmGTA
@@K6ARK very nice... thanks
@@K6ARK yv5fck Armando very difficult to see the electrical connections and the contact points, I think there are in the acrylic parts that form the box
Good job.
Tell me, while not spoken, is Morse code considered a second language?
I have heard some consider it a language, but I think technically speaking it is probably not. That said, learning Morse has a lot of similarities to learning languages.
Awesome Japan good job N2dbi ny
What key did you use in CW mode.
Something microscopic.
Thanks to.😉
Could you explain the ancillary equipment and software?
Is that an Android phone?
Hi Adam, could You show me the schematic conection variable capacitor with specific 3 band capacitor. Thank You so much
Please do a build video! Please!!!
Do you have a parts list avaliable? Im a backpacker and I would love to build one of these!
That should be able to handle alot more power than coax loops. How many watts you think it will handle?
The primarily limiting factor for loops is the capacitor which experiences very high voltages. Because mine is built with 500v fixed value caps and a small air variable cap, 5 W is pretty much the limit. To push it up to 100 W, I would need a much larger, more expensive vacuum variable capacitor or a very large air variable with big spacing between the plates.