I just had a decent contact with VK2KM, near Sydney, Australia on 20 meters. I'm located in Florida. It was PSK31 and running 40 watts. That is about 15,000 km with an antenna not much bigger than a bicycle wheel. This technology never fails to amaze me.
Dennis Blanchard I have been playing with mag loop antennas made out of off cut and used RG6 coax from a couple of CCTV strip outs For my coupler I have been using computer RFI toroid cores I found in some old computer cases. Also grabbed a couple out of a dead computer PSU Put the coax through one and 3 turns of hookup wire as the feed I made one prototype for 10-15m and used stubs of RG6 cut to size as capacitors to tune the loop for each band segment. I made a larger one for 17, 20 and 30 which I tuned down to 40 with some 6KV ceramic capacitors I picked up from a wholesaler for 25 cents or so each. Managed to get a Pixie Kit my son built, across the Tasman from Sydney into The New Zealand SDR S5 running around 800mW into a kite shaped RG6 loop with a circumference of around 6m. Sadly no time for a QSO as my CW is pitiful, but I just started to work on it. The longer the loop and the smaller the capacitor, the more efficient they become. The limit is around 1/4 wavelength. More than 3/8 and the capacitors become too small. 8 - 27pf seems to be ideal. That’s my findings so far using. RG6. I’ve taped it to the wall, I’ve hung it from trees, now I just use a couple of frames of scrap timber from the renovations. Going the larger diameter radiator helps with efficiency when the diameter of the loop is limited. I have yet to test 150mm / 6” aluminium foil duct you can get from the hardware and electrical wholesalers. You would still have to secure the capacitor to the loop, but it’s one of those things I want to test.
The very best part of Amateur Radio! Being inventive and trying new (and often revolutionary) ideas in radio communication. Well done Dennis and thank You Sir for sharing it with the rest of the ham community. 73's VK2 xxx
That loop is a very interesting design as spiral wrapping the conductive tape around the plastic pipe without the edges of the tape touching then, that meant that a coil was wound around the plastic tubing. This resulted in a magnetic loop in the lane of the plastic loop as if it was a long solenoid and the radiating component of the " solenoid current was that current parallel with the plastic loop. The edges due theor sharpness of the conductive tape was breaking down in voltage stress mode, and would limit the power that " wound loop" could take. Nice idea but that " wound loop is certainly not a simple loop to analyse in depth . Congratulations,
Yes i vry much agree... i used an indoor mag loop i built from scratch on 40 M but discovered it also worked grt on 80 M ... it is a two turn loop for 40 but also worked grt on 80 and possibly on 160... my qth Ctuation is like trying to work DX from deep inside the grand canton and the HOA & neighbors are Adversaries from Hell , but with the Mag loop i was able to work vry good DX on 40 & 80 specially in the winter... Grt video there Shipmate ... keep up the good work & Inventive spirit...73s
This is a clever design that inexpensively overcomes several of the challenges in constructing an efficient mag loop antenna: low resistance loops and expensive high voltage capacitors. I'm off to the hardware store.
Since you are using coax for your capacitor, I would suggest putting a SO-239 at the antenna end and cutting additional lengths to get you on 30 and 20 meters by just switching your cable capacitor. I appreciate you showing a way to make a loop antenna for 100 watts for little cost.
I've just completed a slightly smaller loop than the one in the video. It is working really well on 18 MHz. Here are some log results: I've been building a few mag loops over the last few years. My latest one is 31 inches (78.74 cm) in diameter. I use FT8 to test them out for two reason: 1. it is usually very active and is easy to make quick contacts. 2. Unlike most other modes, the signal reports are automated and give true meaning. 599 is not very helpful. Using the latest loop, controlled with an Arduino and stepper motor, here are some quick results. The first one, from Cuba, was on a wire for 6 meters, the others on the loop. I'm located in central Florida. These antennas DO work well. The radio is an FT-817nd running 5 watts. The digits in the list, such as "+03, -12" are the signal reports, first theirs, then mine, id dB. For those that don't use FT8, a 0 (zero) dB signal is very good, -10 to -20 is fair and getting weak is down around -25 and below. My signal is, understandably, lower than most of theirs, but I'm using an antenna the size of a bicycle wheel and five watts. Once in a while my report is actually better than theirs. When I use the FT-857D at 40 watts, the reports are usually about the same as I give them. de K1YPP 2020-07-08, CO8LY, FL20, 50.313860, FT8, +03, -12, 5w, Cuba, (not on the loop) 2020-07-08, AH6FF, EM64, 10.137300, FT8, -07, -12, 5w, AL, 2020-07-08, OQ4U, JO20, 10.136979, FT8, +02, -24, 5w, Belgium, 2020-07-08, K1NZ, FN32, 10.137072, FT8, -09, -18, 5w, MA, 2020-07-09, W4DAN, EM75, 10.137583, FT8, +02, -14, 5w, TN , 2020-07-09, KF7JZ, EM44, 18.101016, FT8, -07, -13, 5w, WY, 2020-07-10, ZL2IFB, RF80, 18.101016, FT8, -15, -20, 5w, New Zealand, Enjoy your loops and see you on the air.
i used to build and sell loops. if you look for pex al pex water pipe it has the foil layer built inside. there are several diameters that fit inside each other. my best seller was 2 turns of pexal with a smaller diameter pushed in to join the loop and form the capacitor. tuning was done with nylon threaded rod to spread the 2 turns slightly. one of these sitting on my workbench in bulgaria got me into new york on 1w
This works excellent, I built one for cb. My attempt at the trombone wasn't successful (it my first attempt at building any capacitor and I didn't have any understanding of the feel for it ) so I built a simple variable variable plate. It's just two steel plates from the electrical aisle (junction box covers I believe) attached in their corners by a plastic bolt and spaced with plastic nuts and washers. The tape-loop ends are wrapped and soldered around two short bits of copper that are bolted to either plate and a long piece of plastic zip tied to the movable plate and to the mast at the other side allows adjusting with a firm hold. Whether or not it would handle 100w without better connections, I don't know but it works great for 4w. My outer loop is just shy of a 1/4 wave and it doesn't seem to require very much capacitance. Were it smaller or like for multibanding it would need a more so I think my trombone was just too big and I do intend to try again at some point. Anyways, thank you for the video! 👍
There are 2 basic sorts of loop antennas, a 'small' loop that has a circumference of only about 15% of a wavelength, set up like this one. It transmits and receives best in line with the loops and is quite directional. Then there are larger loops, such as yours, whose field is largest in the broadside direction. Being larger, it is more sensitive on receive, but it is not nearly as directional as the small loop and thus can't eliminate local noise sources on receive nearly as well.
Thanks for making this! Very clever design. In addition to the expenses of a variable capacitor, it's getting hard to find them! I'm going to give this a shot
As the Brits would say, this is brilliant! Thank you. I gave away my vacuum-variable cap a few years ago because I had no idea how to use it in anything, and I do have some air-variable caps, but I really like this antenna for its electrical conductivity. Do you know its Q? Its bandwidth compared to other loops? Perhaps a sweep with a NanoVNA. I need the bandwidth to be very narrow to deal with the noise at my locale and because I'm running QRP. I ask because the trombone cap has that plastic pipe as a dielectric between the plates, so it will have a somewhat lower Q than an air variable cap.
Thank you for taking the time to share your innovations to the mag loop antenna. I particularly appreciate your low cost DIY approach. I'm going to make a slightly larger version for more efficient use on 40m, to use as a dedicated antenna for a JS8 message server. The frequency is fixed at 7078 KHz so I only need to tune it once. I may use a parallel connection of fixed value high voltage capacitors as a cheap and compact solution. I'll probably use LMR400 coax for the radiating loop. Your trombone slide tuner is very clever.
Hi Dennis Great vid. I watched/Liked/Saved this this last year and now just Subbed. After a 3.5 yr hiatus from HAMing, I'm in a new Apt and gearing up to get back on the air. Re-watching your vid was inspirational. I'm contemplating building a few of these over the next few months. 80/40 20/15/17 17/24/10-Lo 10-Lo/Mid/Hi Too energetic? Maybe, but my plan is scaled and I have all the time in the world. Well, in my world at least. HaHa Will be ordering a 12M SpiderPole in a few weeks to operate EFHW 40M, and higher, for weekend outings. BTW: Your construction explanation was very good. Tnx for putting the time into this vid and showing us the Whys/Wherefors. Knowing Why you did This/That is very helpful. Knowledge is a powerful tool! It'll be Duck Soup to construct one, or more, of these. Tnx.....
Something similar in process, using surplus'd ethernet hose for the loop. Motor driven small capacitor. Tests are promising. Just waiting on parts to finish the remote tuning set up for it. Nice work. I've use the foil tape on a couple 6m dipoles and 2m beams. Makes for interesting fiddling ;-)
Dennis, what a great solution!! I´ve been searching for a cheap solution and you presented us this genial idea. I will construct mine and will let you know about the performance. 73 de Eger PY2EX Sao Paulo, Brazil
Very interesting design! I’ve been thinking of building a magnetic loop antenna, but had put it off due to finding a suitable capacitor. 73, Tom WA1LBK
For some reason, looking at you explaining, had me expecting to see you float in weightlessness like on these ISS videos 😀😝 Must be the lightning and all the machinery! Cheers
Great idea! Very creative! Nice work. Costly condenser requirements is something that limited use of such antennas mostly for QRP. Your solution may help more hams start building them now. I wonder, when you used Al foil you had to make small spiral spacing to prevent current taking shortcuts. But when you use Al tape which has isolation on the back site it seems to me those gaps are not necessary, but you still do them. It seems to me, most cumbersome part of the build is attention to make those gaps. Can we skip them?
The isolation of the insulation on the back is not a very high voltage insulator. I suspect it may try to flash through on higher power. Even if the insulation is removed and the glue is allowed to stick, it wouldn't be a good contact and would lead to problems. I would leave the gap in any case. The gap is not difficult to maintain.
Thanks for the neat video and ideas, now i am going to try your tape idea for a vertical base antenna. I have lots of large pvc pipe that will stand up by its self. 73s, N5UEB
Very innovative Dennis, but this is little info on making the driving loop and how to attach it to the main loop. Your blog post really didn't describe it well either. How about a part 2 for this?
The small loop is literally a loop of wire, tubing, whatever, that is about a foot in diameter. Solder one end to the center conductor of an So-239 and the other to the case of the So-239. Hang the loop as close as possible to the top center of the main loop. I use a few tie wraps. If it isn't too stable, a non-conductive rope can be tied down to the bottom of the main loop to force it to stay fixed in position. That's it. If the small loop is bare copper, I usually insulate it with a piece of plastic tubing to keep it from touching the main loop. I can touch, but it could be a source for static as it doesn't make good contact to the main loop. It does not have to be "connected" to the main loop, just close. de K1YPP
Great video and a great project. Wonderful that your loop can accommodate 100 watts without needing a Vacuum variable cap. Have you tried anything similar using copper tubing for the whole loop ?
Yes, I have built some versions using copper tubing (1/2 inch for the main loop and capacitor and 3/4 inch for the outer capacitor plate). It worked about as well but I had a difficult time bending it properly. It was the flexible copper and it was difficult to make it straight enough for the capacitor to slide freely. I also tried a Delta feed and connected the delta wires directly to the main loop, eliminating the small loop. It did work and I may go back to look into that at a later time.
The stepper motor design is something I'm submitting for publication. If it doesn't get published, I will post it here. I've had some luck with getting things published in QST, 73 and CQ over the years, so I am hopeful.
How is it on receive compared to a G5RV? I used to have multiple towers on 250 acres at 4000 with clear view to the Pacific Ocean so has a perfect location and tall trees to rig any wire antennas but 20 years ago from Northern California 5 miles from the nearest neighbor to St Petersburg Russia, a city of 7 million all living in apartments My apartment is on the second of 5 floors and no access to the roof Brick walls are 3 feet thick since my city center apartment is in a 1828 building. Love living here and he location is perfect for everything except ham radio. It is hard to get on the air so I have various wire antennas in a backpack for excursions out to the woods with an Elecraft K2 10 watt QRP transceiver. I also brought a Kenwood TS-50 100 watt rig but battery drain for the reciever is 5x higher. A slingshot and some string allow rigging wire antennas up to about 100 feet up. The 10 watts works all of Europe pretty easily in the summer but for winter I forget about ham radio. I created a Mag loop using 1 inch copper tubing and a 70-460 pf 10kv vacuum variable that worked with low SWR but receive was hampered by noise in the city...internet leakage and electric trams generating a lot of noise so I was looking for a lighter collapsable version to be small enough to take to friends high balconies. One friend lives on the top floor of a 25 story apartment outside the city center. This looks like it would be light and small enough to carry to his flat easily. Great idea to use the tape and PVC. My GF is asking me to move in with her where she has two balconies at the 4th of 5 floors but she lives just far enough to not be able to walk to all the great restaurants, museums, ballet theaters and palaces. The main incentive to do that, however, is my leased apartment versus her free apartment. Almost everyone here owns their apartment free and clear so it would triple my monthly disposable income. Now, we send all weekend in mine so we are out dining, clubbing, ballet, jazz clubs or drama every night. Decisions decisions....
I am collecting parts right now to make one of these. I was wondering if the diameter of the copper tube will change other dimensions. I was able to locate 5/8 ' rather than your recommended 3/4' tubing.
Hey Dennis I was wondering if it was possible to set this up as a ring antenna possibly 2 or 3 rings in a horizontal alignment possibly using stainless horse fencing tape to wrap. To build a omni directional. Rooftop antenna for my schoolbus or my jeep? KJ5DQA
It doesn't really matter, I've used various distances. The more important dimension is the distance from the copper tubing to the foil on the outside of the trombone. That defines the voltage breakdown and capacitance of the trombone. The inch or two in the leg spacing is insignificant in the overall system.
Good vid. Someone made somthing similar I think. Although you are getting signals right. He was making energy but with the same rf choke trombone rf kinda. I'm actually a noob looking to make a crystal cap. Few exciter coils I'm off and good to go. What do u think?
Dennis, could you thread a 12ga wire thru the center of the pen in the primary loop and bring it outside through a small hole and wrap the 1" shield"? 73 KF0IDJ
Sorry if this is a newbie question... Is the alum tape in contact with the "trombone" cap? I am guessing the current travels over the straight pvc pipe to the copper trombone.
No, the aluminum tape shouldn't touch the copper. The whole point of a capacitor is that the electric field builds up through the insulator (in this case the PVC pipe). If it can flow directly through a connection it defeats the purpose.
Hi Dennis. Can one use aluminum tape with a sticky/tacky side pressed around the circumference of the tubing & the trombone capacitor without the gaps? I don't understand the significance of the gaps? Also white or black plastic/pvc irrigation pipe can be purchased at home depot in various lengths. Thank you for a most interesting & practical project.
In answer to your question about spiral wrap overlapping vs. not overlapping. Picture a length of pipe from A to B. An electron starts at point A and travels towards B. If the pipe is copper, no problem it will traverse the shortest distance and arrive at B. Now we use a plastic pipe. There is not path for travel. If we take a piece of conductive tape that has a width that fits all around the pipe, then we have the same situation as the copper pipe and there is a direct path from A to B. Our tape in the video is not wide enough to cover the whole pipe, so we spiral wrap it from A to B. If we overlap the wraps, the electron now has two paths, one following the spiral and one jumping directly from one wrap to the next. This jump has several problems. It is the shortest path, and the electron will seek the shortest, and lowest resistance path. Consider too, there is capacitance across this path, the connection is not a good one. It isn't bonded well, such as with solder or welding. Ultimately some current will "jump" across this connection and some will follow the spiral. The overlap connection is variable, the glue offers some resistance, creating a "gap," inviting arcing and variation in the current path. In my early tests I found it had a dramatic effect on the SWR and stability of the system. By creating a gap between the turns of the spiral, the current is forced to follow the more stable path, around the spiral. If there was a way to make a perfect bond on the overlaps, then it would be fine. Hopefully, this helps clear things up?
I am tempted to make one of these, but gap between the floor of my balcony and the balcony is restrictive, so I ask, is it feasible to have the 'trombone' on the horizontal?
I have read somewhere that you can put the capacitor/trombone anywhere on the loop but the trans loop needs to be opposite to it(180°). The price I read also said that there maybe slight differences in performance depending on location factors. ie height agl. Buildings etc. 73 2E0LFD💯🇬🇧👍😎👍
Excellent vid Dennis. Thank you. You made part of my Saturday, that and a great cup(s) of coffee! I too live in an HOA. I'm curious about noise levels. I had a homebrew wire vertical sort of a cheap knock off of DX Commander for 40-17 with proper radials etc. Transmit was great and I worked pretty decent DX with 100w, especially given current band condx. However, noise was S7 no matter the band. I turned off mains in my home, operated battery, same deal. I figured it was neighborhood. So I scrapped the vertical and have only been operating remote stations lately. I still would like to tinker with something here though. How's this thing on noise? Again, thank you for helping make my Saturday!
I have a high ambient noise here as well. The typical noise floor is about S9 +10dB. The antenna drops it down to about S2-S3. On 40 Meters I switch in the 10 dB attenuator on the FT-857D and the noise floor drops down to nothing. The larger loops are not as noise immune as the smaller ones (Higher Q?). If you have lots of noise, try making the loop about the size of a bicycle wheel. It will be more fussy to tune, a bandwidth of 10 kHz or so will likely be possible. The tradeoff is a low noise floor and less efficient transmitting. The ideal situation is to build a small shielded receiving loop and another, larger loop, for transmitting. I worked with N1BYT (years ago) and designed some receiver boards for his QST articles concerning the SLR and OCR small-loop receivers. They were EXTREMELY immune to noise. For more on that: om6bb.bab.sk/files/HAM%20kniznica/Magaziny/QST/09%20September%202000%20QST.pdf
Hey Dennis. I can probably search for this, but what is the coupling between the transmit loop and the mag loop? Is it just zip tied in your demo, one to the other? They are touching? Is it necessary to bond them together? Also, enjoyed your Three Zeroes book very much. Great inspiration. 73 N0SHU
thought about it a bit more...bit more expensive but easier than bending the copper...simple right angle olive joints will work...or just right angle bend the pipe
In place attach about 5 ft of 300 ohm twin lead , using alumoim foil, wrap a piece around the twin lead. To change capacitance, move the foil up and down the length of the twin lead.
I am close to finished. Your design seems to show a 12 Secondary loop (shark bite). So should the primary be 1/5th of the secondary? That would mean the primary should be a loop 2.4 feet. Yet in the credits I see a piece of house wire at 5 feet. So which is the primary 2.4 feet or 5 feet?
Very interesting design! I live in a different kind of HOA, one created not by local rules but by a complete lack of yard space on which to erect an antenna. A loop such as yours might finally get me on the air. I wonder why you chose to put the trombone below the loop. Could you not move it up 90 deg and incorporate it into the base structure somehow, maybe even build a box around it for weather protection? That way it would easily clear the feed loop, allow easier access for tuning and/or stepper motor adjustments and allow you to mount the antenna and trombone on a wooden picnic table. 73 KD2ORG
I did try a trombone that went out ninety degrees from the bottom of the main loop. For whatever reason, it just didn't perform well. The SWR was fine, but the on-the-air performance was dismal. I didn't spend a lot of time on it. Maybe one day... I have a much better design in the works for weather immunity. More on that later.
I found 3" X 10ft - 1 Mil Copper Foil EMI Shielding Conductive Adhesive Tape the cost is supposed to be $7 for a roll. What improvement might be realized by using the copper ?
I've measured the DC resistance as being very low, however, at RF what really matters is the skin effect resistance. That is much harder to measure and I don't have that kind of instrumentation. However, doing side-by-side comparisons of a copper version, the performance difference is not measurable. I suspect this is due to the width of the tape being so wide. It is essentially like having a two inch tube for a radiator. I would estimate that it is comparable to most other designs. Since most beam antennas are made from aluminum tubing, the world seems to have accepted this material for most applications. Running a key-down test for 20 minutes, at 100 watts didn't lead to any noticeable heating around the capacitor.
Great video. Wondering what the difference is with and without the spiral if using a copper conductive adhesive tape? Any thoughts regarding? Thanks for sharing.
This looks a great project even though Im very new to the hobby I would like to try it...but I dont have the analyser to 'tune' the different bands as you did. Is there another way to do that?
Borrow one. Set up your antenna where you will be using it. Get a sharpie. Start marking frequency points on the slide of the capacitor. Do this on one leg. Wait till conditions change. Then do it to the other leg and see what if any changes there were. Then wait a few days again, and test it again to make sure your markings are holding stable. Return meter.
Here is a link to THE COPPER TUBE HANDBOOK pdf document. Bending is described on page 30. www.copper.org/publications/pub_list/pdf/copper_tube_handbook.pdf
Very nice video. I do use a homemade loop on 40 QRP. I was wondering what happens to the loops directional characteristics because of the trombone compared to the use of a standard butterfly capacitor? Thanks Jimmy, WX9DX
I can't honestly answer that. I have use a few butterfly caps for these, but haven't seen any real difference. I suspect there is some radiation from the cap as well, due to its size. Maybe I will try to model this sometime and see what happens.
@@DennisBlanchard Thanks for the reply. I got out my diy 4 foot mag loop last night and am taking it to Florida with us this year for qrp on the beach. It has a 365pf butterfly at the junction and is 3/8" soft copper "used normally for ice makers etc". It covers 20 to 80 meters but only at qrp levels. That is why I'm interested in the trombone capacitor idea. 73s Jimmy, wx9dx
I haven't made any effort to do an actual measurement. I have both copper and aluminum versions and can switch between the two on-the-air and I don't see any difference in performance. Mathematically, the copper should be better, but I haven't observed that. This may be because it is only a dB or two different.
Big difference, due to higher ohmic resistance of the aluminum tape compared to copper tubing. But.... the aluminum tape design will get you on the air! The ARRL antenna book explains how efficiency is calculated, even 1 ohm loop resistance means mediocre efficiency.
Thank You, Very Interesting, and Outside the Box !! Because of weather conditions, rain - ice, snow etc, what do you think of adding shrink rap over the tape, for both the Antenna and Capacitor, would it change the capacitance to much ? 73's VE2TSM
Yes, I have thought about those harsh weather conditions. I used to live in New Hampshire! The shrink wrap might help, I don't think it will do much to affect the RF. In fact, it will make the aluminum tape stay in place very well and make the antenna even more stable. I keep thinking that if frost builds up inside the capacitor, it cause it to jam. However, feeding some RF into it would probably melt very minute amounts of ice since these antennas have losses, so they develop some heating. Based on the band, loop size and efficiency, one can estimate how much heat. It may not be enough to melt serious ice?
Your username does you no justice💯🇬🇧😂😂😂😂😂🇬🇧 So let's help you out here. Simple really! 80÷40=2 so 40×2=80 so the loop would need to be ×2 bigger for 80m This is only by rule of thumb because of factors such as frequency differentials and materials used. But it's a good place to start. Then the finer adjustments can be made. Remember the antenna makers mantra. "Cut long, make shorter" 💯%🇬🇧👍😎👍
Yes, it is somewhat directional. The main lobes are off the ends. It seems to be about 10 dB or so. It seems to be more directional on stations that are close-in. Stan, W9SMR winters here in Sarasota and lives about four miles away. I can almost null him out from an S9 +10 signal. From his home QTH in Indiana, I only see about 5-10 dB variation.
Isn’t it very complicated to tune? imagine you have to listen to the increase in the noise floor to find the operating spot for the capacitor at a given frequency: touching the trombone capacitor with your hands will detune the antenna and make it more difficult than a plastic knob on a butterfly air capacitor. Another point that is not clear to me is how you physically mount and keep the antenna erected. Don’t you have a hard time to hold the trombone fixed, in place?
Most of the ones I've built I've just strapped to a 4 inch board with tie-wraps. The wood doesn't bother it, unless wet, that does change the tuning some, but it still works. Drill some holes in the board and put the tie-wraps through. I lay it flat on the board and then put some small plastic pipe pieces under the capacitor so it doesn't drag on the board. In the beginning I would take my MFJ Antenna analyzer and tune by moving the trombone, then back away and then adjust as necessary. The trombone also just had a few tie-wraps to hold it in place. I have a more permanent design coming up, but all of the ones prior were built to be very portable and I would just keep them in my shed when not in use. The one I'm using now is an all-weather affair and has survived two tropical storms thus far.
Hey man awesome vid, the tape you have is hi speed tape used in aviation we use it a lot to make perminantvrepairs also called 500 mile an hour tape great stuff hope this helps 73's 2E0OOW
Just found this today, and it's insanely clever! I think I probably will build one, maybe next weekend. I like the idea of a magloop, but variable capacitors are harder to come by these days. I like the DIY nature of this. I'm curious how you've rigged a stepper motor to control one of these... Any follow-ups? :) :) :)
@@riz94107 I'm still waiting on a magazine publishing the article on the controller. If it gets published, or falls through, I will post something here.
I just had a decent contact with VK2KM, near Sydney, Australia on 20 meters. I'm located in Florida. It was PSK31 and running 40 watts. That is about 15,000 km with an antenna not much bigger than a bicycle wheel. This technology never fails to amaze me.
Dennis Blanchard I have been playing with mag loop antennas made out of off cut and used RG6 coax from a couple of CCTV strip outs
For my coupler I have been using computer RFI toroid cores I found in some old computer cases. Also grabbed a couple out of a dead computer PSU
Put the coax through one and 3 turns of hookup wire as the feed
I made one prototype for 10-15m and used stubs of RG6 cut to size as capacitors to tune the loop for each band segment.
I made a larger one for 17, 20 and 30 which I tuned down to 40 with some 6KV ceramic capacitors I picked up from a wholesaler for 25 cents or so each. Managed to get a Pixie Kit my son built, across the Tasman from Sydney into The New Zealand SDR S5 running around 800mW into a kite shaped RG6 loop with a circumference of around 6m. Sadly no time for a QSO as my CW is pitiful, but I just started to work on it.
The longer the loop and the smaller the capacitor, the more efficient they become. The limit is around 1/4 wavelength. More than 3/8 and the capacitors become too small. 8 - 27pf seems to be ideal. That’s my findings so far using. RG6. I’ve taped it to the wall, I’ve hung it from trees, now I just use a couple of frames of scrap timber from the renovations.
Going the larger diameter radiator helps with efficiency when the diameter of the loop is limited. I have yet to test 150mm / 6” aluminium foil duct you can get from the hardware and electrical wholesalers. You would still have to secure the capacitor to the loop, but it’s one of those things I want to test.
@Carl Erick Stop spamming your malware filled website / app.
@Devon Ahmed Creating sock puppet accounts to talk to yourself is cringe.
Incredible. Really helps those with limited space still run.
This is why HAM is still alive. Thank You and please continue innovating.
The very best part of Amateur Radio!
Being inventive and trying new (and often revolutionary) ideas in radio communication.
Well done Dennis and thank You Sir for sharing it with the rest of the ham community.
73's
VK2 xxx
That loop is a very interesting design as spiral wrapping the conductive tape around the plastic pipe without the edges of the tape touching then, that meant that a coil was wound around the plastic tubing. This resulted in a magnetic loop in the lane of the plastic loop as if it was a long solenoid and the radiating component of the " solenoid current was that current parallel with the plastic loop. The edges due theor sharpness of the conductive tape was breaking down in voltage stress mode, and would limit the power that " wound loop" could take. Nice idea but that " wound loop is certainly not a simple loop to analyse in depth . Congratulations,
This is the best idea of HF antenna design, You are genius person. Thank you and "73"!
At half of the video I see the best idea of making a loop antenna, very clever.!
Yes i vry much agree... i used an indoor mag loop i built from scratch on 40 M but discovered it also worked grt on 80 M ... it is a two turn loop for 40 but also worked grt on 80 and possibly on 160... my qth Ctuation is like trying to work DX from deep inside the grand canton and the HOA & neighbors are Adversaries from Hell , but with the Mag loop i was able to work vry good DX on 40 & 80 specially in the winter... Grt video there Shipmate ... keep up the good work & Inventive spirit...73s
This is a clever design that inexpensively overcomes several of the challenges in constructing an efficient mag loop antenna: low resistance loops and expensive high voltage capacitors. I'm off to the hardware store.
Since you are using coax for your capacitor, I would suggest putting a SO-239 at the antenna end and cutting additional lengths to get you on 30 and 20 meters by just switching your cable capacitor. I appreciate you showing a way to make a loop antenna for 100 watts for little cost.
That would work, but one of the things that I try to avoid in this design is having an contact resistance and a connector would introduce that.
I've just completed a slightly smaller loop than the one in the video. It is working really well on 18 MHz. Here are some log results:
I've been building a few mag loops over the last few years. My latest one is 31 inches (78.74 cm) in diameter. I use FT8 to test them out for two reason:
1. it is usually very active and is easy to make quick contacts.
2. Unlike most other modes, the signal reports are automated and give true meaning. 599 is not very helpful.
Using the latest loop, controlled with an Arduino and stepper motor, here are some quick results. The first one, from Cuba, was on a wire for 6 meters, the others on the loop. I'm located in central Florida. These antennas DO work well. The radio is an FT-817nd running 5 watts.
The digits in the list, such as "+03, -12" are the signal reports, first theirs, then mine, id dB. For those that don't use FT8, a 0 (zero) dB signal is very good, -10 to -20 is fair and getting weak is down around -25 and below. My signal is, understandably, lower than most of theirs, but I'm using an antenna the size of a bicycle wheel and five watts. Once in a while my report is actually better than theirs. When I use the FT-857D at 40 watts, the reports are usually about the same as I give them.
de K1YPP
2020-07-08, CO8LY, FL20, 50.313860, FT8, +03, -12, 5w, Cuba,
(not on the loop)
2020-07-08, AH6FF, EM64, 10.137300, FT8, -07, -12, 5w, AL,
2020-07-08, OQ4U, JO20, 10.136979, FT8, +02, -24, 5w, Belgium,
2020-07-08, K1NZ, FN32, 10.137072, FT8, -09, -18, 5w, MA,
2020-07-09, W4DAN, EM75, 10.137583, FT8, +02, -14, 5w, TN ,
2020-07-09, KF7JZ, EM44, 18.101016, FT8, -07, -13, 5w, WY,
2020-07-10, ZL2IFB, RF80, 18.101016, FT8, -15, -20, 5w, New Zealand,
Enjoy your loops and see you on the air.
Brilliant. This oughtta win a design contest. Thank you! I want to give this a try. 73 DE NØIP
Very smart. It would be interesting to see a video about your loop with a motor
i used to build and sell loops. if you look for pex al pex water pipe it has the foil layer built inside. there are several diameters that fit inside each other.
my best seller was 2 turns of pexal with a smaller diameter pushed in to join the loop and form the capacitor. tuning was done with nylon threaded rod to spread the 2 turns slightly. one of these sitting on my workbench in bulgaria got me into new york on 1w
Certified, genius. A great and simple solution.
Thanks for this, gave me some ideas to overcome some problems I'm having building my own.
This works excellent, I built one for cb. My attempt at the trombone wasn't successful (it my first attempt at building any capacitor and I didn't have any understanding of the feel for it ) so I built a simple variable variable plate. It's just two steel plates from the electrical aisle (junction box covers I believe) attached in their corners by a plastic bolt and spaced with plastic nuts and washers. The tape-loop ends are wrapped and soldered around two short bits of copper that are bolted to either plate and a long piece of plastic zip tied to the movable plate and to the mast at the other side allows adjusting with a firm hold. Whether or not it would handle 100w without better connections, I don't know but it works great for 4w. My outer loop is just shy of a 1/4 wave and it doesn't seem to require very much capacitance. Were it smaller or like for multibanding it would need a more so I think my trombone was just too big and I do intend to try again at some point. Anyways, thank you for the video! 👍
There are 2 basic sorts of loop antennas, a 'small' loop that has a circumference of only about 15% of a wavelength, set up like this one. It transmits and receives best in line with the loops and is quite directional. Then there are larger loops, such as yours, whose field is largest in the broadside direction. Being larger, it is more sensitive on receive, but it is not nearly as directional as the small loop and thus can't eliminate local noise sources on receive nearly as well.
Thank you for spending so much time sharing your design!
Let us know how yours turns out. Incidentally, I've received a Worked All States and am very near a DXCC with this design.
Great video, I'd like to see your stepper setup , I can imagine it but would like to see it..
Hello,
Nice video. Is it somehow possible to make document (PDF) wth dimensions and process of making antenna ???
Can't wait to try this antenna. Excellent Video.
Great idea for an inexpensive but Very Effective Var. Tuning Cap. Specially with the Aluminum Tape and pvc tubing , TYVM for sharing a Great idea 73s
The proof of the pudding etc.... would have been nice to see it set up, receiving and transmitting.
At some point I just may do that. Good idea.
Genius way of getting around the expensive capacitor issue! Didn't think of using metallic tape either, excellent, thank you :-) 73 M7GTX
Thanks for making this! Very clever design. In addition to the expenses of a variable capacitor, it's getting hard to find them! I'm going to give this a shot
As the Brits would say, this is brilliant! Thank you. I gave away my vacuum-variable cap a few years ago because I had no idea how to use it in anything, and I do have some air-variable caps, but I really like this antenna for its electrical conductivity. Do you know its Q? Its bandwidth compared to other loops? Perhaps a sweep with a NanoVNA. I need the bandwidth to be very narrow to deal with the noise at my locale and because I'm running QRP. I ask because the trombone cap has that plastic pipe as a dielectric between the plates, so it will have a somewhat lower Q than an air variable cap.
Very interesting and inventive. I’m a new ham and plan on using a mag loop because we are moving in a year.
Wow. I’m not real handy with tools but I think I can do this. Thanks so much.
Thank you for taking the time to share your innovations to the mag loop antenna. I particularly appreciate your low cost DIY approach.
I'm going to make a slightly larger version for more efficient use on 40m, to use as a dedicated antenna for a JS8 message server. The frequency is fixed at 7078 KHz so I only need to tune it once. I may use a parallel connection of fixed value high voltage capacitors as a cheap and compact solution. I'll probably use LMR400 coax for the radiating loop. Your trombone slide tuner is very clever.
ABSOLUTELY Fantastic. Ham radio LIVES
Simple and inexpensive, great video.
Hi Dennis
Great vid. I watched/Liked/Saved this this last year and now just Subbed. After a 3.5 yr hiatus from HAMing, I'm in a new Apt and gearing up to get back on the air.
Re-watching your vid was inspirational. I'm contemplating building a few of these over the next few months.
80/40
20/15/17
17/24/10-Lo
10-Lo/Mid/Hi
Too energetic? Maybe, but my plan is scaled and I have all the time in the world. Well, in my world at least. HaHa
Will be ordering a 12M SpiderPole in a few weeks to operate EFHW 40M, and higher, for weekend outings.
BTW: Your construction explanation was very good. Tnx for putting the time into this vid and showing us the Whys/Wherefors. Knowing Why you did This/That is very helpful.
Knowledge is a powerful tool!
It'll be Duck Soup to construct one, or more, of these.
Tnx.....
Something similar in process, using surplus'd ethernet hose for the loop. Motor driven small capacitor. Tests are promising. Just waiting on parts to finish the remote tuning set up for it. Nice work. I've use the foil tape on a couple 6m dipoles and 2m beams. Makes for interesting fiddling ;-)
Very creative and ingenious! My compliments and 73, de KD8ZM!
Dennis, what a great solution!! I´ve been searching for a cheap solution and you presented us this genial idea. I will construct mine and will let you know about the performance. 73 de Eger PY2EX Sao Paulo, Brazil
Great Loop Dennis. Hope it works well for you
Thanks for the video… this is the epitome of ham radio
I like the ideas you used, is it possible that the trombone slide capacitor could be 90 deg. to the loop and still perform well?
Have you tried a square loop of PVC or pex tubing
Very interesting design! I’ve been thinking of building a magnetic loop antenna, but had put it off due to finding a suitable capacitor.
73,
Tom WA1LBK
For some reason, looking at you explaining, had me expecting to see you float in weightlessness like on these ISS videos 😀😝 Must be the lightning and all the machinery! Cheers
Great idea! Very creative! Nice work. Costly condenser requirements is something that limited use of such antennas mostly for QRP. Your solution may help more hams start building them now.
I wonder, when you used Al foil you had to make small spiral spacing to prevent current taking shortcuts. But when you use Al tape which has isolation on the back site it seems to me those gaps are not necessary, but you still do them. It seems to me, most cumbersome part of the build is attention to make those gaps. Can we skip them?
The isolation of the insulation on the back is not a very high voltage insulator. I suspect it may try to flash through on higher power. Even if the insulation is removed and the glue is allowed to stick, it wouldn't be a good contact and would lead to problems. I would leave the gap in any case. The gap is not difficult to maintain.
@@DennisBlanchard ah, that makes sense.
Thanks for the neat video and ideas, now i am going to try your tape idea for a vertical base antenna. I have lots of large pvc pipe that will stand up by its self. 73s, N5UEB
Very innovative Dennis, but this is little info on making the driving loop and how to attach it to the main loop. Your blog post really didn't describe it well either. How about a part 2 for this?
The small loop is literally a loop of wire, tubing, whatever, that is about a foot in diameter. Solder one end to the center conductor of an So-239 and the other to the case of the So-239. Hang the loop as close as possible to the top center of the main loop. I use a few tie wraps. If it isn't too stable, a non-conductive rope can be tied down to the bottom of the main loop to force it to stay fixed in position. That's it. If the small loop is bare copper, I usually insulate it with a piece of plastic tubing to keep it from touching the main loop. I can touch, but it could be a source for static as it doesn't make good contact to the main loop. It does not have to be "connected" to the main loop, just close. de K1YPP
How much would increasing the copper pipes to 1" copper help???
Just come across this, very impressed
Great video and a great project. Wonderful that your loop can accommodate 100 watts without needing a Vacuum variable cap. Have you tried anything similar using copper tubing for the whole loop ?
Yes, I have built some versions using copper tubing (1/2 inch for the main loop and capacitor and 3/4 inch for the outer capacitor plate). It worked about as well but I had a difficult time bending it properly. It was the flexible copper and it was difficult to make it straight enough for the capacitor to slide freely. I also tried a Delta feed and connected the delta wires directly to the main loop, eliminating the small loop. It did work and I may go back to look into that at a later time.
73 Dennis from... Dan K1YPB. Got my ticket in July 1962. We must have been doing it around the same time. BTW... Nice Video!
Hi Dan: I was in Bristol, CT back then. Who knows, we may have had contact over the years.
Awesome video and a great idea !!!! Thanks for sharing.
The Trombone AKA Gamma Match seems to be a nice touch versus an Air variable or a Vacuum variable .
The trombone is in no way a gamma match. The match here is the ratio between main loop diameter and feed loop diameter, IOW, 5:1.
Clever and inventive your fabulous money saving loop concept.
Sure, we'll give it a shot in our mag. loop project group. Thank you, 73 de DL8ABH
Nice. Thanks for providing this video and your BOM at end of video.
VERY interesting antenna!
Thank you; will give this a try in September.
Very intrested in how you set up the stepper motor to tune the ant. Also interested in hoe you support the ant when deployed. Great job!
The stepper motor design is something I'm submitting for publication. If it doesn't get published, I will post it here. I've had some luck with getting things published in QST, 73 and CQ over the years, so I am hopeful.
I've posted a blog page with specifics on how to build this antenna at: k1ypp.wordpress.com/2019/05/25/the-k1ypp-magnetic-loop-antenna/
How is it on receive compared to a G5RV? I used to have multiple towers on 250 acres at 4000 with clear view to the Pacific Ocean so has a perfect location and tall trees to rig any wire antennas but 20 years ago from Northern California 5 miles from the nearest neighbor to St Petersburg Russia, a city of 7 million all living in apartments My apartment is on the second of 5 floors and no access to the roof Brick walls are 3 feet thick since my city center apartment is in a 1828 building. Love living here and he location is perfect for everything except ham radio. It is hard to get on the air so I have various wire antennas in a backpack for excursions out to the woods with an Elecraft K2 10 watt QRP transceiver. I also brought a Kenwood TS-50 100 watt rig but battery drain for the reciever is 5x higher. A slingshot and some string allow rigging wire antennas up to about 100 feet up. The 10 watts works all of Europe pretty easily in the summer but for winter I forget about ham radio.
I created a Mag loop using 1 inch copper tubing and a 70-460 pf 10kv vacuum variable that worked with low SWR but receive was hampered by noise in the city...internet leakage and electric trams generating a lot of noise so I was looking for a lighter collapsable version to be small enough to take to friends high balconies. One friend lives on the top floor of a 25 story apartment outside the city center. This looks like it would be light and small enough to carry to his flat easily. Great idea to use the tape and PVC. My GF is asking me to move in with her where she has two balconies at the 4th of 5 floors but she lives just far enough to not be able to walk to all the great restaurants, museums, ballet theaters and palaces. The main incentive to do that, however, is my leased apartment versus her free apartment. Almost everyone here owns their apartment free and clear so it would triple my monthly disposable income. Now, we send all weekend in mine so we are out dining, clubbing, ballet, jazz clubs or drama every night. Decisions decisions....
I can't predict what a three-foot brick wall will do, but it is so simple to make this; give it a try. I'm curious to see how it works out.
Experimenting is priceless fun. Great
I am collecting parts right now to make one of these. I was wondering if the diameter of the copper tube will change other dimensions. I was able to locate 5/8 ' rather than your recommended 3/4' tubing.
Hey Dennis I was wondering if it was possible to set this up as a ring antenna possibly 2 or 3 rings in a horizontal alignment possibly using stainless horse fencing tape to wrap. To build a omni directional. Rooftop antenna for my schoolbus or my jeep?
KJ5DQA
The video mentions that the copper leg spacing is 6" but the blog loop diagram shows a spacing of 4-5". Which to use?
It doesn't really matter, I've used various distances. The more important dimension is the distance from the copper tubing to the foil on the outside of the trombone. That defines the voltage breakdown and capacitance of the trombone. The inch or two in the leg spacing is insignificant in the overall system.
Good vid. Someone made somthing similar I think. Although you are getting signals right. He was making energy but with the same rf choke trombone rf kinda. I'm actually a noob looking to make a crystal cap. Few exciter coils I'm off and good to go. What do u think?
Dennis, could you thread a 12ga wire thru the center of the pen in the primary loop and bring it outside through a small hole and wrap the 1" shield"? 73
KF0IDJ
Brilliant idea!
Sorry if this is a newbie question... Is the alum tape in contact with the "trombone" cap? I am guessing the current travels over the straight pvc pipe to the copper trombone.
No, the aluminum tape shouldn't touch the copper. The whole point of a capacitor is that the electric field builds up through the insulator (in this case the PVC pipe). If it can flow directly through a connection it defeats the purpose.
Hi Dennis. Can one use aluminum tape with a sticky/tacky side pressed around the circumference of the tubing & the trombone capacitor without the gaps? I don't understand the significance of the gaps? Also white or black plastic/pvc irrigation pipe can be purchased at home depot in various lengths. Thank you for a most interesting & practical project.
In answer to your question about spiral wrap overlapping vs. not overlapping. Picture a length of pipe from A to B.
An electron starts at point A and travels towards B. If the pipe is copper, no problem it will traverse the shortest distance and arrive at B. Now we use a plastic pipe. There is not path for travel. If we take a piece of conductive tape that has a width that fits all around the pipe, then we have the same situation as the copper pipe and there is a direct path from A to B.
Our tape in the video is not wide enough to cover the whole pipe, so we spiral wrap it from A to B. If we overlap the wraps, the electron now has two paths, one following the spiral and one jumping directly from one wrap to the next. This jump has several problems. It is the shortest path, and the electron will seek the shortest, and lowest resistance path. Consider too, there is capacitance across this path, the connection is not a good one. It isn't bonded well, such as with solder or welding.
Ultimately some current will "jump" across this connection and some will follow the spiral. The overlap connection is variable, the glue offers some resistance, creating a "gap," inviting arcing and variation in the current path.
In my early tests I found it had a dramatic effect on the SWR and stability of the system. By creating a gap between the turns of the spiral, the current is forced to follow the more stable path, around the spiral.
If there was a way to make a perfect bond on the overlaps, then it would be fine. Hopefully, this helps clear things up?
There will be several thousand volts on that metal tape. The gaps prevent arcing between the edges of the tape.
I am tempted to make one of these, but gap between the floor of my balcony and the balcony is restrictive, so I ask, is it feasible to have the 'trombone' on the horizontal?
I have read somewhere that you can put the capacitor/trombone anywhere on the loop but the trans loop needs to be opposite to it(180°). The price I read also said that there maybe slight differences in performance depending on location factors. ie height agl. Buildings etc.
73
2E0LFD💯🇬🇧👍😎👍
any videos of your out door version ?
Excellent vid Dennis. Thank you. You made part of my Saturday, that and a great cup(s) of coffee! I too live in an HOA. I'm curious about noise levels. I had a homebrew wire vertical sort of a cheap knock off of DX Commander for 40-17 with proper radials etc. Transmit was great and I worked pretty decent DX with 100w, especially given current band condx. However, noise was S7 no matter the band. I turned off mains in my home, operated battery, same deal. I figured it was neighborhood. So I scrapped the vertical and have only been operating remote stations lately. I still would like to tinker with something here though. How's this thing on noise? Again, thank you for helping make my Saturday!
I have a high ambient noise here as well. The typical noise floor is about S9 +10dB. The antenna drops it down to about S2-S3. On 40 Meters I switch in the 10 dB attenuator on the FT-857D and the noise floor drops down to nothing. The larger loops are not as noise immune as the smaller ones (Higher Q?). If you have lots of noise, try making the loop about the size of a bicycle wheel. It will be more fussy to tune, a bandwidth of 10 kHz or so will likely be possible. The tradeoff is a low noise floor and less efficient transmitting. The ideal situation is to build a small shielded receiving loop and another, larger loop, for transmitting. I worked with N1BYT (years ago) and designed some receiver boards for his QST articles concerning the SLR and OCR small-loop receivers. They were EXTREMELY immune to noise. For more on that: om6bb.bab.sk/files/HAM%20kniznica/Magaziny/QST/09%20September%202000%20QST.pdf
Hey Dennis. I can probably search for this, but what is the coupling between the transmit loop and the mag loop? Is it just zip tied in your demo, one to the other? They are touching? Is it necessary to bond them together? Also, enjoyed your Three Zeroes book very much. Great inspiration. 73 N0SHU
The inner and outer loops are not electrically connected.
thought about it a bit more...bit more expensive but easier than bending the copper...simple right angle olive joints will work...or just right angle bend the pipe
Nice! You can do with this concept, 3 fixed capacitors and a little trombone as a trimmer? Only for a compact new design! 73 CX1GU
Suggestion
Instead of the thrombone variable cap
In place attach about 5 ft of 300 ohm twin lead , using alumoim foil, wrap a piece around the twin lead. To change capacitance, move the foil up and down the length of the twin lead.
In a few weeks.... news about my copy of this project.
Really good video, just what I need for 40M QRP work! God bless, Bill, G6ATO
I am close to finished. Your design seems to show a 12 Secondary loop (shark bite). So should the primary be 1/5th of the secondary? That would mean the primary should be a loop 2.4 feet. Yet in the credits I see a piece of house wire at 5 feet. So which is the primary 2.4 feet or 5 feet?
Sorry for the long delay, I've been busy. It isn't fussy, but 2.5 to 3 feet should work. de K1YPP
Very interesting design! I live in a different kind of HOA, one created not by local rules but by a complete lack of yard space on which to erect an antenna. A loop such as yours might finally get me on the air. I wonder why you chose to put the trombone below the loop. Could you not move it up 90 deg and incorporate it into the base structure somehow, maybe even build a box around it for weather protection? That way it would easily clear the feed loop, allow easier access for tuning and/or stepper motor adjustments and allow you to mount the antenna and trombone on a wooden picnic table. 73 KD2ORG
I did try a trombone that went out ninety degrees from the bottom of the main loop. For whatever reason, it just didn't perform well. The SWR was fine, but the on-the-air performance was dismal. I didn't spend a lot of time on it. Maybe one day...
I have a much better design in the works for weather immunity. More on that later.
Nice job. How do you think it performs compared to one using a solid copper tube for the loop?
I would think it would just be more expensive.
I found 3" X 10ft - 1 Mil Copper Foil EMI Shielding Conductive Adhesive Tape the cost is supposed to be $7 for a roll. What improvement might be realized by using the copper ?
Lower resistance, higher efficiency.
What is the loop resistance? Asking because the efficiency is dependent on that being very low.
I've measured the DC resistance as being very low, however, at RF what really matters is the skin effect resistance. That is much harder to measure and I don't have that kind of instrumentation. However, doing side-by-side comparisons of a copper version, the performance difference is not measurable. I suspect this is due to the width of the tape being so wide. It is essentially like having a two inch tube for a radiator. I would estimate that it is comparable to most other designs. Since most beam antennas are made from aluminum tubing, the world seems to have accepted this material for most applications. Running a key-down test for 20 minutes, at 100 watts didn't lead to any noticeable heating around the capacitor.
Great video. Wondering what the difference is with and without the spiral if using a copper conductive adhesive tape? Any thoughts regarding? Thanks for sharing.
The spiral would be electrically longer, and you get increased self-capacitance (both of which lower the min and max frequency you can tune to).
I built one that does 15, 18, 20, 30, and 40 meters.
This looks a great project even though Im very new to the hobby I would like to try it...but I dont have the analyser to 'tune' the different bands as you did. Is there another way to do that?
Borrow one. Set up your antenna where you will be using it. Get a sharpie. Start marking frequency points on the slide of the capacitor. Do this on one leg. Wait till conditions change. Then do it to the other leg and see what if any changes there were. Then wait a few days again, and test it again to make sure your markings are holding stable. Return meter.
@@isaacleeper3127 Thank you thats really useful
@@utkf16 just remember, if you move the antenna or bump it hard, you should retune it using the meter.
interesting. thanks, I starting to buy/collect all the parts
Very nice, I homebrew one with a trombonne for 27 MHz. Nice idea. 7351.
Dennis, just curious....what is the impedance when the swr is low, like around 1.2:1?
I don't think it was mentioned in the video. Tom W4TMW
It is usually around 40-60 ohms, at least on the analyzer.
Here is a link to THE COPPER TUBE HANDBOOK pdf document. Bending is described on page 30.
www.copper.org/publications/pub_list/pdf/copper_tube_handbook.pdf
Very nice video. I do use a homemade loop on 40 QRP. I was wondering what happens to the loops directional characteristics because of the trombone compared to the use of a standard butterfly capacitor? Thanks Jimmy, WX9DX
I can't honestly answer that. I have use a few butterfly caps for these, but haven't seen any real difference. I suspect there is some radiation from the cap as well, due to its size. Maybe I will try to model this sometime and see what happens.
@@DennisBlanchard Thanks for the reply. I got out my diy 4 foot mag loop last night and am taking it to Florida with us this year for qrp on the beach. It has a 365pf butterfly at the junction and is 3/8" soft copper "used normally for ice makers etc". It covers 20 to 80 meters but only at qrp levels. That is why I'm interested in the trombone capacitor idea. 73s Jimmy, wx9dx
It will definitely affect the radiation pattern. Everything does! The trombone section is radiating in this case. Proof? Model it using MMANA-GAL.
Добрый день! Скажите ,на 27 мгц какой нужен диаметр рамки?
I would guess 1 meter would be fine.
Brilliant!
That is a really creative antenna. 73
foil band dont touching copper tube right? TA1APD 73!
Yes, that is correct, they should NOT touch at all.
What would you say the difference in efficiency is between this and a mag loop made of copper tubing and a butterfly cap?
I haven't made any effort to do an actual measurement. I have both copper and aluminum versions and can switch between the two on-the-air and I don't see any difference in performance. Mathematically, the copper should be better, but I haven't observed that. This may be because it is only a dB or two different.
Big difference, due to higher ohmic resistance of the aluminum tape compared to copper tubing. But.... the aluminum tape design will get you on the air! The ARRL antenna book explains how efficiency is calculated, even 1 ohm loop resistance means mediocre efficiency.
Thank You, Very Interesting, and Outside the Box !! Because of weather conditions, rain - ice, snow etc, what do you think of adding shrink rap over the tape, for both the Antenna and Capacitor, would it change the capacitance to much ? 73's VE2TSM
Yes, I have thought about those harsh weather conditions. I used to live in New Hampshire! The shrink wrap might help, I don't think it will do much to affect the RF. In fact, it will make the aluminum tape stay in place very well and make the antenna even more stable. I keep thinking that if frost builds up inside the capacitor, it cause it to jam. However, feeding some RF into it would probably melt very minute amounts of ice since these antennas have losses, so they develop some heating. Based on the band, loop size and efficiency, one can estimate how much heat. It may not be enough to melt serious ice?
How much bigger would it be if you added 80m and/or 160m?
Your username does you no justice💯🇬🇧😂😂😂😂😂🇬🇧
So let's help you out here. Simple really!
80÷40=2 so 40×2=80 so the loop would need to be ×2 bigger for 80m
This is only by rule of thumb because of factors such as frequency differentials and materials used. But it's a good place to start. Then the finer adjustments can be made.
Remember the antenna makers mantra.
"Cut long, make shorter"
💯%🇬🇧👍😎👍
Did u find it at all directional?
Bill
K9WEN
Yes, it is somewhat directional. The main lobes are off the ends. It seems to be about 10 dB or so. It seems to be more directional on stations that are close-in. Stan, W9SMR winters here in Sarasota and lives about four miles away. I can almost null him out from an S9 +10 signal. From his home QTH in Indiana, I only see about 5-10 dB variation.
Isn’t it very complicated to tune? imagine you have to listen to the increase in the noise floor to find the operating spot for the capacitor at a given frequency: touching the trombone capacitor with your hands will detune the antenna and make it more difficult than a plastic knob on a butterfly air capacitor.
Another point that is not clear to me is how you physically mount and keep the antenna erected. Don’t you have a hard time to hold the trombone fixed, in place?
I believe he said he has a stepper motor which he uses to actuate the trombone.
Most of the ones I've built I've just strapped to a 4 inch board with tie-wraps. The wood doesn't bother it, unless wet, that does change the tuning some, but it still works. Drill some holes in the board and put the tie-wraps through. I lay it flat on the board and then put some small plastic pipe pieces under the capacitor so it doesn't drag on the board. In the beginning I would take my MFJ Antenna analyzer and tune by moving the trombone, then back away and then adjust as necessary. The trombone also just had a few tie-wraps to hold it in place.
I have a more permanent design coming up, but all of the ones prior were built to be very portable and I would just keep them in my shed when not in use. The one I'm using now is an all-weather affair and has survived two tropical storms thus far.
Hey man awesome vid, the tape you have is hi speed tape used in aviation we use it a lot to make perminantvrepairs also called 500 mile an hour tape great stuff hope this helps 73's 2E0OOW
This has got me looking at the trampoline in the the back yard...hmmmm.
アルミテープとは奇想天外で面白い。そして、僕にも作れそうです。
Has anyone successfully built one of these antennas yet? I'm curious to see what the results are like.
Just found this today, and it's insanely clever! I think I probably will build one, maybe next weekend. I like the idea of a magloop, but variable capacitors are harder to come by these days. I like the DIY nature of this. I'm curious how you've rigged a stepper motor to control one of these... Any follow-ups? :) :) :)
@@riz94107 I'm still waiting on a magazine publishing the article on the controller. If it gets published, or falls through, I will post something here.