Quest for the Best Mag Loop Antenna
ฝัง
- เผยแพร่เมื่อ 5 ส.ค. 2022
- This video explores the design and construction details of small loop (Mag Loop) antennas.
Here is a link to Part 2 of this video.
• Part 2 Quest for the ...
Here is a link to a good video reference on the subject.
• Optimum Magnetic Loop ...
Here are links to 2 must see videos that I discovered after publishing this video.
• Small Tuned Loop Radia...
I wasted a lot of time trying to duplicate the results shown in this video. I built a loop antenna for the 2M band and rotated it manually. I could not detect any directionality with a passive field strength meter. All I could show was that the far field was horizontally polarized.
• Magnetic Loop Mysterie...
Please comment on the technical information in these videos if you are knowledgeable on the subject matter.
Here is a link to a single turn loop inductance calculator.
www.qsl.net/in3otd/ind1calc.html
Here is a link to a resonant frequency calculator.
goodcalculators.com/resonant-...
Here is a link to a source of construction materials for mag loop antennas.
www.mcmaster.com/
For our metric friends (wish the U.S. was metric) here are conversion factors for the "inch" and the "foot".
1.0 inch = 2.54cm = 25.4mm
1.0 foot = 0.3048M = 30.48cm - วิทยาศาสตร์และเทคโนโลยี
Thanks for the video. It's also interesting to look at the loop with a thermal camera. I noticed the wooden frame got warm if it was too close to the high voltage parts.
Thank you for this information.
Thank you for so much useful information ! I hadn't thought of rotating the coupling loop ! Please keep making videos 🙂
Thanks for your nice comment. I am still working on mag loops when I can find the time.
Outstanding video, full of good information. Thanks.
Thanks for your nice comment.
Thank you Sir. Very informative video.
Thanks Jim!
"Feeling for hot spots" Good idea.
Thanks for your comment.
Best checked when the transmitter is off :-)
Cool beans.
I made two months ago a 4 foot square loop using 4 inch diameter aluminum dryer vent. By trial and error I found a square of 3/4 inch copper water pipe having 23 inch sides for the sense or drive loop was perfect for giving me a 50 ohm impedance at the feed.
Its good from 40 m to 20 m with 79% efficiency at 20 m and 27 % at 40 meters.
The reason for the trial and error on the drive loop is the larger they are the lower the impedance & it took me two efforts to find 50 ohms was able to be dialed in.
I use two different variable capacitors deprnding on band.
I learned to use my nano vna after it was built. I did eventually test it with the namo vna and its spot on.
I really like these antennas too....
Thank you for sharing your experience. I am planning to get back to mag loop antennas soon, but I keep getting distracted by other fun projects.
Excellent video and information. 73's
Thanks for your kind comment, 73
Thanks for the video. The reason for the welding or silver soldering instead of bolts is to get the absolute lowest possible loop resistance at interconnect points, since the Q of the loop is the reactance divided by the resistance, and the highest Q is best for both transmit and receive, at least until it makes the bandwidth so narrow it causes you to lose information you are trying to receive. For the same loop inductance 50 milliohms of resistance gives you twice the Q of a loop built with 100 milliohms of resistance. The higher the Q the narrower the bandwith of noise and extraneous signals received, and also the higher the transmit efficiency. High Q is a win, win at least until you want to tune around the band. Then it becomes a nuisance. I live in an apartment with power lines right outside the window, and the small mag-loop's high Q and directionality are what allow me to make at least some contacts without having to go to the neighborhood park to get away from the power lines.
Thanks for your comment. A capacitance in parallel with a resistance is a lower impedance to RF than the resistance alone. Because of this, bolted connections of flat surfaces works just fine. Capacitance is proportional to area divided by the separation distance. As the separation distance approaches zero the capacitance approaches infinity. I am working on a loop made of 1.0 inch by 2.0 inch rectangular aluminum tubing. The corner connections are made with bolted aluminum angle. The perimeter of this rectangular tubing is 6.0 inches. This is almost equivalent to 2.0 inch diameter round tubing. The loop is a 3.0 foot by 3.0 foot square. It is showing a very high Q. I plan to make a video about this design soon. Best regards.
@@Jimscoolstuff, I look forward to seeing how narrow the bandwidth is at resonance.
@@Jimscoolstuff Bolted connections, particularly of dis-similar metals, can rectify the RF and produce intermodulation products. Aluminum is particularly prone to this phenomenon because of aluminum oxide. It is still a good plan and I'll probably do something similar. Sanding the mating surfaces to remove oxide would alleviate this problem.
Very interesting 👍💯
Thanks for your comment. I just published a Part 2 of this video. You might want to watch that also.
Thank you for sharing 73
Thank you for your comment,73.
Very inspiring thank you, especially the lighting of the bulb close to the antenna loop is a nice trick, plus your tips to spot poor conductive joints with thermal checks (after power is being turned off!) and rotating the small loop for impedance matching.
I am in the process of making a small loop, but based on thick (13mm diameter) copper coaxial cable for the main loop. I was thinking: Don't we also need a common-mode choke at the entry of the small driving loop to isolate the possible loading effect of the coaxial cable coming/going from/to the radio? I have seen some people recommending its usage, tnx, 73.
Thanks for your comment. Yes, it is best to feed the loop thru a common mode choke. 73, Jim, KQ8E.
I have the 259b, quite expensive at the time but worth every penny. I dont think they make them any more.
great Video !! Jim in the youtube tells you that the skin effect of the U profile is roughly equivalent to a 2 inch round pipe. 2inch x phi = 6 inch. is that really the case? In another YT where you use aluminum tube profile of with dimensions 1 inch x 2 inches you make the same compare perimeter = 2 inch round pipe = 2 inch x phi = 6 inch. Skin effect of this U profile identical to the tube profile ? I have 4 pieces of 2 foot length but that is aluminum angle profile 20mm, is the skin effect comparable to the you and tube profile ?thanks, 73 PA0HTY Theo, 73.
The circumference / perimeter of a 2 inch diameter circle is 2pi = 6.28. The perimeter of a 2 inch by 1 inch rectangle is 6 inches. The total perimeter of of a u shaped channel of 1/16 inch material thickness is 1+1+1 + 1/16 + 15/16 +14/16 +15/16 +1/16=3+ 46/16 =5.875 inches. These surface perimeters are fairly close to each other. Thank you for your comment.
have you tried using an auto tuner on a mag loop?
I am using a Kenwood ts-2000 which has a built in tuner which can tune any antenna with an SWR of 3:1 or less. A properly designed coupling loop will have an SWR of less than 1.5:1 (usually much less). The transceiver tunes this with ease. Thanks for your comment.
Pat, the antenna works on resonance between the inductor that is the loop and the capacitor used to tune it
You match it by feeding it with a matching transformer, either via a smaller loop, a gamma match, a toroid feed or a direct ato transformer tap.
It’s not like a conventional antenna
…that said, there are projects for auto tuning the capacitor and adjusting the feed loop using Servo / stepper motors and Arduino processors to manage the logic
Hello Pat how are you doing.
I'll be searching for the aluminum "Strips" cut to the width. Cutting sheet aluminum is not one of my talents.
This loop was just one of many trials. please watch my other videos "quest for the best mag loop" and part 2, before you build anything. The aluminum strip design is mechanically flimsy. Best Regards.
has anyone tried building the square loop design by John Portune? It's made from pvc that has been wrapped with aluminum tape (much cheaper than buying copper tubing, and a lot more efficient too) It's worth a look -
I like everything John Portune has done except the way he adjusts capacitance, it may work but for myself, my thought is what a PITA to adjust. Going outside each time for an adjustment isn't reasonable to me, not if a single loop is the only antenna I can use on HF and it is located outside a distance away from the ham shack.
Why a PITA to me? I suspect the resonance bandwidth of his antenna, or any MLA is too narrow for my patience to walk outside to manually adjust the antenna each time I wanted to move a few kHz. Perhaps his antenna is 100 KHz wide, if it is, that is wide enough for my use in the CW portion of the band which is where I would want to operate and I'm being too harsh about needing to adjust the antenna manually. I ought to go watch his video again to see how narrow the bandwidth is for his antenna because I just don't remember what he may have reported (edit: I ran calculations for his antenna, approx. 35 kHz which isn't so bad), but I haven't seen a MLA antenna yet which does not have a very narrow bandwidth of a few tens of kHz to less than 5 kHz, nor would I want one with as much bandwidth as a dipole antenna as the efficiency and radiation pattern would suffer if too wide on this type of antenna. If I had other antennas to use such wouldn't be as important as I could just use another antenna if I didn't feel like going outside the adjust the MLA to another frequency.
That all said, I know why he built it that way, to show an inexpensive highly efficient antenna with a simple tuning method and he did just that but not what I want to build. As outrageous as this statement might be taken, that kind of simplicity and economy doesn't appeal to me, although if I wanted to cut costs due to either being uber frugal or having a limited budget, and couldn't find the parts I needed to build-in an adjustable motor driven capacitor, his design would be a good the way to go.
I suppose a motorized remote adjustment mechanism could be made with a jack screw pulling against a large spring, but for that function, I'd rather have a small Comet vacuum capacitor on a remotely controlled motor of some type built inside the PVC tubing. If I built something like his PVC with tape antenna, I'd look into being able have some kind of telescoping adjustment to allow operation from 7 MHz to the higher frequency bands, but that would substantially complicate the design and likely preclude the use of tape as well as be another adjustment I'd need to tromp outside to make. For myself, if I had the room to do so, I think it would be better to build a low frequency version of the antenna and one for the upper bands and switch between them.
Regarding conductor diameter: If you use the magnetic loop calculator at 66pacific and plug in different diameters you can see increasing the diameter of the loop radiator conductor to several inches reduces the IR/current x resistance losses so much the antenna efficiency rises a substantial amount, compared to a 1 inch diameter conductor, 3 or 4 inches makes a big difference. For example; skin effect at HF frequencies and above (actually, down into the kHz, i.e. 100 kHz; 206 microns) reduces the effective amount of conductor medium quite considerably, at 10 MHz the RF will only go about 20.6 microns deep (for copper) into the metal greatly reducing the usable amount of conductor material the RF current can flow through (at higher frequencies even less depth). However hardware store aluminum and copper foil tape are far thicker than the skin effect depth, so it is just as good as solid copper or aluminum.
I was researching using silver plated materials and silver is great, but it only offers about ten percent less resistance than copper, so better to just increase the diameter by ten percent to get the same conductivity at far less cost. I researched the rub on silver compounds for copper and they can only plate 1 micron no matter how much you apply or work at it. 1 micron is fine for 2.4 GHz as that is the skin effect depth at that frequency, but not for HF. Silver plated wires are often only plated about 1 micron thick too, so that won't help at HF.
Here is a link to my square loop design:th-cam.com/video/jB-lxTWl8Q4/w-d-xo.html
I did. I used a normal variable cap. It works well, but not great. It might be how I built it though
And this is the creators instructional video with some lead-up.
th-cam.com/video/fJpV_hGCFEo/w-d-xo.html
Thank you for providing this link.
Hello Gary how are you doing.
Hello Sir,
Why did you stopped making videos?
I am working on the development of a practical mag loop antenna to cover 10M thru 40M. I have made a lot of progress including a new tuning method that does not require transmitting. I am almost ready to make a video showing the results. Thank you for your comment.
Hi Jim i keep on trying to comment on your video but it looks like TH-cam isn't accepting my comments, maybe you are holding them back? regards . . . Andy - GW0JXM
Hi Andy; I got this comment, so please try again.
I cannot post a comment on TH-cam that contains a link to anywhere other than to TH-cam. Could that be what happened to you?
Andy I am receiving your comments (at least this one). Go ahead and comment. Best regards.
Hi Jim I keep trying to comment but keep having problems, so here I go again. Jim I wonder where the current flows in your 'U' section loop antenna. I know for certain that If you make a single turn an induction heating coil out of flat copper strip, instead of the current flowing uniformly across the broad face of the copper, almost all of the current flows in the two outer edges f the strip. I have proven this for myself. For thirty years I have designed and manufactured high power Radio Frequency induction heating equipment for scientific and industrial applications and I experimented to see where the current flowed in flat strip coils. (in order to know where to cool the coils you need to understand where they get hot) I don't have any pictures now but I know that you can see this is a German book ISBN 3-341-00813-6 page 61 the caption to the right of the image is in German but it says 'on a conductor that has not been water cooled the glowing edges clearly show where the current flows' The image is of a single circular turn of cooper strip, (like a small version of your aluminium strip loop antenna) the edges of the copper strip are glowing, this is not simply down to what's called 'edge effect' heating because of the low thermal mass at the edge of the strip but by the strips own inductance forcing the current to the outer edges of the strip. (I'll send you a picture if you give me an address) It would be impossible to demonstrate this phenomenon on a large loop with out several kilowatts of RF power. I demonstrated it for myself with a 25KW induction heater running into a none water cooled single turn copper coil at around 200Khz. I used temperature sensitive paint on the strip and instantly one could see the temperature of the edges getting hot but the edges of the strip will melt if you let it run too long. I only raise this as without knowing where the current actually flows one could fail to achieve the very best mechanical construction.
By the way if you search TH-cam for "About radio 67" you'll find a portable loop antenna I designed for 17, 20 and 40 metres
and "About Radio 64" shows a simple mechanism for turning a 180 degree capacitor with out limit switches and without mechanical damage. and "About capacitors. . . Part 6 coax cable capacitor for loop antenna by Andy Davies" shows the capacitor that I built to run the 17m loop on 40 metres.
Kind Regards . . . Andy - GW0JXM
Hi Andy. I watched your videos; thanks for sharing them.
In one of my long ago careers I worked in the research and development department of a company that made Induction heating equipment. I never worked with a single turn coil, but with a multi turn solenoid coil the current primarily flowed on the inside surface of the coil. This effect becomes greater as the coil diameter becomes very much less than the wavelength of the current . In the typical mag loop set up, things are much different as can be seen by the fact that the magnitude of the current flowing in the loop gets less as we approach the capacitor. This is the same as the current flowing in a dipole goes to zero as we approach the end of the dipole.
Best Regards
Jim KQ8E
@@Jimscoolstuff Hi again Jim I hope that you have had the chance to see the photograph that I emailed to MAC. OK on the current flow in multi turn coils. This is well documented, usually with artists impressions of where, theoretically, the current flows, and I think the typical illustrations can be taken as a good guide. A very large proportion of my work was at around 100 KHz. The skin depth in cool copper at that frequency is about eight thousandths of an inch but of course at ham radio frequencies the self inductance of the inductor forces the current to flow in fraction of that, (for anyone else reading this, you'll find coils in antenna tuners etc are usually silver plated as when working in the MHz range the current is so shallow that it only flows in the silver plating!) It's very hard to find information about the current flow across the broad face of a single turn coil, (as is so nicely illustrated in the photograph that I keep banging on about.) In 1985 - 86 I designed and manufactured a 150KW, 200KHz induction heating system that was used in Reagans Star Wars project. I had to use a single turn coil to keep the voltage down, I used three single turn coils in parallel with a gap between each turn so as to try to mitigate the current end effect issue.
Anyway, I'd love the opportunity to carry out experiments to establish what the current flow actually looks like in various magnetic loop antenna profiles. Not that this would necessarily make them work significantly better but to simply have a real understanding of what actually goes on. I guess with aluminium baking foil (for low thermal mass) and a thermographic camera it would only take a few moments to get the complete picture.
By the way, my company was Cheltenham Induction Heating Ltd, here in the UK, my business partner and I subsequently sold it to Ameritherm Inc in Rochester USA some 16 years ago, it was a lot of fun working on some fantastic projects.
All the best . . . Andy GW0JXM
@@AndyDaviesByTheSea Hi Andy: I did get your e-mail; thank you for the information. The induction heating co. that I worked for was called TOCCO. These letters are derived from "The Ohio Crankshaft CO". We worked with frequencies ranging from 60 Hz to 4 MHz. As you are aware, everything is a compromise. I was curious about the current distribution in the loop, but could not come up with a way to measure it. I found the flat strip and the U channel to be very flimsy mechanically. I am now using 2 inch by 1 inch rectangular aluminum tubing (1/16 inch wall). With a lot of effort I now have a capacitor design that can cover 10M thru 40M with a square loop that is about 3 feet per side. I am achieving very good Q based on the narrow bandwidth of the antenna. I am making contacts on all bands (10M, 12M, 15M, 17M, 20M, 30M, and 40M). The capacitor was the most difficult part of the project. It is hard to get enough capacitance for 40M and with the same capacitor get a low enough capacitance for 10M. This is why MFJ has 2 models to cover this range. I will be making a video about this design as soon as I can get to it.
Best regards
Jim KQ8E
@@Jimscoolstuff OK on TOCCO Jim. It's a good name I know well. Big, good quality equipment and well respected. Much bigger than we ever made. A couple of hundred KW's was a big machine for us. The majority of our kit was in the
@@AndyDaviesByTheSea Hi Andy, Don't have a thermal camera, but that is a very good idea. Here is a link to a video showing a Mag Loop made from aluminum foil.
th-cam.com/video/mDL6dea_aZk/w-d-xo.html
As you suggested, the low thermal mass of a thin material might make it possible to determine where the current is flowing with a thermal image. I would love to investigate this but I must discipline myself to stay on the path of my current project. When I am done with my 40M to 10M loop, I want to investigate the possibility of an E-H antenna for 160M and 80M. Perhaps we could collaborate on "small antennas" in some way. Best regards, Jim
Awesome loops I’ve built 80m high efficiency twin turn and lots of others I never get tired of playing msg loops I give my prototypes to my friends so they can build their own which leaves me space for my next loop project hmmm topband loop seems a good idea keep it up love the video and thankyou for reminding me every antenna I look at gives me an idea for the next one Dylan m0dsy🏴🫡
Thanks for your comment. I have not made a video recently because I have been very busy developing a 10M thru 40m loop. I have made several technical breakthroughs which I plan to show in my next video.
@@Jimscoolstuff I can’t wait I’ve found a ww2 cap of 1100pf so should do 10-40m two I’m contemplating spray painting the surface of the plates would that cause issues with the capacitor?