Optimum Magnetic Loop Antenna - John Portune - W6NBC
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- čas přidán 10. 07. 2024
- Mag loops are very popular, but few are optimized for size, shape, performance, cost, building material or neighbor and HOA appeal. This presentation critically but briefly examines ALL the factors that make up an optimized mag loop, and also presents an example, a low-cost optimized PVC and foil tape loop for the largest majority of hams.
portune@aol.com
www.w6nbc.com
0:00 Intro
0:40 Mag loop basics
2:55 Why optimize?
4:40 How to optimize
7:25 Conductor Diameter
18:55 Construction Material
23:27 Loop Shape
28:48 Max Loop Size
31:02 Optimized Example Loops
41:45 Ending/Q&A - Věda a technologie
I spent the whole weekend building a loop accordong to your instructions. Each side is 1 metre and I have a wooden pole coated in aluminium foil which slides perfectly through the top section of the loop. I am blown away by the results ! 1:1 SWR on all bands 7MHz to 30 MHz but on 10 and 14 Mhz there seems to be no resonance at all. I will look in to why this is in the future. I can even tune it to the 5MHz band. Finally I can get signals out of my flat in a tower block and at last I can be heard on 7MHz. The bands have come alive ! A big thank you to John ! I will probably make a short video tomorrow showing progress so far. 73 de G4EYR
I had been knocking around ideas on how to get the surface area of the conductor up without making a large aluminium fabrication. It never occurred to me to use stick on aluminium foil like that.
Thanks for posting!
I love your method of achieving the tuning capacitor both cheap and efficient (great Idea)
Mr Fortune, thank you very much for sharing your design with us. When my daughters and I complete our Magnetic loop we will send you photos. You are very kind.
Hello John, tnx for the interesting video. Very enlighting. I made a 10 feet diamator loop for the 2020 PAcc contest, because I never had a good antenna for 80m and 160m. I used 1,5 inch Cellflex coax and coupled using two stacked toroids. I had to switch the number of windings ( 3 or 6 windings) between 160m and 80/60m for optima coupling using a 12v relay. The results were spectaculair, solast year I bought a Circo Mazzoni midi loop, conductor is about 3 inch diameter, working fantastic on anything between 20 and 80m. Some 5 years ago I built a large loop using your methode; 3 inch pvc covered with thin copper foil. It worked bettter the expected. So, 73 from Holland! Rienus, PA0RBA.
First of all thanks for this wonderfull presentation ! But there's one thing i would really wanted to mention. We don't think about it a lot but aluminium oxidises very easy. The minute you stop sandind/filing it it will oxidise. Thats why you cant't solder it in the tradional way. I,m affraid the foil/pvc elbow method will induce al lot of junction-resistance. This wil negatively impact the "Rr". Maybe not measureable with a normal multimeter, but it will be noticeable with a dedicated resistance meter (for low resistances). I dont't want to split hairs here, but low resistance is key for magloops .. Best Regards and 73's
Absolutelly great presentation, specially for non english born speakers (like me!), very easy to understand. Showed what I think to be the main key factors in choosing loop size and the right materials without spending too much money, in order to achieve the best possible results (From PY2FZU, Brazil).
I wish I had professors who present as skillfully as you do.
Best presentation I have seen on the topic.
This is absolutely amazing. So much knowledge.
Thank you for validating my experiences. I have been building different magnetic loops for a while, however, with my PVC pipe capacitor I made, I managed to burn out a number of times with just 100W when using an 8m circumference 1' flat aluminium loop on 40m. That was using 20mm piston on some 25mm grey PVC. So far, I haven't burnt it out with the 32mm orange PVC tube...yet
@@laserhobbyist9751 not exactly. The tuned loop (inductive loop and capacitor has an impedance at resonance that’s less than 50 ohms, so your coupling loop, or link, or gamma match is sized to present 50 ohms to the transceiver. The loop is most efficient at resonance, and as you move up and down the band, the impedance of the loop will change and so you need to tap you gamma match, or resize your feed loop to get the best match at 50ohms.
As far as I can tell, the feed loop doesn’t have the same currents and voltages that the main loop has
Excellent tutorial - can't wait to try this out !!!
Thanks for the crash course in mag loops. When I get around to building one, this will save me a lot of time and frustration. 73 de KS1U
What a great video. It solved the issues I have with the loop I made. Thank you
Great video. Thank you for sharing your knowledge
I like his mental attitude. He knows 700 dollar loops are an act of racketeering. I get tired of some channels that show off antennas that cost 700 to 3000 dollars. I don't waist my time with that. To many radio hobbyists are writing out a check in lue of rolling up their sleeves and getting their hands dirty.
At the Hamcation in Orlando today I was told to try a magnetic loop antenna so I asked if my 1969 ARRL handbook would have magnetic loop antennas listed. Heading for my book shelf!
Great presentation, John
I love hearing opinionated speakers who can back up their opinions. I'll have a got at these sometime.
Gareth, M5KVK
Wow! What great insight,
I constructed a magnetic loop antenna tuned to 144.30 MHz in the 2 metre band. This was made out of copper water pipe of 22 mm diameter. The loop was square with external dimensions 156 mm x 156 mm. The necessary capacitor was formed by using a 22-to-15 mm "reducer" by which a short 15 mm pipe was inserted into the 22 mm pipe. Hardly a "variable" capacitor! The co-axial feeder cable was connected to a wire loop of much smaller size located inside the antenna. I used the antenna mounted horizontally a few feet above the roof of my car.
This antenna worked very well (within the limits of the fixed frequency to which was tuned). My impression was that it was at least as good as a half-wave dipole. I had a QSO with a French station from southern England during a "lift".
Frankly I wouldn't recommend it. Its function would be severely upset by rain, and the very narrow bandwidth is a great disadvantage. Also I was fearful of damaging the Tx output transistor by transmitting at a non-resonant frequency, hence into a gross mismatch.
This would work GREAT with the loop taped all solid except at the capacitor point, use another small loop and a variable capacitor and a 12V 1 rpm motor, rocker switch, resistor to slow the tune down. I built a 5 foot 1/2 copper loop in this manner and it worked great on 40 and 60 meters.Vertical loops are directional and you can really null out noise/QRM.With a small 10" pickup tune loop just connect the cap across the main loop and tune it for noise, it will be very sharp.Adjust the smaller loop for best receive, and on transmit there will be a sweet spot where to tune just use 5 or 10 watts max.A $50 variable cap will get you 100 watts.Its a lot of fun especially when you get it working !
This is a great video with lots of good information and I thoroughly enjoyed it. I'm curious particularly what you used to measure efficiency, I get when you effectively say " it has a skin effect give it more skin" but how is efficiency on this chart calculated? Is efficiency how much bandwidth you get when you're tuned? How much power the material can handle? And based on that chart what would a loop with 90% efficiency look like? I also felt like you were going to touch on why a circle isn't the optimal shape then to preface it you touched on how people started with circle or octagon and then continued onto explaining how the square is just easier to achieve with pvc pipe, I guess when you said "optimized magnetic loop" and efficiency I thought you meant because you're trying to show how the shape maybe results in a radiation pattern that's results in higher efficiency. The way I interpret this video is more like "there are cheaper and easier ways to make an efficient magnetic loop" rather than "optimum magnetic loop antenna"
I have some questions about the top of the loop with the 1" or so gap of aluminum at the center of the antenna. First question: doesn't that make the antenna a dipole? Second question: what is the purpose of the gap, and why not just complete the circuit and make it a loop? Are you counting on the internal variable capacitor and its skin effect to complete the loop electrically? I am asking because it just looks like a dipole to me and I'm trying to clear up whatever is causing me to think that, but I don't really recall designs of magnetic loop where the loop is a split piece which sort of reminds me of a moxon antenna or dipole
Hi, I’m really interested in your design John & the physics behind it. I’m keen to have a go in constructing the larger version using small pulley wheels and a low rpm geared motor located near the bottom of the loop for remote tuning. One question with regards the foil covering of the 1 1/2” pipe, are you using for example three parallel overlapping strips to completely surround the pipe? God bless, Bill G6ATO
Thank you.
I love magnetic loop antennas
John, this is an extremely interesting video. Thank you. How would this antenna work as a receive only antenna? If it would work as a receive only antenna, and the goal is to reduce QRM, would it work best mounted horizontally? TNX Bret C/AC0AE
And one more question: what would an upper limit be for the pipe diameter. How far will the efficiency increase with increasing diameter? Thanks for your appreciated answer, Flurin
very nice article.. especially the min size/diameter restrictions. I would like to optimize for 80 and 40 meters. Also what kind of capacitor voltage rating is required as power is increased. I'm a fan of the vacuum variable since it is easily adjustable with a stepper motor remotely. The 3 section "Tap" match idea is great!
Very inspiring and instructional video, finally some real facts and analysis have been shared around the loop antennas. I was wondering: Is the use of a commom-mode (or balun) necessary at the entry point of the small loop an option, in order to minimise any potential interaction (i.e. loading/detuning/currents on shielding, etc) of the coaxial line to/from the radio with the main loop? tnx, 73!
OK we've completed the 4FT version but we used 2" PVC.. I'm not sure about what the wiring needs between the antenna and my PlaySDR srcdx. What do I use to power the antenna? I can see the capacitor makes some difference but I'm unshure how to tune the bottom clamp.
Hi. No toes. I have one question: Why always vertical? horisontal chould be omnidirectional, or am I totally wrong about the radiation pattern?
Optimized!
I think the equation for optimization is 1/4 the wave length. Wavelength = 300,000 km / Frequency. So divide by 4 and that is the circumference of the loop.
It would have been fantastic if he had supported each statement with sources and actual experimental measurements. While I like his charisma and believe in his hands-on experience, I would love to have had a backup and a reference (like books and scientific paper do).
What's your perspective of the the Ciro Massoni Mag loop (either Midi or baby)?
Is there an electrical effect of the different color PVC pipes? Thank you for the great presentation!
I would really like to see a build it video on this. A step by step guide on how to do this for us that don't know a left handed from a right handed wrench. It's a bit confusing on the capacitor and the inside foil on the elbows. Can you overlap the foil? Also what is that thing that looks like a gamma match, and how do you hook up the coax to it?
Ok, gostei da sua proposta, pois tem muitos radioamadores que precisam de mais detalhamentos ... pois, é no detalhe que as fazem funcionar ou não. TNX. Rubens py2pvb.
Hi and thanks for the exciting and motivating presentation. I have one question: how do you fix the coax braid to the aluminum tape such that you get a good electrical connection? Thanks a lot for your help! Kind Regards, Flurin
Use copper tape and solder it.
@@timhogan8170 That was not the question.
Wow, impressive, and so against the "common understanding". Will definitely be trying this. Can several loops be "stacked" to create in effect a multi-band set ?
OK but does this not also apply to the linear application as you are suggesting unless you have found foil in sufficient length and width to completely cover the 4 inch plastic pipe without overlap or creases.
Thanks John for the info,
Just one question here. Have you tried conductive spray paint to coat the tubes?
For example: MG Chemicals, "Total Ground Carbon Conductive Spray Paint."
Bye...and good luck. :)
I am enjoying this discussion very much! Davey - KU9L
Thanks from Ireland 73s
Hi, I am just now looking into building an antenna for use on a bus I am converting to a mobile home. My armature radio use has been hindered since I got my license years ago due to stringent home owner societies that I did not want to fight in court to defend my rights. But on the motorhome would be my chance to finally use more than 2 meters. and mag loop looks like the way to go. I do have 2 questions about mag loops though. 1) because of the radiation patterns of the loops being rather directional and a lack of side side to the plain of the loop would it be ideal in keeping a low profile if laid parallel to the roof and radiating 360 degrees toward the horizon? and 2) How does the tape used in this design stand up to the bakeing of the sun and the corrosive effect of the weather?
73 from Münster in Germany. I'm really impressed. Great tweaks.
Why is there no balun at the feeding point?
Would metallic dryer vent work? Is it important that it's smooth?
Did you get an answer, sounds like a do-able idea for 80m
Hi, I have just finished building a magnetic loop antenna a week ago. I worked on this project for more than one year now. It is now completely installed on the roof of the house with remote control for the (30 to 250pF vacuum) tuning capacitor and hermetic enclosure for the snowy winter. The real McCoy antenna... There is just one problem, it does not work! It has a low gain, both in receive and transmit modes. I am writing this memo in order to get some advise. Please do not hesitate to comment on any incoherent aspect of my design. I am seeking help:
The loop is made of one long 30 ft (10m) section of 3/4 in (2 cm) copper pipe coiled with no joint. The antenna diameter is 4 to 5 foot diameter therefore there are TWO turns spaced by about 6 inches (14 cm). The loop is connected to a vacuum capacitor and it tunes very well over the whole 80 meter band. At 3.8 MHz for example, the capacitance is around 120 pF. I don't think there is anything wrong with the resonance itself. But wait, the juicy stuff is at the end.
The coupling loop is a simple wire about 20 inch (50 cm) diameter positioned in the same plane as the antenna, the usual way. I will not mention the Q factor nor SWR because I did not precisely measure it in a precise meaner, but I believe this is all normal: when I tune to a station, I can easily go left and right of the station and the SWR goes down to almost perfect 1:1 match. I repositioned the loop placement and saw no change. So, again I do not think there is a problem with the coupling or matching.
My antenna has two differences with the most common antennas:
i) it has two turns; that means that the radiation pattern is a pure magnetic mode. No interaction that looks like a folded dipole. The radiation pattern has the shape of a perfect symmetrical doughnut. (usual one turn antennas have a slightly directional "cardioid" shape. This can not be the case here because of the symmetric coil having TWO turns).
ii) In order to avoid having to use a ROTATOR, I put the antenna IN THE HORIZONTAL PLANE. This way the radiation pattern is truly circular: no need to rotate the antenna...
There are two problems with that, and here is the rationale behind that choice:
1 - The maximum transmission angle is horizontal, but the beam width would cover the necessary 15 to 20 degrees necessary. The antenna is mounted on a wooden cage about 20 feet (15m) above the ground. I believed I would get a nice over-the-horizon angle, good for DX.
2 - This is the part that I may have overlooked. The polarization of ground wave is VERTICAL, while our antenna has HORIZONTAL polarization.
I am located in a semi urban environment with buildings, trees, electricity lines and hills all around my QTH. At the time I simply assumed that the polarization would quickly rotate to vertical.
I drive this antenna with 100 W signal. I can barely go 300 Km BOTH in reception and transmission. From the same location, using a simple wire antenna and the same rig, on 40 meter band, everyday, I do QSOs all over across North America. In spite with the fact that I am a newbie, I never had a 80 meter antenna I really believe that antenna in not usable as it is.. Why?
Thank you.
I have built this antenna with poor results. The use of PVC pipe degrades the antenna Q.
The 2:1 SWR bandwidth is about 130KHz at 14, 18 and 25 MHz. This indicates a fixed lose due to the use of PVC. I have since read a number of articles about the poor performance when using PVC for inductors or capacitors.
Does this loop tolerate 100 Watts?
What about wrapping the foil tape around the plastic pipe rather than the straight or linear application
because the adhesive side will behave like an insulator so in fact you would wind a coil on your pipe.
Can it using for mini hifi system
Rather than PVC pipe: what about perspex?
One (or more) strips of perspex, 4 inches wide, with foil on one side (or maybe both sides). Carefully apply heat to bend the loop into the shape you want.
Sooo much thx.
ufb :)
73 from germany de dg2r?
I thought 1 s Unit was 6 db
At 6:05 says "maxixum size" at 18:12 you say that 24:1 means in a 4 ft loop 2ft pipe. I Think you meant to say 2 inch pipe
Resistive loss in the friction fit elbows are not optimal.
Yes welding everything is a must, no bolts no screws aluminium will oxidized inside the elbows
Basically, there is no good mag loop antenna in typical sizes. Just different degrees of bad loop antennas. I get it, it’s a compromise, it’s small, “but I live in an apartment or HOA”, ect…. If it’s all you can do, it’s all you can do. No judgement. If you want better efficiency, multiple bands, no tuner needed for applicable bands, cheap, and you can fit in your pocket or at worst a small bag, get an end-fed half wave.
If the shape doesn’t matter, then why square? Why 2D? Why not spherical/cubed/pyramidal?
I’m not a physicist…. But Faradays law deals with 2D area…. i.e crossectional area…. So 3D wouldn’t be optimal …. It would work but adding the extra dimension would not improve the area as we are slicing that cake!
@@TheArtofEngineering then why bother with tubes if that is the case? Wouldn’t flat outlining of a square area using copper tape be better/easier?
Also, thank you for the reply…very interested in what may not have been tested dealing in this area
Mr. Portune is defining "optimum" as a magnetic loop antenna design that performs well, is inexpensive, can be home-build easily, and is robust/strong. When considering all of these optimization design goals, an inexpensive tubular, square structure is the result.
says at end u dont have to tune it. but yet he says u have to. so whitch one is it lol iam cornfused .
I built one in the 80's out of copper
This video would be a lot more interesting if you showed us how you measured each side, showed how you actually connected the coax, showed how you made the tuning device, etc.
Unfortunately we don't know how you measured it. We don't know how you hooked the coax to it. We don't know why you didn't use a small loop inside it. We don't know how high you have it off the ground. In fact you didn't inform us of much of anything at all other than the shape . Very disappointing
Great information, a bit too preachy though.
There are issues i can see with this design.....The biggest problem is the manual tuning given the High Q of these,this is a real pain. You skipped over this because im not sure you dont really have a plan for this. To move a tube within a tube requires lots of gear driving, moving in tiny tiny increments. This design would just about make a single frequency loop maybe for FT8 only. Personally i think you are trying to redesign the wheel and i'm not sure we need to.
One can integrate an electric motor with gearing into the PVC pipe, which simply needs to be thick enough. A polyamide threaded rod, well lubricated, guides the inner pipe back and forth along a guiding rail, preventing the pipe from rotating. For this purpose, guiding rails or three guiding rods, also made of polyamide with sleeves, can be used. Powering the motor is quite straightforward with alternating current. Rectifiers with capacitors can also fit inside the pipe. Power is supplied through a transformer, thus isolating the component. To ensure the antenna stays dry and protected from corrosion, it should be coated with Vaseline, preventing moisture from seeping in.
You do come across as what I saw as a graduate student in Theorectical mathematics. That is undergraduates at the sophmore level copping a superior attitude.
I believe this has been around a bit and is called sophomoric. Once they make it, if ever, to the last stage they often realize that they might have been like a star home run hitter at the college level, but here they are only one bright bulb in a collection of bright bulbs and they are not necessarily the brightest.
Those that sacrifice, such as in Theorectical Mathematic's case, almost all else including from roughly 4 to 8 years of time to come up with a seminal contribution to Field theory through Formal Logic as opposed to toying around with experimentation almost surely lost their arrogance along the way because they have come to realize there is no finite end to what remains to be discovered and that nature will humble any human regardless of how capable he assumes he is in his mind's comparison to others.
As far as the symbol 'optimize' and it's derivatives are concerned it's definition when Well Defined includes all that's needed and sufficient to use it as a Stand in or Symbol of Representation thus when Well Defined it more or less means "provide the most or least of what is wanted or unwanted with respect to the aim of, or relative to, the speaker using the symbol."
Obviously 'optimize' when examined below the surface has exist for it being essentially a complex Emotive attitude thus subjective or in part due to faculty for emotion. Additionally this emotive attitude is not a constituent part of what ever the attitude pertains to. The attitude also does not have to be with respect to an ideal and can be instead relative to the given materials you have to work with as opposed to ideally were one to have unlimited access to everything.
As far as the skin effect pertaining to alternating current I suspect it is fairly well known among the ham community and not in general like unaware of how to tie one shoes as your rehtoric suggested.
On the other hand while PVC pipe and foil tape certainly is a good way to minimize cost in the pursuit of the ideal surface area any method using smaller components similar to the concept pertaining to Litz wire will to some degree provide a larger surface area too.
As a matter of personal taste I only operate QRP or near QRP and often with home built transmitters because I enjoy the challenge that is lost by dropping a few thousand dollars on a 100 watt transceiver, so for myself having the highest degree of power radiated from the antenna may be your aim but not necessarily mine where simply radiating can be the aim and less efficiency in radiation essentially means more of what I like aka the challenge to succeed given the materials at hand.
I don't think mag loops are ugly far from it , I think loops are beautiful .
You can Call me ' l o o p y ' that's ok. most people think hams are strange, unusual, or silly anyway,
Thank you -- Great video 73
SpoilerAlert - Ads every 2- 4 minutes.... too much disruption.
will 7ft dia loop made with 2.5 inch aluminium tape work on the top end of 80,ie 3.775 megs?
Happy new year de sv4arx