The Truth About Magnetic Loop Antennas - MYTH BUSTING!

There are many many myths out there on the internet about magnetic loop antennas and so this presentation and demonstration will focus on myth-busting by presenting the facts, demonstrating them in real-time and busting some of the myths that many ham radio operators hang on to about these fascinating antennas.
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This presentation is given by Justin VK7TW at the Radio and Electronics Association of Southern Tasmania Inc.
www.reast.asn.au/
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[@johnwest7993]

This is very interesting, and mostly accurate. But I don't think a solid loop material will change much over a tube material because of skin effect. The losses are resistive, but only sort of DC resistive. The resistance can only be thought of as a DC resistance for a loop with less available material through which to conduct the current as frequency goes up.

[@allancopland1768]

So let me get this..... The current distribution in a small transmitting loop stays constant while the voltage varies greatly. Another of those myths. It's easy to prove that is simply not true.

[@izzzzzz6]

I was trying to calculate a loop the other day to help combat terrible rfi. I was wondering if I could feed it with a 9:1 balun and if so then would the loops tuning network be less necessary? I was thinking a simple capacitor like a flat piece of aluminium at the top open end of a flat aluminium loop, while keeping the point of capacitance central the idea is to slide an overlapping piece over and above the main top section of loop, adding capacitance the more it overhangs the top section. Regarding the matching to inductance with a bar or smaller fed loop it cam to me that if your feeding a smaller loop you can add some variables by orientating the smaller loop like a clock and then clamping it back down, in other words the feed point on the smaller loop, rather than it being at 12 o clock, you could loosen a bracket and move the feed point towards 9 o clock or towards 3 o clock for tuning then clamp it back down. Then I thought, might as well add another variable and make that clamping point be able to clamp to different points of the main loop, so either clamping slightly up towards 8 o clock or sliding it up towards 4 o clock for further adjustments. The calculator told me that my design would have an Inductive Reactance: 465 ohms This is why I was thinking to have a 9:1 balun to feed it with. Regarding diameter i have seen that large diameter works better but then the flat sheet metal loop also looked interesting. I was wondering how making the flat aluminium much deeper would effect the loop. The idea is to have a batter signal to noise ratio as we have noise around S7 S8 at times. No chance getting the French electrical provider to come out and change the transformers. It's hard to know if it's a transformer. I found a very noisy one but we only live around 3 miles from a hydro electric plant. I'm wondering if they have noisy generators and then that noise comes down the power lines to us only to be re-transmitted by all of the power lines. I need to do some more walking but an area of around 10 Km square where I live is extremely noisy. I've driven around and the noise keeps cropping up all over the place. If I drive to other villages then they do not suffer the same noise. However, driving around in general the noise is apparent in many other places. I was also wondering if it could be the noise from all the smart meters sending data back down the lines. I'm at whits end and my friend who lives around 10-15km from here is suffering also. Possibly more than me but I think my radio has better filters than his. Tried noise cancellers like the VK5 but they only reduce noise with the gain down quite low, this is ok but it's not really enough. Next is current baluns and or 1:1 unun's then as many ferrite beads as possible on coax and all cables. I have a sound cancelling box also but i've not tried it yet. Thinking that selling the house is the only option.

[@MINI-4X4-RADIO]

I have 1M Magnetic Loop in the Loft, 176 DXCC's worked on 17M from UK/G inc 7 ZL's and all with 5 Watts "Any antenna" is better than "No antenna", you work with what you have.

[@reedreamer9518]

What software did VK5KLT use for that variable graph?

[@martymctry20]

As material for my loop, I am using a flexible exhaust hose with an aluminium coating. The hose is 5 meters long and has a resistance of approximately 5 ohms. Does the ohmic resistance affect the high-frequency properties in qrp?

[@LarryAllenTonar]

What does "0.049"" under "Wavelength" column in the top row "3.5 MHz" mean in the interrelationship tool summary table mean? Units (or dimensionless)? Is the minimun useful size 1/8 wavelength or the 1/10 wavelength of highest desired frequency of use I've seen elsewhere?

[@AcydDrop]

Was the audio for this talk recorded with a potato?

[@W1KAB-9]

To further the performance research, I would be interested in a side by side comparison of the loop vs a dipole (all other factors equal) using the WSPR data collected.

[@uploadJ]

We 'played' at that in 2013 - 2020 thereabouts. I hit EU from Texas most nights using a QW circumference loop (which this presenter misrepresents, as usual) running against others ops here stateside. I captured a lot of that data - it needs to be graphed using Excel or R or something and presented.

[@thomasmaughan4798]

All other factors tend not to be equal. A dipole suitably high above perfect Earth is the ideal antenna. If you don't have all that, a mag loop antenna works pretty well where a dipole in NOT ideal circumstances would do even more poorly.

[@W1KAB-9]

@@thomasmaughan4798 Then the proper test would be comparing a dipole at an optimal height against a mag-loop at perhaps 6 feet or so and measure the dB difference, or, using WSPR data. When I stated “all factors equal”, I meant using the same transmitter and power level. The antennas would be in their normal configuration.

[@stevewithnell911]

I have a Toploaded Marconi Outside, the vertical section is around 9 metres. Indoors I have a 1.6m diameter broadband loop made from scrap RG213. I ran concurrent WSPR sessions over 24 hour periods on 630m and 160m. No real difference, for RX I'd go with my indoor loop -. There is a lot of data with lots of curiousities.

[@liesofgasandpilesofshoes]

I used pexal monoband loops for pedestrian mobile many years. Transatlantic on 1w often. Build high q

[@DaninVirginia]

I really appreciate the presenter's sense of humor!

[@reedreamer9518]

There are some advance design secrets that improve bandwidth and efficiency, but those are very rarely mentioned anywhere on the internet. But the real challenge is building all that into a weatherproof package that can withstand the extremes of weather outside up on a pole for 5 or 10 years with minimal maintenance. Few hams ever attempt or achieve this, but it can be done.

[@johnratcliffe6438]

Such as?

[@lyingcat9022]

@@johnratcliffe6438yes agreed, please tell us if you know. Do you have any references to point us to?

[@AC7WH]

Nice demonstration! Thanks for sharing. ~ 73 ~ AC7WH

[@Robert-cd5zr]

New to all this, sorry if it's an irrelevant question but does radiation pattern essentially provide both ground wave and NVIS characteristics? If so, is it possible to orient the hole up and down such that you achieve an omnidirectional pattern WRT azimuth, and despite losses straight up still have some emissions vertically enough to still fill in the skip zones like an NVIS?

[@petertyrrell6690]

Great information. Thank you. It is enough for me to understand that my Mag loop is going not be optimal with "any old" capacitor, (limits power) and to keep my connections and as low resistance as possible. If I insist on building an optimal mag loop, I'll never build one.

[@stevewithnell911]

I wholly disagree with the definition of the STL as being

[@AdamosDad]

I built a hexagon loop out of 3/4 copper water pipe soldered 45's, using an air variable capacitor 250pF Antenna circumference is: 8.75 feet or 8’ 9” 21-inch circumference input. I will tune 40-to-15 meters, at 20 watts we made digital contacts from my friend's basement to all around the US I will take it outside this Monday when he returns it and see if I can make voice contacts, over the pond.

[@eziomonico7173]

I am the italian swl and operated with Radio Bye is loop amplifier by 81 cm ,is alumentation by 9 v with trasfirmer and 2 out of bnc x cable "j use 7 meter of rg 58,tthe antenna's is difficokt for 160/80 meter and 11/10 meter is about mute,73 by i2/03897

[@justinruth9729]

Your the man I'm Justin as well I use all your stuff and I run a LFAQ 27mhz b ast

[@fotografm]

Excellent presentation !!! Thank you 🙂

[@NamasenITN]

A bit difficult to follow for me, due to the presentation style and the format. Th first slide was a good reference to read independently.

[@Ei2iP]

Always considered getting a loop, perhaps the Italian Commercial option, Midi Loop.

[@ralfkruse7565]

Very interresting lecture. If you want to build a loop from coaxial cable, you can do it without expensive or infindable capacitors. Of course, only monoband. Nearly all LDF cable resist up to about 4000V. So, use the capacitance of the inner conductor to the outer. It's in the range of 75 to 90 pf/m . Just connect at high point the inner conductor to the outer. If it resonates with a dip meter at the high edge of the band you only need a small variable capacitor two or three plates, 50pf to tune the whole band. It worked fine, i built one for 160m some 15 years ago. With lower point 30cm above soil, it was about 10db weaker than a full size dipole at about 10m high. Mine was from LDF 1/2" . F1VEL ex DB3YZ. 👍🏻🇫🇷

[@paulsmeltzer4414]

Great video, but what makes a capacitor lossy? He shows a chart that explains how capacitance influences radiated total, but what is it about "any old valve capacitor" versus a vacuum tube capacitor that makes such a big difference? Are old air variable capacitors just too crusty and corroded for RF? I just didn't see where this myth was busted.

[@uploadJ]

A search for "VK4AMZ loop" will yield his experience with doorknob caps, which are lossy. I use 4 ft lengths of 1 7/8" Heliax as 100pf caps in a design and those are about as low loss as one can get besides air variables.

[@thomasmaughan4798]

"any old valve capacitor" has wipers. That is to say, the rotating plates have electrical contact through wipers and those delicate little wipers are not designed for the 20 amps or more of RF that will be circulating in the loop. A good capacitor for this is called a butterfly capacitor; no "wipers". Such a capacitor can handle enormous current. Also, the voltage is going to be pretty high. A 100 watt transmitter will produce anywhere from 1000 to 4000 volts on the capacitor and remarkably high current.

[@thomasmaughan4798]

A conventional air-spaced dual gang variable capacitor can be used. Ignore the rotor (mostly). Connect one end of the loop to one of the stators and the other end of the loop to the other stator. The shaft that joins the two rotors then conducts the RF current and is effectively a butterfly capacitor. Also, it doubles the voltage rating of the capacitor.

[@reedreamer9518]

This was a very good presentation. But I've been studying and building HF transmitting magnetic loop antennas for about 6 years and I've never heard any of these myths.

[@aeron-mw7ofs]

Very interesting, cheers Hayden 🍻👍

[@HamRadioDX]

Thanks Aeron!

[@ripping]

wish you understood microphones as much as you do mag loops !

[@HamRadioDX]

Ever experienced technical difficulties live-streaming before?

[@lyingcat9022]

@@HamRadioDXyup! Murphy is a real SoB sometimes. I’ve done live demos many times and you will think you have everything working before you start the presentation but then out of nowhere something breaks and it’s never easy to fix while mid presentation. So you just make do.

[@largestache]

The tuner probably didn't have enough capacitance to tune that long of a wire on 10m. 50 feet is way longer than the approx 17 feet that would be a half wave on 10m.

[@thomasmaughan4798]

"The Truth About" I am automatically suspicious of any KZbin video that declares itself "The Truth About..." 2:55 Already an error. The mag loop antenna couples with the incoming magnetic field, not the electric field (as a receiver) and as transmitter, excites the magnetic field. 9:30 Misunderstanding the nature of the solenoid. Of course the current is uniform around the loop and that creates a strong magnetic field through the center of the loop.

[@Swede_4_DJT]

Fire the soundguy!!!!!

[@xamesm]

Should be good for NVIS in suburban/urban areas.

[@uploadJ]

I work the 160 m evening net on 1900 kHz from Texas given the low radiation angle from a QW loop on 160 meters from a city lot in Texas ... I have trouble hearing those stations with low dipoles though, because, they do not have that low rad angle ... a remote receiver SDR helps in that case!

[@victorcharlie7491]

My flux capacitor is resonating over the like button, great info tnx bro, I like it.

[@HamRadioDX]

No problem 👍

[@ldrigg1]

I found this style of humor during the presentation to be childish. Just my opinion. Still a very good technical presentation overall. I gave a thumbs up anyway.

[@HamRadioDX]

Maybe you don't understand Australian humor?

[@davidharmer9398]

Interesting... you have not considered skin effect of conductors.. this changes calculations dramatically.. low omicron resistance is of course good but skin effect dominates.

[@Migsterification]

The calculator he used does consider the skin effect of conductors.

[@MINI-4X4-RADIO]

Magnetic Loops are the absolute "Dog Bollocks" The only issue is the Very High Q Overcome with Stepper Motor controlled "C" with CAT Control

[@gabrielsansar6187]

audio recorded on a potatoe.. watch out for the loud bursts.. ironic cant get even average audio in the same room but the talk is on audio broadcast globally....

[@HamRadioDX]

Boohoo

[@gabrielsansar6187]

@@HamRadioDX do better

[@HamRadioDX]

@@gabrielsansar6187 Or you could just not watch, that might be a good idea...see ya!

[@gabrielsansar6187]

@@HamRadioDX i can watch i just couldn`t hear - 20 diff volume levels and cut outs... i`ll send u a new potatoe to record the next one

[@Bond2025]

What is Q ? No one has ever been able to explain this, but all talk about it.

[@liesofgasandpilesofshoes]

Q is resonance. Like how a good knife goes tiiiiing when you flick it or a bell rings. It makes tuning ever so sharp. Hard to tune but amazing performance. Low q is flat, dull easy tune and not great on air

[@Soupie62]

Potentially interesting, but over an hour long = pass. Is there a summary / abbreviated version somewhere?

[@HamRadioDX]

Nope. Watch it at 2x speed, that'll reduce it down for you

[@uploadJ]

Oh brother ... another op who has never in his life used a QW (1/4 WL) circumference loop in his life. Oh well, continue to tell yourself its an "STL" and be 'very afraid' to use one. Meanwhile, I'll enjoy mine on 160, 80 and 40 meters.

[@HamRadioDX]

Have fun champ

[@uploadJ]

@@HamRadioDX Yes ... the model equation is wrong. We have been thru this on QRZ forum a few years back. The nice things is, today, we have antenna analyzers with which we can test ANY theory of this type, we don't have to just accept repeated error propagated forward time and time again ...

[@erwe1054]

@@uploadJ Почему бы просто не собрать петлю и не измерить ток с помощью инструмента. Но они просто используют формулы и насмехаются над этим

[@uploadJ]

@@erwe1054 re: "Why not just build a loop and " Yes, and, what do you think I did? Look up callsign G0CWT and see his measurements and tests. It is where I started. I am working across US right now on 160meter band on WSPR mode.

[@fm71450]

Wow! Mean, snarky comments! Sorry that you have to experience poor manners.

[@HamRadioDX]

I have to put up with it all the time on here

[@ianwalker3922]

You would have thought some one in to radio would sort out (sound) in vidio before they put anything live on hear... 90 percent for effort better luck next time buddy 👍

[@HamRadioDX]

Because you've never had technical issues before? Guess not...

[@kirkfitis8038]

terrible audio

[@ferrytadema2424]

Uhm eh eh 72 minutes.

[@99corncob]

Terrible audio drove me away in 3 minutes.

[@chromexfz0991]

😂

[@NShellhopper]

It got better...but not much.