The Truth About Magnetic Loop Antennas - MYTH BUSTING!
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- Опубліковано 4 кві 2023
- 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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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.
The AGC pumping on the audio is really hard to listen to. The volume is all over the place.
I'm with you, friend. I turned it off because I couldn't handle having the volume up all the way on the computer, to hear the low audio, then it BLASTING back in every now and then. :( Was really interesting in the Mag Loop, but not at the cost of my hearing. 73
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.
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.
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.
Was the audio for this talk recorded with a potato?
Excellent presentation !!! Thank you 🙂
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.
Such as?
@@johnratcliffe6438yes agreed, please tell us if you know. Do you have any references to point us to?
I really appreciate the presenter's sense of humor!
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?
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.
I used pexal monoband loops for pedestrian mobile many years. Transatlantic on 1w often. Build high q
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?
wish you understood microphones as much as you do mag loops !
Ever experienced technical difficulties live-streaming before?
@@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.
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.
Always considered getting a loop, perhaps the Italian Commercial option, Midi Loop.
I wholly disagree with the definition of the STL as being
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
Very interesting, cheers Hayden 🍻👍
Thanks Aeron!
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.
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.
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.
@@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.
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.
Your the man I'm Justin as well I use all your stuff and I run a LFAQ 27mhz b ast
What software did VK5KLT use for that variable graph?
It's a web page. It appears to be javascript.
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.
Hi all
To overcame the cap tuning issues on low power.
You can use aluminum tubing formed inside some electrical PVC pipe and and slid it in the PVC and use silicone spray as it going inside.
And once inside carefully form a 1200 mm circle size loop with 300mm aluminum ends poking out.(A bit of huffing and puffing.)
Then drill 2 holes opposite each other on one end so you could tie some stainless steel wire and gently pulled the aluminum out of the formed loop.(huff and puff)
It comes out in a big circle and is slippery (a bit of hard pulling and tugging and it slowly pulled out of the aluminum tube to create a perfect circle).
Then strip a length of RG 213 @ 900MM and the inner insulation and core then slide it back and forth to tune from around 20 to 10 meters.
To stop flash over use some inner sheath 2x 40mm with out any inner conductor and hot melt glue to fill the internal length of the 40mm insulation holes.
Use a heat gun to make a bond to the inner center conductor end 900mm and carefully melt the end 40mm lengths and bond them both together and trim with a Stanley knife.
Now insulate the bond of the insulation sleeve 50mm over the bond you made, with heat shrink tubing could use with insulating glue inside and you have made a high voltage sleeve insulator.( may be a bit tight in the loop)
Phew! Now what you end up with is about 900 mm of inner coax that that travels from one side of the loop to the other insulated at the ends with 40mm of insulation filled with clear hot melt glue where the center conductor was.
As you now have say a 100 mm space between the ends of the aluminum you can slide the center coax backwards and forwards on the aluminum tube to tune the bands, and mark on the center insulation with a marker pen for the lowest SWR on the band you want to work.
I have powered up my loop till flashover about 50 watts max ---so 5 to 20 watts will be safe(you could build a high voltage using a ignition coil) to test your cap slider.
The inside dia of the aluminum is determined by the outside dia if the inner insulation plus heat shrink. the length of PVC pipe thin wall communication 4 meters.
I have considered using a small motor an making a system to open and close the gap between the two ends of the loop to tune it ( expand and contract the loop) from 300mm to 25 mm.
An other idea is to cut the bottom of the loop fixed to aluminum "c channel" and make the slider move backward and forwards though the openings of the cuts using a marlin fishing line tied to the both ends of tuning coax(lubricate) via a small motor near the "c channel".🤓
My flux capacitor is resonating over the like button, great info tnx bro, I like it.
No problem 👍
Fire the soundguy!!!!!
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.
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.
Maybe you don't understand Australian humor?
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.
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.
"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.
Interesting... you have not considered skin effect of conductors.. this changes calculations dramatically.. low omicron resistance is of course good but skin effect dominates.
The calculator he used does consider the skin effect of conductors.
Should be good for NVIS in suburban/urban areas.
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!
"The Truth About"
I am automatically suspicious of any UA-cam 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.
Magnetic Loops are the absolute "Dog Bollocks"
The only issue is the Very High Q
Overcome with Stepper Motor controlled "C" with CAT Control
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....
Boohoo
@@HamRadioDX do better
@@gabrielsansar6187 Or you could just not watch, that might be a good idea...see ya!
@@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
What is Q ? No one has ever been able to explain this, but all talk about it.
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
Q is the Quality factor of a resonant circuit. It measures how well the circuit resonates. The higher the Q, the higher the amplitude will be and the narrower the bandwidth it responds to. That means the circuit is more sensitive, and more selective.
Potentially interesting, but over an hour long = pass.
Is there a summary / abbreviated version somewhere?
Nope. Watch it at 2x speed, that'll reduce it down for you
Uhm eh eh 72 minutes.
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.
Have fun champ
@@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 ...
@@uploadJ Почему бы просто не собрать петлю и не измерить ток с помощью инструмента. Но они просто используют формулы и насмехаются над этим
@@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.
Wow! Mean, snarky comments! Sorry that you have to experience poor manners.
I have to put up with it all the time on here
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 👍
Because you've never had technical issues before? Guess not...
terrible audio
Terrible audio drove me away in 3 minutes.
😂