HAM RADIO: Twin Capacitor Mag-Loop Works on 40M to 80M
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- Опубліковано 30 бер 2021
- On my continuing dive into the magnetic loop I try to increase the range and efficiency by using Twin Capacitors, one to select the band the other to tune within that band. Will it work or will it fail, join me and let's see.
Enjoy
I do hope you enjoy it and subscribe for more..
Many thanks
Mike - M0MSN
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Brilliant material!
This continues to be a fascinating project. Thank you for sharing you progress with us.
Hope spring is just around the corner for you.
73
Spring yes I hope so! and many thanks
Brilliant. great job on the Mag Loop and capacitors!.
Thanks Peter
Good to follow the progress here and see the developments as they happen.
Nice job with the engineering again Mike. Great results.....cheers
Thanks 👍 Roly. I have to keep trying different things.
Thank you Mike!!
Great info. thanks.
With the arcing caps.in the garden and shouts of "its alive!" from kitchen the neighbours must worry.....73
Yes, exactly
Amazing results! Now you’ve got me rethinking the stepper driver for multiple caps. Looking forward to the Russian pencil (pneumatic) video. Sharp Q my friend!!
Ha, funny because I have just replaced the twin with a large single to play with step motors...............
i love the idea of hydrolics to adjust !!!
I've watched all your videos on magnetic loops and capacitors and this one was great. Thank you for showing the difference that using the air variable cap can make compared to the trombones, I haven't been able to find an objective comparison between cap types like this anywhere else.
I'm going to see if I can get two air caps for my loop now and switch between using them in series and parallel for 80 and 40 meters.
Glad to help, thanks Nicholas.
Mike I was going to try this a few weeks ago after I made the bikewheel loop. Still going to at some point. Great video as always
Go for it!
Great project 👍👏👏
Thanks 👍
I really like your home brew variable caps . The use of glue is something I wouldn't do but its a solution,
The trombone cap worked well so maybe it would have been better to keep it and add the other variable cap below the loop and shield the servo assembly with a nice tin can or similar. The performance is outstanding I'm building one and I'm thinking a tunable loop reflector and a director. So much food for thought a great video.
Great idea, good work! 73 from Russia! R2SCM.
Thank you! Cheers!
Very interesting indeed! I saw somebody else singing the praises of that blokes figure '8' Loop, and I'd be very very interested to see how it's put together, he mentioned something about direct coupling for example which got me intrigued... Could be a very interesting video series.
Yes but as I have no idea how he has done it I will have to start over. all fun :)
@@mike-M0MSN yeah I realise I wonder if he is willing to spill the beans on what he did. He mentions a couple of Tesla patents on his qrz as I recall.
I enjoyed watching your video, very informative. I was wondering ( and I think many others might also be thinking, or wondering the same thing), what other bands you might be able to work with this antenna in this video, besides just 40 and 80 meters? How many bands does this antenna work on, if not transmitting, but at least receives.
Great point! it was only made for 40/80 meters but with a little help you could get 60 and 75M
Great work Mike. Can't wait until you start bending copper tubing into a figure 8. Then try making two figure 8's in a four leaf clover pattern. BTW my 80m coil for my EFHW is still going strong. Thanks for the idea. 73 Joe
That would be cool,
Mike is it possible to build a double mag loop for the 27 Meg thanks
Still looking good 👍🏻
Me or the loop?
@@mike-M0MSN Ha Ha, you decide....😁
Love your videos. I am hopeless with the DIY approach (just ask Mrs R, putting up a shelf is a major challenge). So I went with a Ciro Stealth Magnetic Loop, quite an investment for me, but worth it. I am really impressed with Magnetic Loop antenna performance, mine just sits on the grass. Low noise, and listening to the US and Europe. Only on 10W currently but it is getting to Italy. Still scratching my head re the physics lol. Anyway, much appreciate your channel. Mark. M7MSR.
Cheers Mark, Ciro Stealth Magnetic Loop nice. :)
The physics: All electromagnetic waves have two components, an electric field and a magnetic field. Most antennas sense the electric field (voltage) which is polarized orthogonally in space from the magnetic field. Think of a vertical antenna as one plate of a capacitor and the receiving antenna as the other plate. Exciting the transmit antenna creates a voltage gradient in space expanding at the speed of light, and the gradient exists along the direction of travel but it *also* exists as a gradient in the same orientation as the antenna, namely vertical at the point of origin. It might not be vertical at the receiving end because of the shape of Earth and the ionosphere can rotate the polarization but that's a different topic.
But at the *same time* you insert current into the antenna, the fact of a current in a conductor creates magnetism and it also radiates at the speed of light in a donut/toroid shape and its polarization is 90 degrees from the electric, or in this case, horizontal.
Interestingly, you can maximize the electric field and in a vertical antenna, your highest voltage is at the tip highest above Earth. Maximum magnetism is at the feed point so that's why verticals aren't designed to interact with the magnetic field. But it's there!
A loop antenna is designed to interact with the magnetic field. It is basically a solenoid and as such makes a BIG difference how big is the loop. When the loop is 1/2 wave it's just a folded dipole basically and maximum strength is through the axis perpendicular to the plane of the loop. But miniature loops, which is what people usually mean by one of these things, less than 1/4 wavelength around the circumference, receive best "edge-on" to the arriving signal and the magnetism will be perpendicular to the loop. That is to say, if the loop is standing upright which is common, the magnetic field will be horizontal, and that's important because the horizontal magnetic field has not interacted with Earth. The wavelength is likely MUCH longer than your antenna above Earth but that's okay because the waves are sideways or horizonal and the waves thus do not interact (much) with Earth.
And that is why a small loop antenna can be operated much closer to the ground as compared to a dipole.
Vertical antennas generally need to be ON the ground because they interact with the Earth; the earth becomes part of the antenna system. But not with a small loop antenna.
Because magnetism is directly associated with current, you seek to maximize current. Resistance is very bad and that is why you see these antennas made with copper pipe. Thin wall is fine; "skin effect" means the current is confined to a few microns at the surface. You also use "butterfly" capacitors so that this current does not cross a wiper or sliding contact. The actual current can be substantial, 20 amps or more in the loop, and the voltage at the capacitor can be very high, 2000 volts or so for a 100 watt transmitter.
Much is said of the immunity to nearby electric field noise. Static electric discharges have huge impact on conventional antennas and receivers; lots of electric field, almost no magnetic field since there's very little current. Consequently, mag-loop antennas tend to ignore nearby electric field disturbances and you can "null" a particularly nasty nearby source by simply pointing the donut hole in its direction.
Because of the sharp tuning, it also eliminates powerful transmitters interference on nearby or even distance frequencies. I live near an AM radio broadcast antenna; tuning directly to the transmitter frequency I get an S9, which is nice, but if it wasn't for the loop antenna that nearby transmitter would probably wipe out the front end of the receiver on all frequencies. Think of it as a "pre-selector".
Being able to remotely and conveniently tune this kind of antenna is something I am still working on. They require frequent tuning and the lower the frequency (80 meters for instance) the sharper they seem to be.
@@thomasmaughan4798 cheers for that !! Will need to read a couple more times but basically get it. There is also a substantial paper by someone (you ?!?) which I read online, cannot find reference right now. But it goes into significant detail too. But what I can understand is the results. S1 Noise, compared to significantly more with my 5/8 vertical. Works of the grass (care needed to keep kids away!!). Working from UK into Europe no problem on 40 and 10m band).
@@markramsay6399 I have the same experience with noise, particularly atmospherics and utility poles. The mag-loop has much less noise which can be tremendous in the lower frequencies.
Absolutely useful video, thanks for sharing. Is it possible to soak this variable capacitor in transformer oil?
Yes, absolutely
Thank you.
Good result! When the cap was arcing over, could you detect the problem on the radio, or was it purly visual? Also, that figure 8 is intriguing...
Yes that is what alerted me ( the SWR meter was jumping around )
Is there a commercially available capacitor that can handle 100w on 80m? I have a home brew magnetic loop I was given but is not resonant on anything so think the capacitor is stuffed - so looking for one to buy… unless you can make me one to buy off you… Thanks. Dan
As an assistant junior farm hand I find this fascinating. And I thought milking cows was high tech.
Thanks Ade, on point as always. :)
@@mike-M0MSN The great thing about mag loops is their ability to pull signals out of mud and make them loud. I hope your new alteration adds a new dimension to the receive. Keep up the good work. Cheers.
Great as always. Still it,would be nice if you could do a comparison: "3D Print: PLA/PETG/ABS etc. In terms of "start capacitiy". Why?: Well for those of us, who live in a "city" environment, one wants to cover as much bands as possible. And fairly often you are loosing the higher bands by getting the resonant circuit off a few pF.
Great suggestion! and when I get some more PETG I will do it. :)
Ideally you have one loop for each band. A two-turn loop exists for space convenience but you lose a LOT of signal. It might not impact transmit that much but can sure make a difference on receive. Using a lot of capacitance to bring the antenna into resonance works, but less capacitance and more loop will produce better results, generally speaking. The idea, particularly on receive, is to intercept as many magnetic lines of force as possible. Circular is better than square (maximum area inside the loop).
In other words, a loop that works wonderfully well on 10 meters will barely work on 40 and probably cannot be tuned down to 80. Conversely, a loop that works well on 40 probably won't even reach 20, never mind 15 or 10, even with minimum capacitance. There's just too much loop.
Swapping loops is a nuisance so I tend not to do it often.
Hi. May I request you to share the min and max pf values for both the capacitors. I have made a dual loop - 24ft total length. Get a flat response from 5.5 to 8.5 mhz. But after adding an additional capacitor don't see a similar response ar 80m. Your inputs will be of great help. Thanks and 73
Both capacitors are 15 - 120pF, you can get a lower SWR on 80M by moving the coupling loop away or turning it into the loop (around the pole).
Great video Mike de 2e0ree
Cheers Andy
In the States, we call that "ground braid".
Are you still using mag loops? My dipole on 40 meter band a little lower then 1/4 wave up in the air has 2 s points in excellent and txt over my mag loop. My mag loop is 5/8 heliax 6 meter in circumference twin loop home made capacitor inspired by yours truly. About 50% efficient I experimented at only 6 feet up. Maybe too low to the ground maybe it need to be more efficient. The capacitor I made couldn't handle more then 70 watts pep on ssb. I'm struggling to txt dx outside Australia, just wondering whitch way to go about it🤔👍
One of the biggest issues with mag loops is the TX power for high power you need to use vacuum tube capacitors or larger spaces between the plates, also it is not a replacement antenna, you will find some signals are simply better on a dipole yet if you tune your loop carefully it will receive signals that get lost in the noise of a dipole…. Have fun
Would this idea work for a 40 to 15 Magnetic Loop to work on 60 meters?
Yes but the efficacy will be poor
Good morning Mike! So the original air variable capacitor connected the large elements together and you ran the 2nd capacitor in parallel with the 1st one?
I like this man. What you get for the very small space taken up is amazing!
What did you have in the yellow/green tubes?
I assume they were pre tuned caps that you could switch on / off to tune to the different bands?
That is correct
Much like a gameshow I'm wondering: " Do I choose your loop behind door number 1? door number 2? ... or... wait to see your figure 8 behind number 3? ... I'll wait to see how the figure 8 turns out. Nice video 👌
May be some time but I will get there. :)
3D print a large diameter knob for the MFJ analyser to make fine tuning easier.
good idea
Whats the power handling of this?
now, around 150Watts
Can you fill the capacitor with dielectric liquid?
you could.
Impressive. As a new radio amateur I really enjoy homebrew antenna projects.
Great to hear!
Me to David. All my antennas are home brewed. My 2 meter/70cm is a "J" pole made out of copper pipe. 73 Joe
@@Joe-KN4IFI I certainly find it interesting. Made a simple coax magnetic loop antenna, really good fun....
Hi Mike,
You can control the yellow capacitor with two RC servos that are modified to run a full 360° and connect them with only two wires. They become a master and slave. You spin the shaft of one servo and the other follows at the same speed. I have done the mod to two servos about 5 years ago and it does work. You could use cat5 cable and connect together two pairs to increase the length between the servos. I can not find a single video that shows the procedure, but have two links that show making the 360° mod and another showing the two wire mod. You can use the system to control the yellow capacitor from within the house without using any other electronics. Stay safe. Hope this helps. 73 WJ3U
Two wire mod ua-cam.com/video/BO71jNzbr_4/v-deo.html
360° rotation mod ua-cam.com/video/jSFGBqhqvfk/v-deo.html
Thanks Don, great idea there many thanks.
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