Building a Magnetic Loop Antenna For My Apartment, Part 2.

The only way I can get on HF in my small apartment now is using a magnetic loop antenna. Follow the build and learn more about this awesome and efficient small antenna. This one turned out pretty good :-)
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[@sderhy]

Very nice work, you should make some tests with a small loop inside .. with the same kind of wire, same BNC connector. I am sure that you will get à largest range ... with this nice dimension ! Thanks again Gil

[@RadioPrepper]

I might try thanks.

[@JimN5QL]

Common practice is to place a piece of wood between the part you are striking and the hammer! No tool marks.

[@RadioPrepper]

Definitely. I did not have any..

[@Liberty4Ever]

A hiking boot makes a pretty good improvised soft faced mallet.

[@RadioPrepper]

I'll get the real thing ;-)

[@elmarwild4755]

Gil, you could also heat up the brass a bit (so it expands slightly) and at the same time cool the copper. This should give you a bit of space to fit them together.

[@OH8STN]

Nice build Gil, congratulations 👍

[@RadioPrepper]

Thanks Julian!

[@charlieb.4273]

How about a rotary switch on the toroid to choose the number of turns. That way you can adjust on the fly to change the band. Great project. 73 Charlie KM4ZZ

[@RadioPrepper]

Thanks. I probably will try taps.

[@MrPerrey]

Gil, on the analyzer You have around 100kHz bandwidth for one point SWR increase whats almost respectable regarding Your build method. I don't think that soldering of Your Camp will make the ML eaven better rather the stabilizing and maintaining a good low resitive and durable connection. If You want to make the loop even better the use of cheap soft copper tubing (18mm diameter) is a good choice. Its easy to bent around to a nice and round circle, even by hand and some food work. That makes a very low resistance solid round loop without any solder joint between. For feeding I made the best experience with Faraday feed build by low capacity 75ohm TV cable. I found that this feed gives the best QRM attenuation for apartment operation and the best overall SWR on a 40-20m ML.

[@RadioPrepper]

Good info thanks.

[@orangmakan]

Amazing work, very interesting!

[@douglasdreger3852]

I want to make one of these optimized for 40m. Can you post a link for the capacitor? Also would you be interested in making and selling more of the brass plates? They are fabulous. How much power do you think it can manage?

[@RadioPrepper]

The plates? More than any capacitor! I found mine on EBay. No link sorry. You may contact the French site for the plates, they must have an English speaker there...

[@massoud999]

Cool, très joli B-) GL GDX 73 F4WBY de 4Z5UY

[@RadioPrepper]

Merci!

[@gaborjordan7243]

Hello, very nice and pretty effective setup. If you allow me, I would add some things. 1, after you remove the loop from your workbench, use something to avoid stress on the vacuum variable. I had one loosing vacuum. SImilar type. I do not know what was the reason, but I suspect this was the problem. I have used 2 plastic clamp and a piece of wood. Now I use a longer and larger cross section piece of wood and 6 clamps. 2, Do not use 45 degrees joints. I have used recently 22mm soft copper tube, coming in a coil, it was easy to make a 2m diameter loop for 20/40. Before, I had 15mm hard tube, marked where to bend and made a not very nice, but jointless loop. 3, what is the reason to use brass? I'm using 3mm copper sheet, your brass may be better. Also, it may be better to make it tight as you do, but FYI, when I made it tight, soilder did not get between and soldering was bad. I had to open up the hole and resolder, now it works well. You thick material may work better with direct clamping, but than do not solder it. It will not flow into. Regards, JG

[@RadioPrepper]

Thanks. They did not have copper in stock. I plan on putting a rod inside the tubes below the capacitor..

[@1958johndeere620]

O and as far as a torch, MAP gas should get you hot enough with just a standard propane torch head.

[@RadioPrepper]

That is the plan!

[@eddy4011]

Excellent all your video about magnetic loop antenna only one question.For 20 and 40 meter a can use ft240-43 or ft240-31 wish one work better thanks in advance Eddy

[@RadioPrepper]

Not sure. With a bigger diameter tube I might. I would make sure the tube is centered in the toroid.

[@eddy4011]

Radio Prepper Thanks for your answer my good friend Eddy from 🇺🇸

[@gbamck]

Nice work, Gil. Don't worry too much about the marks in the brass. It will begin to discolour soon and you'll forget about them. Loop works so that's the important bit 👍

[@RadioPrepper]

Thanks.

[@thomasmaughan4798]

Comparing antenna designs and dangers; 40 watts into a whip on the balcony of your apartment is no different than 40 watts into a magnetic loop antenna. The danger is that in a loop the high voltage is at the capacitor usually close at hand whereas in a dipole the high voltages are at the tips usually high in the air, same with a whip. There's an online calculator for how much voltage to expect. www.66pacific.com/calculators/small-transmitting-loop-antenna-calculator.aspx "FCC Guidelines for Human Exposure to Radiofrequency (RF) Electromagnetic Fields" As you can see, it is considered safe for the radio operator to be within 1 meter of a 100 watt loop operating in the 20 meter band. I'm not exactly comfortable being that close but there it is. Controlled Population Exposure for 100 watts (Distance in meters) 7.01 0.36 7.02 0.38 10.01 0.57 10.02 0.69 14.01 0.72 14.02 0.77 18.01 0.85 18.02 0.87 21.01 0.92 21.02 0.93 24.01 0.98 24.02 1.02 28.01 1.05 28.02 1.05

[@dougtaylor7724]

The down side of a loop is the narrow band width. Yours actually covers quite a large portion. Nice project.

[@wolfmonk9d]

Wow, I see antenna analyzer from Belarus and old soviet vacuum capacitor. Thet's great. But I'd like to warn about safety. The magnetic loop creates an electromagnetic field intensity proportional to the quality factor. In the case of QRP, this is still acceptable, but I would not even radiate 50 watts. 73 de R2ATO!

[@RadioPrepper]

Absolutely! I would not either!

[@thomasmaughan4798]

There's nothing particularly special about a mag loop other than high voltage at the capacitor. The idea is that if you are putting 40 watts into it, the best you can hope for is 40 watts of radiated power, and because the electric and magnetic fields both exist and are orthogonal, all antennas look the same once you get a wavelength or so away from the antenna. So if you don't mind 40 watts into a whip on the balcony of your apartment, that's no different than 40 watts into a magnetic loop antenna. The danger is that in a dipole the high voltages are at the tips usually high in the air, same with a whip, the high voltage is at the tip. But in a loop, it is common to have the capacitor at the bottom and that's where the high voltage is going to be. The maximum voltage is achieved in resonance when the capacitive reactance is high (ie, small capacitance) and thus large loop for the band. There's an online calculator for how much voltage to expect. www.66pacific.com/calculators/small-transmitting-loop-antenna-calculator.aspx "FCC Guidelines for Human Exposure to Radiofrequency (RF) Electromagnetic Fields" As you can see, it is considered safe for the radio operator to be within 1 meter of a 100 watt loop operating in the 20 meter band. I'm not exactly comfortable being that close but there it is. Controlled Population Exposure for 100 watts (Distance in meters) 7.01 0.36 7.02 0.38 10.01 0.57 10.02 0.69 14.01 0.72 14.02 0.77 18.01 0.85 18.02 0.87 21.01 0.92 21.02 0.93 24.01 0.98 24.02 1.02 28.01 1.05 28.02 1.05

[@caulktel]

Great video Gil, it would be interesting if you could find a way to switch different inductor values in to make it more efficient on other bands.

[@RadioPrepper]

Yes, thinking about taps...

[@yurimodin7333]

AWESOME project......heads up you don't want to force it with an antenna tuner because it can damage the vacuum capacitor.

[@RadioPrepper]

Good to know thanks!

[@MeineVideokasetten]

Hahaha. I enjoyed the part you build the antenna. Very funny! Nice job!

[@DanielVergeles]

Hello, can you help me? It's about your calculator, what is "Quality Factor (Q)"?? why it's being bigger if "Length of Conductor" making smaller?

[@RadioPrepper]

AsI understand it, it is how selective a circuit is. A thinner wire will have less bandwidth, higher Q, more selective.

[@douglasdreger3852]

So I have a vacuum variable capacitor now, and I have 0.5 in copper tube on the way. A question I have is what is the benefit of feeding the loop as you did with a torroid vs a smaller feed loop? I like the neatness of your solution and the simplicity of tuning by the number of turns. On the other hand I plan to put as much as 50 watts through it digitally or CW and 100 ssb so I wonder if the choice of feed mechanism matters in that case?

[@RadioPrepper]

In that case I would use the inner loop method..

[@davidj.wilcox6053]

Gil, You are my kind of guy/ham. I can see me doing everything you are doing, including the mistakes. Isn’t this fun! Dave K8WPE

[@RadioPrepper]

And expensive, LOL.

[@douglasdreger3852]

I was wondering if you have experimented with torroid mixture to get better performance on 40m? Some reading I have done suggests that mix 31 would be better on 40m.

[@RadioPrepper]

Only 43... Maybe I'll try a 31, thanks.

[@no5x937]

Next time try a circular loop. The octagon with 8 45 deg elbows adds 16 small series resistances which will greatly effect your efficiencies at all frequencies.

[@RadioPrepper]

True.

[@CripSkillz]

Gotta do what you gotta do to get the job done!

[@JohnDuncan0347]

Thanks I always enjoy your videos.

[@vr2zgr]

Very well made loop antenna

[@vincei4252]

2:15 Yes, I did actually cringe. Yikes. Good deal anyhow. Three thumbs up!

[@petarpetrov6388]

Great! I build MKARS80, 80m QRP SSB toy. Work exelent. This was in Canada where I had 1 bedroom apt. So I started with a piece of thick copper wire and two pieces of kitchen foil between the pages of a magazine as capacitor. And it worked! Later I just used the first air variable capacitor I found. Your antenna shuld be capable of 100W power... Best Regards from Bulgaria de VE7BUL

[@RadioPrepper]

Great improvised capacitor!

[@KL3NCH]

A simply great video! I had a Jennings VVC for 30-odd years and I broke it last year while making my loop, so I ended up with a Rooskie one too like you. I couldn't figure out a way to connect to those electrodes for decades. In the end, I cut two "L" shaped pieces of 12mm wide copper sheet made from an old copper water cylinder, and I rolled one leg around each electrode and clamped it with a "Jubilee" clip. The other leg connected to the loop (LDF5-50 in my loop). I hope that the steel railings on your terrace didn't impact significantly on your initial experiments at tuning? Another superb video Gil. TY.

[@RadioPrepper]

Thanks, no effect from the rail apparently...

[@StreakyP]

A coil of soft annealed copper pipe used for air-cond (or "big bore" hardline Co-ax like LDF5-50) can allow the loop to be simply formed from a single piece of copper which is both easier than having to construct the octagon plus it does away with the loss from 16 solder connections so helps efficiency so can be worth considering too. For QRP TX use a "receiving grade" dual gang split-stator air variable cap is generally good enough for 2 band coverage up to 20W (and is about $100 cheaper). Vacuum Variables are beautiful but just allow you to drive further LF into the less efficient areas of any particular loops performance. Yours is a beautifully constructed loop, but for those will less access to machining and VVC it should be remembered that the right junk-box air-variable capacitor and an unbroken loop can offer similar on-air performance. For a mag-loop the highest performance is always for the highest band it resonates on (with the lowest capacitance). For ultimate performance don't go for VVC (jack of more bands but master of few).. if you do need the max performance then go for single band operation with a smidgen under a quarter wave loop circumference.

[@RadioPrepper]

Definitely, or a thick stiff coax for the loop...

[@arniep740]

Merci for this video. I like how real it is. I am in the USA and wonder how I would find someone to fabricate a vacuum cap clamp like you did. What did you search for in order to find a fabricator? Also, are you willing to share you 3d print and design files for that clamp? Tnx es 73 de Arnie W8DU

[@RadioPrepper]

Sure, it's on Thingiverse, search for Radio Prepper. To have one made search for laser cutting or water-jet cutting...

[@charleswoods2996]

I don't have the space or means to build an antenna so I went with a Chameleon CHA MIL HYBRID and put a 102-inch steel whip that of course with a tuner works great and mounted to my balcony railing with ease and convenience. I'm hoping to talk Chameleon Antenna to build a matcher that will take full legal limit, told them that I'd be happy to buy it.

[@RadioPrepper]

It's a good antenna. Anything more than the proverbial 100W is an absolute waste of power and money. I'd even be tempted to say 30W max, but since most radios come with 100W...

[@drnv150]

All you need to remotely tune your mag loop using a cable and motor, is to scrap an old printer motor, they have not only the bidirectional DC motor, but usually they have a belt and gear to give it more torque, for the variable vacuum cap. The other side of the cable in a small can, I put a 1k ohm 3- 5 watt potentiometer and a 3 position DPDT switch, to control the direction. Magnetic loops are amazing for their small size, they are worth the time to build.

[@RadioPrepper]

Thanks, I might...

[@1958johndeere620]

Throw a tag line across the street and have the neighbor tie it off for a endfed. LOL. cool build. I wish I was better at cw, but have a hard time wanting to practice. My fault. I can't get better if I don't put in the time.

[@RadioPrepper]

I'd like to throw a wire out, but a bit risky.. Maybe at night...

[@roogalater]

The standard coupling loop method (about 1/5th circumference of main loop) would give a better SWR, I think. I've tried shunt feeds and the coupling loop always works best for me. A 1 metre diameter loop matches very well from 60 to 12 metres with a 365 pF capacitor. 73 de G0IFI

[@RadioPrepper]

I might try it! Thanks.

[@vk6op648]

Hi Gil, really enjoyed this project. If you're intent on having other bands on there just tap your inductor and switch between the turns. I did this with the g4fon and it works well. Cheers!

[@RadioPrepper]

Thanks Marc, yes, that's the plan!

[@nelxonmiranda]

Where’s the finished pic?

[@MyTube4Utoo]

A very interesting, informative, and entertaining pair of videos. Except for the cringe-worthy assault on the brass. *lol* Thank you Gil-Git. :-)

[@RadioPrepper]

Thanks, there is that...

[@TrystansWorkbench]

I admire your work, and sharing your experience so honestly in how you made it, with the mistakes that many of us (me too) would do. Not all tools are at hand, and I think it's great that you take the great amateur radio spirit forward with your experiments. I use a homebrew magloop on HF too. Thank you for your videos I find them very useful.

[@RadioPrepper]

Thank you!

[@USXPOP]

Good work for small balcony working space. Get a hotter torch and re-sweat all joints and the brass clamps too. What will be the highest power you plan to use, or are you staying with QRP? A good bit of work.

[@RadioPrepper]

Thank you. I will. Max 30W with the PRC-320.

[@StarlancerAstro]

Try a coupling loop, I find it to be better then a toroid for coupling. You may get far better results on 40 meters.

[@RadioPrepper]

I might try it...

[@Bro-f3h]

Good build Gil, I will be an apartment dweller, I'm going to first try using the gutters as an antenna then I will have to make a magnetic loop, I hope something goes right.

[@RadioPrepper]

The loop works awesomely from 15 to 60m, but you need to retune almost every time you change frequency..

[@stephenjones9153]

Very Nice loop Gil. Brilliant that you are now able to work 20Mtrs and 40Mtrs from home and if it rains the vacuum capacitor should still work much better than open variable capacitor. It's a shame they are so expensive. Good luck with the loop.

[@RadioPrepper]

Thanks. I think it was worth it. The capacitor has 22 turns; much easier to tune.

[@stevesus3295]

A toroidal transformer needs to have multiple taps, one for each band. My mag loop has a motorized selector switch.

[@RadioPrepper]

That's the plan!

[@ElektroLUDIKITS]

Vu comment les tubes sont enfoncés en force dans les pièces, les contacts électriques et mécaniques sont largement suffisant, tu n'as pas besoin de les braser.

[@RadioPrepper]

Sans doute...

[@JohnTarbox]

Great build! You did an excellent job, it should be very efficient. Will you be taking it out to the field to try it there? DE WA1KLI

[@RadioPrepper]

Probably not, it won't fit in my truck..

[@yvesperrey3297]

Hi Gil, Congrats for this project, and thank you for sharing your experience and tips building this loop antenna in this video! Glad to know the company's web site link that is able to cut such a brass or copper thickness here in France. 73 Yves F5PUY.

[@RadioPrepper]

Merci Yves.

[@qrpradiolistner7232]

Congratulations ... you are a true perfectionist ... 73. Giuseppe iz0gzw qrp.

[@RadioPrepper]

Than you :-)

[@clifffiftytwo]

Do you plan to experiment with a loop feed as well? I wonder if that would give different bandwidth - wider or narrower?

[@RadioPrepper]

Maybe, we'll see... I'll try taps on the toroid maybe..

[@pathopkins4500]

Great job Gil on the HF loop for the apartment ( I'm probably will be making one as well SOON as I can get some $$$ and time the next few weeks =) I think I live in a tropical zone now ??? Rain, storms, flooding .....oh my :-))) I have forgot yet .... if it will stop raining and flooding around here /-)

[@pathopkins4500]

The river valley is not looking so good now /-( Hills are not to far away too /-)

[@RadioPrepper]

Sound like you need a boat rather than an antenna ;-) Maritime mobile!

[@pathopkins4500]

@@RadioPrepper Yes; it is looking like a move is needed and maybe to a place I can have a place to setup an antenna outside as well =)

[@mostlypostie1]

Great work Gil! I would love to see if changing the troriod out for a single larger loop would provide greater tuning range.

[@RadioPrepper]

That would be interesting...

[@MrPerrey]

Of cause, a wire feed increase the low SWR tuning range a lot, specially when using a Faraday feed with 75ohm low capacitance coax. Further on I observed with the Faraday feed a considerable attenuation of QRM pickup. This is very good for apartment operation!!!

[@RadioPrepper]

What do you call a Faraday feed?

[@MrPerrey]

@@RadioPrepper : Goto www.nonstopsystems.com/radio/frank_radio_antenna_magloop.htm This site is a huge source of any aspect of ML Antennas. I made good feed experience with option D of Figure 24B. For good ML calculation I use DG0KW Magnet-Loop-Antennen-Rechner: Its free and download here: www.dl0hst.de/magnetlooprechner.htm Choose language (French for You) and go to ? Help. There is a fine description of farradey coupeling called also "shiled coupling" I found it good as it is broadband and picks up less QRM.

[@cwguy8960]

I've been looking forward to seeing you make contacts on the loop! I have built two of them over the years, and had reasonably good success from a condo balcony. As you said, it's good to have HF at home!! Congrats!

[@RadioPrepper]

Thanks. There will be more videos about it..

[@Testequip]

Have you been able to use this loop for DX work?

[@RadioPrepper]

All of Europe from here, just not trans-continental yet, but I did on my previous loop.

[@Testequip]

@@RadioPrepper Wonderful! I'm out in South Africa. Roughly 20km west of Johannesburg. I moved into a complex and I'm currently looking for ideas on magnetic loops for the 40 and 20m bands.

[@RadioPrepper]

The same would definitely work. 5m perimeter..

[@andrzejpl9897]

👍

[@mthomas6]

Thats how we learn, by our mistakes, and then we move on and then upgrade. love the videos keep them coming.

[@RadioPrepper]

Will do, thanks.

[@denniswilliams8747]

Would larger tube get a broader/ flatter SWR? THanks

[@RadioPrepper]

Probably a little yes.

[@LeeLocke]

400 likes congrats😃73 Lee

[@RadioPrepper]

Wow yes! More contacts on the loop tonight, 30m..

[@thomasmangeot1203]

Salut tu pourra faire le même type de vidéo mais sur la fabrication d'une antenne 446mhz

[@RadioPrepper]

Bonsoir. Désolé, mais c'est illégal. Je ne posterais donc pas de design pour 446MHz.

[@JonathanAdami]

Awesome work! Really enjoyed watching you do this! I was thinking of going down the magloop route for home too. But with a coaxial cable as capacitance and a gamma match, any opinion on the topic that I could use before making all the mistakes? :D

[@RadioPrepper]

The coax works great, but not sure a gamma match still makes it a mag loop..

[@JonathanAdami]

@@RadioPrepper aha! I'm interested as to why it wouldn't be a mag loop then? (Genuine question) From what I gathered, most people feed the loop with an internal smaller loop, only a small arc of that interior loop will interact with the main loop and the gamma match is just that same interior loop spread out so 100% of it is used but I might be completely off there :/ Admittedly I should probably take a book and study on the topic :/

[@thomasmaughan4798]

@@RadioPrepper "but not sure a gamma match still makes it a mag loop." What makes a mag loop is that the antenna is part of a tank circuit with high circulating current and corresponding high voltage on the capacitor. using a gamma match, as I do, through a variable capacitor makes it considerably easier to get 1:1 SWR at any frequency the loop is capable of tuning. It is still magnetically couple if you think about it. Instead of a true transformer magnetic coupling, it is an "autotransformer" magnetic coupling. The RF from the radio transmitter flows into the tank through a matching capacitor and creates a current in a small portion of the loop. It is that current that produces a magnetic field that "excites" the loop into operation. The fact that the exciter current is physically the same wire as the antenna does not change its operation in the slightest, any more than using a tapped transformer changes the behavior of stepping up or stepping down of the transformer. Where it might matter is that inductive coupling has no electrical connection to the loop; where a gamma match ties the loop to the radio at DC usually the ground. This is probably irrelevant at radio frequency but at DC will have the effect of grounding the loop and maybe you want that and maybe you don't.

[@RadioPrepper]

Right, that makes sense..

[@Magicalmike1]

Merci beaucoup formidable! tres intressant 73s de G4IJI

[@RadioPrepper]

Merci!

[@nr3rful]

Always interesting stuff. ..tks

[@RadioPrepper]

Thanks.

[@Dread438]

Forget the toroid.. use a gamma match:)

[@RadioPrepper]

Wouldn't that make it a simple loop, not a magnetic loop?

[@Dread438]

@@RadioPrepper No everything else remains as it is.

[@ssubaihi]

Very good finish , Professional industrial finish , but it cost Time and Money yet no much efficiency

[@RadioPrepper]

When propagation will cooperate it will work very well.

[@ssubaihi]

Thank U for quick reply By the way ... in your Opinion ... How much dB's (improvement) we might get in Such (Vacuum Capacitor) VS a normal-Classic variable Capacitor ? .... keeping in the Loop circumference /loop material and thickness /Frequency of Operation (same) in comparison ??

[@RadioPrepper]

I don't think you gain anything. It just can take higher voltages.

[@MrPerrey]

@@ssubaihi - What really pays of is the low impedance connection between capacitor and loop. There any mOhm counts, independent of what type of capacitor is applied. Vacuum cap is good for high power on small dimensions, but, If You want to experiment on QRP power level You will get almost the same results with a dirt cheap mecanical Ebay cap for 10 bugs - Considering that You do all to make a LOW IMPEADANCE connection!!

[@RadioPrepper]

Sure, but I get a 22-turn capacitor that way, easy to tune..

[@davidportch8837]

Excellent project Gil...

[@RadioPrepper]

Thanks!

[@terrymac9570]

Great video Gil, try it /p

[@RadioPrepper]

It won't fit in my truck!

[@Liberty4Ever]

Another great project and another great video! This makes me want to build a magnetic loop antenna. I might make one for 20, 40 and 80 meters.. I would probably hang the vacuum variable capacitor with stranded wire to avoid stressing it mechanically. It would also be nice to have stranded wire for the toroid and be able to quickly change the number of turns to retune for different bands and have more optimal performance on each band.

[@RadioPrepper]

Yes, I will use taps. 80m would be extremely inefficient, maybe 2-3%..

[@Liberty4Ever]

@@RadioPrepper - I meant with a larger loop so it'd be more efficient on 80m. I might try using a large and fairly stiff coax for the loop with the shield shorted to the center conductor in the box that contains the tuning capacitor. A semi-rigid coax would be easier to fabricate and also more portable.

[@RadioPrepper]

Got it, but make the calculations. An efficient 80m loop would be gigantic!

[@MrPerrey]

@@RadioPrepper, of cause, BIG size! The common solution is a two turn loop and remains inefficient on 80m, but better than nothing.