Ham Radio - Magnetic loop transmitting antenna overview and details.
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- Опубліковано 25 кві 2015
- A quick rundown of a transmitting magnetic loop antenna that I built for ham radio.
Details including schematic on the control box here:
• Ham radio antennas - M...
I also built a mini loop out of junkbox parts for fun. It's 1 foot square and works really well.
• Ham Radio - Junk Box M...
Also, check out my quick and easy field day vertical.
• Ham Radio - Quick and ... - Наука та технологія
Kevin, it is gratifying to know that HAMs like you are still into DIY antennae, QRP xcvr, and new ideas rather than always just 'buy it.' Without HAMs like you, the hobby will ultimately be swallowed up by Internet SDR. Keep up the excellent videos. Even we old moldy HAMs can still learn from you young whippersnappers. 73s
Great Loop !
I use to build these back in 1993 and operated portable with home built radios. I broke a pileup to many places using these loops. Fun !!
Thank you for the excellent demo and explanation of power and swr. Now I can start building one of my own.
I'm a member of the magnetic loop ham radio group on Facebook. Good group of knowledgable people. Bruce KQ2E
I jumped into your time machine because I was building one as well. I used a capacitor out of an old full power tuner, and soldered sections of 3/4 rigid copper using 45-degree fittings. The feed is also 3/8 refrigeration tubing, like you, I got from the bottom of 40 to the top of 15 at 1:1. What a fun project.73's🎙KD9OAM
I am so happy to see hams taking on basic research like this,
Thanks for putting this on. Loops work well considering their small size. I worked a few stations in Europe with mine indoors and 5 Watts ssb/cw. I used a small motor with a gearbox bought from Maplin, now all stores closed, and D cell batteries, 3 Volts for a fast tune and one battery for a slow tune. Tune for maximum signals on receive then tune using a homebrew resistive SWR meter, transmitter never sees above 2:1 SWR but shows all SWR.
Bill, G4GHB.
GREAT VID. I LOVE THAT 1950s TABLE
Late to your video, but I have built 4 loops recently (since January 2023), and my loop conductor of choice is surplus RG-11/U. I got a "reel end" with about 175 feet of coax. I have a single-turn 52" diameter loop that covers 4.8 MHz - 22 MHz, a 52" 2-turn loop that covers 3 MHz -8 MHz and a single-turn 36" loop that covers 6 MHz - 32 MHz. I worked a station in MD from our radio club meeting on 80 meters with the 2-turn loop from inside the hall where our meetings are held. 5 watts on FT8 from indoors. A very impressive demo.
My 4th loop is based on VK3YE's Summer Loop, and uses a bicycle wheel rim, 22" diameter and 1.4" wide. It covers 17 MHz - 60 MHz. Lots of fun and getting ready to go for a big outdoor fixed loop with 20 - 30 meters of coax for a 6.t meter to 9.5 meter diameter loop. Looking for good efficiency on 160 meters, no?
73, Keith, WB2VUO here near Buffalo, NY.
Keith, did you short circuited the braid with the center conductor of the coax? 73 from py2top
@@fabiomeneghim4149 : Yes I did. Effectively, the coax became a fat "wire". The coax I used was the cable-TV version of RG-11/U, so the braid was stainless steel. I had to mechanically crimp a bullet splice to the center and braid, then solder to that. I used high-temp oven crimp splices for the transition...
de WB2VUO
Kevin just found you on youtube,It warms my heart to find people who know what they are talking about, especially with antennas. We have too many so called Elmers who work with hams that end up discouraging others from learning the truth.
+rod byam Thanks for the kind words Rod. I'm no expert! My experiments are about 45% intuition and guesswork. But I'm always happy to share what I've learned that works. Check out my other video on my field day vertical antenna. It's the best performer I've ever used in the field.
Just happened to be browsing YT and came across your interesting and informative YT video. Thanks, N8CA
great video man! I like your project
Dear Kevin! Very informative and precious video! ...I'm just about to make a comeback in the world of ham radio. Due to the lack of space I'm willing to build an M-loop. Watching your videos sure gave me some motivation, and your "tuning RF probe" is a must build!!! Thank you! 73s from Pityu YO6PNQ
Great video. Thanks for uploading.
This is the best mag loop antenna vid on youtube. Thanks.
Actually, no. Its good but there are a few others that are at least as good. Vk3ye has many videos on mag loops and Andybythesea has a few very good videos on his loop antenna with efficiency figures etc. on different bands given. Have a look, you'll learn a bit more about these interesting antennas. Fantastic if you don't have much space!
Sorry that should have been Andy Davies by the sea
that was a great job on your building the loop and also wonderful video. I did sub and thanks for helping others learn more about ham radio. thanks , Fred
Nice and simple hey? If he had a really good capacitor to put on it, that thing would be even more surprising.
Thanks for the video of your well made construction. I sm collecting inspiration to build my own and I take away a lot from here.
I just went back to see your 1st couple videos...You've really come a long ways !
Yeah, I'm almost embarrassed by the lack of quality on those old vids.
Kevin, for future copper tube bending pack sand into the copper tube. This prevents the copper tube from kinking. If you cut a 3ft plywood disc, you can bend the tube around the plywood disc. The disc can be cut into the diameter you require. Old wiring rolls may be big enough to bend the tube around. Kf2ms...
Another excellent video. I have some 1/2" flexible tubing and I think I will go that route versus the spiral you showed.
Just spent almost an hour watching other videos on mag loops after watching this one. Pretty much learned everything I needed to from this video. Great job Kevin! KI5UML
Nice job, really like the control box setup...
budleyca1 Thanks. I was kind of proud of that little box. I used a tricky bit of wiring with two relays as reversing switches, and each relay needs the other one to be off in order to operate. That way you can't press both buttons and short out your supply! I suppose someone using more modern approaches would just use a microcontroller.
Super informative great antenna
Great video. I'm disabled with a back injury. Took up HAM radio to have something to do. Hanging a wire between two tall trees is not an option for me but I think I can build a small magnetic loop with a little help. I wish I would have hung on to those tuning caps that used to be so plentiful. Thanks, Mike KE8EUI.
Hi Kevin, Thanks for your video. I am experimenting over here with making a loop, and like your ideas. I have so far had a couple of contacts with a local friend on 40m and 10m so am delighted that they work. I am now trying to make a real one rather than just an experimental one, but the fact that such small aerials can actually work interests me. Thanks again. Mike G4HLT.
Great job. Thanks very much for you video.
Excellent demo, Kevin
Thanks
John DJ0QS
great video! Thanks
This is excellent information, thank you for making the video. I'm going to build one myself, too, for the 27Mhz band.
So, how did it go?
@@ERICtheLATE Very well, I built one with copper pipe and PVC tubing
My Dad repairs, builds and modifies trumpets for fun and does a few customs per year. Copper work hardens easily. You need to anneal it to bend it easily and to keep from kinking you need to fill it with something to support it a bit. Lead is fantastic but toxic and a pain to work with. Bending alloys that melt at below the boiling point of water is next, than pitch and last is semi-frozen Murphy Oil Soap and Water.In theory you could use wet packed sand but keeping it from moving out of the way as you bend is the problem. Look at annealing copper and bending copper. Hope this helps. One of the reasons copper trumpet bells cost more is the number of annealing steps as you work it to keep it from tearing compared to 70/30 yellow brass.
Fantastic video! Well Done Kevin! K1GMM
Good stuff ! Thank you !
This is a very nice to the point and well-illustrated video. The field strength meter is a great add on. I will build one tomorrow for receiving only. In my application the narrow band width and high Q. Is exactly what I want.
Thanks for a great video. From one hosier to another 73
KA9UCN Joe
Great video, thanks.. what size pvc pipe, looks like 1/2 in.
These are nice antennas, they can be over 75% efficient, can nearly be tuned by ear, and cb radio swr tactics, and for how often we really get the chance to operate, setting up like Field Day, and putting it all away, is a real cherry on top. These are also a better alternative to setting up longwires, dipoles, and delta loops, and stressing when a lil storm runs through when you're not home.
🤣 75% is a joke I think. That antenna needs a ground plane. I would put it right under the driven loop.
Very interesting video. I liked your RF or field strength meter a lot.
BTW... The larger the tube is, the higher the Q factor, the higher the voltage on the capacitor and the smaller the bandwidth.
What a fantastic video I am currently in the process of planning the construction of one of these fantastic antennas, after seeing this mine is going to be pretty much like yours, the remote tuner will come afterwards I need to build me one of these baby's first
73s Paul M0SHZ
Thanks Paul, they're fun antennas. If you haven't seen it yet, check out my junk box magloop.
Build:
ua-cam.com/video/b9KSDvjycyw/v-deo.html
And the final design:
ua-cam.com/video/ZTsYRyEkCkQ/v-deo.html
He Kevin, thanks - this was a simplest VDO for mag loop antenna & i understood the connections very well. Do you have the soldering diagrams between the outer loop & air capacitors- where do you connect the two wires from the copper tube on the capacitors. do help me out- thanks 73 Val
Thanks for uploading. Some comments I may offer:
I would have used wide copper strips to connect the cap to the loop. All in the interest of Q-preservation (loop efficiency). Also: wood as an insulator is probably not the best idea. Wood is an organic material and will affect the Q of the loop and may also in fact be a fire hazard. Field strength meter is a good idea but I did not see any caps after the rectifiers. Without caps you will get rectified RF on the detector wires. The VSWR=2 bandwidth is a good loop-Q indicator. A wide VSWR bandwidth indicates a poor loop-Q.
Loop tuning via max. fieldstrength is pretty rough. I would always tune a loop for best VSWR. Max. fieldstrength does not necessarily imply low VSWR. 73
How critical are the measurements? If my small loop is 7.25 instead of 7.2 what happens?
I would think copper ground strap inside plastic tubing like Pex or a hulahoop would work just fine and be easier to make?
Great video. Learned a lot! I just wonder what it have taken to bring the range to ten meters (28mhz).
It's being limited by his capacitors minimum capacitance. If the loop was made smaller, that would also fix that, but efficiency would suffer more down lower. Another possibility would be to make it only a fraction less in circumference and use larger diameter tubing. These will both simultaneously raise its resonant frequency by lowering the loop inductance but the larger diameter will improve the efficiency. Sure it will get heavier, but you will get 10 meters
What mode are you using? I would think that duty cycle would be a big consideration when running RF power into this antenna. I know the manufactured loops have a much lower power rating for CW and especially digital modes that have a 100% duty cycle.
Hi Kevin, i've been messing around with the magnetic loop antennas for well over a
year now and my favorite is a 5/8" soft copper 3.4 ft. loop using a 1,000 pf HV
variable capacitor. The loop will tune from 3 mhz. to 12 mhz. and like you said, the
tuning is real sharp. I've tested it against a 240 ft. horizontal delta wire antenna and
it will outperform it. The magnetic loop antenna is quieter than the longwire and also
has more gain. For the hamradio guys, if you can't hear the stations, you can't work
them! :) I have a motor drive system that I haven't added to the loop yet but I am
seriously thinking about going to a 2 inch copper loop about the same or more in
diameter for increased bandwidth. A 500 pf HV capacitor is ideal for the 40 meter
band but capacitance in the neighborhood of 750 pf might be more ideal for the
80 meter to 40 meter and lower bands. These magnetic loops antennas will surprise
you with their performance! Thanks for the review!
73s
kb9ezl
Dennis ,
I built a loop with 3/4 copper at 12.5 feet circumference . Its great on 40 meters . But the size of the small loop is a question and my cap was too low . So I am going to upgrade the variable cap to 1000uf as the loop only work on 40 and a little 20m . but very good.. And i am going to upgrade the small copper loop to 3/8 copper. So I enjoyed your post ..thanks for your post as mag loops are fun to build and try .
If you go with a larger cap, it will lower the frequency range. I think you need to go to a smaller cap.
I messed around with several different variable capacitors and a 1,000 pf is a little too much for 80 meters.
A 750 pf might be good and it should get you down to 40 meters. The increase in capacitance will mess you
up on the low bands though. The increase in circumference of the loop also would need to be decreased
which then messes up the coupling loop which also has to be reduced in size. I am thinking with what I have a 600 pf capacitor would get me into the upper end of the 75 meter band and work good across 40 meters.
I want to experiment with some flat bar aluminum stock 2 inches or more in width to see what it does.
The aluminum is cheaper and easier to work with. Good luck on your mag-loop.
Hi Kevin.. very interesting and informative video. What is the reason you used a smaller in diameter piece of copper tubing for the small loop instead of 1/2 inch for all loops.. Thanks
It was easier to bend, no other reason. ;-)
going to run 35 to 50 watts on my loop project what do you think Kevin.
Kevin, could you tell us what the value is on your tuning capacitor and where did you locate one like it ? Thank You for a great video, you are one heck of a speaker, good voice.
+Skip Pickens The tuning cap was in a box of a few of them at a hamfest. I think it goes from 20-150pf or something like that. It's not terribly critical, but you do want decent spacing between the plates to prevent arcing due to the high RF voltages at the cap.
Fantastic video, very informative as well as encouraging! de KM2U
Thanks for your video. As always very informative and well done. I had no idea you'd see voltages that high at such low power from a solid state transmitter. I've always had a fascination with the spooky physics of antennas. Your point about the physical size of the main loop component makes me wonder about band width performance; what if 3 or 4 inch copper pipe were employed instead. It would be a heavy beast to be sure, but it would be interesting to see what it could do. I learned that using large size and ultra high conductivity antenna elements such as using silver coatings can make dramatic improvement to performance. I love to tinker too. 73s from Ted in Ann Arbor, Mi.
Kevin, great video. I'm amazed by your resourcefulness building stuff. I like that you get good results while skipping the EE math stuff. (I'm a geeky EE but prefer to actually build stuff). The field strength meter is very clever.
Commercial magnetic loops are very expensive and not as much fun as building one like yours. I hope to make one like yours one day.
Thanks for watching Michael. I'm surprised more people don't do the FS meter approach. It's much easier to fine tune with it.
Check out my junk box magloop video.
ua-cam.com/video/ZTsYRyEkCkQ/v-deo.html
Michael, I've ran 5 to 100W with 1" diameter wire, wound ~8x to drive an LED without problems.
I saw a video of yours that flattened the small interior coil. Are you able to do that with this loop?
Most hams just don’t realize how far you can transmit with 5 watts or less. It’s THE ANTENNA that makes the most difference. Of course the feedline is important too. I use to use 450 ohm ladder line for all of my antennas. It was way cheaper than coax and worked better.
Show! Você é o unico que mostra com detalhes as conexões dos loops (maior e menor) 73'
Nice control comando and power meter,,73" LU1XAL.
5:32 A wood board between ends of magnetic loop had a big losses in RF, and there is a decrease in effeciency, because the RF voltage is big enough.
I have a question. The electrical neutral point of the loop where the loop can be grounded is exactly opposite the capacitor.
Why is the loop oriented so the capacitor is at the bottom, where the common mode problems are worse? Wouldn't it be better with the capacitor at the top so all of the cables and the feedline exit the bottom near the electrical neutral point of the radiator??
I have seen them both ways. I also recall that current lags voltage by 90 degrees on a radiator, so I suspect that current is higher around the coupled loop area. I have taken a field strength meter and found that radiation does seem to be slightly higher towards that area.
My gut instinct is that with the cap on top, you might be radiating a bit more of your power downward toward the ground.
When I built my junk box mini loop, I tired some experiments with it. Broadcasting WSPR on 20 meters, I looked at the foot print on wsprnet with the capacitor down for 15 minutes and then with it up for 15 minutes. The footprint was noticeably further out with the cap down at the bottom. I repeated the experiment three times over almost two hours with the same results each time.
Current and voltage are in-phase in a resonant circuit. That's the
definition of resonance. Phase has nothing to do with it anyway. The
electric field is highest across the capacitor gradually decreasing to a
null opposite the capacitor. Current is for all purposes uniform around
the circumference of the loop, assuming the loop is a small fraction of
a wavelength.
The coupling loop has only the current of the 50 ohm system and does not need to be large, except for mechanical support and stability.
The main electrical problem is voltage from each end of the capacitor end of the loop to ground is half of the voltage across the open ends of the loop. The advantage of using a split stator capacitor is shaft or frame voltage is closer to zero, instead of half of the open end voltage. A split stator capacitor mitigates that problem, reducing common mode on the feedline and mast. Most articles miss this point, and probably have the feedline doing a lot of the radiating. This is why vacuum caps and other caps with the shaft tied to one connection point are not the best electrical choice for loop balance, which is critical for divorcing the feeder from the loop so the loop alone is the antenna.
No they are not, Jerry. A correctly loaded antenna is 90 degrees out of phase in a resonant circuit. Current drives the RF and the electric field is the unwanted component. This is why mag. loops work so well relative to their size.
That's totally incorrect. Current and voltage are in phase across a parallel resonant system. You better get out the textbooks. hyperphysics.phy-astr.gsu.edu/hbase/electric/serres.html
+Jerrythenerdful that vid was a few years ago, I've learned a few things since then.
Kevin, interesting on the directivity of loop. on coupling loop just rotate 180° see if the direction changes
What is the shaft coupler you are using I looked over stores and no such animal.
I 3D printed it, it's custom.
I am getting ready to build another loop. I have a Vacuum variable and a telescope stepper motor with control box that I will somehow mate together.
So if I made one from 1.5 - 2-inch diam copper pipe on the outer loop, I should be able to cover all bands? Your vid has peaked my curiosity on building my own mag loop... How much power can it handle? Got a good source on where to get those butterfly capacitors?
Are mag loops only for indoors or can they be permanently set outside? If indoors, are you not worried on how much RF you are exposing yourself to?
Thanks! Great channel.
Wow, thanks for the interest.
The larger the diameter, the lower the radiation resistance and greater the efficiency. Bandwidth will also increase just slightly. You'd probably need to go to a larger diameter loop to really get down to 80 meters with any efficiency though.
I've driven mine to 40 watts, it arced across the cap around 45, so I keep it to no more than 30.
Caps, well, I haven't looked online, I picked mine up at hamfests. There's usually plenty around there.
They can be built weatherproof, there are several vids I've seen where people have done so and put them outside.
The field directly around the loop is pretty strong. What I've read indicates you want to be at least 1.5 times the loop diameter away from it. But we are talking HF here, and the wavelength is far too long to have any effect on cells or dna. Plus, it's non-ionizing radiation, so it won't affect you physically anyway. There's 90 year old guys out there that worked in broadcast transmitters for decades in higher fields, and some of them still have hair even. ;-)
Thanks for watching.
What’s the name of that control box
Will a SDR Radio create high voltage and heat on the secondary loop as ham radios do ? Thank you for the great video's. 🙂
Any transmitter will. Receivers will not.
Thank you !
I HAVE THINKING ABOUT BUILDING A LARGER LOOP AND TUNING IT WITH MFJ 962 i don't know if the loop will tune think about feeding it with 2 or 3 feet on ladder line at the feed point maybe will work going to try 160 80 40 a smaller loop 20 15 and 10 with coax and use antenna switch and the balun 4 to 1 for big loop.. going to run 50 watts.
How did it go?
That smoke detector looks like it's long overdue for replacement.
Hi...what is the Part number of variable capacitor you have used...from where I can purchase it online?
I picked it from a box of variable caps at a hamfest. There's always a guy selling them. I think it's around 350 pf when fully meshed.
Does copper tubing work better than coax for the loops? I just finished making a magnetic loop using LMR-400 and got a two-stage variable capacitor. The only problem is that I get no signals, but tons of noise. Any suggestions?
Yes, copper tubing will work a bit better than coax. You want as low of an electrical resistance as possible in the outer loop.
It's a pretty simple circuit, not a lot that can go wrong in building it. There are lots of types of noise that could mean different things. A constant whooshing could be noise from an internet terminal. A buzz could be florescent lighting or power lines. Static is just atmospheric.
You should hear very little until you tune the antenna to your frequency. When tuned, you'll hear static come up quite a bit. If you tune the radio 20kHz in either direction, it should get quite again until you tune the antenna to your new frequency. They are that narrow.
Double check your wiring. If you're using coax for the outer loop, make sure the center and shield are tied together, making it one long single conductor. Make sure you're connected to the right terminals on the variable cap. I don't know what else could go wrong.
Ok, thank you again.
What is the sku or part number for the motor ganged to the variable capacitor?
I found it on amazon.com, I think. It was a long time ago. I think I searched for 1 RPM gear reduced dc motor, and found several options from 12 up to 24 volts.
Wow, Kevin, your videos are great. I've built a couple of magnetic loop antennas which works very well from my apartment balcony.I want to build one for 40 to 80 meters with motor control like yours. I've seen your video on the 80 to 160 meter loop but it's a little too big for me, yours remind me of "Stargate", lol. Thanks again on the videos.
Gwendolyn H. Thanks for the kind words Gwen. And if I tune to just the right frequency, the big loop starts to glow in the center. Maybe I should step though.
My emails on my QRZ page, maybe we can set up a SKED on 40 or 20 and talk antennas.
Kevin Loughin /When I get my 40 meter loop built and the band conditions are right, I hope to hear you on the coax. I'm still working on my CW for Field Day next year. 73, Gwen - K6GRH
Yes,Some people here are right.You can unroll soft copper and if you care tom make it nice and round,bending it around a trash can will do the job.
Very little if any efficiency is gained by going from 5/15th to 3/6th tubing.
The bigger diameter gives you much more efficiency
BOB AF2DX
what is meant by 5/15th? Are you referring to size of the copper tube? 1/2 , 3/8, 1/4 , 5/8, they also sell copper wire , is the key to this project using the tube?
Love your channel. I’m building a mag loop out of dmr 400, 20 feet in circumference , 4 feet inner loop circumference, using a 365pf variable capacitor to tune. The plan is to use it on 40-20 then make one for 17-10. Would it be too lossy to use PVC pipe and wrap it tightly in aluminum foil?
At 6ft. diameter with a cap that large, it's probably going to tune from below 3 MHz and maybe just get up to 7.
The killer on magloops is the resistance of the outer loop. I've seen some use copper foil wrapped around plastic pipe. It will work with aluminum foil, but not as well.
Thank you, I’m having nothing but trouble with it, I think I’m going to make another, 9ft in circumference, which seems to be more standard.
Hello Kevin: Where did you purchase your variable capacitor? I'm going to have to order one up. Thanks, for the information.
Sincerely,
Robert (Bob) Chambers 8P6RC
Hi Robert. I found it in a box of them at a hamfest. There's always some guy there with boxes of old parts.
Hello. Excellent presentation especially the use of the FS meter. How were you able to make those kinks so uniform?
Sure beats using fittings.
73
Fernando N2FQ
Hell Fernando, Figure the number of kinks needed and flat sides, divide the circumference of the loop to determine the length of each flat side. Then kink the pipe at those intervals. Make final adjustments to get a roughly circular shape.
73, Kevin.
Thanks Kevin for the prompt reply and the blurb. Take care. Fernando N2FQ
Hi. Thanks for this video. I'm researching about small antennas for receiving and I got a question, if you don't mind: the use of a HV variable capacitor is justified because the high RF power used on transmission causes very high voltage on the ends of the loop, but can I use a small, low voltage capacitor if I only want to receive, maybe like those on cheap fm radios? Thanks.
Hello Leonardo, yes, you can use any capacitor you like for receive only. The high RF voltages are only created by the power coming from a transmitter.
Hi Kevin good representation about this antenna but I have question what do you think if I want to build magnetic loop antenna from old aluminum chaer? Many thanks 73 de kd5bkw.
As long as it's a circle, it should work. Just make sure the coupling loop is 1/5th the diameter of the outer loop.
This is great. How did you construct the field strength meter? What parts are required?
It's a simple circuit. The diodes with a short pickup wire are near the main loop, two wires bring the rectified DC back to the control box where the pot and meter are.
Have a look at my vid on building a field strength meter, it will be clear.
ua-cam.com/video/8Dd0oEzDepA/v-deo.html
Much appreciated.
Kevin, what is the torque on that motor? Where can I get one like it?
Thanks, de ke4rk
Hello Maurice, I can't remember where I found that one, it was years ago. Search for 1 or 2 rpm geared down DC motor on amazon.com and you'll probably find a few choices.
Hey Kevin. I finally built a couple magloops. The first one started out as a manually tuned loop. Great results! But I wanted to be able to tune it remotely so I added a motor and purchased a $6 controller off the internet. Hook up between motor and controller is with telephone cable and I have a separate battery pack. Everything works great except I am getting some strange sounds that I think are caused by the controller. Sometimes its fine but as soon as my hand gets close to the controller I'll hear the noise. Other times my hand doesn't have to be near it and I'll hear the sound. It's annoying. I bought a few FT80-43's and took the phone cable and wrapped 5 turns thru one of them (near the controller) hoping that the toroid would eliminate the noise. But it didn't. Have you had that problem or do you have any suggestions for getting rid on the noise?
My second loop is manually tuned. I built it to be portable. Works great but the bands have been lousy! hi....
Thanks de wa4chq
The controller probably uses some kind of micro-controller and pulse width modulation to control motor speed. That would make noise for sure. Put a switch on it for the battery. Turn it on when you're tuning, and turn it off when you're done tuning?
My controller is just two relays and push buttons with the relays wired as a reversing switch. I have a switchable resistor to run the motor slower for fine tuning. Since it's passive, there's no noise.
Tnx for the reply and info, Kevin. Yes, the controller is a PWM DC motor controller. A switch would be a simple solution... hi.... Will definitely throw one in until I come up with a controller without the micro-controller and PWM speed control..... 72 de wa4chq
I have a 6 foot RG8 based Magnetic Loop that works for 40 to 15. Best SWR on 20 and 30. Squached primary.
I can run 40 watts.
If you don't mind me asking, do the bends (kinks) in the outer loop adversely affect the performance of the antenna?
Nope. As long as the overall shape is symmetrical.
@@loughkb Ok, good to know. Thanks very much.
Here another more recent video about how to build a magnetic loop:
ua-cam.com/video/Dw1rz0CVn90/v-deo.html
That guy's intense! Ha. Good vid.
Are loops made for DX because I got a MFJ and it's most strange antenna i've ever used. Everything seemed dead and wondered if it was working properly. Then out of nowhere some str 9 Americans boom in 14,000km away :)
Their radiation pattern is toroidal, like a big doughnut. I've worked from the US to europe with the loop in my living room, inside! If you turn it on it's side, it radiates the same as a vertical antenna and become omni-directional. It's always a surprise when I use it.
Great video but all the details are helpful -------- Why the small loop with 3/8 copper and I don't disagree. But are short condenser leads very important and is size of these leads helpful in signal quality . I have a 3/4 copper loop and love it but need to upgrade from the things you learned as it only works well on 40m . Heard NZ on 40m from the west coast
Thanks Gail, I used the smaller pipe for the smaller loop because it was easier to bend smoothly. By making it as uniform and circular as possible, the loop's very linear across it's whole range. The shorter the wires to the condenser, seems to also help with linearity across the whole range. It will come right down to 1:1 easily at the top end as well as the bottom end.
Kevin, early this summer I threw together for grins, a FM broadcast magloop. The capacitor had to be
real small value like from 9 pf to 2 pf. The loop does work and tuning is real sharp and directional.
I need to have time to refine it and haven't done anything for a few months since we have been busy
and now we are in the harvest season. I want to try something different on the HF loop and would want
to increase the diameter of the tubing to at least to 2 inches for a broader bandwidth plus more gain.
I might op-out and use flatstock aluminum bar at least 2 plus inches and a longer length than what I
currently have. A good butterfly capacitor is what should be used with these loops.
What type and size is your capacitor. Brand new ham , just upgraded to general would like to build this antenna. KI5EGD
Thanks !
It goes up to around 160pf. I picked it out of a box at a hamfest. There's almost always one guy at those with a box of variable caps.
how about a capacitor whit end-stop but I use a servo motor ?
Mechanically that will work. However, a Servo motor moves in steps, and it's probable that the optimal Tuning Point might not line up precisely with one of the steps. It might be harder to get a perfect tune.
Outstanding video and great creativity! Approximately how much money for all the parts ?
It's been awhile. I think somewhere in the area of 40 bucks.
Kevin, Regardless, it's still a great video and cool idea using PVC pipe.
I worked for the Navy for 24 years in Avionics and did some Doppler Radar antennas. You're video reminded me of one of the antenna for the AWG-9 Weapons Radar for the F-14 Tomcats. Thanks for the cost too.
Hi Kevin, i was wondering what is the inductance value of the primary and also the secondary ? Thank you.
Sorry, I don't know. I didn't use a mathematical approach to this build. I copied the very common dimensions and it worked out fine.
Thank you, your work is fascinating and has inspired me to build my own. 🙂
It's the ratio. To match 50 ohm co-ax its about 5:1 (fifth diameter/circumference for the Faraday loop).
A ferrite ring through the main loop, about 9 turns for the co-ax.
Or maybe if you use a twin feeder to the open ends where the capacitor is.... Around 250 ohms or so(?) but I've only played receive here.
Great summary, might be a solution for many ham operators living in the cities, having ( as always problems with suspicious neighbors ) SP9UVB
"What is our neighbour doing inside his living with that copper doom device? Is he going to irradiate us?"
Just emailed you. this is a great simple design for your own indoor apartment ham radio magnetic loop. The alternative full commercial production cost is around $500, but you seem to have made one with less than $100. Great job.
Hello, I want to ask something;
The transmitting loop antenna emits electromagnetic waves at certain frequencies like other antennas?
Another issue I wonder is this; why is not it called a electromagnetic loop antenna? So, why is it called magnetic?
It's called magnetic because the inductive coupling between the small and larger loop is magnetic in nature. The near field around the antenna is a magnetic field. A short distance from the antenna, those magnetic waves create an electrical field which propagates away from the antenna as an electro-magnetic wave.
@@loughkb Thank you for your answer.
Did I get right;
Nature is in a magnetic position that calls electromagnetic waves towards it. This magnetic medium attracts the electromagnetic waves from outside.
However, my question was this; Why magnetic? that is, why isn't it called "electrik loop antenna" instead of "magnetic loop antenna"? After all, EM wave, which is a combination of two components, is produced by the antenna.
You can bend the tube very easily by pouring sand inside with ends closed and bend away .
Daniel Block good tip!
Daniel Block you can also buy the tube in 10 and 20 foot lengths already rolled up in a box. You just make it larger by unrolling it and you are done.
Richard, that is the soft copper and is meant to be bendable whereas the straight tubing is meant to have greater rigidity for straight, strong, rigid runs. KC0GMF
Don Riedel You can also put irrigation tubing into the copper tubing to give it more strengh and prevent smashing or cracking. Irrigation tubing is usually sold coiled up and is made from very strong and hard plastic but it does flex well. This will allow you to use the bendable copper and get a better loop shape.
I'm currently ordering 1.5 inch OD and 2 inch ID plastic tubing and copper foil to make a completely flexible loop to mount on a vehicle.
The foil wraps the smaller tubing which slips into the larger tubing, then a strong platic rope goes through the small tubing and is pulled tight and tied. The goal is to survive tree branch assaults at highway speeds.
richard vaughn That’s a great idea 💡
Greetings Kevin. I made a loop with. this capacitor, mfj 282-2005. My antenna works very well on 15, 17, 20, and 40. Little difficult to do setting. I would like your opinion about the capacitor. I only use five watts. Large loop is 8.5 feet and driven loop is 1 foot and seven inches. Good video and nice antenna.
I don't know what to say about that capacitor. I'm not sure what you're asking. If you're talking about how sensitive it is to tune, then, yes, it is very sensitive. I use a DC motor that is gear reduced to 4 RPM and that's really too fast also. A series of plastic gears would be needed if you're going to tune it by hand. Or a large and really small pullly and belt.
Good stuff, thanks. Have you experimented with a gamma match yet?
I've tried four methods. Coupling loop, gamma, wrapped loop, and torroidal transformer. I didn't see any major difference between them.
@@loughkb Thanks Kevin, I have seen that gamma matching can change the directionality of small loops favoring the direction of the match side of the loop. Upsides and downsides to this I suppose, if it is true, you then need to rotate 360 opposed to 180 :) I didn't know if there were any other advantages/compromises though. Thanks again!
nice video,please can you give more details about the fieal indicator specialy wath diodr have you used and the value of the indicator?tks and 73
+Cristian Anastasoaie They were germanium diodes, glass body types low forward resistance. The meter movement can be any type, non-shunted. I used a 10K pot for sensitivity. Oh, and you want a .01 capacitor across the wires at the diodes to prevent RF going along the wire back to the control box.
The capacitor to be in series with the diods? :D tks for answering 73
No, not series, you wouldn't get any DC voltage to drive the meter! At the antenna end of the control cable, you put the capacitor across the two wires from the diodes. It will pass RF like a short, leaving the rectified DC to travel down the cable to your meter.
+Kevin Loughin If si not to much to ask...can you make a schematics with all the values of the circuit?
Cristian Anastasoaie It's almost identical to this one, with the diodes and 470pf cap at the antenna and the rest in the control box. The 'antenna' is a 1 inch bit of wire, near the big loop.
home.alphalink.com.au/~parkerp/gateway/fsm.gif
OK, I missed it, what are the 2 diodes for?
Thanks Eddie kj4fgi
There's a small half inch bit of wire near the main loop. The diodes rectify the RF picked up by the wire and send a DC voltage back along the control line to a meter in the control box. This gives a nice relative radiated power indication for fine tuning. I can tweak the loop for peak radiated power. A bit finer adjustment than what is capable with most radios built in SWR meter.
Good Idea Thanks
Hi Kevin!
You have nice videos about your magnetic loop antennas. I'm ham too (UT3UHR) and I build my magnetic loop on 7MHz. Please tell me how you approve your magnetic loop with tranciever?
I'm sorry, I don't understand what you mean by "approve". If you want to know how I tune it, maybe this will help.
ua-cam.com/video/-fVhYwqYci4/v-deo.html
Sorry about my bad English. I mean antenna matching with transceiver. Because input resistence of magnetic loop and output resistence of feeder are different.
When tuned to the operating frequency, my radio see's an SWR of 1:1. The coax from the smaller loop goes directly into the radio.
It is interesting. Ok, thank you. I will continue to experiment with my magnetic loop.
Дима Еременок .. Ahh, the land of the vacuum capacitor ;)
Try this site. Ignore the big words, the pictures say plenty.
www.nonstopsystems.com/radio/frank_radio_antenna_magloop.htm
What is magnetic about it? Thank you.
The coupling loop and the main loop couple together via a magnetic field.
So, the coax connected to the smaller loop, the other end goes directly to the radio?
Yes. That's correct.
Ok, thanks.
If I wanted to make one of these antennas just for receiving only, would you tell me what kind of variable capacitor would be needed? I mean, I guess it wouldn't need to be able to handle much voltage. But I would guess a capacitor with no 'stop' would still be a better option.
Oh, and does the small loop actually make physical contact with the big loop? Or is it just in 'proximity' only?
To answer the first question, no, it doesn't need to handle voltage if it's just receiving. So any variable cap should work. It should have a range from 10 to 300pf at least.
Second, no, they're not touching, just close to each other.
30 years ago before the internet We bought a SWR meter / antenna tuner for your CB radio with 25w amp. But when I followed the instructions people had given me for using it to tune I ended up with very loud angry 50hz buzzing as the 25w amp was using 140w + , more then our 10A 14v power supply could provide. I am pretty sure a 25w amp is not meant to use 140w + ? .
I never found out how to actually use that SWR meter and tuner... It is much simpler now when you can log on and get instructions how to do anything on internet :)
Can I ask what kind of SWR Meter you used?
Well, in this application, that's not actually indicating Standing Wave Ratio. It's indicating a relative power reading and is non-calibrated. We only want to see maximum deflection.
That meter movement was originally in an old CB radio SWR meter enclosure, but I'm not sure of it's full scale current rating. It might be 100ua or 1ma. Shouldn't really matter though. You're going to get more than enough energy from the pickup wire near the loop.
Perfect. Thank you very much for the response.
Manual focus is logical. :)
+Randy S Indeed. Were it that I had a camera with such capability, I would set the focus and exposure manually.
Hi Kevin, quite informative. I have never tried a magnetic loop antenna but from this presentation I conclude it is Ideal for a QSO on a scheduled frequency, however due to the narrow bandwidth of the loop and tuning the receiver looking for a weak signal over a full band can be quite demanding having to continually tweak the capacitor for the resonant freq and performance in order to hear a signal. Too easy to miss a signal. Even using LDF750 Heliax (about 1.8" dia) for he large loop the bandwidth is still very narrow. I figure this would be a major negative for the Magnetic loop antenna. Your thoughts... Cheers Mike VK5LX
Hello Mike, I thought I'd mentioned that in the video. I know I have on my other magloop vids. If you bounce around a lot in frequency, magloops need retuning constantly. If you're doing a POTA activation, or something else where you tend to sit on a frequency, they are fine.