Ham radio antennas - Magnetic loop remote tuning control box details schematic and demo
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- Опубліковано 22 лип 2024
- In response to a viewer request for more detailed info on my remote tuning solution.
The control box schematic can be downloaded from my channel's Facebook page at this link.
kb9rlw/photo...
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W9TE (Node: 519521) - Наука та технологія
Hey Kevin,
Craig here... W5ZYM
Just wanted to say thanks for the overview of the control box! I have never supported a channel on Patreon, you are the first! It's a humble support, I too have recently been laid off. Surprisingly, I saw a link to this video on the "DIY Magnetic Loop" facebook group. Imagine my surprise when I viewed it to find that you had so quickly made a VERY informative video detailing this little unit. Thanks!
Cheers and 73!
W5ZYM
Glad to do it Craig. And thanks for the support.
Nice simple, but elegant solution. The RF strength meter is a definite plus.
Great video. You obviously love to teach and are very skilled at it. Thought I share my experience with loops. Sorry if a bit long but thought it might help some people with large building rooftop situations like me. I’ve played with magnetic loop antennas for over 20 years. For portable use I’ve had great luck with Alexloop. Routinely worked Europe from Texas with various QRP rigs. Worked America from Thailand with it too.
I’ve also tried various larger rigid fixed loops.
Mag Loops will never equal even a dipole at height in a quiet location. But, they do have several advantages in some situations.
I’ve sold my software company and retired and spend most of my time in Thailand at my condo on the ocean. There is no place in Thailand even near a town, even in the best neighborhoods, where there is not terrible electrical noise. Wires are strung between power pole, often dropping almost to the ground. There seems to be noisy transformers and neon everywhere. If I’ve tried verticals or dipoles I’ve often had S9 to 15 db over noise levels. But, noisy locations is where magnetic loops shine.
Even at my ocean front location I seldom saw below an S7 noise level and often much higher. Fortunately I have the top 2 floors and my roof gardens. On the north and south ocean corners that are about 40 meters apart I thought would good places to put a couple of magnetic loops. Unfortunately for me to the East is a gigantic metal structure towering above and along the entire Easter wall that contains a water tank and acts as a electrostatic field dissipator to prevent lightning strikes since this is the tallest building in site at over 56 stories. But, another advantage of magnetic loops is that as long as there at least 2-3 meters from metal structures, even ones higher than the loop is, they function quite well. Any kind of a beam was thus out of the question. Also, wanting to avoid any dispute with the Juristic, I want a reasonably small installation and I wanted 80-10 meter coverage. All a tall order. But, I’m extremely pleased with my solution.
I think the absolute best magnetic loops made are made by the Italian company Ciro Mazzoni designed by I3VHF. The are expensive but worth every bit of the money. Expensive but a bargain. I put their MIDI 2 meter diameter loop made from 3” diameter aluminum tubing that covers 3.5-14.5 MHz continuously on the Northwest corner. And their 1 meter diameter Baby loop that covers 7-30 MHz on the Southwest corner. They have gigantic air gap capacitors at the top that have servomechanisms to open and close to tune. You auto tune with a serial connector from your rig to the auto tuner or you can type the frequency in on the keypad. There are several videos on UA-cam that demo them. Such as
ua-cam.com/video/XTDRzJqbMRQ/v-deo.html
So now I often have S 0.5 or less noise and am getting often worldwide coverage in digital modes with 2 watts. While magnetic loops work very well only two loop diameters above the ground, another loop advantage, I think I’m get some benefit from them being 150 meters up and on the ocean.
W5MMT / HS0ZAC
Simplicity of your solution is beatyfull. I like that kind of solutions. I tuned CB radio antenas with field stranght meter to highest voltage just becouse simply SWR-meter wasn't able to do the job.
Great video and design. Thanks for sharing your design.
Thanks Kevin for sharing your simple and bright idea. I am building one for myself as I live on 6th floor with limited space for an HF antenna. Thanks again. 73 de TA2SR from Istanbul
Great video. All your work is done well; understandable and straightforward. Thank you.
Thanks for sharing, I'm in preperation mode for building a magnetic loop due to lack of space for large dipole antenna. With your kiss design, It is a great help. Thanks again
Great Video -- thanks for the ideas. I've been going through gathering intel on these for building one myself (in fact my first HF antenna).
Only just come across this video, what a great simple solution. Keep at it M0UDB
Nice! not many people go over this part of a mag loop build. If I can ever get my hands on a cap, I'll be building a mag loop. I'll probably this box when I do.
I found this 12 - 300 pF at RF Parts Co., an online ham parts store for $25: www.rfparts.com/20apl300de.html
I'm not sure 300 pF is quite enough to tune this antenna all the way down to the bottom of the 40m band. I figure i can always parallel a 47 to 100 pF cap to help it out. I'm going to build this antenna over the next few weeks. I'll report back how the cap works if I remember ;-) - Brian, KN4RDF
Excellent video and design for a remotely tuned Mag Loop Antenna. One addition to the schematic may be to add diodes across the relay coils to prevent any spikes from getting back to the power supply.
I actually did. I left them out of the schematic at first, oversight, fixed it later.
I really like your RF sensing method. Great idea and very simple!
It makes fine tuning very easy and quick.
I really enjoyed your videos and am making similar mag loops for myself. The major problem with them over here is obtaining the variable capacitors to make them with as they cost nearly £200 for new ones in the UK and are rare as hens teeth secondhand! Thanks for the videos. 73's Mike G4HLT.
Kevin, for a connector between the motor and air variable capacitor, we used an arrow shaft with a round piece of wood dowel inside. Leave enough space at each end for the shaft of the motor and capacitor. A hole was drilled at both ends and a cotter key put through the hole to secure it, a small diameter bolt and nut could also be used. Solid as a rock
Good solution! Yep, you don't want any play at all in that link.
As long as it stays dry. Wood get ever so slightly conductive when the humidity rises.
Got it. Thanks for your videos! I will sign onto Patreon shortly.
Many thanks for this info Kevin.. I'm just getting back into amateur radio from a 30 year break. Can't believe the changes that have gone on during that time. ! I'll be going for a loop as my accommodation is downsized from where I used to be .. Being in the UK, some of the parts are going to be challenging to source, ha-ha.. It'll probably take me longer to gather them together than to build the antenna.. Appreciate your videos that are helping me 'catch up'. 73.. Pete G4RYO
Hamfests are the best place to find parts. There's always one or two guys there with piles of parts for sale. The only thing you'd probably have to shop for would be a 1 RPM geared motor. But those are readily available with a quick search on amazon or ebay.
You're the best! You've earned my subscription.
Thanks Kevin, You are a great teacher and a really nice bloke, I am going to give this a crack. Cheers Tim VK8LLA
I think there are kids ready to learn from you, maybe consider teaching tech studies or computing.
Thanks for the videos, I just found these today. I have never used one of these antennas but I will now. 73'S N5UEB
brilliant i only need the sensing part of your circuit hope it works as well as the last project of yours that i built the "easy end fed " which works really well thank you dave c
You would make a great teacher! I will add you to my patrion list.
Maybe you should make kits. Like Heathkit you can provide a service too teach or help those who need to create. Many people don’t know what a screwdriver is. They never had a shop class. RWB
Thanks Richard, always happy to know my work is helpful to someone.
That's a very neat little gizmo. Thanks for sharing it with us. 73 DE K7RMJ Frank
Nice setup. Thank you for this tutorial. 73, KB9K
Great video Kevin, Love the simplicity of the tuning arrangement. I was thinking about rf pickup and using it as negative feedback for a loop autotuner. (Probably overcomplicating it!) But it would be neat, Thanks again for the video. 73 de Mark GØUSL
Hi Kevin .. Great design. Quick question I have the same motor from servo city do you recall the size resistor you are using to slow the motor? Thanks in advance de Mike N2PPI
simple? for you.... for me, amazing. I do like it.
Thanks for the videos
Brilliant !!..subscribed !.
Hi Kevin I'm wanting to make your unit for the magnetic loop I mean M7 not to Up On electronics I just wondered whether you had a few pictures of inside the unit so I could follow the wires rather the diagram if you have any many thanks Cyril
If it is possible can YOU do a video on YOUR Control Box viewing the inside.... I can follow the Schematics, but I also do much better when I can see what YOU did. I am a Visual kind of learning person.
Thank YOU
JAMES
Kevin, what relays do you use or recommend for this ?
I might recommend the reinforced pneumatic distribution "air line" tubing 1/4" ID for the motor coupling. That stuff is surprisingly stiff and a foot is less than 2 bucks at ace hardware. I used it on all the stepper motors on my 2'x4' cnc router and they work fine. Just used a couple pipe clamps to attach it to the shafts. This method also has just enough give in it so that if the motor shaft and whatever you're attaching it to aren't perfectly alligned it won't bind up the motor. But don't get me wrong if you have a 3D printer this is great!
I had tried very thick vacuum line. It felt completely rigid, but it was just too much play. It's crazy sensitive. You really need something completely solid.
Kevin Loughin, Interesting, that's good to know. I really like your videos. Seems to me like a lot of hams have gotten away from building their own simple equipment and would rather throw away their money for something that could be built in a couple hours or less. BTW - I'm still using my version of your DuinoVOX circuit and have found a couple vhf packet bbs stations in the area. It's working like a champ. Couldn't be happier with it. Who needs a $140 Signalink when you can make one for less than $20!
I am asking you for your input on an idea I have for a quarter wave multi band tri wound antenna , by that I mean a winding for each of three different bands such as 6 meters , 10 meters , and 15 meters or any other tri meter antenna . What do you think about this idea for say field trip meetings ?
The loops would interact with each other and make things hard to get working. You could use thick coax for the loop and just have different lengths prepared. Attach the loop you need when you need it.
Would a Stainless steel loop made with 3/8" OD be very effective? I have some "soft" stainless at home I could use. Could I use the 3/8" OD for both loops? I know the small loop is 1/5th the diameter of the large loop, but does the OD of the material also need to scale down?
Yes, you could use what you have, and no, the smaller loop doesn't have to be a smaller conductor, just 1/5th the diameter of the big loop.
Wow! What an amazing video. I'm encouraged to possibly build this control box. I'd be interested in knowing where you sourced the meter as well as the relays, P/N's etc. Many thanks, de KM2U
Mostly parts from my junk box. The meter and box was an old CB swr meter. You can find them cheap at hamfests or on ebay.
Hi Kevin great video. I have a question about the servo motor. Do you think that motor has enough
Torque to turn the tuning capacitor on the chameleon magnetic loop?
Sure. But You would need to rig up limit switches since the chameleons cap has end stops.
Hello Kevin,how are you?
First at all thanks.
As many fellows say; you are a great teacher.
You don’t keep hidden things, always show how to and explain at the easy way.
Let me ask something:
In this case you are using QRP and Ethernet cable between the antenna and controller.
If I use 100 watts, RF can go back to the shack thought Ethernet cable and cause problems with my computer and USB connections for digital modes?
If yes, can I roll Ethernet cable as an ugly balum, ferrites, etc.
I really appreciate your comments.
Thanks
Claudio
OA4BMG
Yes if you're running any kind of power you would definitely need some serious RF filtering on the control cable. You might use shielded cable too and ground the shield. But in a magnetic loop if you want to run that kind of power you're going to have to use a very expensive vacuum sealed capacitor for the loop. The RF voltage across that capacitor is going to be extremely high thousands of volts
Hi, I was watching your video, interesting and simple control for the magnetic circuit, could you tell me what value to use resistor and how many watts to withstand the voltage drop of the motor? thank you and 73s of LU6FLZ
You'll have to experiment with your motor to find the value that slows it enough yet still provides enough torque to turn. Measure the resistance of the motors coil and start with that value to halve the power.
Hi Kevin,
What a great video this is. It's such a brilliant idea, & something that I've often wondered about how to do. Unfortunately, I now have a bad tremor in both hands, so soldering is impossible for me. Ive been thinking of trying to build a Mag Loop aerial for myself as well, preferably one that will cover from 80 MTRs to 10 MTRs.. I also like the design by Paul, OM0ET. However, his MC20 MagLoop on covers from 40 MTRs to 10 MTRs.. There are no Amateur Radio clubs close by to me, & the odd few people who I have asked for help with projects that require soldering always have something '"More Important'" to do, rather than help me. I have bought myself a 1RPM 12 volt motor on line for this project after seeing this video prior to asking people for help Do you have any suggestions for me please Kevin.
Many Thanks in Advance,
Kind Regards,
73,
Ray.
M0RAY, ~~
Sittingbourne,
Kent,
South East England, UK
Locator:- JO01ii.
thanks for sharing.
Great Video Kevin. Thank you for sharing. I am currently working on remotely tuning my mag loop. I am having trouble finding the meter you have used in your controller. Are you able to tell us where did you source it from of can a regular dc voltage meter be used? Cheers.
Pretty much any meter movement can be used. That box was an old CB SWR meter I picked up at a hamfest for a buck. I see them at yard sales occasionally too.
Thank you Kevin, much appreciated. Kind Regards, Sands (VK2WXW)
you could also use a standard hi torque servo to run the cap. that would also have the advantage of absolute positioning so you could quickly set it where you want it.
Well, yes, but no. The servo wouldn't have the resolution to precisely tune the cap. It would get close enough to operate, but not quite dead on. You can't even see the movement on the cap during those fine tuning clicks.
I've thought about a stepper motor, geared down maybe 1:4 or more, then use an arduino to do the fine tuning, using the sense voltage. Others have used that approach. It gets more complicated and more expensive though.
Kevin Loughin I was thinking about that. I did find some servos with .1 degree resolution which would give 1800 steps across 180 degrees. I wonder how much finer it would have e to be
No, nowhere near enough. 1/10th of a degree would probably be ok.
Kevin Loughin that's exactly what the ones I found have .1 degree resolution
Didn't see the period. Give it a shot. I doubt it will be accurate enough to return precisly to a previously tuned spot. You'll still need to tweak it. It's really that sensitive.
Nice solution for max efficiency! How long the cable between sensor diodes and control box could be or is recommended?
It's low voltage and relatively low current, so you can probably go long. I'd have to guess, so I'm not sure.
Kevin couldn't you have used small nylon gears to connect the motor and variable cap shafts together? I know you.made a clamp like device using your 3d printer but I'm curious as to whether gears would work better?.
If you had a spring loaded split gear to overcome lash it might be ok. Fine tuning is hard if there is the smallest amount of play.
Thanks for showing your look tuner. Very nice indeed!
Can you tell what drawing software you are using?
KG8NS Chuck
I drew the schematic in Libre Office Draw. During screen recording, I had it loaded in GIMP so I could draw on a second layer while illustrating my narration.
Thanks for watching!
Thanks for the reply Kev. I like your 80-160 loop also. Nice work. I have Libre Office installed but never tried the draw.
I'm having a hard time locating the .01 caps. What unit are these caps? pf? nf? µf? I did find some 1pf caps. Would those work?
Small ceramic disc caps, they show .01 on the side, 10nf I believe. Yep, my cap tester read out 9.8nf, so 10nf it is.
Wonder did I miss where you have the files for this little box? What spec of meter is that? Thanks!
The schematic is over on the facebook page, or you can pause the video and take a screen shot. Any meter movement should work fine as long as it's not shunted internally.
Excellent vid of yer antenna, great job. I'm currently getting interested in loop antennas for Rx due to their low noise. Tx will be done on a separate antenna (G5RV). I'm assuming I can use a varactor diode for this since it's for Rx. Your thought appreciated, thanks! 73 De KD5MHQ
If it's for RX only, a varactor should work. However, it has to be in parallel with the loop, which has a very low DC resistance. So I don't how you'll get a bias voltage across the diode since it's shorted by the loop it's in parallel with. :-)
@@loughkb That's simple, a .01uF in series with the varactor. ;-) This is how he did it ua-cam.com/video/AaPdHu-Dsio/v-deo.html (6:57)
@@bob4analog Of course. I missed that possibility.
Went to your FB page but was unable to find the schematic for the controller. I would also like to know if you have any "Mag Loop Construction For Dummies" instructions. I'm very handy but not particularly adept in electronics. I'm looking to build a Receive only or QRP rated antenna for HF use. Thanks, Jack N2LBI
Try this link.
facebook.com/kb9rlw/photos/a.261111871002490/286572448456432/?type=3&theater
@@loughkb I am planning to build a receive only mag loop. I'm not sure how that will change my design. What value/range would you recommend for variable capacitor? I am gathering the components for your tuning control as we speak. Also, what distance apart do you think my vertical (butternut hf6v... which is anything but resonant... maybe another time for that) and the mag loop antenna should be? I typically do not exceed 450 watts when transmitting. BTW, I will be picking up my "Brand New" 2009 Keystone Montana 5th wheel in late January and will be primarily Full Timing it from that point forward. I foresee terrible troubles in my future. Lol!
On my 3ft diameter loop, the variable cap goes up to just over 150pf and I can just get down to the bottom end of the 40 meter band. Keep the loop broadside to the other antenna and the null will help to reduce pickup from the other antenna. But that can be a problem. It's a resonant circuit so it likes to ring with the right frequency RF present.
Dear KB9RLW,
Many thanks for the great simple mag loop capacitor control! Actually it’s a great construction using simple components! I have seen lots of controllers using advanced components and things like that, of course I thank them too. Lots of U tube things are mostly demonstrations ONLY, constructional details are not shown! Some times especial components are used! I am from Srilanka and for me it’s a bit difficult to find those in local markets! I have constructed your construction, but still not used it practically, sure it will work for sure! I have a professional diode probe I am going to use for detecting the signal strength !
I thank you once again!!
Kindest Regards........Best Of 73!
Leonard Fernando.
4S7LF/ OZ6ZV ( closed)
Kevin - that capacitor across the motor, is that .01uF? That's what I used on mine, but I'm still getting a lot of hash. Any suggestions?
You could change the value, go smaller. I do get hash from the brushes on the motor. They spark and generate a lot of RF.
Good morning Kevin
You did a great job, Congratulations, quick question, where did you buy the meter that you are using in your control box?
Thank you in Advance,73 de K2WC
The meter movement was in my parts bin. I probably picked up a box of meters at a ham fest years ago.
You need to make sure it's just a raw meter movement with no built in shunts.
@@loughkb Thank you
nifty setup.
Hi Kevin,
This is awesome. Any details on the Diodes please.
Any germanium diodes will work. (glass case) They're not critical.
Thanks Kevin
But be careful where you buy. I just acquired some 'Germanium' diodes from ebay that turned out to be cheap silicon Schottky diodes that don't seem to work in this application. Would that seem right Kevin? I get no sign that any rectification of rf is taking place at all. I have now ordered a couple of known good Germanium units and I'll try those.
Nice 👍
Hello Sir, i hv an old HP printer laying around and i hv been pondering about canibalizing the two servo motors to use as a remote motorized tuning control/drive for the mla's tuning capacitor. Just wondering if this is possible.... tnx & 73s
Yes. I've seen other projects that used arduino's to drive stepper motors for tuning control.
me gusta mucho la manera de sintonizar la antena por la mayor emision de intensidad de campo pero al variar el capacitador no varian las SWR??? en el video no mensionas si usas un sintonizador de antena o si hay que usarlo obligatoriamente para poder usar esa antena gracias .....sorry i don´t speak english i hope you understand 73´s
La emisión más alta está en el punto de menor S.W.R. No se necesita sintonizador de antena.
Gracias por la respuesta es bueno saber eso tengo dias buscando fabricar una antena para espacio reducido porque vivo en un apartamento pero nunca he experimentado con las loop magneticas y quiero hacer una para trabajar 40 y 20 mts de todos los videos que he visto por aca el tuyo es el que me parece mas acertado y mejor explicado asi que pienso hacer exactamente esa antena que tienes y la idea del medidor de intensidad de campo me impresiono mucho que genial esa idea de verdad te felicito incluso pienso hacer la caja de control asi como la hiciste tu pensaba hacer eso con arduino pero como lo hiciste me parece mas practico gracias por la informacion y si te es posible mandarme el plano de tu loop a mi correo te lo agradeceria mucho gracias YV5-JAU
mi correo yv5jau@msn.com
No tengo esquemas para el bucle.
El bucle más grande es 1 metro, el pequeño es 1/5 del tamaño.
El condensador es 20-150 pf.
Gracias Kevin con esos datos me basta para hacer una
Hi Kevin, any links to that motor please. Thanks
That was a long time ago, I don't have the link. However, I found it by searching for "1 rpm dc motor".
I had a thought. The relays are simple SPDT. Soo, why not replace them with SPDT switches.
Then there is less draw. Important if battery operating portable.
With the push buttons, it's possible to move the motor in very small increments with a quick tap of the button. Much harder to do with switches.
Who said the switches weren't push button or return type toggle.
thanks for the video, name your patreon in the begininng and end of the video
It's tagged at the end and in the description. I don't want to be annoying about it by over doing it.
Thanks for watching!
most of videos aren't completed, put it in about 2 minutes on a 15 minute video. I am supporting you 5/month for a while, I hope it helps! and when you give your patreon, say it slow and deliberate. it will be worth more $$ in the long run.
I had trouble finding the PVC X fitting to make a frame, still have not found one.
I've seen them at most hardware stores.
@@loughkb Not in the UK
@@rushymoto www.amazon.com/Schedule-White-Socket-Cross-Pack/dp/B00TOOLS6I/ref=sr_1_1?dchild=1&keywords=pvc+cross&qid=1617716082&sr=8-1
Just wondering. Shouldn't the diodes be reversed? I think in your schematic the negative end of the sense diode is going to the positive end of the sense meter. Seems to me the voltage at the cathode end of the diode is going to be negative.
Yes I wondered about that as well?
Well now I'm really confused. I just snipped the diodes out of my previously non functional circuit and switched them around. The meter immediately started to register rf but was reading backwards! I've now also reversed the meter connection and everything is working great. I can only assume that I must have had a bad joint in the first configuration that is now good. Anyway the field strength indicator is now working and provides a perfect indication of when the loop is properly tuned. Yay Result !
The field strength sense circuit is funky. Kevin stated in the video it was a full-wave rectifier but it's only a half-wave. It takes a 4-diode bridge to invert one half of the waveform for full wave rectification. But half-wave may be enough to drive the meter. Also the placement of the capacitor is unusual, not sure of it's function. It may have been added experimentally to accidentally solve a problem with the two diodes because if you try to make a rectifier with the two diodes as shown but the cap is replaced with a wire you just end up with AC RF on the meter which probably won't display it. I don't think the lower diode is doing anything so you may want to just remove it and let the .01 cap filter some of the pulsating DC. Maybe Kevin will chime in and explain how this works as a full-wave rectifier.
You can use a double pole double throw switch for motor control, less parts, same action.
I can tap one of the buttons for a very short amount of movement. Much harder to do fine adjustments when you have to toggle a switch back and forth.
what software do you use circuits digram N9IWW
I drew the schematic in Libre Office Draw, copy pasting symbols from other schematics.
What's the range on that meter? 0 to ? Thanks
Doesn't really matter, it's only indicating relative signal strength.
I hope you find something soon.
Any reason you didn't simply use a polarity reversing switch instead of the relays?
I liked having separate buttons for up or down. It's a bit quicker to tune than if you had to pause, switch a switch and then tap again.
I was thinking the same thing when I saw the circuit, the relays are not needed. Just replace the relays with the switches, one for up and one for down. Another option is use one switch for fast-slow as shown and a three-position, spring-centered rocker or slide switch. Press one way for down, the other way for up, and release for off. No way to energize up and down simultaneously.
There isn't one loop video that properly explains the hookup of the capacitors. Now I've wired it in both ways, just in series with the bottom, non-rotating plates. I've hooked it up in series from the one side of the loop to the plates capacitor and the other side of the loop to the rotating plates. I don't know how much time you have. Is there any place I can send you some photos of my antenna that you can look at and possibly point out the obvious mistake that is eliding me? I'm getting really frustrated. I can't put an outside antenna up due to 100% restrictions plus My apartment is a hundred years old. That means lath & plaster walls with chicken wire throughout. I basically live in a faraday box. Thanks for your time. James KA9TII
If you have a capacitor with two equal sets of plates, the best way to wire the loop is one side to each of the non-rotating plates. So the capacitor is basically two variable capacitors in series. That way hand capacitance doesn't affect the tuning as much when you reach up to the knob to turn the capacitor.
Search my channel for the word magloop, or magnetic loop. And you'll find many other videos.
@@loughkb The stationary plates are not split, although there is a solder lug on each side. It would be like soldering both sides of the loop cut to one side of the cap, just completing the loop again directly. Do I need to use a different cap?
@blugoose86 usually if you look between those sets of stationary plates there will be a little metal bridge that can be removed or cut to separate the stationary plates into two groups.
Very interesting Kevin 73 VK6NJP
Germanium......