Antenna winding questions - Page 1
Forum section: electronics / rf-microwave

author: Amish_Fighter_Pilot
author_rank: Regular Contributor
timestamp: May 29, 2025, 03:33:51 am
content: I am new to antenna design, but in the world of transformers and motors there are three primary winding styles: jumble, helical, and orthogonal. These primarily come into play when many layers are involved. I don't know how this logic may apply to an air core loop antenna for example. It seems like lot of people who are doing VLF-AM range use either jumble or single-layer flat windings. The metal detector coils are similarly a mix, but most seem to be jumble type.Does anyone have good resources on winding styles and how it affects antennas?Also, the frequencies I am working with are very long wavelengths; so a quarter wave antenna is not even close to possible. I could maybe do a 1024th of a wavelength for 5Khz for example. How do I determine the lesser harmonic frequencies?Thanks.

author: RoGeorge
author_rank: Super Contributor
timestamp: May 29, 2025, 05:08:01 am
content: I've seen spider-webhttps://duckduckgo.com/?q=spiderweb+coil&t=ffab&ia=images&iax=imagesand basket-weavehttps://en.wikipedia.org/wiki/Basket_windingstyle for MW and LW antennas.If you search forindoors loop MW or LW antennapics you'll find the typical designs. For lower than that, I remember some tubes stuffed with ferrite bars, and a normal cylindrical coil around them, but I don't think they were for 5kHz, more like 50kHz.I don't know what's the typical antenna style for VLF.

author: radiolistener
author_rank: Super Contributor
timestamp: May 29, 2025, 05:20:07 am
content: In general - a turn wound against the main winding direction create local cancellation and reduce the overall efficiency. Any inconsistency in the winding uniformity may introduce parasitic resonances, which degrade performance, especially at higher frequencies.When it comes to antennas, especially air-core loop antennas, the winding style affects both inductance and Q-factor. For tuned or high-Q loops, uniform helical or flat spiral windings are preferred.Also, wire length matters. Longer wire means higher resistive (thermal) losses. For VLF and low-frequency applications, ferrite rod antennas are often a better choice for receivers. They’re compact, require much less wire than air-core loops, and therefore exhibit lower resistive losses. Ferrite saturates easily, so it's not suitable for transmitting antennas, but for receiving - especially in portable or space-constrained designs - it’s ideal.However, I would caution against the misconception that a physically small antenna inherently requires less surrounding space. In practice, electrically small antennas often demand just as much, if not more, clear space around them. This surrounding volume must remain free of conductive or dielectric materials and noise sources (such as electronic devices), as nearby objects can significantly impact radiation efficiency, introduce additional losses, and distort the radiation pattern.

author: Amish_Fighter_Pilot
author_rank: Regular Contributor
timestamp: May 29, 2025, 02:11:08 pm
content: Quote from: RoGeorge on May 29, 2025, 05:08:01 amCool! Those spiderweb coils look perfect for my project. At really low frequencies I know the ferrite makes a denser antenna, but I think the spiderweb could give me nice clean signals..... So cool thanks

author: Amish_Fighter_Pilot
author_rank: Regular Contributor
timestamp: May 29, 2025, 02:21:11 pm
content: Thanks Radiolistener. Do you know why VLF devices seem to get rid of the ferrite core when the antenna gets much bigger than an inch or two(a few CM)? Is it just a cost factor?If I am understanding what you're saying in general though: a long tube covered in a flat layer of windings would be a better antenna than the same windings jumbled together in one spot on the tube?

author: Amish_Fighter_Pilot
author_rank: Regular Contributor
timestamp: May 30, 2025, 05:56:14 pm
content: Can anyone please tell me what the difference between honeycomb(aka basketweave) and cobweb type small antennas. I am aiming to make antennas that are about 1/1024th wavelength, but I am not sure which weaving style between these two is superior and in what way.So it's down to either this web style(less work):Or this honeycomb/basketweave style(way more work!):Is the weave antenna really better? It seems like way more work, but they look so wild. Are they just showing off their weaving skills or do these weaves actually help its function?edit - I forgot to mention that these will not be transmitting! These are intended to be receiving-only.

author: RoGeorge
author_rank: Super Contributor
timestamp: May 30, 2025, 06:10:12 pm
content: The second one has higher quality factor Q. So if you need selectivity for a certain frequency, the second (basket weave) will have a slightly narrower bandwidth. Might have a lower capacitance, too.My guess is, neither will be good for 5kHz. You'll have to use ferrite, or else the coil will have to be the size of an opened umbrella, if not the size of a wall.What are you trying to receive at 5kHz?

author: RoGeorge
author_rank: Super Contributor
timestamp: May 30, 2025, 06:31:47 pm
content: There is a spreadsheet to help you calculate a spider-web coil:A Spreadsheet for Magnetic Antennas Pt.1: Loop AntennasKainkaLabshttps://youtu.be/8m3WbY9wx6s(this is part 1, there are 3 parts about the use of the spreadsheet)There is also a series of 5 videos (on the same YouTube channel) explaining the loop antennas. The 4th talks about the skin-effect and proximity-effect:Resonant Magnet-Field Antennas Pt.4: Skin-Effect and Proximity-EffectKainkaLabshttps://youtu.be/FUCRB9UdfUgThis page shows how to do basket weaving coils:https://www.jogis-roehrenbude.de/Spulenwickeln.htm

author: Amish_Fighter_Pilot
author_rank: Regular Contributor
timestamp: May 30, 2025, 09:54:48 pm
content: Thank you for all the resources and the detailed replies! I am sorry to be unclear, but 5KHz is only within the spectrum I want to work with. I intend to make specific antennas for lower frequencies that are bigger. My operating range is realistically from about 1KHz up to maybe 500KHz. I know there isn't going to be a one-size-fits-all solution for this. I just want to make something that has a good range of frequencies it can pick up and hopefully can be made from 50' of 18ga bell wire(what I have already). It seems like the basket woven antennas might be too purpose specific for my needs. I'm doing a sound art project with the system, but it will have other uses probably. What I am doing has a lot in common with radio direction finding, but that's mostly because I want stereo samples.

author: Perrold
author_rank: Contributor
timestamp: May 30, 2025, 10:36:05 pm
content: Is your antenna tuned or untuned? I'm guessing the latter. Size in terms of specific tiny fractions of wavelength does not matter; you're just looking to intercept as much signal as possible. Basketweave coils and such are great for reducing parasitic capacitance and increasing Q neither of which, as a generalization, really matter for an untuned antenna. For intercepting a signal area is your friend, number of turns is secondary. Had good luck with a tuned loop for VLF made from ribbon cable. Could tune it from under 20kHz and up high enough to hear some NDBs. This was with a bunch of switched capacitance. For something broadband covering 500kHz and down I'd make the loop as large as practical, keep its self-resonance well above 500kHz, and feed it into a low noiselowimpedance pre-amplifier. Treat it as a current source and keep the parasitic capacitance low enough that it doesn't want to resonant where you're listening. Common mode rejection has been a critical issue in my experience but that's a separate exercise.

author: Amish_Fighter_Pilot
author_rank: Regular Contributor
timestamp: May 31, 2025, 08:36:24 am
content: Quote from: Perrold on May 30, 2025, 10:36:05 pmI believe the antenna would be considered untuned. I am trying to learn the jargon as fast as I can. I think what you're saying about tuning it above 500KHz actually makes a lot of sense once I really thought about it. It seems to me like the untuned antenna is sort of a "Jack of all trades", and thus is better served to be good across a lot of tasks rather than specialized in any one. Is that a correct understanding of the logic?em to bThe signal path will go from my antenna to my AD831 mixer. I've been told the LO needs to be higher power than the RF input, so I didn't know if an LNA was going to be a problem. Do you think I'll need that LNA to even get a signal at all to the mixer?Would it be possible to modify the filters on a class AB amplifier to act as a makeshift LNA for testing purposes? I need to figure out which LNA to get that can work in my target frequency range. I had hoped I was done buying parts for this project. Its getting expensive by my standards, but I almost have everything now. I'm going to test-weave a web antenna this weekend, but then I'll perhaps only need the LNA for the system to be complete!

author: radiolistener
author_rank: Super Contributor
timestamp: May 31, 2025, 12:22:28 pm
content: These don't look like antennas, this looks more like inductors used in induction hobs. Such inductors are specifically designed to minimize radiation in the far field and maximize energy dissipation in the near-field reactive zone - so this would make a poor antenna.But since the wire is too thin for an induction hob, it seems more likely to be some kind of near-field sensor, possibly for RFID, NFC keys, or a similar application.For a magnetic loop antenna with air core, using multiple turns is generally inefficient due to high resistive loss in the wire. It will also suffer from numerous issues due to parasitic capacitance and mutual inductance between the turns, leading to multiple unwanted resonances.If you need a low-frequency magnetic loop antenna with air core, a more effective approach is to use a single turn of the same size made from a thicker, high-conductivity conductor (pure copper or silver). This helps minimize resistive losses and improve overall efficiency by reducing heat dissipation.

author: radiolistener
author_rank: Super Contributor
timestamp: May 31, 2025, 12:38:41 pm
content: Quote from: Amish_Fighter_Pilot on May 31, 2025, 08:36:24 amno, you have a bit of a misconception here. In RF systems, the more precisely and sharp an antenna is tuned to a specific frequency, the better its sensitivity and efficiency at receiving or transmitting signals on that frequency. An "untuned" or broadband antenna does indeed cover a wide range, but this comes at the cost of performance - it has poor sensitivity and is very inefficient.Very high Q-factor antennas are very selective and sensitive, but have a very narrow bandwidth, which makes them impractical for general-purpose use since even small frequency shifts can require retuning. On the other hand, very low-Q antennas (broadband ones) are less sensitive, meaning they miss weaker signals entirely unless the signal is exceptionally strong.Thus, the most effective antenna is one with the highest possible Q-factor and precise tuning for the intended frequency range. The narrower the antenna's operational bandwidth, the more efficient it tends to be within that range.So, while a broadband or "Jack of all trades" antenna may seem versatile, it is generally not antenna, but just a piece of junk. A properly tuned antenna, matched to your target frequency, will always perform much-much better. Such broadband "Jack of all trades" antennas are derisively called as "rusty nail antenna type" by amateur radio enthusiasts, emphasizing that they are essentially useless junk rather than real antennas due to their very low efficiency.

author: iMo
author_rank: Super Contributor
timestamp: May 31, 2025, 07:44:21 pm
content: Afaik in US you may buy a ferrite rod of say 80mm diameter and 1meter long..Pretty heavy, though..

author: Amish_Fighter_Pilot
author_rank: Regular Contributor
timestamp: May 31, 2025, 08:17:22 pm
content: I only need the antenna to receive at very short distances: So I don't think it matters if it isn't a great antenna

author: coppercone2
author_rank: Super Contributor
timestamp: May 31, 2025, 08:55:37 pm
content: the way old ass radios that relied on high Q antennas used to work is you would have a box of different coils for different bandwidths that would plug into some kind of connector (like a double banana plug) and you would pick a coil to use. When electronics got better it was 'pick a crystal to use'. Ever see "A bridge too far" where they shipped the wrong radio crystals to the market garden commandos?Then as things got even better it was just dial a frequency.The idea is there is like a atmospheric noise floor for MOST COMMON radio uses that eventually makes it possible to surpass some giant pain in the ass like having a box of coils or crystals with advanced circuits. But there is always some penalty for integration and automation.Coil = big fragile cumbersomecrystal = fragile, less cumbersomeelectronic control = easy (cheap)If you have a low noise amplifier you don't necessarily need a little more Q from a custom basket weave coilSome old precision radios come with literally a crate of shielded inductors that you would swap out for different frequency operation (often in a vacuum tube connector form factor). Extremely expensive solution.The intrinsic benefits of these old solutions is still there. Its just that the LNA compensated enough for it that its not worth the hassle for what we consider general use. Supposedly. For a while in like 1980 when HAM was still popular and before mass proliferation of inverters lol. Now it seems like people are getting really interested in antenna shielding, of all things, for LW receptions in places there is humans. (which used to be way less relevant unless your in a major metro area or something)

author: radiolistener
author_rank: Super Contributor
timestamp: May 31, 2025, 09:21:12 pm
content: high Q-factor antenna and crystals are different things. High Q-factor antenna give you noise free gain which you cannot get with other ways, so it cannot be replaced with something other and plays the same critical role (or even more critical) with any modern technology receivers, such as DDC SDR, low-noise amplifiers and other things.Crystals pack can be replaced with a good low noise oscillator and synthesiser, but high Q-antenna cannot be replaced, there is no replacement.

author: coppercone2
author_rank: Super Contributor
timestamp: May 31, 2025, 09:22:39 pm
content: What I am saying is that having to plug in accessories into the device is something engineers work very hard to eliminate to facilitate ease of use. The electrical function is in a different place but none the less when is the last time you saw a radio for sale that comes with a dominos tray of crystals or a storage case of different basket coils? Its unheard ofthey went variable 'tunable'I doubt you can exactly replace the specific nature of a socket crystal with another circuit either. Close or even very close (for current uses) maybe. It is like comparing some adjustable tool to a gauge block (in a theoretical sense, practical execution is another matter). It's just development of those technologies stopped. I often wonder what would happen if you rebuild some of those parts with the latest techniques in material science and circuit layout...

author: Perrold
author_rank: Contributor
timestamp: May 31, 2025, 10:01:17 pm
content: Quote from: Amish_Fighter_Pilot on May 31, 2025, 08:17:22 pmWhat are you trying to receive and at what distance? That is probably the better question to start with.

author: TimFox
author_rank: Super Contributor
timestamp: May 31, 2025, 10:09:34 pm
content: The old National Radio "HRO" receivers used a plug-in bank of coils to change bands, rather than a large rotary band-switch dial.The contents were basically the RF coils used on the RF amplifier and mixer circuits, along with the oscillator coil for each band of the superheterodyne receiver: all of the coils that other receivers changed with switching.See the examples shown inhttps://www.radioblvd.com/national_hro_part1.htmand look up parts 2 to 4 linked therein.The beautiful "epicyclic dial" used in these sets had the numbers in the five windows change with rotation.A graph on the front of the plug-in coil sets related the actual frequency to the dial.The HRO-500, I believe, was the last "HRO" and used a synthesized local oscillator instead of switched coils.The epicyclic dial gave a linear readout in each of the 60 500 kHz bands.However, theQof the antenna circuit is due to the resistive (lossy) part of the circuit that contributes to the overall noise.Also, at hf, there is a lot of noise seen as field strength due to atmospheric effects and electrical interference.Once noise is added to the circuit, it can only be removed by further reducing the bandwidth (done in the IF in a normal short-wave receiver).

author: radiolistener
author_rank: Super Contributor
timestamp: May 31, 2025, 10:52:07 pm
content: Quote from: TimFox on May 31, 2025, 10:09:34 pmI wouldn't describe it as atmospheric noise - it's more industrial in nature. During the bombing of my city, there are times when the entire power grid of city fails. In those moments, the radio spectrum becomes crystal clear, almost free of noise, revealing broadcast stations from around the world that are usually completely flooded in noise floor.I captured a screenshot during one such event - the entire forest of peaks visible represents broadcast stations from across the globe. It’s truly incredible. I believe that by moving far away from urban areas and power lines, one could achieve a similarly crystal clean reception environment.

author: Amish_Fighter_Pilot
author_rank: Regular Contributor
timestamp: May 31, 2025, 11:00:48 pm
content: Quote from: Perrold on May 31, 2025, 10:01:17 pmI'm doing a sound experiment based on the concepts of Radio Direction Finding BFO. I'm using it to make sound samples of selected interference. The transmission distances are less than 5 meters typically. Often less than 1 meter. That's assuming I am even transmitting and not just listening to something ambient. I have a few ideas for the system.

author: TimFox
author_rank: Super Contributor
timestamp: May 31, 2025, 11:02:32 pm
content: "Atmospheric noise" is a common term of art, to distinguish the noise from thermal noise.Besides industrial sources, there is also lightning as generators of RF noise in this part of the spectrum.List of terminology:https://unacademy.com/content/nda/study-material/physics/terms-used-in-communication-system-noise/

author: radiolistener
author_rank: Super Contributor
timestamp: May 31, 2025, 11:21:58 pm
content: What I meant is that much of what is commonly perceived today as “atmospheric noise” is actually industrial noise from surrounding electronics and infrastructure. If you travel far into remote areas - away from cities, settlements, and power lines - the natural noise floor in this part of the spectrum can be quite low, not much above thermal noise.Lightning, of course, remains a natural and significant source of RF noise. It's clearly visible even in the VHF range - today we had a thunderstorm here, and I observed broadband impulses across the entire 145 MHz band caused by lightning.Even in a large city with numerous sources of interference, it's often possible to receive AM broadcast stations on the medium wave band with pretty good quality if you move just 50 meters away from buildings and power lines. Inside buildings, however, reception is nearly impossible due to the extremely high noise levels.

author: Amish_Fighter_Pilot
author_rank: Regular Contributor
timestamp: May 31, 2025, 11:59:10 pm
content: Quote from: TimFox on May 31, 2025, 11:02:32 pmThanks. I mostly will be listening for phase shifts and beat frequency distortion caused by specific materials inside of an imperfectly shielded space.

author: Perrold
author_rank: Contributor
timestamp: June 01, 2025, 11:24:37 pm
content: Anything being "transmitted" over 5 meters shouldn't require the same level of care and effort as an actual receiving loop. Just do it. It'll all be boring near field stuff.

author: Amish_Fighter_Pilot
author_rank: Regular Contributor
timestamp: June 09, 2025, 08:19:20 am
content: So I have been playing around tonight and came up with an antenna design I haven't seen before that incorporates some aspects of basketweave, loopstick, and simple loop into one antenna. It is made from approximately 25'(7.62 meters) of 18ga bell wire. The idea is to put loading coils directly into the loop while barely affecting it's on-axis profile. I haven't had much time to play with it yet but the reception from it is surprisingly good in the at 17.3KHz(I have a metal detector pinpointer and was watching the antenna on my oscilloscope). I will try to get pictures when I can. I didn't expect this antenna to work so well and just really made it for fun. The design gets best reception in parallel to the transmitter, but the off-angle reception is significant. I would estimate it to be 30% signal at 90*. For what I am doing that isn't great, but it was surprising to me anyway.

author: Amish_Fighter_Pilot
author_rank: Regular Contributor
timestamp: June 09, 2025, 11:27:23 pm
content: Here's my new antenna. I call this design a "Loaded Basket Loop". I wanted to try and add loading coils directly to a loop antenna. The off-angle gain of it is better than anticipated(or wanted). I wish I had a VNA to check it with, but it seems to pick up the best clean signal at 2.3Mhz so it might be resonant at or near that. I can see it plain as day on my oscilloscope. I was seeing a modulated signal at that frequency.

author: TimFox
author_rank: Super Contributor
timestamp: June 10, 2025, 01:44:37 am
content: If it’s self-resonant at 2.3 MHz, you can easily tune down to the AM band (550 to 1600 kHz) with a good air variable capacitor. If you measure the inductance at 100 kHz or below, what do you get?

author: Amish_Fighter_Pilot
author_rank: Regular Contributor
timestamp: June 14, 2025, 07:49:08 am
content: I am saving up to buy a NanoVNA. Hopefully within the next couple of weeks I can get one. I am not sure what it's inductance at specific frequencies is, but I was able to do a bit of a trick with my DSO-TC3. It can't measure inductors under 50uH, but if I put them in series with a known inductor that is big enough to read; I get the combined inductance of both inductors. I tried a few known transformers and it consistently was showing it to be 30uH and the DC resistance is less clear at somewhere between 1-2 ohms in the various readings.I found the coil below on a web search and it is rated at 30uH, but I don't know a lot else about it aside from it being a similar diameter to mine(mine has 13 turns and that one has maybe 20). It leads me to believe that number is at least roughly accurate.

author: coppercone2
author_rank: Super Contributor
timestamp: June 14, 2025, 07:57:44 am
content: what material is the frame of that coil lol, it looks just like steel/iron

author: iMo
author_rank: Super Contributor
timestamp: June 14, 2025, 08:07:52 am
content: Quote from: Amish_Fighter_Pilot on June 09, 2025, 11:27:23 pmNice basket, indeed..Do not forget to include those 104 small inductive loops into your L calculation..

author: Amish_Fighter_Pilot
author_rank: Regular Contributor
timestamp: June 14, 2025, 09:30:00 am
content: Quote from: coppercone2 on June 14, 2025, 07:57:44 amYeah they're just nails lolI thought about using ferrite but I didn't have a matching set

author: radiolistener
author_rank: Super Contributor
timestamp: June 14, 2025, 11:23:17 am
content: Do you understand that these nails and windings around them significantly affecting your coil properties and increasing energy loss?

author: coppercone2
author_rank: Super Contributor
timestamp: June 14, 2025, 07:05:27 pm
content: Oh I meant the commercial coil frame, is that dark bakelite? I never saw it like that beforeFor your own antenna you want plastic hardware or ceramic if you have the money ideally.https://www.mcmaster.com/products/bolts/material~plastic-1/But your design with ferrite in the antenna is some weird LF hybrid.

author: coppercone2
author_rank: Super Contributor
timestamp: June 14, 2025, 07:07:26 pm
content: What you did seems most similar to thishttps://www.eevblog.com/forum/rf-microwave/ferrite-sleeve-antennas/Read the document it has something conceptually similar and you see the result is like potential material savings but it seems difficult to engineer.if you scroll down page 100 or so, you will see actual pictures of what they built. But it does not have individual loops (series inductance in the antenna). What you did probobly does something but no one is gonna know what IMOKeep in mind the point of ferrite sleeve antennas is low frequenciers, like longwave and VLF and stuff. Your idea is HF so IDK how relevant any math or analysis in there is related to distributed cores.The only simple one that most people know is adding a small coil to a monopole antenna to change the electrical length (I.E. wifi antenna). I never saw inductance in series with a loop beforeAt least you can do a simple experiment to tune something and remove nails to see what they do, then retune and see how the signal strength is

author: Amish_Fighter_Pilot
author_rank: Regular Contributor
timestamp: June 14, 2025, 09:59:21 pm
content: The ferrite sleeve antenna is interesting. I had to look around a little to find pictures of it.https://swling.com/blog/tag/ferrite-sleeve-loop/The nails are necessary structurally, but I do intend to try a version without them when I can find something strong enough. At this point it isn't intended to be anything serious. I just made it on whim and was surprised by how good the reception is from a couple of different transmissions.

author: TimFox
author_rank: Super Contributor
timestamp: June 14, 2025, 10:46:28 pm
content: To avoid iron nails, etc. when holding down wires for high-Q coils, I have used polypropylene (notnylon) "ty-wraps" into holes on a low-loss substrate (e.g., polyethylene or polystyrene).Donotuse black polypropylene (sold for UV resistance), which is stabilized with carbon. The good stuff for this purpose is green.

author: coppercone2
author_rank: Super Contributor
timestamp: June 14, 2025, 10:56:50 pm
content: usually what they seem to say in general is that conductive objects near the antenna cause loss. I don't know anything about using them on purpose

author: Amish_Fighter_Pilot
author_rank: Regular Contributor
timestamp: June 14, 2025, 11:11:51 pm
content: Quote from: coppercone2 on June 14, 2025, 10:56:50 pmIt kind of reminds me of a tiny version of this:https://commons.wikimedia.org/wiki/Category:Circularly_Disposed_Antenna_Array

author: TimFox
author_rank: Super Contributor
timestamp: June 14, 2025, 11:18:58 pm
content: In the "near field" region, close to the antenna, conductive objects will have currents induced in them (not radiation) and absorb energy from that field (which is oscillating, not radiating, and storing energy).For example, putting an antenna close to a tree will increase loss (lower Q).Similarly, ferromagnetic objects in the near field will dissipate power: each traversal around the hysteresis loop dissipates an amount of energy equal to the area of the B-H curve enclosed by the loop.

author: Amish_Fighter_Pilot
author_rank: Regular Contributor
timestamp: June 15, 2025, 08:23:59 am
content: That must make radio towers a real pain to design. There's tons of steel in them. I'm guessing there's tricks to deal with it or we wouldn't be having this conversation because I'd have no hotspot

author: TimFox
author_rank: Super Contributor
timestamp: June 15, 2025, 02:39:01 pm
content: One trick is using “egg” insulators along the guy wires that stabilize the tower to break up the conductor.Properly installed, should the insulator fail, the guy wire is still mechanically sound to avoid catastrophe.