Help understanding ferrites, I want saturation  - Page 1
Forum section: electronics / rf-microwave

author: Qmavam
author_rank: Regular Contributor
timestamp: August 21, 2019, 01:40:00 am
content: I have found I need to give detail, or the answers go everywhere but where I want. So have a seat! :-)I am putting down a 250ft "Beverage On Ground" Antenna, BOG. It is possible to reduce the velocity factor by placing about nine inductorsspread out along the length of the antenna. The effect is to make the antenna longer. I hope to make the antenna more broadband by adjusting theinductance of the nine inductors. I'd like to use it from 500kHz to 4MHz.I personally have not modeled it, but someone I assume modeled it says I need 70 uh at 500MHz and 0 uh at 4MHz.So, I want a ferrite that will only haveonewinding of 70uh. I expect to pass dc through the antenna and thus the70uh inductor(s). The more dc I pass the lower the inductance of the inductor(s).I'm looking for an inductor that will somewhat softly saturate over 0ma to maybe 500ma of dc current.. (Everything is subject to change as needed.)Maybe there is a material that does just what I want. Probably not. So is there a material I could put in the gap of a pot core that would saturatemuch easier than the potcore material itself. I might be only 0.001" or 0.1". But it needs t go into saturation as I increase the dc current.Preliminary drawing of Idea below.Thanks for reading and any help you can give me[ Specified attachment is not available ] [ Specified attachment is not available ] [ Specified attachment is not available ] [ Specified attachment is not available ][ Specified attachment is not available ] [ Specified attachment is not available ]

author: coppercone2
author_rank: Super Contributor
timestamp: August 21, 2019, 03:43:32 am
content: I find this project really interesting but I don't know. It has like every feature of magnetic RF device that I would want to work on in a project.

author: radiolistener
author_rank: Super Contributor
timestamp: August 21, 2019, 08:16:01 am
content: Quote from: Qmavam on August 21, 2019, 01:40:00 amInductor cannot make your antenna longer. It just changes it's resonance frequency by adding inductance, but don't improve it's efficiency. On the contrary, inductor adds loss. Also note, that ferrite has high loss.If you want to use it with transmitter, then use iron powder core for inductor. More power requires bigger core:https://vvvv.aliexpress.com/store/group/Iron-Power-Cores/346423_507303475.htmlFor 2 - 30 MHz range you're needs powder mix #2 (see material #2, red), for example:T200-2For 0.5 - 5 MHz range you're needs powder mix #1 (see material #1, blue), for example:T200-1You can use online calculator to calculate your toroid:https://www.changpuak.ch/electronics/amidon_toroid_calculator.phpFor example, if you needs 70 uH for 0.5 - 5 MHz, then use T200-1 with 53 turns. It will give you 70.23 uH.Also, I don't understand - for what reason there is a DC bias for antenna which don't have LNA. This is useless.Quote from: Qmavam on August 21, 2019, 01:40:00 amif you use inductor with saturated core you will get just high loss, low inductance and burned out inductor core. What is the reason to do it?Instead of using variable inductors across antenna, you can just use antenna tuner with the same effect.Antenna efficiency depends on it's physical size and the presence of RF energy absorbers in the near field region (such as Earth, any metal things, water and other).Resonance is needed just to to turn your antenna into LC circuit to use it a preselector. It allows you to get some gain in cost of reduce antenna bandwidth, nothing else. You can get the same result by placing antenna tuner at the feeding point.

author: Qmavam
author_rank: Regular Contributor
timestamp: August 21, 2019, 02:20:03 pm
content: Quote from: radiolistener on August 21, 2019, 08:16:01 amPlease read about beverage antennas and then BOG, they are not like a resonant antenna. Here's a search of BOG antennas.https://www.startpage.com/sp/searchHere's a short video of my comparing my previous BOG to other antennas.Mikek

author: Qmavam
author_rank: Regular Contributor
timestamp: August 21, 2019, 02:38:23 pm
content: coppercone2 said,I find this project really interesting but I don't know. It has like every feature of magnetic RF device that I would want to work on in a project.Well please jump in!I'm lacking the knowledge, but I'm in for the fight.I need a material that saturates at a low H or Oersted or A/m or Tesla. It's pretty crazy!The lowest I have seen so far IIRC is about 2 Oersted.One concern brought up was non-linearity of a core in saturation, however, that person didn't really understandwhat I was doing. So I don't know if that is a real possibility, I related it to mixing products in a diode, but I also suggested,aren't all ferrites non-linear even in normal operation.So, Your mission coppercone2, should you choose/decide to accept it, ...As always, should you or any of your EEVblog Electronics Community be caught at the bench working late nights, the Secretary will disavow any knowledge of your actions. This tape/disc will self-destruct in five/ten seconds. Good luck, coppercone2.Any help you can provide will be highly appreciated. :-)Mikek

author: radiolistener
author_rank: Super Contributor
timestamp: August 21, 2019, 06:08:23 pm
content: Hm... Beverage antenna is a traveling-wave antenna, it don't needs inductors. It just uses very-very long wire to radiate/receive EM wave. And there is no standing wave in traveling-wave antenna. In order to eliminate standing wave it uses load resistor on the end of wire, so the part of energy which is not radiated by wire will be consumed by dummy load resistor at the end of wire.Such kind of antenna uses very-very long wire to radiate/receive EM wave. If you replace part of wire with inductors these parts won't works, because inductor will not radiate/receive EM wave. Using shortened wire leads to more loss on dummy load resistor at the end of wire, nothing more. Inductor cannot change this.This is not resonant antenna and there is no standing wave, so using inductors makes no sense at all.So, I'm confused, for what reason you're using inductors in your antenna?In resonant antenna there is a sense to use inductor. It allows to make phase shift to create standing wave in a short wire. Standing wave allows to increase I and U amplitudes in a short antenna by accumulating oscillations. And it leads to higher E and H field strength which leads to compensation of short physical size of antenna by high field strength. As a side effect it also leads to the narrowing of the bandwidth and increased heat loss (because higher currents).But traveling-wave antenna don't uses standing wave, so there is no sense to make phase shift with inductors...

author: Qmavam
author_rank: Regular Contributor
timestamp: August 21, 2019, 06:42:47 pm
content: Quote from: radiolistener on August 21, 2019, 06:08:23 pmHere's a page from an antenna guru, W8JI.It's short, but gives some info about loaded beverages.https://www.w8ji.com/slinky_and_loaded_beverages.htmA little on his bona fides,https://www.w8ji.com/I'm just applying the loading to a BOG to get it to be more directional in the BCB.Mikek

author: radiolistener
author_rank: Super Contributor
timestamp: August 21, 2019, 07:01:11 pm
content: I'm not sure.. Is this some kind of alternative science antenna? Some kind of a technology like EH antenna?Because classic Beverage antenna don't needs inductors and it's efficiency cannot be improved with any kind of inductors or capacitors. All power which is not radiated by wire in a single pass will be consumed by a dummy load and there is no way to return it back, because such modification will turns antenna into classic resonant antenna. Isn't it?

author: Qmavam
author_rank: Regular Contributor
timestamp: August 21, 2019, 09:35:46 pm
content: QuoteWhen the Beverage antenna is shorted considerably, to about 20%, and then laid it on the ground, I would say it is no longer a classic Beverage antenna, so now lets fix the problems created when we shorted and lowered it. Let's start by considering using inductors to reduce the Velocity Factor.From W8JI,"When space is limited and a Beverage antenna is too short for normal operation, increasing inductance along the length of a "Beverage" will increase directivity.""As Vp is slowed, the antenna shows increased end-fire response and a gradually narrowing pattern. End-fire arrays fire in the direction of lagging phase, and the slower Vp causes more optimum phasing but only within certain limits.""They exhibit improved directivity because wave velocity is slowed, altering phase shift along the length of the antenna."(snip) and loaded Beverages show increased directivity because velocity of propagation along the antenna is decreased."https://www.w8ji.com/slinky_and_loaded_beverages.htmMikek

author: coppercone2
author_rank: Super Contributor
timestamp: August 21, 2019, 09:38:47 pm
content: the reason I don't chime in is because while it sounds very interesting I never heard of anything like this before.I do find active biased inductors interesting, for whatever reason. I only heard about it for use with magnetic amplifiers.I also don't like the term saturation (it sounds like something with textiles) when it comes to magnetic devices, I like 'maximum alignment or something.

author: Qmavam
author_rank: Regular Contributor
timestamp: August 21, 2019, 11:40:13 pm
content: Quote from: coppercone2 on August 21, 2019, 09:38:47 pmHow about doing a search on, variable inductors, Transductors, DC controlled Inductance, tunable toroids and any other search term you might think of.over the years I have seen a good article on using a 4C6 or more likely a 4c4 material as a tunable inductor. But in the last few days, I have not been able to find it.Please post if you find any articles with good info, especially real builds. That's what the 4C4 article was. I thought it was neat but never had a use, now I want it,can't find it.Especially important, if you see info about mixing products caused by non-linearity.I recently saw an article about a very flat amplitude over frequency oscillator built with a dc controlled inductor.But again my want is an inductor that will dc saturate at less than 500ma with the same turns used for the 70uh inductance.Been on it a couple days and haven't had any one saw sure no problem. But lots of detractors.MikekI found the Inductor tuned OSC.and a transductor, [url=https://www.robkalmeijer.nl/techniek/electronica/radiotechniek/hambladen/radcom/2003/01/page78/index.html]https://www.robkalmeijer.nl/techniek/electronica/radiotechniek/hambladen/radcom/2003/01/page78/index.html

author: Qmavam
author_rank: Regular Contributor
timestamp: August 22, 2019, 12:29:32 am
content: I might have found a solution.It was in the OSC page above, but I found a page with pictures, I can read pictures! :-)Here's my thought,The electromagnet saturates the core, and the 0.47uf by passes the RF around the electromagnets inductance.I just took a random core with 100uh and put a Neodynuim magnet on each side, it went for 100uH to 4.6uH.Now to find a relay to destroy.From this article,https://elektrotanya.com/sites/default/files/comment/2018/04/crvco.pdfMikekAfter some more thought, this would require a HV power supply. Even If I found an electromagnet with only 50 ohms resistance, I need ten, that would be 500 ohms.If I could get saturation at 500ma That would require a 250dcV power supply.Now, how to maximize magnetic force, with a minimal resistance coil.

author: Qmavam
author_rank: Regular Contributor
timestamp: August 22, 2019, 02:11:53 am
content: Another thought.How do I get maximum flux with a minimum resistance coil and 500ma or less.Mikek

author: radiolistener
author_rank: Super Contributor
timestamp: August 22, 2019, 11:12:00 am
content: For what reason you're needs it?If you want inductor with smaller inductance, just place smaller inductor, it will have smaller size and better efficiency and don't needs DC supply.But inductors are completely useless for Beverage antenna, they don't give you any profit, except additional losses.Also keep your Beverage antenna away from the ground, in such way you will improve it's efficiency.

author: ejeffrey
author_rank: Super Contributor
timestamp: August 22, 2019, 04:25:57 pm
content: Adding periodic series inductors (or shunt capacitors) to a transmission line will lower the phase velocity. For a fixed physical length that increases the electrical length and therefore should increase the directivity of the radiation even if it doesn't increase the total radiated power. But it also creates a lowpass filter -- you are basically making a lumped element transmission line.If you bypass the inductors with capacitors it won't do anything! All the RF will go through the capacitor not the inductors so it doesn't matter that you are tuning the inductance!

author: coppercone2
author_rank: Super Contributor
timestamp: August 22, 2019, 10:08:33 pm
content: I assume it has something to do with thishttps://en.m.wikipedia.org/wiki/Loading_coilI never thought about a non air filled loading coil,I wonder if you can make a telescoping loading coil

author: Qmavam
author_rank: Regular Contributor
timestamp: August 22, 2019, 10:59:46 pm
content: Quote from: ejeffrey on August 22, 2019, 04:25:57 pmYes, I only have 250ft, great for 40M, 80M maybe 160M, but not for the BCB. For the BCB I need to add lumped inductors. But then I need to get rid of them for the other bands, or at least reduce them.QuoteNotice in the first drawing, I bypass only the electromagnet, not the inductor.Second drawing is incomplete, but still shows bypassing of the electromagnet only.

author: Qmavam
author_rank: Regular Contributor
timestamp: August 23, 2019, 04:33:55 pm
content: I found a core in my junk box that worked for the"Designing an interesting inductor"Here's the physical shape.As you can see I dropped it and chipped the most important part off and now it has an air cap.But, importantly, I found with only 60 turns on the dc coil I could reduce the inductance down from 100uh to 4uh with under 500ma.That was using my 100kHz inductance meter, so next I put it on the Q meter and found it runs out of steam at about 300kHz. Q goes to nothing.The AsubL of that core was around 2800. That core is about 2" per side and 11/16" deep, I don't need or want anything that big, but I do need room for enough turns of larger wire to keep the resistance low.Where can I buy an ferrite E core that has that shape in a material with a 2000 or 3000 AsubL, that will work up to 4Mhz, or even higher?I expect any geometry that necks down to a small cross section willwork.Mikek

author: Qmavam
author_rank: Regular Contributor
timestamp: August 24, 2019, 04:00:24 pm
content: I've decided to try an EFD shape core, reasoning for the choice;I can turn one side 180*, the center leg over lap area is reduced to 14%.My theory is, that reduce area will saturate at lower flux.Is that reasonable?I don't have a lot of material choices.TDK materialAvailable materials, N87 and N97Material data here>https://www.tdk-electronics.tdk.com/en/529404/products/product-catalog/ferrites-and-accessories/epcos-ferrites-and-accessories/ferrite-materialsFair-riteAvailable material, 78Material data here>https://www.fair-rite.com/78-material-data-sheet/Which of those materials will work from 500kHz to 4MHz as a 100uh inductor?If you would like to educate me,Does the permeability curve relate to how well a material will performas an inductor over frequency?Or, ask another way, For a given material Does AsubL fall off as frequency increases like it's permeability curve?Thanks, Mikek

author: duak
author_rank: Super Contributor
timestamp: August 26, 2019, 05:41:15 am
content: Mikek, yes AL falls off with increasing frequency. If you want to wade through some math look at equations 3 through 12 in:https://www.edn.com/Pdf/ViewPdf?contentItemId=4324131The core materials you've linked to are probably not so good for what you want to do - they talk about a 500 KHz limit. It's not a hard limit but losses really increase when going past it.I had an idea to reduce the DC current needed to saturate the cores by using two wires instead of one and have the wires go through each core in opposite directions. The far ends of the wires would be tied together and the DC current would be applied to the open ends through some isolating inductors. The RF would be applied to both wires by way of coupling capacitors. What this does is double the effect of the DC current because it goes through twice (once there & once back) while the RF goes through once on both wires. The problem is that I don't think the RF will be affected by the variation in impedance presented by the cores because the RF currents in the two wires cancel because they're passing through the core in opposite directions. I then thought of having one wire go through each core twice while the other goes through each core once in the opposite direction. This now gives 3 turns for the DC current and one net turn for the RF. There's probably some other coupling I'm not considering that makes this all moot, but it might just work. If this actually works, then it should be possible to increase the number of total turns to what is needed to saturate the cores and make the difference in the number of turns equal to what's needed to develop the required inductance. Does this make sense?

author: Qmavam
author_rank: Regular Contributor
timestamp: August 26, 2019, 06:44:05 pm
content: I had a nice talk on the phone with a Fair-Rite tech, he taught me a lot in just a 15 minute phone call.Unfortunately, the gist of it was, the geometry I want is not available in the material I need.I finally found the permeability curves for TDK 87 and 97, it should not have been so hard to find.I'm sorry, as much as I want to understand, I don't.The dc core can have as many turns as I can fit on the bobbin.I can use relatively big cores, so not a huge problem.I don't understand the using two wires, are the currents opposed? Can't wrap my head around that, I might have to try it.Expound on that if you can, maybe even drawings, I can read drawings :-)On the variable inductor that worked, I used a core having a 2800 AsubL, I only needed 6 turns for my 100uh inductor. that was great.I had 60 turns on the DC winding and room for more. Unfortunately that was poor core material.I'm still digging, the proper material is available, just not sure what shape I need.Some other ideas,

author: duak
author_rank: Super Contributor
timestamp: August 27, 2019, 05:41:57 am
content: Qmavam, I've attached a drawing of what I mean. The arrows show the DC current going out and back over the two wires. Because the back wire enters from the opposite side of the core and the current flowing flowing in is opposite to that of the other wire, the magnetic flux is doubled. This is because there are two turns.There is a problem though because the RF current will be going the same way at the same time in both wires thus cancelling any RF magnetic field in the cores. By increasing the number of turns on all the cores on only one of the wires, the RF current does not cancel and it will now see a reactance from the core. Do you see this? That being said, this scheme would have to be tested as I may have missed something. Each one of those cores is also a transformer and so there may be some coupling that I can't see.To get on with core sizing whether you use my scheme or not. Do you expect to transmit with this antenna? If so, do you know what the expected RF current will be? Now comes the juggling act. Assume the RF current has a peak value of 1 amp. You'll have to find a core that can give the inductance you want without saturating. You'll probably want to operate the core at a low flux level (B in Gauss or Tesla) to minimize non-linearity. It might be better to use core pairs or two balanced windings on an E-I or EE core as a saturable reactor to get around non-linearities. Seehttp://osbornetransformer.com/saturable-reactor-winding-configurations/If you're just receiving then it's a lot simpler because the RF current is negligible. You just have to figure out how much DC current is needed to cause the flux (B) to go to Bmax given the number of turns you determined for the RF inductance. You also have to confirm that the wire can handle the DC current without overheating.About the core shape. I'm not quite sure why you want a gap which is then filled with a higher mu material. Are you thinking that the total core flux range will be up to the Bmax of the high-mu material? ie., the larger core pieces are there only to complete the magnetic circuit? This is an interesting idea and it may work. Note that the high-mu material in the gap is doing most of the work and the maximum RF power handling capability and linearity is detemined by this material.Rather than filling an air gap you may find it easier to reduce the cross section of the center leg in a E core or grind away part of a toroid. Sort of what a flat tire looks like. One way to look at this is to think of how many iron atoms are being magnetized. When the magnetic circuit cross section is reduced more magnetic flux has to pass through the same area so the flux density there goes up. Because there are fewer iron atoms there, the material is closer to saturation and so is controllable by a DC flux. It may make sense to attach a high-mu bar over the flat spot thus introducing high-mu material into the magnetic circuit. The toroid would then be more 'D' shaped.The classical way is to control the mu of the entire core. All ferromagnetic cores saturate given enough amp-turns. An air gap is added to a core to increase the number of amp-turns needed to saturate it. An air gap also tends to linearize the B-H curve ie., the magnetic flux generated more faithfully follows the current. This is great for a signal transformer. Since you want to saturate the core you will probably want to use the least amount of DC current and to do this you want the greatest flux from the amp-turns and so there is no gap.Does this make sense? I feel that I'm rambling here. I have worked with magnetics but haven't worked with varying the magnetic properties of a material with a DC bias. I wish I had more time to try some of these ideas out myself.Cheers,

author: Qmavam
author_rank: Regular Contributor
timestamp: August 28, 2019, 12:19:07 am
content: Quote from: duak on August 27, 2019, 05:41:57 amHi duak, First let me say how much I appreciate the thought you put into this.QuoteI haven't thought this out as much as I hope to, but one nice thing about that scheme is I wouldn't need a dc control wire at the far end. The dc control current can all be done at the feedline end. Also, I expect to use army surplus field phone wire, it's two wires, so the idea is brilliant! (if it works) :-)QuoteNo transmitting on the antenna. µvolts to millivolt signals only.QuoteI need to spend time studying that page, I am curious about non-linearity, and if any of those configurations would reduce non-linearities caused by saturation in the cores.I have been told that I'll create non-linearities if I saturate the core, I likened that to a diode causing mixing products, I don't know if that was correct analogy or not.QuoteI wound a 4C6 potcore with 50 turns, put it all together and then wound 16 turns through the hole across the bottom up the side and through the hole again. The 16 turns was about 80uH. The 50 turns was for dc saturation. I didn't find this especially good. It reduced inductance from 80uH to about 50uH with about 1.5 amps. It didn't get hot at 1.5 amps. I think I will end up with bigger cores, because I expect 9 of these in series, if I had 5 0hms each, that's 45 ohms at 1 amp is 45Volts, possible, but I was thinking more like 12 volts on my control line. My first test, a custom E core, went from 100uH to about 4uH. But the material was not suitable for HF.QuoteI'm not sure I'm smart enough to think of that! I don't recall that I said I wanted higher mu material, what I want is a smaller cross section, thinking it will saturates easier.QuoteI don't follow that, but again, I want a necked down area there, AND if it was material that saturated easier than the rest of the core, I think that would be good.QuoteBelieve me I have thought about grinding ferrite, but dropped the idea because I need so many and I'd like some consistency. I did cut a slot partiallythe way through a toroid and it did reduce the current to cause saturation. I need to revisit that core again.QuoteYes, that shows me you know exactly what I'm trying to do, even with the disks on the E core, less area, fewer iron atoms there.QuoteI don't get this! Why do I want the High mu bar? I wanted to make that area saturate.QuoteYes. no air gap.QuoteNo rambling, all good info.You have made more sense and added more information for me than I have got sense I started this project.The biggest problem I'm having is getting a material that will work 500kHz to 4MHz and in a geometry that allows me to do what I need to.That's why I used the 4C6 it is HF material, and I had it. But it is low permeability and hasn't acted like I wanted.I'm starting to think I might be able to use a standard E core, just use more turns. Or As I'm rereading the article, maybe a simple toroid.Don't know if you took time to read it, but I think I'll reread, I just saw something I didn't see the first time, that may help.https://elektrotanya.com/sites/default/files/comment/2018/04/crvco.pdfThanks very much, I think I have a few questions above if you have time to respond.Mikek

author: rf+tech
author_rank: Frequent Contributor
timestamp: August 28, 2019, 04:06:04 am
content: Qmavam,The techniques discussed so far all rely on the continuous flow of direct current, to maintain a desired inductance value.I am presenting the attached patent as an alternative approach to permeability tuning, for your consideration.This patent sets forth a means of varying the degree of static magnetic bias applied to an inductor, incorporated into an antenna coupler. Continuous flow of DC is *not* required, to maintain the desired inductance value.The AN/PRC-70 military portable HF-VHF transceiver implemented this technique in its antenna coupler. Schematics are available, if there is interest.RF+ Tech

author: Qmavam
author_rank: Regular Contributor
timestamp: August 28, 2019, 05:10:45 am
content: I appreciate you posting that patent.You say, " Continuous flow of DC is *not* required, to maintain the desired inductance value.I don't see that. Figure 1 is pretty much what I want to do, vary the dc on one winding to alter the inductance of the other winding.Figure 4 seems to by a stepped inductance, controlled by putting a current through winds around 3 different magnets. The currentcan be on on, off or on but reversed to provide differing amounts of saturation. But I don't see that you can remove the current and maintain the desired inductance.As I understand it.Am I missing something?Mikek

author: rf+tech
author_rank: Frequent Contributor
timestamp: August 28, 2019, 11:20:22 am
content: Qmavam,Read the Abstract carefully. Especially the very middle part of that paragraph.Magnets are utilized to bias the RF inductor core, and the degree of magnetization is varied stepwise, by pulses of direct current, under R-Theta detector control.The electromagnets themselves do not directly influence the RF inductor core. The electromagnets control the magnets' degree of magnetization.RF+ Tech

author: Qmavam
author_rank: Regular Contributor
timestamp: August 28, 2019, 02:30:54 pm
content: Quote from: rf+tech on August 28, 2019, 11:20:22 amOK, I'm sure it's above my ability to pick a magnet that I can increase, decrease and reverse the magnetization of with pulses of current.I would think they would need to be pretty large pulses to magnetize a magnet or even reverse the magnetization of a magnet.Neat idea though.MikekEdit, I should not have used increase and decrease. Each magnet is either not magnetized, magnetized , or has reversed poles. All by way of pulses on the coils.Any way not the way I want to implement.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: August 29, 2019, 02:33:40 am
content: Hah so it's a saturable inductor with latching-relay operation? That's pretty cool.Tim

author: rf+tech
author_rank: Frequent Contributor
timestamp: August 29, 2019, 04:08:20 am
content: Tim,As implemented in the AN/PRC-70 antenna coupler, the solenoid electromagnet winding has a cylindrical magnet for its core.The magnet's charge is altered, from essentially demagnetized to maximum magnetization. From one end, to the other and all points in between.Two ferrite pot cored inductors, one with 2 turns, the other with 4 turns, are stacked on the magnet/solenoid assembly and then enclosed in a mild steel frame, to complete the magnetic circuit.When the tuning cycle finishes, the magnet is left to bias the the ferrite pot cores at the required inductance. Cool operation, since no further DC power is required.I have some of these antenna couplers and can contribute a tear-down of the permeability tuned components. Not intending to hijack Qmavam's thread, I'll leave the decision to him as to whether I should add further content to his thread.RF+ Tech

author: coppercone2
author_rank: Super Contributor
timestamp: August 29, 2019, 04:12:25 am
content: what material is used for highest remenesence?

author: rf+tech
author_rank: Frequent Contributor
timestamp: August 29, 2019, 09:59:02 pm
content: @coppercone2I cannot say with any certainty what material the core is made of. I would guess an iron-nickel alloy. In it's present magnetic state, the core exhibits a mild attraction to a non-magnetized screw driver, not what one would expect from an Alnico magnet of these dimensions.There are grinder marks visible from the length finishing operation. Core measures 0.66" diameter x 1.25" long.The pole piece next to the frame fills the gap between the pot-core stack and transitions the 0.66" pole piece diameter to the 1.0" pot core diameter.RF+ Tech

author: coppercone2
author_rank: Super Contributor
timestamp: August 29, 2019, 10:13:20 pm
content: is it pulsed or biased with a slow current source which is disconnected?that might give us an idea of the flux required so a material can be chosen

author: rf+tech
author_rank: Frequent Contributor
timestamp: August 30, 2019, 12:06:08 am
content: @coppercone2:It's pulse driven, under microprocessor control.There are two reactors in the antenna coupler, R Reactor and Theta Reactor. Current pulse polarity is reversed, to demagnetize the core as needed. Both magnetic poles (N/S) are utilized for minimum inductance. The microprocessor keeps track of which magnetic polarity was last used, then on the next tune cycle, if more inductance is required to obtain a match, the micro drives the current pulses with the opposite polarity to gradually demagnetize the core and stop at the new, higher inductance value.An the end of each tune cycle, the core is left with a level of magnetism, that in turn biases the ferrite pot-cored RF inductors to the value required to obtain a match with whatever long-wire antenna may have been tossed up in a tree. (Obviously, there are capacitors switched in/out by latching relays, as needed.)All of this action is in response to the R and Theta signals from an RF bridge detector.Schematic attached.RF+ Tech

author: Qmavam
author_rank: Regular Contributor
timestamp: August 30, 2019, 12:10:06 am
content: Hi rf+tech,While I find it interesting, I like the idea of a continuously adjustable inductor. Just turn a knob from 0 to 10 and find the lowest S/N.I have figured out 4C65 is most likely the material I will order, but 4A11 and 3D3 are options, with regard to my frequency of interest. I like both 4A11 and 3D3 because of there initial permeability, 750 and 850 vs 125 for 4c65, and if found in the right geometry I add some to the order.I think this thread has run it's course for me. I may even start looking for relays to modify for the electromagnet.I'm sure I will have more questions, but I'll probably start another thread then.Thanks, Mikek