Best toroid / magnetics for non resonssnt verticals?  - Page 1
Forum section: electronics / rf-microwave

author: cdev
author_rank: Super Contributor
timestamp: August 11, 2020, 03:14:44 am
content: I'[m getting ready to run some ling wires to get a lay of the lansd as it were. What do you think is best>Many suggect #43 material for ununs, it seems.An FT-240 -43 ?Two or more of them?Some people put two, one inside of another?Some people even use other materials, like 52,This is for an vertcal antenna in a tree,,,

author: fourfathom
author_rank: Super Contributor
timestamp: August 11, 2020, 04:10:02 am
content: Frequency and power?

author: cdev
author_rank: Super Contributor
timestamp: August 11, 2020, 02:23:48 pm
content: 3-30 MHz , and my goal is to make a unun that could handle a future power upgrade from QRP to mid power.So the main toroid needs to be a biggish one. Ive read that one way to get a higher impedance and power handling capacity and efficiency into a smaller space is to use two toroids of the same material with a smaller one inside of the bigger one.At the shack end there will be an antenna tuner. Both ends of the coax will be grounded with ground rods, and I plan to also have a counterpoise or radials, but how I do that I am still contemplating..What I am most wondering about is which kind of transformer and material and turns ratio has the best chance of handling the situation gracefully at a full range of frequencies and not being that lossy at any of them.

author: A.Z.
author_rank: Super Contributor
timestamp: August 12, 2020, 10:53:06 am
content: Quote from: cdev on August 11, 2020, 03:14:44 amAn FT240-43 should fit pretty well for the 3 to 30 MHz range (and possibly even lower), checkthisfor informations; using a properly dimensioned wire the resulting UnUn should allow you to work with 400W continuous (or probably more), willing to go up with power, you may stack two toroids one above the other and then wind the wire through them (seeherefor an example), as for the UnUn,this oneworks quite well (but then it depends from the ratio you need), just replace the T200-2 with an FT240-43 since the "T" has linearity problems and you may face issues if using it, in short the T200-2 and T200-6 are high-Q toroids, they will serve you well for resonant antennas, but this isn't the case for a wideband/multiband oneMy 2 cents

author: A.Z.
author_rank: Super Contributor
timestamp: August 12, 2020, 11:54:55 am
content: Quote from: cdev on August 11, 2020, 02:23:48 pmok got it now; would you be so kind to post some more infos about your kind of setup ?Just curiousAlso, you're referring to a vertical, but if you have enough space, did you consider running a random ? It may be start from the feedpoint up a tree and then sloping down again; that could possibly allow more length and the ability to cover the "top bands", then willing to improve reception there, and assuming you've room, you may consider the idea of adding to the combo KK5JY "loop on ground" antenna for receive-only purpose, the resulting combo may surprise you

author: cdev
author_rank: Super Contributor
timestamp: August 12, 2020, 02:17:20 pm
content: I don't have a super large lot, I have what in my area is pretty much the smallest size lot. I have two candidate trees. Likely the one thats the best for this is a large hardwood tree thats already been hit by lightning once and so is scarred by that. For all that I know, it may even have a carbonized conductor inside it. But I have used it for receiving antennas previously and it works well. I think that under ideal conditions there may be 50 feet of vertical there, probably more like 45. I also want to leave room for growth. So my antenna will be held up by rope with a pulley and an adjustable size weight that the antenna doesnt cause problems for the tree.I have a 43 foot wire and unun in a closed plastic box currently. Its wired as a 9:1 unun.In the box is a toroid that is small, not really large enough for any power. It was bought premade and the box its very well made, clearly by somebody who knows how to do such things, so I suspect it would be a fine choice, still, it seems a shame to waste such a large box on such a small toroid.It's large enough for a much larger core. So I think I want to bring it indoors and test it and probably redo it with a larger toroid ringThe core thats in it now is white. It looks very good quality, its likely a iron powder core. A close relative to the #2 and #6 material cores that many projects use.But I don't know exactly what core it uses. The seller told me it could handle at least 100 watts which sounds reasonable but I don't think it could handle that continuously.Also, as a receiving unun, I have had much better luck using #43 material anything (even a ferrite split bead) as a core than I have for the #2 red material thats so popular.So I particularly want to experiment with different turns ratios and core materials, to get a better feel for the problem;.I want to use a nonresonant wire, as using a wire length. 43 feet is good for this and seems like a good amount for this particular tree, now, (which is still growing. ) Its such that the tip is non resonant on any ham band - if it was that would make it more difficult to tune and probably increase the cable loss if its not anywhere close to the transformed (by the unun) impedance. I am not really that into the idea right now of putting an atenna tuner at the base of the tree. Thats a bit much for me right now (Doing that right would likely be expensive) For all I know I might not get out so well here.Its very noisy here RF wise.Quote from: A.Z. on August 12, 2020, 11:54:55 amThere definitely might be room for another long wire in the future but doing that would require my buying at least one perhaps two long poles to get it up into the air much more. And that might be costly doing it right. Ive used a long wire on receive for a long time but at a lower height than I would like. So its radiation pattern is likely much lower than it would be if it was higher. This is likely part of the reson my best receive DX has often been with loops. To get out I think a vertical would offer the best all around chance of a low angle of radiation.As far as a counterpoise I think that I can do that fairly easily now, within my budget, and I may also buy some material to create a "screen" (like some chicken wire, maybe? if I can weld or solder to it, somwhow) a high density conductive screen to supplement radials. This is another area that I think is likely to be worth experimenting with. Using low power digital modes its now possible to get a sort of statistical understanding of how well ones signal is getting out, using very low power and digital modes.Supplementing the ground with some additional capacitance in order so that there is more ground current going into the ground and not into heating up the dirt. Solder thick wires to bond it to make sure there is a good contact and bury it under a layer of good dirt. Cut it so that the tree still has room to grow, and bond it with thick wire so that the whole ring of chicken wire is well connected to its entirety and also to the ground connection and grounding rod.I can add more grounding wires. the unun and 43 foot wire actually can do okay without much of a counterpoise.Adding more grounding is to have a high density of grounding near the foot of the tree. Otherwise it uses the coaxial feedline as its ground.Also I should put at least two ground rods in. That may even be required. I'd like to have a decent safety margin for lightning. Given as two trees on my property have been hit by lightning within the last several decades. It killed one of them.

author: A.Z.
author_rank: Super Contributor
timestamp: August 12, 2020, 02:31:03 pm
content: Using an unknown toroid and using the coax as the counterpoise isn't exactly a good way to put up an antenna, I'd rather go for a know toroid core with the appropriate number of windings, a good counterpoise/radials setup and, at least, a common mode choke at the feedpoint (right after the UnUn); as for the wire lenght, just ensure that it is longer than 1/4 wave at the lowest frequency and that it isn't 1/2 wave (or multiple) on ANY band you want to use the antenna, at that point, the impedance will be in the ballpark of a 9:1 UnUn (on ham bands) and, if properly installed, you won't need an ATU

author: cdev
author_rank: Super Contributor
timestamp: August 12, 2020, 03:15:12 pm
content: I think that judging from the overall quality of the workmanship and the apparent literacy of the seller, and the fact that the core in question looks to be high quality manufacture, I am almost certain that the white core is Amidon #7 material. Which is quite similar to #2 and #6 material but has significantly better temperature stability.Still, I am really itching to test it.Quote from: A.Z. on August 12, 2020, 10:53:06 amThank you for these links!It will be interesting being able to use digital modes and getting some statistics on what works best and what doesn't!My gut feeling from my experience so far is that what you are saying here is right.I am really looking forward to the recovery of the sunspot cycle and getting my ham license!

author: A.Z.
author_rank: Super Contributor
timestamp: August 12, 2020, 03:43:08 pm
content: Quote from: cdev on August 12, 2020, 02:17:20 pmwhy don't you consider the idea of using BOTH trees to setup a "random wire" (seehere), that's a really simple and cheap antenna, but, if properly set up, it will allow you to make good contacts, plus, if you have at least 148ft (consider that the wire may also be sloping up/down) it will allow you to cover all the band from 160 to 10 meters and, if properly setup, you won't even need an antenna matching unit, so it may be a win/win approach

author: cdev
author_rank: Super Contributor
timestamp: August 12, 2020, 08:25:33 pm
content: They are too close to one another and one of the trees is abutting a neighbor's property and hence not suitable for anything that requires radials or anything really to go over the property line. It might make a good support fror a very small loop that encircles the property in the future with some additional supports, but that would require some non-conducting poles as supports. Fiberglass would work.

author: A.Z.
author_rank: Super Contributor
timestamp: August 13, 2020, 06:49:00 am
content: Quote from: cdev on August 12, 2020, 08:25:33 pmI see; well, I'd suggest you to think at a way to put out a bit more wire (see the "random wire" link in previous post), that would allow you to go down to (40 or 80 meters), as an example, the wire end may be connected to the tree while the feedpoint will be near your house, the wire may then be sloping up or down, no problem, but it may also slope "sideway" as long as the angles it describes are at or above 100°, that could allow you to put up more wire even if you don't have "linear space" to put it straight

author: cdev
author_rank: Super Contributor
timestamp: August 13, 2020, 12:55:50 pm
content: In other words, less coax, more wire.Thats reasonable. Maybe I will see if I can give that a test. If the best I can do is make a big"C" what would you do with the far end? The longest wire that I think I could string at a decent height would come around and and in the front of my garage. Not far from the house. At that point, I could bring it back to the house to make the other side of a loop. As it left the house, it would fairly soon have to diverge. The length at that point would likely be around (just guessing 50 meters (the entire circumference of the loop.)So, much longer than the medium sized wire I have now for SWL but still not super large. And would require I put up some supports, like at least two long fiberglass poles or similar. (or metal one with insulators. And maybe a weight and pully for windstorm flexibility. And for the last few feet, perhaps 450 ohm ladder line.A classic loop design.Then I might still be able to pull off the vertical inside the loop.

author: A.Z.
author_rank: Super Contributor
timestamp: August 13, 2020, 01:24:47 pm
content: Quote from: cdev on August 13, 2020, 12:55:50 pmI doubt it will work well (as a TX antenna). Please re-readthisI was suggesting to put up a "random" wire, not a loop antenna, the remote end is just hooked to the support, the near one to the UnUn and then to the coax (add a choke there); your idea seems to be to build a "sky loop", but in such a case, you'd better go for a 40m total size with 10m each side, the problem there would be that such an antenna would be too low to work well; in such a case (low placement) an antenna likethis onecould probably work better

author: iMo
author_rank: Super Contributor
timestamp: August 14, 2020, 09:09:02 am
content: With random not resonant wire the unun ratio is not always 1:9, that is a myth.My 9m long wire requires 1:4, even 1:3 would be a bit better.The actual impedance ratio depends on many factors, ie. how the antenna is positioned (distance of the wire from nearby objects), the length of the feeding coax, coax choke type/position, etc.The 1:9 unun always include 1:4 ratio as well (when trifilar), so best do a measurement with VNA and pick up the better ratio.For SSB you do not need large cores, the average power is a pretty small fraction of the peak power (ie. 5%).43 material is better for lower bands (160-40m), the 52 or 61 for higher bands (20-6m).The impedance (inductive reactance XL) of unun's primary winding should beat least 250ohm at lowest frequency of interest(ie. 250ohm=2*pi*f*L - that gives you number of turns). On the other hand the more turns the more losses through capacitive coupling and core saturation. For example the 61 material has got almost "nil" losses against 43, but also has much smaller permeability, thus you need much more turns on the primary to achieve 250ohm at lowest frequencies, so not good for lower bands.The powder material -2 and -6 is not the best for ununs, imho (very low permeability - those materials are for tuned circuits where low TC and high Q is required). You would need large amount of turns to get 250ohm at lowest frequencies - not good.To summarize: the best unun for say 80-10m bands would be 1 turn primary to 3 turns secondary for 1:9 ratio (or 2 turns for 1:4) with 10-15uH primary inductance, wired on a material with no saturation losses..

author: A.Z.
author_rank: Super Contributor
timestamp: August 14, 2020, 09:19:44 am
content: Quote from: imo on August 14, 2020, 09:09:02 ama 9m (8.80 if we want to do it "by the book") random will do fine with a 9:1 UnUn from 20 to 6 meters, but since it's shorter than 1/4 lambda on 40 and down the 9:1 won't be able to match it "down there" plus, being so short it won't be so much efficient on those bands

author: iMo
author_rank: Super Contributor
timestamp: August 14, 2020, 09:25:13 am
content: Quote from: A.Z. on August 14, 2020, 09:19:44 amFYI - The Z of the 9m balcony antenna (1:4 unun, coax choke on the coax, coax is around 4m long, grounded at balcony metal). The gray bands are the ham bands.

author: A.Z.
author_rank: Super Contributor
timestamp: August 14, 2020, 10:45:58 am
content: Quote from: imo on August 14, 2020, 09:25:13 amLooking at the picture, let's say your impedance is in the 95 to 142 range, now, assuming that the UnUn is linear, this means that the impedance at the antenna feedpoint ranges from 380 to 568, this in turn means that, using a 9:1 UnUn, if my math is correct, the impedance seen at coax end would then range between 42 and 63, don't you think it would be a better match? Also, are you using a counterpoise ?

author: cdev
author_rank: Super Contributor
timestamp: August 14, 2020, 12:29:49 pm
content: I've already tried lots of combinations of random wires, and the performance of none of them have been what I have hoped for, with different kinds of matching inside the house. The main reason, I suspect, being lack of vertical height. As far as trees, its a roughly square lot. The largest trees are two trees in the midrear and left rear of the back yard. (the leftmost one if on the property line which is square. Both seem to be around 15-20 m high. With the tops hard to access for antenna purposes, because of lack of space to throw horizontally. In the front (of the back yard) near the house there are no longer any trees. Historically, Ive used long wire antennas run from the house to the centermost rear tree, a shortish distance of around 25 m. However I've been unable to get a weight and cord to pull up a wire up over the tree and back down again. Because the trees are too close together and crowded and I have neighbors around whose property I dont want to impinge upon. So my long wires have not gotten as far up as I have liked.There are a lot more options if I can get a wire or even two wires higher into the two tallest trees. The leftmost one is on the perimeter of the back yard and if it could support either a random wire or as a support for the left side of a loop that would be great.The circumference that might be achieved with a single long wire loop around the outer perimeter brought into the house by either ladder line or a balun and coax might be fairly substantial. Not 100 M but maybe 60 or 75.The ends can be closed to make a loop or either side could be left open. With open eands each direction might offer a different pattern. If I can purchuse two robust nonconducting telecoping poles, that could become a long term solution with a fairly good chance of being usable on the low bands.Shorter term I think an end fed 43 foot vertical is my best short term bet, from what I have read. I'm curious about what toroid would be the best performer, assuming my intent was to tune the wire for use on bands from 80 or perhaps with some additional length if I can get it higher up perhaps 160 meters) up to 10 m.Both of my neighbors use their garages a lot and use power equipment.Also my house has its share of noise sources..Getting any loop up high enough to give the garages a lot of room to emit their interference and even more in the future seems wise. So at some point I will likely be shopping for two telescoping fiberglass (not aluminum or carbon fiber) poles.Quote from: A.Z. on August 13, 2020, 01:24:47 pmA electrically modifiable antenna with a remote switch to change its pattern would be a great way of making the best use of the space, and it fits my goal of making forays into antenna experiments with the aim of making the most out of my fairly typical constraints.Thanks to the new NanoVNA hardware, the possibilities of testing fully and matching all kinds of interesting antennas and baluns seems bright!With a 9:1 balun wound on a FT50-43 core Ive been able to receive a lot of HF including some DX when contests are going on. Sometimes the bands seem very crowded. But as I said the real long distance DX seems to come in only when I use my loop, indoors, (typically on cold, quiet winter nights) so I get the feeling my current "long wire", which is fairly horizontal with the highest terminus maybe at the most 5 or 6 m off the ground, is mostly receiving low angle of radiation signals. A vertical, implemented properly would likely be much better.

author: A.Z.
author_rank: Super Contributor
timestamp: August 14, 2020, 12:56:35 pm
content: Quote from: cdev on August 14, 2020, 12:29:49 pmAre you using the antenna for RX only ? If so, given your available space, give a spin tothis antennacan be built and laid out in very short time, just ensure to build it "by the book", in particular the balun; if otherwise you're willing to transmit, did you consider putting upthis antenna? It should fit your available space (25m or so) and would give you quite a wide frequency coverage

author: cdev
author_rank: Super Contributor
timestamp: August 14, 2020, 04:39:54 pm
content: Yes, thats all Ive been doing, is using my antennas to receive.I've made a great many receiving loops, both tuned and untuned, and as I said Ive had good luck with them with some caveats. (Because I want to rotate and tune them easily, by hand, they have been indoors)Ultimately, I want to get my ham ticket and then transmit.And as i said I don't have a lot of money to spend, either.The balun is important because its a potential source of loss, that is fairly amenable to optimization, as is the antenna.