DIY Biconical antenna 30-300mhz? - Page 1
Forum section: electronics / testgear

author: RogerThat
author_rank: Regular Contributor
timestamp: March 07, 2019, 08:03:59 am
content: Hi,Been reading up on EMC testing the last weeks.To be able to do basic pre-compliance tests I need to add a 5uH LISN (I'm just doing DC 12-24v products)and a biconical antenna to my arsenal of test stuff. The antenna should be the basic 30-300mhz.After some intense days of searching the web I found a decent design for the LISN (here on the forum) but with the antennaI'm drawing a blank. Can someone point me to a proven design for this antenna?

author: tautech
author_rank: Super Contributor
timestamp: March 07, 2019, 11:24:24 am
content: For such low frequency you shouldn't need much more than a good scope, maybe with FFT and a near field probe, just something like Dave cobbled together recently:https://youtu.be/2xy3Hm1_ZqI

author: RogerThat
author_rank: Regular Contributor
timestamp: March 07, 2019, 12:36:18 pm
content: If I use a near field probe , how do I translate the measurement to that of the EMC standard (biconical antenna at 3m distance? I think).

author: David Hess
author_rank: Super Contributor
timestamp: March 07, 2019, 05:36:27 pm
content: Quote from: RogerThat on March 07, 2019, 12:36:18 pmThe measurements can be translated by also using an EMC standard biconical antenna at 3 meters distance and comparing them.This is not quite as useless as it sounds. Compare them once at the beginning when you pay for EMC testing of your design and it fails and then use the near field measurements to determine when you have gained enough reduction to pass. There is just too much going on between the near and far field in a given design to compare near and far field measurements except through direct measurement and sometimes even that is not enough.

author: EEVblog
author_rank: Unknown
timestamp: March 09, 2019, 12:16:58 pm
content: Quote from: tautech on March 07, 2019, 11:24:24 amA near field H-probe is quite different to the biconical (EM) far field antenna the OP is talking about.I've been looking myself and it seems to be rare as hens teeth, even 2nd hand.The DIY log-periodic PCB based antennas are usually only useful for above several hundred megs.

author: tautech
author_rank: Super Contributor
timestamp: March 09, 2019, 01:24:07 pm
content: Quote from: EEVblog on March 09, 2019, 12:16:58 pmQuite so but for DIY EMC, near field is where it's at.Leave the far field to the experts in the labs.Or could this be a good subject for a future vid ?Further, far field testing is at risk of erroneous results without using a anechoic chamber.

author: EEVblog
author_rank: Unknown
timestamp: March 09, 2019, 01:28:19 pm
content: Quote from: tautech on March 09, 2019, 01:24:07 pmI think it's possible to get decent far field measurements in the lab (or at a DIY OATS) just need a decent low cost DIY biconical for the 30M-300M range.I want to do a video on it but getting a suitable antenna is not easy. I could rent one or ask a manufacturer to send me one, but I'd prefer a DIY solution.I'm surprised some chinese company hasn't just taken an existing biconical and simply copied the design down to the mm, would be fairly trivial. BUt then you have the issue of the balun matching.

author: EEVblog
author_rank: Unknown
timestamp: March 09, 2019, 01:31:04 pm
content: You can get these cheap to do >200M, it's the lower frequency stuff that is tricky.https://www.aliexpress.com/item/1PC-Broadband-wideband-antenna-EMC-EMI-antenna-Directional-antenna-290M-1-1G-EMI-rectification/32966314464.html

author: tautech
author_rank: Super Contributor
timestamp: March 09, 2019, 01:39:16 pm
content: A customer and member here sourced a range of PCB antennas for his EMC work using a SSA3021X.AFAIK they served his needs well.Might have been these guys:https://www.wa5vjb.com/products1.htmlBut here, the OP hasn't given us much to work with, not even what equipment he has or what he's trying to get compliance for.

author: hagster
author_rank: Frequent Contributor
timestamp: March 09, 2019, 02:49:07 pm
content: Just make a 1 meter tall bow-tie antenna(copper tape on a bit of wood will work). It will be close enough. As shown on Antenna theory, spot solder the coax to one arm of the antenna, thia will help isolate the cable.http://www.antenna-theory.com/antennas/wideband/bowtie.phpYou may need to do a characterisation of signals that are already present so you can discount them.

author: tautech
author_rank: Super Contributor
timestamp: March 09, 2019, 11:27:05 pm
content: As mentioned in previous posts in an exchange with Dave here's what my customer did:https://www.eevblog.com/forum/testgear/howto-calibrate-diy-emc-pre-compliance-antenna/Some good advice and links to suppliers and papers in that thread.

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: March 09, 2019, 11:52:31 pm
content: Hi,To the original poster.You need to find a copy of MIL-STD-461A. This is the first version. Fortunately, I have a copy and I have attached here.There is a dimensioned drawing for the biconical antenna in this spec. If you build it to the drawing it will match the curves in the spec.The dimensions are in inches.I have built a copy of the antenna from these drawings.Regards,Jay_Diddy_B

author: HalFET
author_rank: Frequent Contributor
timestamp: March 09, 2019, 11:55:36 pm
content: A fellow student built one for his master thesis back in the day because the university was too cheap to buy one. I don't know how he designed it specifically, but I do remember how he physically constructed it. He started from two circles cut out of insulating foam panels. To keep them at a distance from each other he used pieces of PVC pipe around the periphery of the foam panels. The "cones" were constructed from a radial mesh of thick copper wires tensioned between the periphery of the disks and the feed gap. To support them in the centre he had a thick PVC tube that they ran through. Think he either crimped something onto them or knotted them to keep them in place. It wasn't pretty, but it performed quite well in measurements. I suspect if you want something more solid you could probably build it out of thin copper plumbing pipes. Keep in mind, at 300 MHz the wavelength is still quite long, so you don't need an ultra dense wire/rod mesh to represent a solid structure. Alternatively, you could grab some thick copper foil and put it over something made out of rotan or wood I suppose?In terms of design, I think the evaluation version of Antenna Magus was capable of calculating biconical antennas.

author: David Hess
author_rank: Super Contributor
timestamp: March 10, 2019, 08:31:42 pm
content: Self-calibrated far field measurements are possible but time consuming. I did it by building reference antennas to generate calibrated far field intensities to then calibrate wideband directional antennas which made the actual measurements at a relatively RF quiet and flat location.The better option if you can afford it is to treat the near field measurements as relative so when the first EMC compliance test fails, you know how much they need to be reduced. And before the first expensive EMC compliance test, use near field measurements to evaluate basic good EMC practices.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: March 10, 2019, 08:51:24 pm
content: I built a bowtie antenna that I'm happy enough with. I don't have any way to test its response, mind -- it seems to have good reception from ~100MHz to 1GHz+, but relying on ambient sources, this isn't very meaningful...Quick terrible pic,Anyway, it's flat, about a meter long, constructed from 18ga. bare wire, using five radials fanned out about +/- 30 degrees, then a few odd-angle crossings to stiffen things up. Wires are twisted and soldered together. The on-axis wires are supported by a 1"-wide strip of G10. At the vertex of the bowtie, a 1:2 balun is made from two twisted pairs and a couple ferrite beads. The pairs are wired in parallel going to the BNC connector (each pair is about 100 ohms characteristic impedance, so two in parallel gives 50 ohms), and wired in series (centertap grounded) at the antenna side (for 200 ohms differential, close enough to what I would expect from a bowtie).Much better closeup of the balun,Note that the left pair doesn't need to go through ferrite beads (it's wired ground to ground, no common mode voltage ideally), it just looks nicer this way.As for bicons -- you'll want one that's constructed right to begin with, and preferably that has some kind of calibration. I've heard reasonable deals (like under $1000) can be found on eBay if you keep looking around a while?Tim

author: tautech
author_rank: Super Contributor
timestamp: March 10, 2019, 09:23:57 pm
content: Quote from: David Hess on March 10, 2019, 08:31:42 pmThis ! ^^It really doesn't need to be anymore complex, the KISS principle need always be tried first.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: March 10, 2019, 09:37:22 pm
content: Quote from: tautech on March 10, 2019, 09:23:57 pmAnd to add to that -- there are design practices you can follow to facilitate testing and early passing. The most obvious case, throw everything inside a solid metal box, and filter all connections passing through it. You can connect these to a CDN or LISN, to measure the RF coming out directly, or going in (if you have a generator and amplifier) to do immunity testing as well. In short: you can approximate these connections as zero-dimensional connections -- ports -- and do conducted testing to much higher frequencies than is justified at the end of a long power cable.This extends to the board level, where for example, a ground plane design allows you to know, at a glance, where the image currents are flowing, and what trace impedances are (and therefore equivalent capacitance and inductance).Such a design may not be the cheapest possible approach (it may use more space between components and routing, it may use more layers, or it may use more metal, including the PCB, shields, enclosure, etc.), but it reduces extremely costly lab time, and time-to-market.Tim

author: tautech
author_rank: Super Contributor
timestamp: March 10, 2019, 09:46:36 pm
content: From another thread:Quote from: MilkmanCDN on March 10, 2019, 06:16:38 pm$40 for a set of 5How could you go wrong ?

author: cpuerror
author_rank: Regular Contributor
timestamp: March 11, 2019, 02:20:44 am
content: I'd really like to see someone just come up with a design for this sort of antenna, and have it 3d printable. The elements can be painted with conductive spray paint to make it effective.

author: coppercone2
author_rank: Super Contributor
timestamp: March 11, 2019, 04:23:25 am
content: thanks j, another projectlooks very home build able even on a simple drill press so long you have reamerslots of filing and grinding for the base pieces though if you don't have a lathe.

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: March 11, 2019, 05:33:56 pm
content: Quote from: coppercone2 on March 11, 2019, 04:23:25 amHi Coppercone2 and the group,I am going to share some pictures that show the construction of my biconical antenna. I am not going to provide dimensions for the parts, they can be found in the document attached to this message:https://www.eevblog.com/forum/testgear/diy-biconical-antenna-30-300mhz/msg2257035/#msg2257035Overview of the completed antennaThis picture shows the complete antenna assembled and ready for use.Center StructureThis is the center rod assembly. Two of these are required.Cone 1This is the inner cone. It has a section of threaded rod, to screw into the center assembly. The cone is held on the rod with a 10-32 set screw.Cone 2This is the outer cone. It is also held in place with a set screw.Antenna ElementsThe construction of these differs from MIL-STD-461A, in that they were bent from one piece of rod. The MIL-STD uses to straight rods and coupler. I cut these to length after bending.Center ConnectorThe housing for the center connector is waterproof electrical conduit. I made aluminum inserts that the two antennas screw into.Center Insulator openThis picture shows how the thin coaxial cable is attached.N connectorThe N connector is also mounted in a plastic conduit fitting.Balun - Not ShownThere is a balun consisting of ferrite beads threaded on the coax inside the support arm.The aluminum is all 6061 purchased from the Metal Supermarket.The plastic conduit fittings were purchased from the Home Depot (or similar store).Part were machine on a 8x14 lathe and a mini-mill.Regards,Jay_Diddy_B

author: coppercone2
author_rank: Super Contributor
timestamp: March 11, 2019, 06:59:31 pm
content: I am thinking about casting those parts

author: coppercone2
author_rank: Super Contributor
timestamp: March 11, 2019, 07:00:39 pm
content: I noticed it looks like you decided to go for a bend rather then make the elbow pieces . I was thinking about this myselfwhy do you think they went with them? higher precision then bent aluminum?

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: March 11, 2019, 07:06:38 pm
content: Hi,I used a pipe bender like this one:Very cheap from Harbor Freight:https://www.harborfreight.com/tubing-bender-3755.htmlJay_Diddy_B

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: March 11, 2019, 07:08:33 pm
content: Hi,I should add, although I have built this antenna, I don't find it very useful.Jay_Diddy_B

author: coppercone2
author_rank: Super Contributor
timestamp: March 11, 2019, 11:17:08 pm
content: put it in the attic with hard line running down so you can plug various antennas into a SA to measure any anomolies when you feel like it. I intend to get my big bicone, this antenna and smaller bicone + a electronically motor steered horn antenna or two into a radome type deal with a coaxial switching boxonly problem is eventually its going to start to look like a airforce baseyea thats what back yards are for, so you can setup a buncha antennas ominously moving aboutI thought about making my shed roof open up so an antenna could be deployed remotely

author: HalFET
author_rank: Frequent Contributor
timestamp: March 11, 2019, 11:35:27 pm
content: Quote from: coppercone2 on March 11, 2019, 11:17:08 pmDon't forget to hide a few log-periodic ones centred around the ISM band in trees pointed at all the houses in the neighbourhood

author: coppercone2
author_rank: Super Contributor
timestamp: March 11, 2019, 11:39:55 pm
content: Quote from: HalFET on March 11, 2019, 11:35:27 pmcrazy people are going to think you cracked it no matter what you say. High neighbors calling cops etc

author: Kean
author_rank: Unknown
timestamp: March 12, 2019, 12:08:24 am
content: A number of years ago (probably 5+) I bought a couple of Aaronia "EMC" antennas based on recommendation from some EMC consultants I was working with. I got a biconical for 30MHz to 1GHz and a log periodic for 680MHz to 8GHz from the Aussie Aaronia reseller.These are the ones:https://www.aaronia.com/products/antennas/BicoLOG-30100-X/https://www.aaronia.com/products/antennas/HyperLog-6080-Pre-Compliance-Antenna/Very nicely made, and appear to work well (based on my limited RF background). But like others here I can't overly recommend dropping the cash on them (or building your own) unless you're going to be using them a lot. I generally just test with a LISN or do a quick scan with near field probes, and then get stuff tested properly at a local lab. Then if necessary I use the near field probes or LISN to do relative measurements to rectify any issue before sending again for retesting.For a LISN, I use the AC & DC model made by Tekbox: TBOH01 & TBLC08. Dave has featured the former in a video, and maybe the latter as well. I also splurged last year and got a TBTC2 TEM Cell from Tekbox, but I've hardly used it.Dave, maybe contact these guys about the Aaronia antennas and see if you can get a demo unit for a video - or you are welcome to borrow mine.http://www.measurement.net.au/c/4339127/1/antennas.html

author: David Hess
author_rank: Super Contributor
timestamp: March 12, 2019, 02:58:10 am
content: When I have built antennas like this, I used copper forms and bronze wire and silver brazed them.

author: RogerThat
author_rank: Regular Contributor
timestamp: April 11, 2019, 11:59:34 am
content: Haven't been to the forum for some time, nice to come back and see such good repliesI've resorted to measuring with a 5uh LISN ( design found here on the forum using SMD inductors) and a near field probe. I have a similar product which is already CE marked which I use as reference....then just design with a healthy margin to that one.

author: RFDUK
author_rank: Regular Contributor
timestamp: April 11, 2019, 01:20:13 pm
content: Bit late getting to your earlier question, but in short reliable correlation between radiated emissions absolute levels as measured at a compliance lab above 30 MHz and 'close field probe' observations are an elusion, particularly below say 300 MHz and with EUT (Equipment Under Test) cables attached. Perhaps the exception is for very small EUT's with no cables attached.The close field probe IS useful for identifying sources of the energy at PCB level, that then go on to radiate free field through 'electrically long' (as a proportion of wavelength) paths. Usually these are external cables or long PCB traces if present.The focus on doing actual antenna based measurements reflected in the other responses to your questions are spot on. Do measurements at 2m spacing and compare with the regulatory Standard 3m limit line. In this way you compensate for the lack of the in phase ground reflection that is achieved by scanning the height (typically 1 to 4m) of the measurement antenna required by the standard. When you get to record final levels, move the antenna around just a little and observe levels, to ensure you haven't an out of phase cancellation going on from ground or object reflections in your test environment. The 2m measurement distance errs on the side of caution and may well return results that are slightly high.In the early days I made a Bicon to the MIL doc but another very useful 'self calibrating' antenna is a simple dipole with 2 quarter wave telescoping elements. Even without a balun this provides very reasonable results. Unfortunately down at 30 MHz the element lengths are prohibitive, but reasonable down to say 50 MHz (1.5m elements).For a first class reference dipole FCC 'Roberts' broadband baluns are ideal.The dipole element lengths have to be adjusted for any particular frequency of interest before recording an accurate level value, hence the saving in time of a broadband Biconical or Log Periodic.The 'K' factor (dB) for a halfwave dipole is simply given by 20log(MHz)-31.9. The field strength is given by dBuV (in 50R at the test instrument) + K(dB).

author: hulk69
author_rank: Contributor
timestamp: October 05, 2020, 06:24:34 pm
content: I was thinking to buy the BicoLOG-30100. I see that it was made to be used for radiated emissions but do you guys think it should be good for radiated immunity as well?

author: KevinA
author_rank: Regular Contributor
timestamp: October 05, 2020, 06:50:44 pm
content: You can have mine free, along with a spectrum analyser, LISN, magnetic field antenna(s) software etc.It will be burried about 100 feet down in Seacroft landfill by now.My company made me redundant ten years ago; I was replaced by two young chassis swappers. The two youngsters had no idea what any of my equipment or spare parts were, and neither did the used car salesman who took over my job; so the lot was sent to landfill.

author: hulk69
author_rank: Contributor
timestamp: October 05, 2020, 07:29:59 pm
content: Then we will need another antenna to find all of that

author: cdev
author_rank: Super Contributor
timestamp: October 05, 2020, 07:50:00 pm
content: Here we go...https://nvlpubs.nist.gov/nistpubs/jres/66d/jresv66dn1p1_a1b.pdfA Survey of the Very Wide Band and Frequency Independent Antennas-1945 to the PresentJohn D. DysonContribution from University of Illinois, Urbana, Ill.(Received August J6, 196J )Thc last few years havc witnessed major developments in the field of antennas whichare suitable for use over a range of frequencies. Operating bandwidths that were connsideredan impossibility as little as...

author: coppercone2
author_rank: Super Contributor
timestamp: January 23, 2021, 07:20:28 pm
content: Quote from: KevinA on October 05, 2020, 06:50:44 pmWell I will defiantly remember the words chassis swapper. I can imagine in my mind nice HP supplies being replaced by cute generic Chinese lab supplies that are 1/8th the size, 30+ times more noisy and about 50 times less stable. Hey look, we upgraded the archaic equipment(no, I don't totally hate those supplies, they are ok for testing pumps and fans or providing a isolated power supply to something weird).. the place where you work sounds ridiculous.But hey don't feel like they got off the hook, I am sure the experts they call in to do anything more complicated then a board replacement (i.e. lets hire someone to redesign this arduino so it passes emissions) have accrued them costs greater then 100x your salary by now and required 3 managers and an accountant to perform regular work regarding the management of interbuisness relations of said 'odd jobs'. And how many meetings to decide to finally call them LOL.

author: Dr_Ram
author_rank: Contributor
timestamp: November 08, 2021, 03:19:11 am
content: Posting on this old but rather interesting thread rather than start a new one. I tried designing a completely portable version of the Mil-spec biconical antenna (that people would want to buy for "garage" EMI tests) and I think it turned out quite well. A video of the antenna is on Youtube.https://youtu.be/3B9nc3yCEYMBest - Ram

author: _Wim_
author_rank: Super Contributor
timestamp: November 10, 2021, 04:49:59 pm
content: Quote from: Dr_Ram on November 08, 2021, 03:19:11 amNice work! Maybe you should try to also post some actual measurement results with it to demonstrate how useful it can be.I would also add a link on youtube directly to your ebay store, so it is easier for potential buyers to find your store. When I searched for "RBA1 Biconical" (on ebay.be) with the world wide option enabled I got zero hits. I had to go to Ebay.com to be able to find your listing.

author: Dr_Ram
author_rank: Contributor
timestamp: November 10, 2021, 05:28:16 pm
content: Thanks _Wim_. Indeed I've been trying to get someone local to do a measurement on one piece for me so I can share that with potential users, but strangely enough while there are dozens of EMI test labs in Bangalore, many of them being big names, not one I approached will calibrate a biconical for me. I'll keep trying...eBay India will not allow me to list on eBay.com and eBay.co.uk at the same time for some strange reasons. Thanks for reporting the issue. I'll take your suggestion and put in a link.Cheers - Ram.

author: KevinA
author_rank: Regular Contributor
timestamp: November 10, 2021, 07:26:28 pm
content: You need to get hold of a set of Ministry of Defence EMC standards, these are the ones that the EMC standards were written from, and they contained full constructional details and calibration of all the various test fixtures.In Britain, they are called DEF STAN, other countries will have their own names. I used to have a full set, but it is many years since I retired, and no one at my old company will know what they are or where they are archived; neither would they be interested in looking.They are out there on the web, that is where I got them.

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: November 10, 2021, 07:51:25 pm
content: Hi,I posted part of the MIL spec 461A that gives the details on how to construct the antenna in this message:https://www.eevblog.com/forum/testgear/diy-biconical-antenna-30-300mhz/msg2257035/#msg2257035If you follow the construction detain carefully, the antenna should match the published data. The data is included in the document.I posted a picture of my version in this message:https://www.eevblog.com/forum/testgear/diy-biconical-antenna-30-300mhz/msg2261550/#msg2261550I did two modifications:I bent the rods to eliminate the need to make 12 corner blocks.I made the central portion using PVC conduit fittings, as shown in the picture.I have found very little use for the antenna. I do not have a anechoic chamber. There is too much background noise for the antenna to be useful.I have got much better results with an Open TEM Cell.Regards,Jay_Diddy_B

author: _Wim_
author_rank: Super Contributor
timestamp: November 10, 2021, 08:21:47 pm
content: Quote from: Dr_Ram on November 10, 2021, 05:28:16 pmI did not really mean calibration, but did not explain myself clearly. What I meant was that you also show in your video how you would practically use this antenna in a non controlled environment. There are a lot of video's on youtube about the use of near field probes and open TEM cells, but non about using an antenna like this in a "normal" environment. As I think an antenna yours is amed at the serious hobbyist or semi-professional (and many of them are probably unsure how they would use this in a useful manner), it is important you try to show the benefits of your product also.

author: Dr_Ram
author_rank: Contributor
timestamp: November 11, 2021, 04:07:54 am
content: Quote from: _Wim_ on November 10, 2021, 08:21:47 pm@_Wim_, Got it. Yes you are right about the target audience and I think your suggestion does make sense. If I feel lazy I'll probably link to someone else's video showing how a biconical is used :-P.Yes @Jay_Diddy_B, I owe you a Thank You for the Mil 461A post and your fabulous attempt which got me started thinking in exactly the same direction...so my version of the antenna allows you to adjust the rod lengths to exactly match the Mil spec, and all parts and measurements, including the elbows, caps, inter-cone spacing etc are made exactly as per the Mil spec. But I agree the mileage will vary depending on how your environment is.One article that got me believing that DIY precompliance EMI testing was meaningful is one by Tektronix (yes the same guys whose 'scopes we drool over):https://in.tek.com/document/application-note/low-cost-emi-pre-compliance-testing-using-spectrum-analyzer. I think this is a great overall guide and does mention that rural areas could be good environments.

author: _Wim_
author_rank: Super Contributor
timestamp: November 11, 2021, 05:44:02 am
content: Quote from: Dr_Ram on November 11, 2021, 04:07:54 amYou need to have a chat with Dave I think...Quote from: EEVblog on March 09, 2019, 01:28:19 pm

author: cdev
author_rank: Super Contributor
timestamp: November 11, 2021, 01:37:34 pm
content: You can make a functional "planar disk" antenna that has a similar broadband pattern to a biconical using two circular disks. Reddit user superkuh has a web site where he explains the construction, its very easy and you can use two dollar store pizza pans to build it. I think Kent Britain, who also designs a bunch of other PCB antennas and they are widely sold, including log periodics.. was the original source for the design.A crucial aspect to getting the best out of it is using an approriate balun in the center, and not grounding the lower disk as most would likely do. Because the feedline going down picks up a lot of junk. Also on that antenna the approach of using an infinite balun using copper tape or whatever to enclose the bottom side coax doesnt work for me. Requiring the use of a decent VHF/UHF balun.This is important to get decent performance with it. I have a similar antenna and the balun is what made the antenna work well and be quiet. If you are just connecting the antenna to the two sides of the coax its unbalanced and yes, very noisy. Basically it works like crap unless its decoupled from the feed line properly. With mine I can hear 440 MHz and higher hams quite some distance away with mine, its agood general purpose antenna, but without the balun its basically no more usable than a simple monopole. Also using several ferrites on the coax to it has a similar effect. Best to combine both. I use a slightly redsigned version of the elecraft switchable balun thats smaller that I intended for VHF and UHF use. Its similar to the one that user "Tiscoli" (I know I have this wrong, but he has a balun he built for a similar balanced bowtie style antenna, that I determined was very similar to the Elecraft;s design, and tweaked it a little bit for UHF with different and smaller magnetics. . that antenna also works well for VHF and UHF TV reception (for me) Its in my attic.In a pinch, you can use a CATV balun. (you certainly can and shoiuld use the tiny magnetic cores that are used in those balus which are designed for VHF and UHF. Dont use the same material used for HF. Except one exception. You can jerry rig a binocular core from two ferrite spliut beads, make sure they are the same kind. then use that. Small ones for VHF and above. It has to be small to work well.

author: cdev
author_rank: Super Contributor
timestamp: November 11, 2021, 01:48:40 pm
content: Re: PCB-based RF probe set.I got mine for around $26 on another site, and they even came in a nice little tin box. They seem to work fine.(I have no better ones to test them against) They work okay for following a signal path on a PCB though. There are five of them. I usually use them with my scope or with a receiver.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: November 11, 2021, 02:36:41 pm
content: TV balun isn't quite right; closer than raw coax, to be sure. If you're willing to get out some cores, a 1:2 TLT is almost trivial to make:CAT5 twisted pairs. Join two in parallel at the feedpoint. Two pairs in parallel is 100Ω / 2 = 50Ω, a match to coax.One pair runs straight through. Notice the left one has green grounded on both ends. This one doesn't need ferrite, I put it there just because. The right one has green grounded at the bottom, and white at the top: a 1:1 inverting TLT. The LF bead and HF binoc cores both act as core, with one turn through them. (For lower cutoff, use bigger cores or multiple turns here.)The top end therefore acts as a 1+1 CT winding, so has 200Ω impedance. Note also that two 100Ω pairs in series is 200Ω, a perfect match. Therefore this is a Guanella (matched delay) type TLT, with output balance limited by total electrical length (which can be further improved with a CMC), and ultimate bandwidth limited by wiring strays and TL cross-section (so, some GHz as shown).The top ground connection isn't necessary, but is probably better with, than without. Probably comes down to strays, how well balanced/shielded the pairs are, stuff like that. YMMV.The big twists of wire and solder, are the antenna elements, a wire-frame bowtie; it seems to work surprisingly well despite the hand-waved design. Mind, I have no way to calibrate it, it might be full of notches. Overall length is close to 1m and it works well from FM BCB (and below, as an electrically-short dipole), up to, whatever I've seen around here really (have seen peaks around 1GHz but not sure what, most users seem to be intermittent?). Like I said, not calibrated or characterized.Tim

author: cdev
author_rank: Super Contributor
timestamp: November 11, 2021, 07:53:17 pm
content: Yes, I used the #61 material cores from a TV balun, in a 1:1 instead of 4:1 configuration.I am not sure if I am seeing all the detail in your picture, as I'm not certain about the schematic. I'd like to try the exact same design.I have had good luck with several baluns Ive built that emulate the Elecraft kit. I used the same winding spec as the Elecraft with the super tiny balun cores from two CATV baluns doubled up. (this works better than just one, but if you only have one the winding is the same, just use that. And yes, the solid wire from cat 5 cable works well, the insulation is likely to be low loss too.If you are trying to do this and dont understand what I just said PM me and I will try to make it clearer. Doubling up binocular cores improvises by using two ferrite beads as a binocular core, or use four as you would two binocular cores. You can tape them together as an aid to keeping them in a binocular shape but the wire will usually keep them toogether. balun attempt substantially. As I said you can also use the ferrite coresYou can buy noise reduction ferrites cheap on ebay in large quantities. I now have hundreds of them, on all the electronics in my house. Its nuts. But they help reduce the noiseI receive a lot of a lot. Hams in the EU could save money by using them for baluns.My wife just gave me a bunch of foam thats used for insulating pipes and I am going to use that to make a compact loop antenna. Thats my next project.

author: cdev
author_rank: Super Contributor
timestamp: November 11, 2021, 08:31:16 pm
content: Look for instructions of how to make a hat box online. the two cones, are basically a "frustrum" and are made by making a circle out of sheet copper and then cutting a small slice out of the circle to make something that looks like 75% or something around that represented in a pie chart. The pattern is concentrated and defined by the angles of the two cones. The cones don't have to be equal angle off of the horizon. The pattern variations are complex but roughly the angle enclosed is between the two cones. The bandwidth cuts off rapidly at the bottom but goes much higher. to get good performance at high frequencies the point of the cone should be free of distortions, and avoid anything thats asymmetrical or misplaced bending. One guy who built oe on YouTube used conductive glue to attach the cones to the wire at the feed point. Anybody interested in this kind of antenna should view that. Optimum gain varies by frequency but if you want to concentrate it at the horizon at a specific frequency its worth looking for the formula. The dipole formula if followed will leave you with an antenna that is significantly longer and has less gain than the optimal length. If anybody knows of an open source code that can be used to calculate the impedance and optimal gain at the horizon, I'd love to know.Here is that antenna.. It should be mentioned that this antenna is likely to be too noisy, and unbalanced as its described here, unless its built with a balun, for the reasons discussed. The so called "infinite balun" designs don't work well for me. and my cheap rtlsdrs, etc.Maybe if the feedpoint was lower and at the far end of a copper tube with the ends closed with conductive plugs.. That would be an interesting experiment. Why does that happen? My guess is some kind of proximity effect or coupling from nearby objects or the feedline and the mast leaves it unbalanced in a bad way. A balun might reduce the upper end bandwidth significantly. The kind of balun we were describing only works well up to 1.5 GHz to 2 GHz or so.. And to go above that requires very small core and very fine winding.When I try to wind baluns that are intended to work that high in frequency they vary a lot. Its hard to get them right. Now that I have a capability of testing these baluns, (via NanoVNA2) it would be worthwhile returning to this.I think that would make a good Youtube video..Here is the hourglass conductive glue biconical..Looks like it wouldn't be out of place in anybody's living room.. almost artistic.IMPORTANT,anybodycan make this kind of antenna without special equipment, for an important reason.The dimensions matter little, its the angles and shape, that matter. This is supposed to be a form of frequency independent antenna. There are many more, many of them are quite pretty.If you want to study this kind of antenna, the electromagnetics program at the university of illinois at Urbana-Champaign I think is the place to go to learn more about them. There are a lot of interesting papers published there in the 50s-70s..

author: Dr_Ram
author_rank: Contributor
timestamp: November 12, 2021, 04:28:43 am
content: Quote from: EEVblog on March 09, 2019, 01:28:19 pmI was quite bothered by this actually, and not being an antenna engineer I just decided to provide a connector without a balun assuming it could be used as a direct-feed biconical for DIY purposes OR that a balun could be added externally by someone who wants to experiment with them. (If external then I suppose the N-type connector would not be meaningful.) The center box does have a 3x3x6 cm cavity to accommodate a small balun - I'm thinking a a typical broadband SMD one like a MACOM MABA-011094. Any advice from the experts here?- Ram

author: cdev
author_rank: Super Contributor
timestamp: November 14, 2021, 12:59:11 am
content: A genuine 30 MHz biconical is large its going to be quite hard to handle. A planar disk may be more manageable and similar enough to be useful but still one that functions well in the low VHF range is likely to be larger than most of us would find easy to use. And I dont know of any good way to reduce the size. So, its likely to be quite large. They definitely do become deafer at lower frequencies if they lack the size. Not quite as big as a dipole for thet frequency as the widening of the elements makes them a bit shorter. Look at the elements on the Russian Woodpecker array near Pripyat/Chernobyl. That is basiclly a biconical design intended to work down to (my guess) around 11 or 12 MHz. Pretty large. Broadband yes, though.Quote from: EEVblog on March 09, 2019, 01:31:04 pm