Agree With your findings Jim. I have made Peter’s 1:1 common mode choke and his 4:1 and 9:1 baluns testing as he does in the videos. They certainly test out ok. I have also wound coax common mode chokes which have tested out. Frankly I have not noticed any difference between the two common mode chokes. As to the coax wound chokes, I have to say that I have seen two designs. Some with a cross over and some without I don’t follow the logic or reasons for having a cross over in winding a coax choke.
I saw statements that cross winding reduces capacitance added by coils being next to each other. But I have another question here... According to http://www.karinya.net/g3txq/chokes/ and other resources common mode can be caused by two things: abrupt change in line like end of dipole (can be bad wording but hope you got the point) and induced CMC which is "spill" from outside surface of shield to outside and it depends in first place on impedance of shield which depends on cable length (pretty good described in article). BUT! I've seen tons of choke designs where you have coax open right before balun what doesn't make sense if all above is true because inside-outside surfaces of the shield connected before choke! That being said original post/video makes a lot of sense to me because in this case we have coax running through. Am I missing something?
I have tried following Steve G3TXQ and K9YC’s notes (Cookbook) on chokes and transformers. Clearly lots of effort has/had been put into them but some things, sad to say, simply are not explained well or in a way that does not leave me with as many questions as I had before I started to read them. Frankly I have yet to find an article that explains the ‘Black Art’ of chokes in a way that is readily digestible. Splitting a coax winding as part one way, then cross over part another for instance simply seems to setup a way for one part winding to cancel the other’s effect.
Just makes it easier to place the core and cable in a box with connectors on the opposite sides. The cable starts on one side and ends on the opposite side.
a magnetic core such as that in a transformer and toroids build up a magnetic field, collapse of that magnetic field induces current in the conductor, that impulse can be thousands of times higher ( Basic magneto theory) for a very short duration, but still long enough to damage sensitive electronics. just ask any industrial electrician what happens when power is lost on a 3 phase motor! to explain it better a typical magneto coil on a lawn mower has a primary with several hundred wraps if wire and a secondary with way fewer number of windings. one end of the primary and one end of the secondary are tapped together and run to the points ( or electronic ignition module) when the magnet passes the core it generates an intense flux field when the points are open, when the points close however the secondary is shorted to ground causing the flux field to collapse. this collapse induces a current of several thousand volts on the primary tap to the spark plug. toroids tend to be self shielding outside of their own outside diameter but still generate a magnetic field within the core. whenever you transmit even at low power you are building up a magnetic field, when you stop transmitting the field collapses. circuitry in your radio disconnects the transmit function but does not disconnect the shielding/ ground and that conductor can back feed your radio and cause degraded performance, rfi, and or damage your radio. split or reverse winding halfway through cancels the magnetic field that can generate in the core! while it cancels the field it still resists the current on the outside conductor of the coax. after all what this accomplishes is choking out or minimizing the current coming down the shielding. non split winding is primarily a transformer function regardless of the toroid in many instances specific mixes and number of windings are used depending on the frequency.
That depends upon the size of the toroid. Mine are 4 inch O.D. by 3 inch I.D. by 1 inch long. I can get over 25 turns of RG-400 through them. I'm not sure what you meant by "LL400". Is that the same diameter cable as RG-400, or is it the same diameter as LMR-400? LMR-400 is much larger in diameter than RG-400.
Low loss RG-213 style coaxial cable LL400 - RG8 Type Foam Low Loss Solid Centre/Foil/Braid Diameter 10.29mm Attenuation db/100m 100Mhz 3.9db 500Mhz 9.1db 1000Mhz 13.8db 1800Mhz 18.3db 2200Mhz 20.6db 2500MMhz 22.3db Im not an amateur yet but going for my licence next month. I'm basically using this forum to improve my knowledge and make some new friends along the way, no substitute for experience and there is plenty of that here. If I ask a question that seems to be very basic, please forgive me, its only experience I am missing. I was a missile tech in the Australian Air Force. IR, Torpedoes, Semi Active radar homing missiles. Its trying to restart my brain after 30 years of being out of the service. Its hurting a bit. I am starting a new station from scratch and as far as antennas go when I put one up, if it needs a choke at the antenna end then I want to it now and not have to struggle with it later. Thank you in advance for any help you can send my way.
Hello, Be careful where you look for information. There is a lot of misinformation and bad advice on the internet, and much of it comes from "experienced" hams who should know better. With your background and experience, you should have enough basic knowledge to sort the accurate info from the bad. I'd suggest these websites for accurate info and good advice: https://w8ji.com, http://k9yc.com/publish.htm, https://www.k0bg.com/. Those guys are knowledgeable and do a good job of explaining and illustrating the data, they don't make unfounded assumptions or arrive at conclusions that violate the laws of physics, like a lot of the information on other websites does. The toroids are made by Fair-Rite, they can be purchased here: https://proaudioeng.com/fair-rite-4″-toroid-core/. There is a link on that page that will take you to the manufacturer's website where you can view the full technical data. Pay attention to the minimum bend radius of the coax that you use to wind your toroids. Foam dielectric coax can't be bent less than about a one foot radius, you need coax with a solid dielectric for tight bends. RG-400 has a solid Teflon dielectric and it's smaller in diameter than RG-8 sized coax. It's expensive, but it's worth the extra cost. Good luck with your license and with building your station, I hope to work you on the air in the future. Send me an e-mail if you'd like to set up a sked. 73, Dennis
Than Thanks mate, I really appreciate your help. I did find that cookbook and haven't stopped reading it. Ordered some of those toroids too. When I'm up and running I will send you an email and seek you out. 73 Mick
LL400 I undid the choke I made to check the insides. Autopsy revealed no damage to the braid or the foil. Slight crushing of the dielectric insulator but no where near as bad as I thought it would be being so soft. So this seems to be usable my only thought is, is 7 1/2 turns enough to work as choke for the rig and is it wound too tight to do its job? Would adding another 2 or 3 or 4 torroids help to improve things with only 7 1/2 turns? If I am going down the wrong path I will use them for the power supply input to the rig etc and get the correct torroids.
