Re: [Elecraft] Loading inductor Question
All of that heat is produced by RF heating the core instead of being radiated. It's all a matter of what you want to do with your RF :-) One concern is the curie temperature - that temperature where the properties of the core change dramatically. In an antenna matching network (a.k.a. tuner) the will cause the SWR seen by your Tx to change - often dramatically. 73, Ron AC7AC -Original Message- MFJ-902 tuner uses a single toroid with taps. The toroid becomes hot on some frequencies with 100W but survives. I guess losses are small compared to convenience of a very small unit. From what I understand, the iron cores can have Q in excess of 300 if they are below saturation. How much will they can handle depends on the load. A reactance of 300 will add a resistance loss of 1 Ohm, and a reactance of 3000 will add 100 Ohm. So the same toroid can handle KW with a longer vertical but could overheat at 100W with a short vertical. Ignacy __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Re: [Elecraft] Loading inductor Question
Ken, When you do the research and math, worth bearing in mind that powdered iron (and ferrite) cores can generate intermodulation products. Usually this problem will affect the receive performance of an antenna matching network, or a receiver's front end filters, if exposed to strong signals e.g. SW Broadcast. The root cause of this IMD problem can be traced back to the magnetic flux generated in a core by the incoming signals. The flux density is proportional to the applied voltage (vector sum of incoming signals), and inversely proportional to the core's cross section (area), the number of turns and the frequency. Thus the number of active turns should be as large as possible, the loaded Q of the network should be kept low, the core's mu low in value, and a large core used. Sorry to be late with this comment. 73, Geoff LX2AO On May 01, 2012 at 15:23 +0200, Ken Alexander wrote: Many thanks for all the helpful responses! I do have many toroid cores in stock already but almost all are FT-50-xx and T-50-xx. I'll do the research and the math and give it a try when antenna building season arrives. It's still a little too cold and wet for that at the moment. 73 - Ken __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Re: [Elecraft] Loading inductor Question
Many thanks for all the helpful responses! I do have many toroid cores in stock already but almost all are FT-50-xx and T-50-xx. I'll do the research and the math and give it a try when antenna building season arrives. It's still a little too cold and wet for that at the moment. 73 - Ken From: Ken Alexander k.alexan...@rogers.com To: Elecraft elecraft@mailman.qth.net Sent: Monday, April 30, 2012 11:14:33 AM Subject: [Elecraft] Loading inductor Question Folks, Given that inductors on toroid cores are used extensively in autotuners, is there any reason (assuming I choose the right size core, made of the correct material for the application and winding it with the right size wire) for not using one as a base loading inductor on a vertical antenna? I'm talking 100 watts maximum transmitter output here. Any down side to doing this? Thanks and 73, Ken Alexander VE3HLS __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Re: [Elecraft] Loading inductor Question
MFJ-902 tuner uses a single toroid with taps. The toroid becomes hot on some frequencies with 100W but survives. I guess losses are small compared to convenience of a very small unit. From what I understand, the iron cores can have Q in excess of 300 if they are below saturation. How much will they can handle depends on the load. A reactance of 300 will add a resistance loss of 1 Ohm, and a reactance of 3000 will add 100 Ohm. So the same toroid can handle KW with a longer vertical but could overheat at 100W with a short vertical. Ignacy Fred Townsend wrote Ken: Don't use toroids if you need taps. 73 Fred, AE6QL -- View this message in context: http://elecraft.365791.n2.nabble.com/Loading-inductor-Question-tp7513850p7517125.html Sent from the Elecraft mailing list archive at Nabble.com. __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Re: [Elecraft] Loading inductor Question
Ken: Toroidal cores have many fine qualities for loading coils. Of course not all core have the same qualities so be sure you have the right Al rating. You will want a low rating. Also remember you will lose those fine qualities if you saturate them so be sure your core is big enough for 250 watts (2.5x safety margin). I use Teflon wire on mine for lower losses. Finally, it is very difficult to tap a toroid whereas coil taps are easy on an air core coil. Don't use toroids if you need taps. 73 Fred, AE6QL -Original Message- From: elecraft-boun...@mailman.qth.net [mailto:elecraft-boun...@mailman.qth.net] On Behalf Of Ken Alexander Sent: Monday, April 30, 2012 8:15 AM To: Elecraft Subject: [Elecraft] Loading inductor Question Folks, Given that inductors on toroid cores are used extensively in autotuners, is there any reason (assuming I choose the right size core, made of the correct material for the application and winding it with the right size wire) for not using one as a base loading inductor on a vertical antenna? I'm talking 100 watts maximum transmitter output here. Any down side to doing this? Thanks and 73, Ken Alexander VE3HLS __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Re: [Elecraft] Loading inductor Question
Ken - A toroidal inductor should work fine, it is understood that the core must be of the proper material and size to handle the expected power and frequency range. Keep in mind that many of the automatic tuners use toroidal inductors in their design. There is some advantage to having the loading inductor out in the air, as it dos radiate somewhat, but the convenience and practicality of an actual design may dictate that the inductor (s) be enclosed. Being a conservative sort, I would tend to use bigger cores and larger wire sizes that an absolute engineering solution might dictate, mostly for safety factor and insurance against core saturation when handling unusual situations. - Jim, KL7CC Ken Alexander wrote: Folks, Given that inductors on toroid cores are used extensively in autotuners, is there any reason (assuming I choose the right size core, made of the correct material for the application and winding it with the right size wire) for not using one as a base loading inductor on a vertical antenna? I'm talking 100 watts maximum transmitter output here. Any down side to doing this? Thanks and 73, Ken Alexander VE3HLS _ __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Re: [Elecraft] Loading inductor Question
Here's a program that will let you compare toroid vs air core losses: http://www.dl5swb.de/html/mini_ring_core_calculator.htm Phil - AD5X __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Re: [Elecraft] Loading inductor Question
On 4/30/2012 8:14 AM, Ken Alexander wrote: Any down side to doing this? Suitable core material is crucial here. The core materials used for RFI suppression (including those used for common mode transmitting chokes) work by adding lots of loss into the common mode circuit because they are VERY lossy at RF. The core materials used for inductors are very different chemical formulations. 73, Jim K9YC __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
