Jim, If you don't object, I'd like to save this and forward to people as arguments develop on these subjects.
I wish you had touched on '4:1 baluns'. Except for this group, so many people I talk to think a balun should be 4:1, even in their tuners. I think it is DX Engineering that addresses this well. Dick, n0ce On 1/31/2017 12:50 PM, Jim Brown wrote: > All of this discussion becomes badly confusing by failing to describe > these circuit elements by their real name. The word "balun" is a > bastard -- it is widely used to describe nearly a dozen things that > are VERY different from each other. > > W4TV got it right by adding the correct description, and this post > starts to get at it, but adds another bastard word, unun. > > Two-windings that are coupled by a magnetic field are a TRANSFORMER. > If the two windings have a terminal in common, they are an > AUTO-TRANSFORMER. A coil of coax is a common mode choke (and not a > good one). A section of transmission line wound around a ferrite core > is a COMMON MODE CHOKE, and if well designed (choice of ferrite > material, number of turns) can be a very good one. > > Transformers and auto-transformers transform impedance by virtue of > their turns ratio. Arrays of common mode chokes can also be used to > match circuits of different impedances. > > Last I looked, there was no description of the Elecraft "balun" > telling us what it is. Perhaps Eric or Wayne could add that to the > catalog listing for it. > > Another point. SWR is NOT an indicator of how well an antenna works. > High SWR DOES increase loss in a feedline, but that matters only with > long feedlines and small diameter coax. That does NOT matter for > typical portable (or even mobile) operation, where feedlines are much > too short for loss to matter. > > A high value of SWR as seen by a transmitter DOES limit that power > that the transmitter can put into the antenna. That's where the > antenna tuner comes in -- it transforms the impedance at the > transmitter end of the feedline (or the end of a wire plugged into the > coax connector combined with the counterpoise connected to the > chassis) to the 50 ohm resistive impedance that the transmitter wants > to drive. > > If we make RF current flow in a wire, it will radiate. How well it > radiates depends, of course, on its orientation. A wire laying on the > ground doesn't radiate very well. :) A wire without a counterpoise > will use whatever it sees as a signal return. If that return happens > to be the earth, the earth, which is essentially a big resistor, will > burn much of the transmitter power. The "good" lengths of wire Wayne > and those spreadsheets list are simply lengths that are likely to > present an impedance within range of most antenna tuners for the bands > that the operator is likely to use. > > 73, Jim K9YC > ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to [email protected]
