Someone with sharp eyes will catch my mistake, so I'll correct it first. I should have said, The first time I saw 4:1 baluns being sold to Hams was to make it easy to connect the 300 ohm feeder to such a folded dipole to the output of a rig designed to feed 75 ohms instead of 50 ohms.
Many Ham rigs using pi-network output in the 1950's and 60's specified a nominal load impedance of 75 ohms, although most networks were adjustable over a fairly large range. Ron AC7AC -----Original Message----- In the 1960's one very popular and cheap H.F. antenna was the folded dipole. Often they were made from the ubiquitous 300 ohm "twin lead" used on TV antennas and fed with the same twin lead since the impedance of a folded dipole is close to 300 ohms. The first time I saw 4:1 baluns being sold to Hams was to make it easy to connect the 300 ohm feeder to such a folded dipole to the output of a rig designed to feed 50 ohms. As Hams migrated away from rigs with tunable output networks to rigs with fixed tuned outputs, MFJ and others produced a line of antenna tuners specifically designed to correct feed line mismatches since that could no longer be done at the rig. They included the popular 4:1 balun for those who were feeding various open wire lines (typically 300 to 600 ohms but which may have significant SWR - so the impedance might vary much more). It seems that many Hams considered the 4:1 ratio some sort of magic number, when all it was intended to do was provide a good transfer between 300 ohms and 50 ohms. Ron AC7AC ______________________________________________________________ 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
