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 -----Original Message----- I can attest to what Vic says. I have an 88-foot long doublet, hung about 45 feet up, fed with 85 feet of 600-ohm ladder line. At the shack end I have a 1:1 balun, and then about six feet of RG/8X running to the K3. The K3's tuner likes the combination. I tried replacing the 1:1 balun with a 4:1 from the same manufacturer. The K3 was quite unhappy with the change in components. The 4:1 went back on the shelf, the 1:1 went back inline. YMMV Jim / W6JHB On Thursday, Dec 8, 2011, at Thursday, 9:14 AM, Vic K2VCO wrote: > It is a common misconception that a 4:1 balun is the best choice to feed a tuned balanced > line. The assumption is often made that this is appropriate because the characteristic > impedance of ladder line or open-wire line is higher than the 50-ohm coax that's connected > to the balun's input. > > Actually, since the tuned line is being operated at a high SWR, the impedance seen by the > balun will vary all over the map. It may be very high or very low. This is a very tough > job for the balun, and in some circumstances it can be quite lossy. This is why a real > balanced tuner is better than an unbalanced tuner followed by a balun. > > A 1:1 balun is likely to have lower losses in this application, although there might be > combinations of frequency and line length where a 4:1 is better. I hope that Elecraft is > planning to make their balun either 1:1 or switchable. ______________________________________________________________ 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 ______________________________________________________________ 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
