It is a pity that someone back in prehistoric times started using the word "balun" for two entirely different devices. I use an air core "balun" (a so-called "choke" balun) which is about a foot long and about 4" in diameter, wound as a single-layer solenoid on PVC pipe, on my HF beam. This is in place of the scramble-wound "choke" often used at an antenna feed point.
I also have various matching "transformers" on my 5 beam antennas, none of which is a toroidal transformer. It is possible to make an unbalanced line-to-balanced feed point transition without a toroidal transformer, of course, and when things are managed this way, there is never a question of a toroid freezing and cracking or alternatively roasting from too much RF and cracking. As I see it, one of the truly superior advantages of toroids is as cores for interstage transformers (or for filters), as in many modern transceivers. The devices are beautiful because they are physically small and one can lay them down or against almost any substrate, since their ultrahigh permeability contains fringing fields completely (any that are "left over" from imperfections in the flux closure of a perfect toroid). John Ragle -- W1ZI ===== On 10/17/2011 3:14 PM, Ron D'Eau Claire wrote: > I've never seen an HF Yagi with an air core balun at the feed point. Such > baluns for HF were typically a foot or more square! (The only ones I ever > messed with were mounted in the shack to connect a single-ended rig output > to a balanced feed line.) > > By the 1980s ferrite baluns were very commonly used almost everywhere, so > I'd put money on your having a ferrite balun on that yagi. > > If the balun was abused, physically, with too much RF heating or by moisture > getting into the housing, it may be damaged. The same is true for traps. > > 73, > > Ron AC7AC > > > > -----Original Message----- > Someone mentioned the baluns on older yagis were air-core. I have an > older Hygain TH3mk4 with original balun (big black box connected to > the hairpin stub and driven element. The antenna is probably 20-30 > years old, so I wonder if anyone can tell me if it is likely air-core > or ferrite? Any advantage in replacing it? > > I found that I had to use a tuner after installing it at 50-feet even > with element lengths adjusted to min SWR per manual. Now I wonder if > this may be due to an aged balun? > > The used antenna only cost me $75 so not a big investment. But it > does seem to "work" DX OK. I worked T32 on 10m on Saturday with only > 8w SSB from my K3/10. But eventually I will be running 300w so this > may matter more. > > Note that the tuner is required on all bands 20-15-10m. 10m was the > hardest and would not tune very well in any position of the driven > element. Tuning was done with antenna pointed straight up when at > ground level with reflector essentially at the ground. I expected > some shift in resonance once the tower was raised (all antennas > installed before raising with a crane). > > I suppose this may also point at bad traps (but for $75 it works). > > > 73, Ed - KL7UW, WD2XSH/45 > ====================================== > BP40IQ 500 KHz - 10-GHz www.kl7uw.com > EME: 50-1.1kw?, 144-1.4kw, 432-QRT, 1296-?, 3400-? > DUBUS Magazine USA Rep dubus...@gmail.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 > > ______________________________________________________________ > 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 > > > -- Sent from my lovely old Dell XPS 420 ______________________________________________________________ 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
