I disagree. A center fed quarter wave will have a complex impedance of a few ohms of resistance and a very large capacitive reactance. SWR can be 100:1. I know, I am doing it. Why it works with good open wire line is that the line can transform the impedance to something that is easy to match with a practical tuner. For example, in my case I feed a half-size doublet with about a quarter wave of real open wire line, and it looks like a large INDUCTIVE reactance and high resistance at the shack end! It's easy to knock out the inductive reactance efficiently with a pair of capacitors, and a 4:1 balun transforms the high resistance to a value that gives about a 5:1 SWR on the short coax to the tuner. There is still (in my case) about 2.5 dB loss in the feed line due to SWR even at 40m, but I just run a kW instead of 500 watts and come out ahead.
Vic 4X6GP > On 31 Jan 2017, at 18:53, Ron D'Eau Claire <[email protected]> wrote: > > The intrinsic higher impedance of ladder line helps reduce the losses > through a lower SWR than typical coax. A center fed wire at least 1/4 wave > long end-to-end on the lowest frequency used (e.g. 130 feet on 160 meters) > and fed with typical 350 to 450 ohm ladder line will show an SWR of 10:1 or > less across the HF spectrum, since a real-world wire will show an impedance > of only 4,000 ohms or so even when it is exactly 1/2 wavelength long. > > Feeding the same antenna with 50 ohm coaxial line will result in an SWR > 100:1 or greater and so much greater losses. > > 73, 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 Message delivered to [email protected]
