[Elecraft] The "Kinda Random Antenna"

[Vic Rosenthal]

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 <ron at cobi.biz> 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
>