Topband: Ladder line vs coax loss epiphany

[Tom W8JI]

> That tenuous advantage disappears if one popular 360 ohm heavy duty window
> line variant of "450" line is operated at a mismatch. At that point the
> stranded copperweld conductors (used for physical strength) start to lose 
> a
> lot of power at the current maximums of the standing waves. I confirmed 
> the
> 360 ohms on my particular piece of the window line.
>
> In my case, almost 500 feet of that running through the woods needed a
> surprising amount of finagling the system to present 360 ohms to the
> feedline. That SWR change people see in the rain apparently is a velocity
> factor change, making the degree of change in the rain proportional to the
> mismatch to the window line Z0. The 450 ohm baluns are not all that good a
> match, and most of the baluns are poor at 160..

The ARRL has had some goofy measurements. They had one article that showed 
almost no change in loss with a line laying right on wet dirt!

Lines I measured here with heavy conductors were about 370 ohms, and loss, 
velocity factor, and surge impedance changed with water. They also changed 
substantially when the line was laid against things, or a line enclosed in 
PVC pipe was buried.

It is illogical to have a change in Vf without an accompanying change in 
loss or impedance.

The odd impedance of "450 ohm" lines aggravates the issue of broadband use 
in matched systems. I would stay away from ladder lines for low loss 
impedance matched systems, and stick with real open wire line of a modest 
planned impedance such as 450 ohms.

Surplus hardline is a much better option, IMO.

73 Tom