Topband: Ladder line vs coax loss epiphany

[Shoppa, Tim]

I briefly used the "window line" you all are discussing, before I built my own parallel line from scratch.

I think all the window line that's available today from Wireman, RF Connection, etc is made by JSC. My experience was with JSC 1318.

Yes, the window line had some issues. Change in properties when wet and the way it turns into a "sail" in any wind were my biggest problems.

I think the window line is probably useful under some circumstances. It rolls up kinda nicely (being copper plated steel it will always coil back up!) and is rather lightweight. I know for sure my home-made parallel lines doesn't roll back up nicely! So maybe it would be useful to backpackers etc. especially in dry weather.

Tim N3QE

-----Original Message-----
From: Topband [mailto:topband-bounces at contesting.com] On Behalf Of Tom W8JI
Sent: Wednesday, April 30, 2014 10:46 AM
To: topband at contesting.com
Subject: Re: Topband: Ladder line vs coax loss epiphany

> 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
 

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