[TowerTalk] Open wire line some important points

[Michael Tope]

According to my loss chart (wireman catalog), #12AWG open
wire line is .05dB/100 feet better than 1.25" diameter hardline
at 30 MHz. For a 1000 foot run, this would be a 0.5 dB (about 
10%) advantage to the open wire line. When you include 
impedance matching devices on both ends (9:1 transformers
for instance), the advantage is even smaller.

I suspect that when W1EVT was building his station, the 
open wire line may have represented a better economic 
tradeoff. Nowadays with lots of surplus CATV coax floating
around, the situation is different. Especially if your time is
a valueable commodity (building 1000 feet of open wire line
is no small task). Admittedly though, open wire does have alot 
a nostalgic appeal, but then again I am a little warped in my
perception of these things. 

Mike, W4EF............................... 

----- Original Message ----- 
From: "Tom Rauch" <w8ji@contesting.com>
To: <TOWERTALK@contesting.com>
Sent: Thursday, September 14, 2000 7:17 AM
Subject: [TowerTalk] Open wire line some important points


> 
> > W1EVT, winner of the first 5BDXCC, uses 4 wire open wire
> > lines to run under the road and up the hill to his 19 towers
> > with 3 sets of stacked wire arrays (two half waves in phase
> > stacked every half wavelength) for every band.
> > Several of my dipoles are fed with ladderline and used 
> > successfully on multiple bands.  I have no problem
> > with running the ladderline across my yard suspended
> > from tree limbs and guy wires.
> 
> 
> Marconi and others used spark to set the world's distance record.
> 
> I still use spark in my lawn mower and car.
> 
> All things have their place, but we should remember two important 
> things:
> 
> 1.) When the line is electrically short (less than around 1/4 wl) loss 
> is a function of conductor diameter and current.  Lowest loss does 
> not occur with lowest SWR on the line! Lowest loss occurs when 
> the line has a mismatch in the direction that lowers current in the 
> line.
> 
> 2.) Ladder line, or open wire line with small conductors, has more 
> loss than most conventional coax when used to feed a 50 ohm load.
> 
> 3.) Ladder line really gets lossy when it is wet. You might as be 
> using RG-58 in some cases.
> 
> 4.) If the coax is matched, and the ladder line is mismatched
> by running it to a 50 ohm load, the losses are about the same in 
> dry weather between ladder line and foam insulated RG-8 style 
> cables.
> 
> Real open wire line with large conductors is pretty good, except for 
> physical problems. For most matched line installations, coax will 
> be better.
> 
> 
>  
> 73, Tom W8JI
> w8ji@contesting.com
> 
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