[TowerTalk] Open wire line some important points

[Tom Rauch]

> 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

--
FAQ on WWW:               http://www.contesting.com/FAQ/towertalk
Submissions:              towertalk@contesting.com
Administrative requests:  towertalk-REQUEST@contesting.com
Problems:                 owner-towertalk@contesting.com