Topband: Open wire feeder

[n0tt1 at juno.com]

Hi Dave,

> I've used open wire feeder successfully over the years in some 
> fairly small,
> limited applications.  However, I have a 160 transmit antenna that 
> I'm
> constructing that will be about 800 cable feet from the shack.

You're gonna love the low loss of open wire feed!...far less than
coax.

> I'm considering using 450 ohm open feeder (the PVC coated variety).  
> Any
> particular constraints on how it gets deployed?  

Are you talking about the line that is about 1" spacing?  I would
recommend building your own, really...it's easy to do and inexpensive.
I use solid aluminum electric fence wire...it's been up for at least
15 years....taken down by storm maybe twice.  Easy to repair,
no soldering....just sand clean and use "Western Union" splices.  
Mine is ~600 ohms, spaced at 6", with an spreader every 30-50 feet.
Spreaders are 1/4" thick Plexiglass(r), 5/8" wide and 7" long.  Grooves
cut with a power saw, thin blade....wire goes in the groove, held 
fast by 6-32 SS screws and washers, placed near the ends of the
spreaders.
Screw holes are tapped in the plastic for convenience.  A more deluxe
line would use heavy copper wire....see ARRL handbook for info
on impedances of OW line.

I would like to run 
> it
> parallel to an old barb wire fence with wooden poles, tying the 
> feeder to
> the fence posts about 2' or 3' off the ground.  

Keep open wire feeders out of casual reach from the ground!!...lots
of voltage there.  Keep OW away from other metallic objects, at
least 3-4 times the "width" of your line.  If your line is 6", then
keep away at least 18-24 inches....more is better.  Aluminum
line is light weight...I support mine every 200' or so....keep line
tight so wind won't twist the line and short it out.  Have a way to
lower it to the ground quickly for easy maintenance and ice storm 
avoidance.

I will probably 
> switch back
> to 50 ohm coax as I near the field of the antenna so that I can bury 
> the
> feed line.  

No need to do that...just run your OW feeders up to the tower,
then down to a matching box if you want lo-z output to connect
to the tower.  I use a BAL-BAL and BAL-UN...plans right out
of one of Jerry Sevick's books...I use type FT-240-K cores (Amidon)
total of 4 for the two series connected transmission line xfmrs...all
contained in a 6" square "Carlon" brand PVC box from ham depot.  
OW feeders *and* lo-Z outputs equipped with spark gaps...never 
had a problem with lightning damage even though tower struck many 
times.  Xfmrs run stone cold even with 1.5KW output on 160.
I use my line as a non-resonant feed line....impedance matched at 
both ends.

73,
Charlie, N0TT

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