[AMRadio] open wire line


Jim Wilhite w5jo at brightok.net
Mon Nov 19 20:12:42 EST 2007


Geoff if you really want to know the impedance of line you construct, 
you can use the formula I=276 log b/a
b = center to center distance between conductors
a = Radius of conductor

If you don't want to do the math, there are charts available that will 
do the calculations for you.  If you don't have one and want a copy, 
email me and I will scan and send.

As far as what to try to do, just build it with 2 to 6 inch spacing 
using 12 or 14 wire, your tuner should take care of the rest.  This 
should be more than adequate since you normally run near 100-150 watts.

As for spreaders, use the lightest thing you can find, 1/8 plexiglass 
cut into strips 1/2 inch wide, Lexan the same or anything.  To keep the 
spreader in place, drill holes in the strips then run the wire through 
the holes then cut short pieces of wire and wrap one side of the 
spreader then across it to the other side and wrap, then solder.

Jim/W5JO





>I tried to get on the air a few days ago, and noticed the SWR was 
>extremely high on my loop, fed with ladder line.
>
> After much futzing it finally dawned on me to check the loop for 
> continuity.  There was none.
>
> The 450-ohm ladder line I've been using for two and a half years, 
> before it broke, is 14ga solid copper-clad steel wire. Not conducive 
> for windy (read: outdoor) applications.
>
> So, my solution is going to be to home-brew an open wire feed line, 
> using insulated 12ga stranded copper wire.
> I will still be using the same SA-2060A tuner that's carried me for 
> years.
>
> I'll probably go down to the local hardware store and get either some 
> wooden dowel rod, and chop it up to equal length pieces and cut a slot 
> at the end of each, spray 'em with urethane (for weather protection) 
> and then 'hot-glue' the wire/dowel in place.  Or, get some plexiglass 
> rod and do the same thing, minus the urethane spray paint.
>
> My question is:
> how far apart should the two wires be kept?
> I've seen as little as 4" and as many as 6", and both claim to be 
> ~600ohm.
>
> The 450-ohm ladder line is only about 2" wide.
>



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