[AMRadio] Home-Brew Parallel Transmission Lines (was: Antenna tuner


Stevan A. White w5saw at pathwayz.com
Wed Jan 10 12:06:10 EST 2007


Brett gazdzinski wrote:

> the antenna will likely be about 100 feet
> in a flat top setup, up about 30 feet, fed with=20
> about 30 feet of open wire line, made with #12
> wire spaced an inch or two apart.
  =20
John/WA5BXO built an antenna for 'portable' use, which is about as you=20
are describing.  Except, his feedline is a pair of 12ga stranded lines,=20
spaced around 4 or 5 inches apart.  Being in the Computer Repair and=20
service business, he had access to 'boxes' full of drive-bay covers. =20
So, whatever that distance is, is about where his feedline is spaced.=20
5.25"?  Those drive-bay covers also make it easier to roll up the feed=20
line, but experience has proven over time that they are just as subject=20
to the rigors of UV light.

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

I wish I was as smart as L. B. Cebik, W4RNL, but since I'm not I look =
stuff
up on his web site quite often.  He has an excellent treatise on =
home-brew
parallel transmission lines.  Take a look at:
http://www.cebik.com/trans/par.html

If you're willing to take my word for it, here's the low down:  When =
using
#12 wire, for line Z of (approx.) 300 ohms use 1/2" spacing, for 450 =
ohms
use (approx.) 1-3/4" spacing, and for (approx.) 600 ohms use 6" spacing.

For spacers I'm using pieces of black plastic clothes hangars I got from =
the
dollar store.  Not sure how many spacers you can get at 10 hangars for =
$1, I
still have hangars left.  Hint: It is much easier to drill them =
accurately
BEFORE you cut them into pieces.

Another suggestion (from Cebik's article) was using stiff but =
semi-flexible
plastic, like a liquid detergent bottle, to make your spacers.  You can =
use
scissors to cut it and a hole punch to make your holes.  It should be
oriented such that the more narrow dimension is the width of your spacer =
and
the longer dimension runs in line with your wire.  Bow the spacer =
slightly
to insert the wire, and let it snap back into place to hold the wire, =
and
itself, in place.  Here is a rather crude sketch:

     -------------------
 <---+-O - - - - - - O-+--->
     |                 |
 <---+-O - - - - - - O-+--->
     -------------------

Hope this helps.  Be sure to look at Cebik's article for further
clarification.  If you haven't already, bookmark his site.  What a =
wealth of
good information!

Best Regards,
Steve White, W5SAW
SW Commercial Electronics
mailto:w5saw at pathwayz.com

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