Impedance is about 120*ln(2*D/d) ohms, where ln is the natural
logarithm, and D is the wire spacing, center to center, and d is the
wire diameter. Assumes round wires, and air dielectric. You can
rearrange that: if you want x ohms and have d diameter, D =
d*exp(x/120)/2, where exp(x/120) is "e to the x/120 power". If you
don't have a calculator that handles that sort of math, this table
will probably get you close enough:

D/d impedance, ohms
1.9 150
2.8 200
6.2 300
22 450
75 600

Construction depends a bit on how much you're making and what you have
available for materials and tools. People used to use wooden spacers,
boiled in parafin wax. Someone gave me a bunch of PETE
tensile-strength test strips that are a good size. You can make
spacers from PVC pipe. You can thread wires through holes (generally
not so efficient), or fit wires into notches and secure by with a
plastic or wire wrap, or by melting the wire into an undersized notch,
or with various glues. Undoubtedly lots of other ideas, both
tried-and-true and just waiting to be tried for the first time.

You can drill holes through the glass and install feedthroughs (but
probably not if it's double-pane!), or drill a couple over-size holes
through the wall or possibly through a wooden window frame member, or
install a wood or plastic piece in a partially-open window. You can
also possibly inductively or capacitively couple through the window.
If you decide to go through wood or wall materials, plan to make
oversized holes, lined with decent electrical/RF insulation. What
strikes your fancy?

Cheers,
Tom


Larry Gagnon wrote in message ...
Hello to all. I intend to erect an 80 meter full size dipole and feed
it with homebrew open ladder line. Would anyone care to reply as to how
to construct ladder line easily and effectively? How does one determine
spacing to get X ohms impedance line?

Also any ideas on how such line can easily be fed in through a window
with a wood frame would be greatly appreciated.

Larry Gagnon VE7EA