>
> Googling it, I found that you can make your own, but it is not clear
> what the impedance is, because it depends on the wire gage and spacing.
Kip,
Most hams use open wire line to feed antennas of no particular impedance.
Very few people have antennas that are resonant and 450 ohm input
resistance, but lots of people use 450 ohm window line anyway.
Open wire is popular because it tends to have very low line loss even when
very severely mismatched. The only thing that knowing the impedance gets
you is part of the way to calculating the line loss when you hook it to your
random-impedance antenna! If your load is going to be a random impedance
far from your line's characteristic impedance on most if not all bands, it
doesn't buy you anything to worry about whether the line characteristic
impedance is 800 ohms or 400 ohms or 672 ohms...
That said, it is easy to estimate ... 276 * log (D/r), where D is the
ladderline spacing and R is the radius.
And if you want a flexible calculator that will tell you both the line
impedance the losses with a given complex load impedance for an arbitrary
two wire line, VK1OD has this available on his website.
http://vk1od.net/calc/tl/twllc.htm
73
Dan
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