5 picking a length for your long wire
5 picking a length for your long wire:
End-fed longwire antennas don't have to be any specific length to work, although longer is pretty much always
going to work better. They ARE directional though, and will work best on their sides and worst on their
ends. So for example if you want to work east and west, run the wire north-south. Also try to get it as
far off the ground as possible. If raising up the feed point of the antenna (where the balun box connects
the feed coax to the longwire) all the way up isn't practical, just get it as high as you can.
After you've decided where to put your antenna, figure out the MAXIMUM length of wire you can run. You
will probably be using an antenna tuner to tune down the SWR, but the tuner won't be able to tune for bands
where your wire is a multiple of a half wavelength of that band long. The chart will help you identify at
what length those problems will occur for each band. The chart has vertical columns of blue dots, indicating
"bad spots". Each column of dots is for a different band, so figure out what bands you DON'T care about, and
ignore the column of dots for that band. For example, if you don't plan on using 30 meters, you can ignore
the dots above the 10mhz point on the chart.
Convert your maximum length from feet to meters if needed, then draw a horizontal line on the chart at that
length. Unless you got lucky, you're probably hitting or getting close (within a meter) to a dot somewhere.
Move the line down slowly until you find a "clear path" through the blue dots. So for example, lets say you
want to be able to work ALL the bands, and you have 41 meters of wire to work with. That hits A LOT of
dots. But if you shorten your wire to 38 meters, it passes through the chart without getting near any bad
spots. (38 meters is about 125 feet, it's what I use here)
There's a simplified chart that removes 30, 17, and 12 meters, leaving 80, 40, 20, 15, and 10, which is all
a lot of people will ever need. (160m is very long, you won't hit the first half wave dot until you are out
at 82 meters of wire, which is pretty unusual) With those three bands removed, the chart gets a lot clearer
and easier to read. 10 meters (and somewhat 15) are the biggest hassle to avoid. As a final example, lets
say you only have 26 meters of wire to work with. That's pretty close to a 10m dot, but is just above a bunch
of dots down around 21m. So pick a length between the two, say 24 meters, and that will allow you to easily
tune 80/40/20/15/10.
Shorten your wire to the length you've found you need to use, and just run the rest of the distance to the
tree or whatever you're anchoring to using paracord 550 or something non-conductive. Or you can pad the
length at the feed end by moving your balun box a little.
Don't forget proper grounding and a lightning arrestor!
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