<< How many loops and what diameter would be good for 1/2" hardline? or 3/8"
hardline? Floyd Rodgers KC5QBC >>
Good Question. I'm posting the reply to help others and get it into the
archives for reference.
Hardline cannot flex more than a few times before it breaks, just like
breaking the steel in a coat hanger by bending it back-and-forth. You must
use a jumper of flexible coax, such as RG-213, or any of its derivatives,
having a braided shield and stranded center conductor.
I have run hardlines up to the top of my tower. I installed the antennas
with RG-213 jumpers pre-attached, and long enough to come down the mast,
make 3, 8" diameter rotation loops, and connect to the hardlines just below
the top plate.
To estimate the length of the jumper you need, add up the linear distance
along the boom, mast, etc, all the way between your antenna feedpoint and
the end of your hardline. Add about 6.5 feet for your 3, 8" rotation loops,
and you have your total jumper length.
If you are also making a coaxial choke balun, include this length into the
To estimate length for coils in general, such as choke baluns and these
rotation loops, it's:
L = PI * OD * N
L = length of coax required for coil, in inches
PI = 3.14
OD = OUTSIDE diameter of coil turns, in inches
N = Number of turns
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