From a coil loaded 80m 2L yagi (bought JKantennas) and 80m rotatable
dipole I built and reading here are some thoughts.
My rotatable 80m Tornado loaded 86' dipole at 100' doesn't have much of
a pattern, height is everything and at about 130' or so they really
start to play. The beam is at 157'.
Element gap isn't too important - wide enough to stand the voltage,
strong, and UV durable. 2" is ok. A fiberglass solid rod with paint
would work, or a UV resistant plastic sleeve over the FG. No steel or
SS near the coil if possible.
IMO, there is very little loss difference with 1/4" tubing Cu vs Al.
Good electrical joints are probably more important. Coil L/D ratio
about 1 and turns spaced tubing diameter seems to be about optimal for
highest Q. Any form will reduce Q, so best to avoid them and make the
coil self supporting. I use
http://hamwaves.com/antennas/inductance.html for a coil calculator, it
gives you every value you might want.
Many other issues - truss connections, 3 way truss per Lesson's
designs, wind load calcs, etc. My dipole truss is 2 phillystrans up to
a 5' wide crossbar 5' up the mast. So far no problems, but in a treed
area with modest wind loads. YagiMech predicts 85 mph survival w/o truss.
I'll send a coil picture offline.
Grant KZ1W
On 10/10/2016 21:03 PM, Ray Benny wrote:
I am building a 90 ft, 80m rotatable dipole. I am near the point of fabricating
the inductors/coils that will go about 23 ft out on the element. I am guying
the element just before the inductor. I have several questions:
1. Does the size of the gap between the center element and element tip make
much difference? Is one inch enough, or should it be almost the same size as
the coil length?
2. Is there advantage of winding the coils of copper vs. aluminum? Is it worth
silver plating the copper windings? I'm most likely planning to use 1/4" tubing
either way.
3. Once I figure out the total length of the element, a friend is going to run
EZNEC and tell me the inductor valve I need. I will use a calculator to compute
the physical dimensions of the coils. What is the advantage of building the
coils on either 3 inch vs. a 4 inch form?
Is there anything else to consider in the construction of this antenna?
Tnx for your thoughts,
Ray,N6VRLocated in central AZ
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