I have read a few of the responses to this 'magic length' question but
recall something I found in an older ARRL Antenna Book. I lived in the D.C.
area unit 1998. West of D.C. in Manassas, Va I bought a home with just over
5.5 acres and had my little antenna farm with 5 towers there where I lived
for 9 years. The antenna book came in to play when I was trying to decide on
the NON-resonant lengths that I could use to be safe when I was erecting the
towers. First of all I had torque bars on all of my towers. Just off the
torque bars within the first few feet was my first insulator. The towers
each had 5 sets of guys and only the lowest set did not have an insulator
virtually right off the tower. I think at the time the lengths beyond that
were 39ft 6" to the next insulator. Don't ask me why I remember that but it
just sticks in my head that that length was safe and non-resonant.
Otherwise, look in an Antenna Handbook..perhaps an older copy. The answer is
sure to be there. - '73, Mike
-----Original Message-----
From: jimlux
Sent: Wednesday, March 16, 2016 1:51 PM
To: TowerTalk
Subject: Re: [TowerTalk] "Magic" length from tower to first insulator
On 3/16/16 9:47 AM, Richard (Rick) Karlquist wrote:
On 3/16/2016 9:01 AM, Larry Loen wrote:
Comments? Dissents? What did I overlook?
What you overlooked was that if the wire is
not insulated from the tower, the resonance
is at 1/4 wavelength not 1/2 wavelength.
Seems reasonable (e.g. the tower is "big" compared to the wire, so it's
sort of like a 1/4 wavelength whip over a ground plane..)
I wonder if that's how it works in reality, though?
Maybe that top guy segment (connected to the tower) is really a very
long wire that happens to be bent at the end, and doesn't feature into
the circuit?
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