[TowerTalk] "Magic" length from tower to first insulator

[jimlux]

On 3/16/16 12:31 AM, Larry Loen wrote:
> A friend of mine told me that someone, somewhere had calculated a "magic"
> length for guy cable.  If you went down 10 or 11 or 13 feet (or whatever it
> is) off of your tower and installed your first insulator there, your guys
> would be sufficiently 'non-resonant' so that they wouldn't interfere with
> the pattern of the antenna(s) above.
>
> What is this magic length and where is it documented?

There's a table in the ARRL Antenna Book of "good" guy segment lengths..

I do it by setting up an excel spreadsheet that calculates the number of 
wavelengths for my frequencies of interest for a given length, and then 
just making sure they're not close to a multiple of 0.5

if cell C3 is the frequency (in MHz) and cell A5 is the length (in ft)
C4 = 3.28*299.7/C3			wavelength in feet

C5 = $A5/C$4 - floor($A5/C$4) 	frac part of guy length in wavelengths

Then conditional format C5 to be red if it's in the range 0.45-0.55  (or 
whatever tolerance you want)

I put a sample sheet out on google docs

https://docs.google.com/spreadsheets/d/1rXeWjPMej_TlzN0h8OfzEFAU2mwKGiar_QaxK94tozA/pubhtml