[TowerTalk] Question on Insulators

[Guy Olinger K2AV]

These lengths are not all that effective when used in proximity, directly underneath an antenna. Particularly where we are talking about the top set of guys on a tower, under a tower top tribander. The only effective length for that situation is 3/8 wavelength or less at the HIGHEST frequency in use. A most effective for least effort solution is to START with a 3/8 wavelength insulated section for the first length on the top set of guys.

The lengths in the ARRL book work for far field measurements, but dissolve in their effectiveness in a near field situation, especially where the two ends of the insulation section are not equally coupled by the excited radiator.

On Mon, 19 Jun 2000 08:35:38 -0600, you wrote:

>
>On Sun, 18 Jun 2000  "Randall R. Wing" <rwing@southwind.net> writes:
>>
>> > I have seen the tables in the different ARRL books on the 
>> different lengths of guy cable - does anyone have any preferences?
>> >
>> > Thank you,
>> >
>> > Randy
>> >
>
>Here is a copy of a post I wrote last February on this subject. 
>
>Guy Insulator Placement   de   N4KG
>
>The following lengths between insulators have 
>resonances between the conventional bands 
>(which places their resonances in the WARC bands :-) 
>-  27, 40, 58, and 76 ft.  (per ARRL  Antenna Book)
>
>You may want to make your wires slightly shorter 
>to compensate for the capacitive end loading of the 
>loops through the insulators.
>
>You need to place the first insulator as close to the
>tower as possible to prevent coupling to continuous
>wire from one insulator, through the tower, to another
>insulator.
>
>For the first insulated section, I like to use a short
>piece of 10 to 12 ft between insulators.  This length
>is substantially less than 1/2 wavelength (WL) on
>10M and will therefore be nearly invisible on all frequencies
>below 28 MHz.  For even better isolation, use two 10-12
>ft sections before going to longer spans.
>
>de  Tom  N4KG
>
>
>
>
>________________________________________________________________
>YOU'RE PAYING TOO MUCH FOR THE INTERNET!
>Juno now offers FREE Internet Access!
>Try it today - there's no risk!  For your FREE software, visit:
>http://dl.www.juno.com/get/tagj.

73, Guy
k2av@contesting.com
Apex, NC, USA

--
FAQ on WWW:               http://www.contesting.com/FAQ/towertalk
Submissions:              towertalk@contesting.com
Administrative requests:  towertalk-REQUEST@contesting.com
Problems:                 owner-towertalk@contesting.com