[Boatanchors] Sealing Cobraheads and other Inv Vee Dipole
questions
Glenn Little WB4UIV
glennmaillist at bellsouth.net
Wed Nov 23 16:14:42 EST 2005
At 04:02 PM 11/23/05, Philip Atchley wrote:
>Hi all, this was also posted to the Antenna reflector,
>
>I'm in the process of cleaning up a couple B&W Dipole Cobraheads for reuse
>in some Inverted Vee Fan Dipoles. These appeared to have been sealed with
>some sort of black gasket compound, which I'm cleaning off.
>The coax braid, which was probably VERY old was as shiny as the day it was
>new.
>
>Questions.
>1. I'm planning on sealing with standard RTV. Will the fumes build up
>too much in the Cobrahead and be "trapped", causing future problems?
Standard RTV cures by releasing acetic acid. Acid is corrosive to metals.
No a good choice. If you must seal with RTV use a type that cures with
alcohol. This can be had from an auto parts place and is listed as oxygen
sensor safe. It can also be had from good electronic supply houses.
>2. I realize that when making "fan" multiband dipoles, even harmonicly
>related bands are best (7/14MC etc) due to the unused dipole being of
>higher impedance. How about Non-harmonically related. As they are going
>to be used as guy wires on a pushup pole and their relative lengths, I'm
>proposing the following "band pairs".
>
>1. 7.2 & 10.1MC for the topmost Inverted Vee pair, perhaps using the 7MC
>one for 21MC also. Are the 7 & 10MC freqs too close?
>2. 14.2 & 28.6MC for the next lower pair on the mast. Mounted lower to
>keep the Apex angle a little wider).
>
>
>******************************************************
>73 de Phil, KO6BB
>If it's over 1dB above the Noise Floor, "IT AIN'T DX"!
>
>THE BEACONEER'S LAIR: http://www.geocities.com/ko6bb/
>QSL GALLERY: http://photobucket.com/albums/y123/KO6BB/
>Merced, Central California, 37.3N 120.48W CM97sh
>
>******************************************************
73
Glenn
WB4UIV
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