[Fwd: FW: VHF Antenna Refurb]

Larry NY2US NY2US@hoflink.com
Wed, 12 Feb 1997 20:23:32 -0500

Lipitz, Larry wrote:
This is from another List, lots of good point, speaking of antenna

>  ----------
> From: c1f@juno.com
> To: Witmerjr@aol.com
> Cc: VHF@w6yx.stanford.edu
> Subject: Re: VHF Antenna Refurb
> Date: Sunday, December 29, 1996 8:17AM
> The following is a DIGEST of a lot of good ideas from a lot of  fellow
> hams
>  who have been effectively designing and maintaining antennas for a lot
>  of years......
> I would consider the following refurbishment to an aluminum antenna:
> 1. 100% disassembly and inspection for corrosion and broken parts..
> 2. 100% replacement of the plated steel hardware, CushCraft or other
>                 manufactureres will probably have a stainless steel
> hardware
> replacement kit with everything you need...
> 3. the antennas that originally were designed to have elements
> electrically and mechanically bonded to the boom, MUST have a good
> electrical bond after   refurbishment and throughout the antennas
> useful life....
> Where the metal parts touch, all of the metal parts must be cleaned,
> decorroded, and a corrosion inhibitor added to retard further corrosion.
> 4. Measure the resistance of the solid elements with a milliohm meter.
> The
>  CC elements in the middle have a compression fitting and this may
> corrode
>  internally resulting in the wrong electrical length for the element....
>  If a milliohm meter is not available,  try putting 10 amps of DC
> current
> through
>  it and measure the voltage drop across the compression joint.  If you
>  consistently test each element by injecting the DC over  the same
> length, the
>  voltage drop for good bonds should be consistent.. In other words test
> over
>  a 1 foot length with the compression fitting in the middle.. Any
> corroded joints will show up as a higher voltage drop.   Replace the bad
> element.   I have not found
>  a way to cost effectively repair the compression joints...
> Take a good look at the dimensions of the solid element.  The rod
> diameter
>  is about the same size as the hole bored onto the compression sleeve in
> the
>  middle for mounting to the boom... While the element is one piece at
> the
> start of assembley, after the mounting hole is bored, the element may be
> in two  pieces
>  and will rely on good electrical bonds between the element, to the
> compression sleeve, to the other side of the element...
> The electrical bonds on telescoping tubular elements and the multiple
> boom sections can also be tested for resistance by energizing with DC
> current, and measuring voltage drop across the joint... Use ohm's law to
> determine the resistance. (R=E/I)
> 5. After all of the elements are known to be good, assemble to the boom
> with the following procedure..
>         clean down to bare shiny aluminum all parts that will be touching
> each    other.  Each element uses many parts to attach to the boom,
> all mating              surfaces must be cleaned to bare metal..
>         clean the metal surfaces with an emory cloth or even a fine sand
> paper.
>         I avoid steel wool, because small streel fibers are left behind
> which will              accelerate corrosion.
>         after all mating parts are cleaned, add a corrosion preventive
>         aluminum
> laden grease like NOALOX by Ideal industries. This
>         compound is used by electricians to treat aluminum wire joints.
> The             compound is commonly available at elelctrical supply
> houses and at
>          THE HOME DEPOT. This grease is reasonably tenacious and only a
>         small amount is needed at the exact point where metal parts are
>          touching..  After assembly, wipe off excess grease.
> 6. After  assembly and all electrical (DCand RF) testing is performed
> seal all
>  joints with a RUSTOLEUM clear spray seal to water proof  and to retard
> further element and boom corrosion
> 7. Install the antenna in its final location... Be sure to use a
> anti-seize compound on all bolt threads.. these metal laden greases are
> available at your local automotive parts store and may contain aluminum,
> copper, lead, or nickel  in a tenacious grease.
> I prefer to use the aluminum ladded compound on aluminum hardware or the
> copper laden grease on stainless steel hardware. . The stainless steel
> U-bolts are notorious for galling when over torqued and seizing when
> removal is attempted years later..
> the anti-seize compound prevents the galling and significantly eases the
> removal and reuse of stainless steel hardware.
> I hope this sheds some light on what may be done to extend the life of a
> aluminum antenna.
> Stan, WA1ECF
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