[Fwd: FW: VHF Antenna Refurb]
Wed, 12 Feb 1997 20:23:32 -0500
Lipitz, Larry wrote:
This is from another List, lots of good point, speaking of antenna
> From: email@example.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
> 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
> 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.
> CC elements in the middle have a compression fitting and this may
> internally resulting in the wrong electrical length for the element....
> If a milliohm meter is not available, try putting 10 amps of DC
> 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
> 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
> is about the same size as the hole bored onto the compression sleeve in
> middle for mounting to the boom... While the element is one piece at
> 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
> 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
> 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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