Fred,
Clearly I can't argue with your facts, since that's what they are. My
thoughts were simply that if Alfred really needed to interface with
aluminium then one way he could reduced the risk of electrolytic corrosion,
would be to protect the aluminium and eliminate the electrolyte.
Interesting point you make about ELT saves in the US. Certainly in Europe
there have been several embarassing incidents of false alarms from ELT's.
Dave
----- Original Message -----
From: Fred Fillinger <fillinger@ameritech.net>
Subject: Re: Bolting copper to aluminum
> Reactivity varies widely according to aluminum type and degree of
> oxidation, but for other than an ELT antenna, I actually do think
> copper against aluminum should not be used, Dave. Maybe thin sheet
> steel soldered to the copper mesh would be best.
>
> For an ELT, the reason it's unimportant is that the ground plane helps
> accomplish an ideal radiating pattern (gain). However, where the
> plane doesn't crash with antenna pointed upward, it's all moot. In
> fact for for SAR, a strong signal, aggravated by terrain effect and
> poor orientation, can place the center of signal strength far from
> where you really are. 160mW will xmit clearly for many, many miles,
> and I've read that SAR people will offtune to 121.525 or such if
> necessary. Nowadays, a handheld transceiver to assure ability to hail
> overhead A/C plus handheld GPS assures the fastest rescue. Even a
> cell phone increasingly has a chance in remote areas.
>
> In US accident reports, it's hard to find one clear case annually
> where the ELT resulted in a "save." What they do accomplish is
> reduced taxpayer cost to timely locate the site of a fatal crash, to
> reduce family members' pain and perform a probable cause
> investigation. Still where a flight plan was filed, they can locate
> A/C whose ELT never went off.
>
> Regards,
> Fred F.
>
> Dave Simpson wrote:
> >
> > Copper and aluminium react electrolytically quite readily. The normal
> > solution to this problem where large currents are not involved, (and
they
> > aren't in your receiving antenna application) is to coat the aluminium
with
> > alcromate which is conductive, apply some grease to the interface and
bolt
> > it up tight. You must keep out moisture to prevent electroytic
corrosion, so
> > if it doesn't need to be dismantled very often, paint the whole thing.
> >
> > Dave Simpson
> >
> > ----- Original Message -----
> > From: Alfred Buess <Alfred.Buess@shl.bfh.ch>
> > Subject: Bolting copper to aluminum
> >
> > A simple question from a metallurgic ignorant to the experts out there:
> > I have to bolt the copper ground plane mesh of my ELT antenna to the
> > aluminum bracket holding the antenna. Is there any risk of corrosion
between
> > the copper of the mesh and the aluminum of the bracket? If yes, how can
I
> > bolt it together, keep the joint conductive and prevent corrosion? Any
> > answer is appreciated!
> >
> > Alfred
> > Monowheel #097
> >
>
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