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
>
|