Mounting GPS antennas under panel cover

On Sunday, July 22, 2012 7:32:39 PM UTC-7, Eric Greenwell wrote:
On 7/22/2012 7:13 PM, Darryl Ramm wrote:
> On Sunday, July 22, 2012 5:11:14 PM UTC-7, kirk.stant wrote:
>> I'm thinking of mounting a couple of "mouse" GPS
>> antennas on the inside of my fiberglass LS6 panel cover using
>> Dual-Lock on the TOP of the GPS antenna. Reason is to have more
>> real estate to place the antennas, and still provide a
>> "break-away" function if I have to jettison the canopy
>> (and cover, which goes with it). Any opinions about any effect the
>> plastic Dual-Lock would have on GPS reception?
>>
>> My gut feeling is "no effect", but I claim no deep
>> knowledge of the electromagnetic spectrum (other than how to run a
>> no-lock intercept using an APQ-120...).
>>
>> Comments?
>>
>> Kirk 66
>
> My concern is not RF absorbing (which will be minimal), but more the
> robustness of any adhesive tape on a too-hot-to touch black
> glareshield sitting on the ground on a 100F+ summer day. While 3M
> Dual-Lock is strong, and the adhesive on those strips typically much
> better/more stable at high temps, than any of the Velcro brand
> products I'd still be concerned about the adhesive
> "creeping"/"walking" or letting go on a really hot day. (but that is
> easy to test to see if its a problem)
>
> My facorite under-panel mounts are actually made of thin, one layer
> fiberglass moulded around a foam replica of the antenna that are
> potted under the glareshield and then the foam core is removed. Where
> you pry open a springy entry flap and push in the GPS "puck". I've
> got one made like this under my ASH-26E panel for the XM weather
> receiver puck for my Gamin 496, so not exactly a GPS antenna but it
> works great in this mount (in this case there is no break-away, as
> the 496 goes away with the canopy, but the DC power to the 496 has a
> break-away connector. You could look at GPS options that break away
> at a connector.
>
> Email me if you want and I'll try to find photos of the fiberglass
> mount for my XM antenna that Williams Soaring made.

I haven't seen Rex's solution, but maybe you can make a mount that
attaches to the instrument pod, holding the antenna up close to the
glare shield? That avoids the need for Dual-Lock or messing with
fiberglass. I used some 1/16" x1" x3" Lexan plastic to mount the
antenna, then bolted the end of the lexan to a convenient brace. The
flexible Lexan holds the antenna up to the inside of the glare shield.

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to
email me)
- "Transponders in Sailplanes - Feb/2010" also ADS-B, PCAS, Flarm
http://tinyurl.com/yb3xywl
- "A Guide to Self-launching Sailplane Operation Mar/2004" Much of what
you need to know tinyurl.com/yfs7tnz

I like that idea even more, easy to wire/check with the glareshield removed.

Darryl

I assume that if you have a DG with the very dull grey pod that the pod is carbon and that this won't work?

Brian

A couple of comments and medium-baked ideas;

1) The adhesive on 3M's Dual Lock is especially good, unlike most
velcro you find in stores. Dual Lock *should* stay stuck even in a
hot environment. You might troll the 3M site for temperature specs
(they mention aerospace).
2) I bolted my GPS antenna under the glare screen (which is not
mounted to the canopy). To allow for break away in your situation you
could use nylon bolts instead of metal bolts. To really make sure
they break away, you could remove some concentric material (cut a
groove) around the bolt near the head. Removing concentric material
is what is done for break away mounting of, for example, runway
lights.
3) Double stick tape? That should break away. But might have the
same temperature issues. Again, stick with 3M branded.

Good luck, John

Again, stick with 3M branded.

Good luck, John

3M VHB tape has published specifications, and most of them are rated at 90 lbs/sq. inch tensile, so even at elevated temps. you would probably be OK if you maxed out the area. The fail temperatures are in the 200F to 250F range. Assuming Dual-Lock uses a similar adhesive seems like you would be fine.

Brian