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Old 08-06-2004, 02:37 PM   #1
MiGSel OP
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External GPS antenna mount under GS beak

Under heavy tree cover and along rock walls I often get the "lost satellite reception" message with my Garmin SP2610.

I wanted to know whether it makes sense to mount an external GPS antenna and whether it's bad to mount in under the GS beak instead of on top of something. As I didn't find a clear and straight answer anywhere, I did my own testing tonight.

* [INT] internal antenna patch only
* [ON] external antenna on top of the beak
* [UNDER] ext. ant. under the beak
* [TOP] ext. ant. on top box

Put camera on tripod with interval setting: one pic every minute.

Here are the results:



1) The external antenna clearly gives me more satellites and stronger signals.

2) On or under the beak doesn't seem to make much of a difference.

3) On the top box seems weaker than under the beak.


So in the garage I went and made me a bracket to fix the antenna under the beak. Looks like this:





I'm happy with the result. :)

I'll report back with satellite experience in the Black Forest, by the end of September.

Cheers,
Michel
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Old 08-06-2004, 03:09 PM   #2
NJ_Bob
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Antenna?

Michel, which external antenna are you using?
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Old 08-06-2004, 11:11 PM   #3
zoolndr
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Muy Sano...

I, too, would be curious which antenna you're using. Looks like the GA26C REMOTE ANTENNA WITH BNC ? You installed without the suction or magnetic mounting options, one assumes?

Elegant use of zip ties, and congratulations on admirable application of scientific method to this vital question, though your report did lack reference to the requisite consumption of cold fermented sustenance as the required ritual celebration of triumphant engineering-tude. But much can be forgiven in light of your understandable excitement at achieving such significant results.

I'm curious if you tooled around the neighborhood at all while you were taking readings whether the signal strength of top-box vs under-beak would still have shown such a stark difference in reception.

Were you mounting the GPS antenna unit on top of the top box, or underneath the topbox lid? Is that an OEM top box?

[The endlessly deep black plastic might prove to have passive radio-jamming/shielding properties. Who knew? Perhaps all stock BMW luggage is manufactured from cast-off material from Northrop B-2 skin moldings? Might begin to explain how pricey those sidebags are...]

Now of course you have-- innocently enough--taken the first step towards becoming the source for a new market demand in beak-brackets...vendor forum awaits.

Z.
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Old 08-07-2004, 12:33 AM   #4
MiGSel OP
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This is the antenna:

10052-05 GA 27C low profile remote automobile antenna



It wasn't mounted inside the topbox, just put on top of my Touratech Zega XL box. I wonder whether the funny result could be because of the flat aluminium surface under the antenna?

Cheers,
Michel
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Old 08-07-2004, 06:19 AM   #5
Trevor S
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Quote:
Originally Posted by MiGSel
Under heavy tree cover and along rock walls I often get the "lost satellite reception" message with my Garmin SP2610.
As you would expect

Quote:
Originally Posted by MiGSel
2) On or under the beak doesn't seem to make much of a difference.
This bit has me confused, how the hell does it even work under the beak, there is no L.o.S ??? I put my GPS under the beak as a trial and got NO sat signals at all, as I would expect..... WTF ??????????

Quote:
Originally Posted by MiGSel
3) On the top box seems weaker than under the beak.
That's odd but not knowing the exact metodology, did you do an "up and back" to take into account Sat location ? ie depending on where the Sats where in the sky, your body could have been bloking that bit of the sky where most Sats where when the ant. was on the top box behind you...

I have always thought about just behind the windscreen, on top of the plastic bit in front of the instrument cluster, or another thought was a BT GPS there, talking to the PDA on my bars but then I have never really had a problem with just "on the bars"

PS Try the ext. ant. on top of your helmet
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Old 08-07-2004, 06:35 AM   #6
MiGSel OP
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Quote:
Originally Posted by Trevor S
As you would expect
Yes but with the 2610 it is worse than with my previous SPIII. So I hope it will be better with the external antenna added...


Quote:
Originally Posted by Trevor S
This bit has me confused, how the hell does it even work under the beak, there is no L.o.S ??? I put my GPS under the beak as a trial and got NO sat signals at all, as I would expect..... WTF ??????????
None at all? Did you "put" it there or "hold" it there. Maybe your hand was covering the antenna patch?

Quote:
Originally Posted by Trevor S
Did you do an "up and back"?
Yup, sat in a comfy chair next to the bike, so certainly lower than the top box, while the camera was doing its job.

Maybe the moving clouds in the sky and the changing satellite position had something to do with it too, but it certainly didn't get better than under the beak. So that's where it's gonna stay for now.

Cheers,
Michel
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Old 08-08-2004, 12:49 AM   #7
Trevor S
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Quote:
Originally Posted by MiGSel
None at all? Did you "put" it there or "hold" it there. Maybe your hand was covering the antenna patch?
None at all and my hand was cradling the GPS, not over the antenae itself but I didn't expect there to be any signal, which is why I am totally suprised that you got any signal, put your hand over your aerial, that's esentially what your "beak" is doing.
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Old 08-08-2004, 03:12 AM   #8
iswoolley
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I field tested an external aerial for my Garmin GPS V during a recent month-long trip on my Africa Twin. I mounted the aerial on the rear fender of my bike, under the plastic top box, and it worked fine. Good reception everywhere I would expect it, with only tunnels and really dense trees reducing the signal strength. Even when I had a large metal cable lock stored in the top box performance wasn't affected. My main concern was that the cable passed the engine with all those lovely spark plugs emitting EM interference, but I guess the cable is well enough shielded to not be affected.

Iain
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Old 08-08-2004, 07:29 AM   #9
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Laugh On top....

I did similar experiments without the camera and the antenna now sits on top of my beak. I honestly did not try under....hmmm. I think I might move it just to prove to myself that it works under there. Wow...mabe I can buy more of sigels custom aluminum work!
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Old 08-09-2004, 10:18 AM   #10
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What degrades GPS signals

I was told recently that there are two things that can "Block" or degrade a GPS signal from reaching a receiver. Meat and Metal. Plastic, as long as it is reasonably thin, is not a big factor.
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Old 08-09-2004, 10:59 AM   #11
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Quote:
Originally Posted by witzgall
I was told recently that there are two things that can "Block" or degrade a GPS signal from reaching a receiver. Meat and Metal. Plastic, as long as it is reasonably thin, is not a big factor.
Anything conductive at microwave frequencies (meat and metal!) will block the signals. Even fresh water absorbs microwave energy and turns it into heat. That's how microwave ovens work.

Nonconductors (aka dielectrics) can still cause GPS signal loss by detuning the antenna. But it takes a lot. The GS beak is pretty thin, much thinner than for example a non-metallized car windshield which causes no GPS problems.
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Old 08-09-2004, 04:43 PM   #12
CroMag
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MiGSel, great job testing! Tony's right, plastic won't couple with the antenna like a conductor (aluminum) or water bearing meat. Hmmmm, there's a joke in there somewhere......

Did the signal strength drop after the metal bracket was installed around the antenna?

Dumb Question Department: when you guys did your testing, is only the external antenna pulling a signal or is the attached antenna working in parallel?
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Old 08-09-2004, 05:18 PM   #13
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Old 08-09-2004, 05:32 PM   #14
Sam Buca
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Great testing Migsel.

I use the same external antenna for my 276C. I just stick it on the top of the
tank with magnet and it stays. I completed a 2,500 mile trip to Ouray and back with no problems.

The only benefit I see of having it below the beak is to keep the bike clean from attachments. I once saw an external antenna mounted on top of the beak and it looked quite cool.

Why mount it below the beak?
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Old 08-09-2004, 11:41 PM   #15
MiGSel OP
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Quote:
Originally Posted by CroMag
Dumb Question Department: when you guys did your testing, is only the external antenna pulling a signal or is the attached antenna working in parallel?
I asked the same question before - not so dumb I thought - but never got a straight answer. Should try it myself by shielding the unit when the external antenna is on. If the signal doesn't weaken then...




Quote:
Originally Posted by Sam Buca
Why mount it below the beak?
Why not if it works just as well. There's enough visible junk mounted on my GS already
It looks cleaner, cable & antenna are more protected, nobody's gonna wanna steal it, no silly questions asked when I park the bike somewhere, ...
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