GPS Through Metal?

**Maeveth** · 03-14-2004, 01:02 AM

Hey all, I'm looking to get a NMEA compliant GPS reciver. However I'm not sure which to get. It would be nice if it was accurate and would work efficiently though my metal roof. Any suggestions?

**cproaudio** · 03-14-2004, 01:18 AM

wont work. It'll take forever to lock. Hell, most GPS receivers wont lock even under tinted windows.

**NUIpIsqo** · 03-14-2004, 02:31 AM

Originally Posted by cproaudio

wont work. It'll take forever to lock. Hell, most GPS receivers wont lock even under tinted windows.

ha, i swear, we all met today, but it takes a board to answer this question. it just shows that there just isn't enough time to exchange every idea on our minds.

**Falken** · 03-14-2004, 03:14 AM

Originally Posted by Maeveth

Hey all, I'm looking to get a NMEA compliant GPS reciver. However I'm not sure which to get. It would be nice if it was accurate and would work efficiently though my metal roof. Any suggestions?

Hi, I sell a vehicle tracker which, as an option, comes with a high gain GPS. The manufacturers say this is for covert installations of the unit and GPS and works through metal skins but only updates every 15 seconds. I was rather surprised to see it's a Fortuna U2. No idea why it should be any more sensitive but that's what the tracker manufacturers say.

Doug

**ProCos** · 03-14-2004, 06:09 AM

Originally Posted by Falken

Hi, I sell a vehicle tracker which, as an option, comes with a high gain GPS. The manufacturers say this is for covert installations of the unit and GPS and works through metal skins but only updates every 15 seconds. I was rather surprised to see it's a Fortuna U2. No idea why it should be any more sensitive but that's what the tracker manufacturers say.

Doug

Your supplier could sell sand in the saharah dessert if he is able to convince buyers that his high gain antenna works through the metal skin.....

Come on wake up, the GPS signal link margin is very low (signal is only -130dBm) and therefore very sensitive to any attenuation. What he might mean is that his high gain antenna will help the gps receiver to receive multipathes/reflection and this way operate without clear skyview. This does not mean that you can put it in a place where it is totally surrounded by metal.

High gain antenna are normally used for application where in-door operation is wanted, but high gain antenna's are also more directive and therefore not necessary better for GPS since you need minimum 4 satellites for 3D or 3 satellites for 2D fix.

GPS modules that claims that their module works in-door normally means that you need the first fix outdoor or close to a window, and then you would be able to move "longer" away from a clear skyview. The reason that the GPS receiver needs to be outdoor or close to the windows initially is following: A gps good receiver normally needs C/No of 36-38 dBc/Hz for acqusition (initially) and only needs a C/No of 26-28 dBc/Hz for tracking.

BUT there is a price to pay, navigation on multipathes/reflections results in higher DOP (Dilution of precision) and thereby a worse position accuracy.

/ProCos.

**Maeveth** · 03-14-2004, 11:12 AM

Originally Posted by NUIpIsqo

ha, i swear, we all met today, but it takes a board to answer this question. it just shows that there just isn't enough time to exchange every idea on our minds.

Actually I think that meeting gave us without setups more to think about and more questions to ask. Before yesterday I would have never considered that GPS doesnt work through metal. 8 )

**sxpert** · 03-16-2004, 05:59 AM

there's no way this will work. you need to have the antenna mounted *outside* the vehicle. period... (sorry about that

)
of course, you can use a separate antenna and calculator, with the antenna outside, and the calculator inside. but the antenna MUST be inside^W (oops) outside.

**unsavory** · 03-16-2004, 08:44 PM

Originally Posted by sxpert

there's no way this will work. you need to have the antenna mounted *outside* the vehicle. period...

That is not correct. Mine is inside and it works perfectly fine. It is, however, underneath the front windshield.

**ukchris** · 03-16-2004, 09:15 PM

Originally Posted by sxpert

you need to have the antenna mounted *outside* the vehicle. period

Originally Posted by sxpert

but the antenna MUST be inside.

Covers all the bases..!

Mine is inside too, on the dash, works great.

**ecksray** · 03-16-2004, 11:20 PM

The satelites are 15,000 miles above the earth and the signal is very weak by the time it gets to your receiver. I don't care what kind of high gain antenna you use- you will still need a view of the sky and it is NOT going to work through metal. That's why lojack and now Boomerang Tracking are so successful- they don't use GPS for tracking the stolen vehicles. Cellular and digital signals have much better in-building penetration. Are you saying that your GPS will still work once they roll your Porsche into a shipping container? Nah- I didn't think so.