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

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

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.

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

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

but the antenna MUST be inside.

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.

Great explanation!

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.

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

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.

Thanks for the science lesson, I promise to try and remember it! I agree with everything you say. In fact if you look at the thread about GPS working in the Dartford tunnel you'll see you're saying exactly the same as I was. I've checked out the Fortuna website to see it the U2 is somehow more sensitive. If it is, they don't make a fuss about it. Having said all of that I've seen the results of their demo unit and it does report the position of the vehicle every 15 seconds. Maybe the DOP is diluted but the U2 uses the average of the readings?

intriguing isn't it?