I am looking at finally integrating GPS into my car. Although it already has a GPS receiver for the unused OnStar system, I will have to install another. OnStar is only installed in American Saabs, so documentation is nowhere to be found.

I have been looking at this garmin unit. I will likely mount it in the glove compartment and have an antenna running from there to either the windshield or under the hood. Any comments? That thing looks like it's going to cost $100.

I will need an antenna. I have an 8db WiFi (2.4GHz) antenna doing nothing. Will I be able to use it as a GPS antenna? If it can be used, will I be able to get a signal under my car's hood? I think it should, but I am not positive.

Also, what are the characterisics of the empeg's serial port power? Will I be able to power the reciver off the serial port? Here's the voltages it can use:

60 mA @ 8 Vdc peak current
50 mA @ 8 Vdc nominal current
40 mA @ 12 Vdc peak current
33 mA @ 12 Vdc nominal current
15 mA @ 40 Vdc peak current
12 mA @ 40 Vdc nominal current
100 mA from 3.3 to 5 Vdc peak current
85 mA from 3.3 to 5 Vdc nominal current

Thanks!

As long as you don't need all these voltages, and it can operate on 12V only then you will have no trouble drawing that small amount of amperage from pin 5 of the serial port. One thing about this though, expect to make your own serial cable that just has pins 2,3 and 5 available. The easiest way to do it is to buy one and cut it and use a multimeter to do a continuity test until you find which colored wires go to which pins. But try it before you strip a perfectly good serial cable of course.
I have no idea about the anteanna, I'm not radio expert, but I expect the answer is no if your GPS unit needs an active antenna that can handle a specific voltage. For instance, I needed a 5V active antenna for my Oncore unit to work well.

Also, what are the characterisics of the empeg's serial port power?

If you're talking about the serial port on the docking sled, I seem to recall that one of the serial port pins is spliced directly into the Amp Remote wire. So whatever the specs are for the amp remote wire is the same spec as that pin of the serial port.

If you're talking about the serial port on the docking sled

Yes, that's what I meant. So, one of the pins is 12V then?

Edit: Siberia's post above yours indicates pin 5 is the one with voltage.

GPS signals are transmitted at 1575 MHz, right-hand circular polarized. I doubt you would get any useful signal from a Wi-Fi antenna. Most GPS receivers support/require active antennas to put the preamp as close to the element as possible. Typicallly 5 vdc at 20-50 ma from the external antenna connector is available for the antenna/preamp combination.

If under your hood means your convertable top then yes you will get a useable signal. Metal roofs and engine hoods will block GPS completely. Sometimes the parcel shelf will work but your coverage will be diminished, particularly in obstructed areas.

Often you can mix receivers and antennas from different manufacturers. Active GPS antennas are ofen available on Ebay.

Lynn

So, one of the pins is 12V then?

12v when the display is on, yes.

Note that you can't just plug it straight into the GPS, you'll have to do some custom wiring because there are other lines which you *don't* want to use on that same cable, and the GPS won't be expecting power on that pin.

Metal roofs and engine hoods will block GPS completely.

That's what I meant by hood. Damn.

I will look around for a good antenna. What I assume is the GPS antenna/receiver for OnStar is pretty cool. It is a 1"x1" device attached to the upper part of the windshield. Does anyone know where I can get one of those? I have seen class-mounted patch-style GPS antennas, but they are usually 2.5" diameter which may look a bit ugly.

I took that into acount already, but this receiver forces me to make a custom cable anyway (no DB9 is even available for it yet).

If under your hood means your convertable top then yes you will get a useable signal. Metal roofs and engine hoods will block GPS completely.

My GPS unit's antenna is actually inside my dashboard, underneath the plastic covering, just above the heater vents, as shown by the red circle here:



It works perfectly, the plastic doesn't block the signal much, and neither does the windshield. If I'm not inside a garage, I can get at least 5 satellites locked almost all of the time.

Well, the other unfortunate part is that my windshield has that f**king metal coating. There are sections of it that are not coated for the sake of electronic toll tags.

Where my Garmin GPS V is currently mounted must be in a bad spot because I have lost signal on open highways a few times and the signal meter for any particular satellite never goes over half full. So, in the dash may not work so good either. That is why I said hood or windshield (near my EZPass).

You can buy extension cables and external antennas...

I cannot bring myself to put an external antenna (of any kind) on The Viggen.

Metal roofs and engine hoods will block GPS completely.

Mine (Garmin GPS16) is actually in my glovebox so any signal has to make it through a layer of dashboard, various metal brackets, various electrical wiring and an airbag. I do drive a Jeep so it does not have to go through a metal roof. It does take it a little longer to acquire sattelites (up to a couple of minutes) than if I set it on top of the dash, but it can generally aquire at least six sats with good signal strength.

Anyway, where you can place the antennae is going to depend on a variety of variables and may require some trial and error, but with a decent GPS I would be suprised if you could not get a usable signal from someplace within the vehicle.

-Mike

Have a look by your A-pillar. If the trim is easily removable then you might find that there is enough space to mount an antenna 'underneath' it so that it isn't blocked by the dash material itself. It worked on my Golf.

IIRC,
Pin 5 is ground.
Pin 4 is Amp Remote (+12V, can handle 1A, I believe)