OnStar antenna as external GPS antenna?

**nkotch** · 04-29-2006, 10:21 AM

Originally Posted by ElKeeed

Wrong! The gps is designed to talk to the satellite, the antenna is chosen for the characteristics of the specific gps. Different antennas can be very different. Have you not wondered why you need a huge dish to pick up sky tv from a satellite but only a little antenna to pick up gps?

Umm... you kinda missed his point. He was saying that since it's a GPS antenna it should work with other GPS receivers in general, as long as he can get the right physical connector on it. From the very little I've read it seems like it could be easier to just put a different connector or use an adapter to hook it into another gps receiver you already have than to wire up a serial connection to it.

**W1N** · 04-29-2006, 01:34 PM

Originally Posted by nkotch

Umm... you kinda missed his point. He was saying that since it's a GPS antenna it should work with other GPS receivers in general, as long as he can get the right physical connector on it. From the very little I've read it seems like it could be easier to just put a different connector or use an adapter to hook it into another gps receiver you already have than to wire up a serial connection to it.

MONEY!!!

**joego** · 04-29-2006, 01:53 PM

Onstar isn't GPS though; you have voice communication with the people at OnStar. I suppose the antenna on the thing could be a compound antenna with GPS and OnStar recievers built in, but good luck in you project and for god sakes tell us what you did to make it work.

**W1N** · 04-29-2006, 02:57 PM

Originally Posted by joego

Onstar isn't GPS though; you have voice communication with the people at OnStar. I suppose the antenna on the thing could be a compound antenna with GPS and OnStar recievers built in, but good luck in you project and for god sakes tell us what you did to make it work.

I know few that has done this in the past. I guess you have to know which wire is for voice and which is for the GPS signal. As what I have heard this project shouldn't be too tough. But I let you guys know when I'm done with it.

Thanks!

**Jahntassa** · 04-30-2006, 12:19 AM

Originally Posted by joego

Onstar isn't GPS though; you have voice communication with the people at OnStar. I suppose the antenna on the thing could be a compound antenna with GPS and OnStar recievers built in, but good luck in you project and for god sakes tell us what you did to make it work.

Actually, from what I remember, Onstar is simply a GPS reciever and a Cellphone jammed together. In the newer, digital versions, there's also a databand in the cellphone that allows two-way data between the car and the Onstar service.

'Onstar' isn't exactly some mythological third service that exists out there. It's GPS and cellular.

As for the antenna: Generally GPS antennas are GPS antennas. There's no seperate GPS signals that prevents one GPS antenna from working with one reciever and not another. It's not like trying to use an FM antenna with an AM radio.

You should be able to find the Onstar brain and unplug the GPS antenna from that, adapt it and extend it to your headunit. Finding an extension might be a bit of a pain though, I don't know how common those are.

**W1N** · 04-30-2006, 03:37 AM

Originally Posted by Jahntassa

Actually, from what I remember, Onstar is simply a GPS reciever and a Cellphone jammed together. In the newer, digital versions, there's also a databand in the cellphone that allows two-way data between the car and the Onstar service.

'Onstar' isn't exactly some mythological third service that exists out there. It's GPS and cellular.

As for the antenna: Generally GPS antennas are GPS antennas. There's no seperate GPS signals that prevents one GPS antenna from working with one reciever and not another. It's not like trying to use an FM antenna with an AM radio.

You should be able to find the Onstar brain and unplug the GPS antenna from that, adapt it and extend it to your headunit. Finding an extension might be a bit of a pain though, I don't know how common those are.

Here is the comment from a guy that has done this:

"Well, what I did was to create an "adapter cable" that I connected between the factory Onstar GPS antenna plug and the navigation unit. I bought an extra factory in-dash GPS antenna, cut off the cable, and added a connector to the cut end of the cable that could mate to the factory Onstar GPS antenna cable. I believe it is a MCX connector, and I bought mine from Mouser (www.mouser.com)."

Thanks!

**Wiredwrx** · 04-30-2006, 04:01 AM

A couple of things need to be cleared up here, cause words are being thrown around here with out much regard for what they mean.

First, an antenna is not a receiver, and a receiver is not an antenna. A receiver is what actually "tunes" a frequency, rejects the rest of the frequencies, and then usually converts it to some form that is needed, be it audio, video, or data. Receivers are very specific for the frequency used.

An antenna is usually a passice device that enables the receiver to "catch" the signal. In general, and antenna will work to RECIEVE any signal. However, antennas can be optimized for the particular frequency it is trying to catch. Usually the antenna needs to be a wavelength long. For some frequencies, that can be 100 feet or more, for others, it can be just several inches. Most antennas these days though are on the order of 1/4 of a wavelength. The more "tuned" the antenna is for the frequency, the better it will receiver. Transmitting is a different story, but since no one here is really transmitting, we won't get into it.

There are active antennas. These need voltage on the antenna in order to allow it to work. Active antennas are used only for receiving.

Now, if the onstar unit has a passive antenna, and your GPS unit (the GPS unit is actually a receiver) has a connector for a passive antenna, you could either solder on the correct connector to the onstar antenna cable, and it will work fine. THis is so because the GPS unit is the receiver. However, if your Navi device requires a GPS receiver, like our computers requires a USB GPS receiver, which receives and translates the signal for our computers' Navi program, and all the onstar unit is is a passive antenna, it won't work. Likewise, if the onstar GPS antenna is like what our computers use, which means a GPS receiver (not passive antenna) and you are using it with a GPS unit that only needs an antenna, then it won't work.

Now, you seem to have found someone who said it will work. Well, it might, but that depends on all the things I mentioned. His system mnight be different then yours, Forget that the onstar unit has been changed several times over it's lifetime, no one here knows what Navi unit you are using. ARe you using a carputer, or an AVIC or some other device??

Sooo, you can be the guinea pig if you want, I probably would, but I would get more information before I took the plunge.

Michael

**drawson** · 11-09-2006, 08:55 AM

OnStar has 2 antennas. The one on the glass is for cell phone. There is another, usually under the rear deck for the GPS. The cell phone antenna cannot be used for the GPS. GPS requires a circular polarized amplified antenna. I have hacked my OnStar GPS and can get the serial data stream to a PC. Works with most mapping software. Look at the side of the OnStar box. In my Grand Prix there are 2 boxes. One small with rounded edges, This is the cell unit. The other big square one has an odd wire - looks like a piece of black tubing. This for the GPS antenna. There are instructions on how to get into it on the web. Motorola has software for the module, you must switch it from Binary mode to Text mode to work with a PC. Also you need to add an IC to change levels to RS232 for the PC. Works cool with my Car PC. OnStar indicator will go red as it needs Binary mode and gets upset at tex mode.

**W1N** · 11-09-2006, 08:58 AM

Originally Posted by drawson

OnStar has 2 antennas. The one on the glass is for cell phone. There is another, usually under the rear deck for the GPS. The cell phone antenna cannot be used for the GPS. GPS requires a circular polarized amplified antenna. I have hacked my OnStar GPS and can get the serial data stream to a PC. Works with most mapping software. Look at the side of the OnStar box. In my Grand Prix there are 2 boxes. One small with rounded edges, This is the cell unit. The other big square one has an odd wire - looks like a piece of black tubing. This for the GPS antenna. There are instructions on how to get into it on the web. Motorola has software for the module, you must switch it from Binary mode to Text mode to work with a PC. Also you need to add an IC to change levels to RS232 for the PC. Works cool with my Car PC. OnStar indicator will go red as it needs Binary mode and gets upset at tex mode.

I did it and it works like an angel. My aftermarket GPS uses the OnStar GPS antenna and it is just perfect!!!

**drawson** · 11-09-2006, 10:34 AM

Glad it work for you too. I had a discussion about this witha guy who was parting out a car. He wanted to sell the cell antenna and kept insisting there was no other antenna. So he wanted to sell the $20 antenna and threw out the $50 antenna. I have several of the Motorola modules running with antennas like the one in my car and have used that one. My Magellan handheld GPS will also use the OnStar one as ans external.

OnStar is fun to play with. More fun to hack than use the way it was intended.