OnStar antenna as external GPS antenna? - Page 2

W1N · 04-30-2006, 02:37 AM

Quote: 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, 03:01 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, 07:55 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, 07:58 AM

Quote: 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, 09:34 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.

JasonMK · 07-08-2007, 11:46 PM

Quote: Originally Posted by W1N

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

I know this isn't the newest thread, but sounds like you tapped into the actual antenna (not the OnStar box/receiver). Do you have any pictures or data on what connectors, adapters, or mods were required? I've read dozens of posts from people asking or being told it can't be done, I'd love to know how it has been and can be done. BTW, what year is your car (i.e. how old is your OnStar?)?

drawson · 07-09-2007, 02:19 PM

Actually I did both

1. Used the antenna to work with my handheld GPS
2. Hooked up serial port to Module to use with car PC.

Check this site as it still has the info or most of it. Took some work and good soldering skills but it worked. I used and IC to go from the 5v signals in the Onstar box to true RS-232 levels for the PC. The onstar boxes were very easy to access in the trunkof my car. Depends on your vehicle and year, I had a 2001 Grand Prix GTP.

I have since sold the car-too many leaks and miles.

http://www.hackaday.com/2005/03/29/gm-onstar-hacking/

JasonMK · 07-09-2007, 06:23 PM

Quote: Originally Posted by drawson

Actually I did both

1. Used the antenna to work with my handheld GPS

Seems like everyone likes to direct people to that link or direcly back to the original author's website, but I'd love to see someone post info on using the actual antenna itself. I know you sold your car already, but do you remember what type of connector it was or any issues one might run into?

drawson · 07-09-2007, 09:08 PM

Maybe you misunderstood - the GPS antenna will not get you any data unles you connect it to a receiver. My handheld had an external jack. The internal Motorola module jack matched the one on my receiver. There is a short pigtail that goes from the car antenna to the mudule. I don't remember the connector type but there aren't that many. This was only a test type of thing I never intended to use it. I have another antenna

I used the receiver module in the VIU to to get the NEMA text string for my computer. This data will feed almost any software. This needed a converson to RS232 levels. This was the adapter I used.

Using the antenna was never a real option as a magnetic mount antenna was far easier to connect to my portable. Running a lead from the cable in the trunk where it went into the VIU is real inconvenient. Also building a cable with this type of wire and connectors to run to the dash is not easy either. The other was far more useful.

Regards
Dave

JasonMK · 07-09-2007, 09:31 PM

No, I understood you, using the antenna is all I want to do. My carputer (Infill G4) has the GPS receiver built in. That center input on the lower right is an MCX (female) jack for the GPS antenna.

The nice thing with the double-din style of the G4 is the clean factory looking install. To keep the rest of the car like that I wanted to use the already existing antenna and not need to run another one outside (like I did in my last car). I realize that almost everyone else lookng at the OnStar sees a way to utilize its existing GPS receiver, I figured my question would be FAR simplier, but I guessed wrong.

drawson · 07-10-2007, 08:27 AM

Gotcha, sorry as there usually seems to be confusion on GPS.

Depending on where your OnStar is located you will need an extension cable.

It has been a while but getting the connector off of the Onstar VIU was not a problem- just don't force it as the cable is not happy if you bend it. the center conductor on mine was about the size of a hair. The outer jacket is more of a tube and the conductor floats in it. I don't remember the fitting on the box because as I said before, there is a short pigtail that went to the module inside. I used the module end as it was the same as my hand held and I had everything apart any way.

You could look for a GPS antenna (I found one for 35$ that had a 20ft cable) That would get you cable and one end already to go then you would only have to add a connector on the other end. Reduces the points to inject errors. Seems a waste to chop it up but saves time and fustration.

Wish you luck, keep us posted

dave

Check this site - they have extension cable connectors and such

http://www.pc-mobile.net/gpsant.htm

JasonMK · 08-14-2008, 07:49 PM

After a smooth trouble free year after my first ever carputer install I had to crack the dash open again for something relatively unrelated and decided that while I was in there I would go ahead and look into finally finishing this project. And since my free year of OnStar was up, I no longer needed to leave all the hardware intact for them. Which means I am free to utilize my factor onstar hardware. After hours of scouring the web trying to answer:

What type of connector does my G4 GPS antenna use
What type of connector does my onstar GPS antenna use to connect to the VIU
What gender are the two connectors
What is the correct power needs of the G4 GPS antenna and OnStar antenna
What type of cable would I need
Where in the world can I find one without spending $50

I finally came to the conclusion they both are MCX 3v (3-5v for the G4, according to the magnetic side of the antenna)
So all I needed was a short male MCX to male MCX, found these and ordered one today.

I ordered the first one for $12+shipping from cableorganizer.com out of FL and I'll give it a shot when it comes in. For such a small order, their customer service was off the hook walking me through my best option and finding me the shortest (READ:cheapest) cable for my install. I hope it works, time will tell.