Onstar antenna question

[02Lackey]

I want to install satellite radio in my 2002 STS but I want to use the Onstar antenna as the antenna for the radio. Can this be done? I want to use that antenna because I want my car to look clean and not have that huge black circle on my roof with a wire running into my weather stripping. I've seen the thread on how to install the sirius SR-GM1 interface module, I just want to use the Onstar antenna to receive the signal. Any ideas or thoughts? Thanks.

[submariner409]

The OnStar antenna(e) are tuned for specific frequencies, just as a standard FM antenna is cut (tuned) for the FM band whether it is a stand-alone wand or embedded in the windshield.

So....you need to know if there are any differences in radio frequencies between the OnStar signal and the XM, which would require a different tuning (that base loading coil) for the radio. The existing antenna uses a BNC slip-connector, so that makes cable runs and splicing simple. I have no technical info on the phone or radio frequencies or the necessary antenna gain factors, so that will take some Google.

[JimD]

Originally Posted by 02Lackey

I want to install satellite radio in my 2002 STS but I want to use the Onstar antenna as the antenna for the radio. Can this be done? I want to use that antenna because I want my car to look clean and not have that huge black circle on my roof with a wire running into my weather stripping.

I cannot remember if 2002 Onstar could be upgraded to digital so I have to ask if your Onstar system is "active".

If your Onstar is active, you do not want to use the Onstar antenna. Period.

If your Onstar is not active, I would ask why the antenna is still mounted on the rear glass. You would not be impressed with Sirius performance using a vertically oriented antenna. It would work and you would be fabricating a coaxial cable patch cord, but vertical antennas are famous for receiving equally poor in all directions.

Maybe a package tray mount Sirius antenna would be a better performance option with no ugly black circle on the roof. Even that choice is a compromise.

There is a very good reason for roof mounting antennas that are looking for signals from high above the equator.

[Necrosan]

Might as well try it.
I dont see why it wouldnt work.

[submariner409]

2002 OnStar is available for digital upgrade. Did it when the total cost was $15 + a 1-year subscription. Works great.......I keep 100 minutes in the hands-free phone 'cause it comes in handy once in a while.

For patch antennas and amplifiers take a look and see if www.gilsson.com has anything.

[02Lackey]

I appreciate all the information and advice so far. My Onstar is not active and is analog only so it's just there. I did do a little research and found out the Onstar analog frequency is in the 800MHz range and satellite radio is in the 2.3 GHz range. How about this radical idea...how do you remove that antenna from the window? If I could remove it would I be able to put a sirius antenna in its place? Thanks for the replies and I hope to find out more info.

Matt

[submariner409]

The antenna base and internal connector will come off with careful work with a razor blade and a hair dryer set to warm.

800mHz and 2.3 gHz are so far apart in the frequency spectrum that the old antenna would be useless for the application. Not sure if you could salvage the existing BNC cable which runs down into the trunk/electronics bay behind the rear seat.

[JimD]

Originally Posted by submariner409

....800mHz and 2.3 gHz are so far apart in the frequency spectrum that the old antenna would be useless for the application.

Allow me to comment one final time on the subject of (receive only) antennas. It is not my intent to steer this thread into subjects that are more appropriate to forums other than automobiles.

In reality, the difference between 800 MHz and 2.3 GHz is very close to a harmonic 3 to 1 relationship. And utilizing an antenna that is physically/electronically too long (800 Mhz) to receive a signal at a higher frequency-shorter wavelength (2.3 GHz) has been an acceptable compromise reality forever.

Sirius is a receive only consideration.

The rules change when the antenna must also used to transmit.

[02Lackey]

PROBLEM SOLVED!!! Ok, after doing a little research I found out that there is a glass mount XM/Sirius satellite antenna available for purchase. The Terk SR1 Glass Mount Antenna is the solution to my problem. I'm sure I will have to remove the onstar antenna hardware and replace it with this kit but in the big picture, I am getting what I wanted. So, if you want satellite radio installed on your car without having an antenna on the roof with a wire going through the weather stripping then I recommend this product. I have just ordered it and will update how the install went. Thanks to all that posted to this thread.

Matt