[Rnovrit]

Update:
I found some info on a Chevy volt owner doing the same thing and has tested it out. All you need is the connector adapter and the 50-ohm termination load. Install on the purple antenna connector. It stops the outgoing signal to Onstar but leaves your gps functioning just like Maverick described. I placed the order on amazon ($12 total) and will give it a shot once I pull the car out of it's hibernating spot.



here is the link to the two parts:
https://www.amazon.com/dp/B07PFLZ4HF...p_imgToDp&th=1
https://www.amazon.com/dp/B00BXUYDMM...hk_typ_imgToDp

[CalgaryZL1]

Originally Posted by Rnovrit

Update:
I found some info on a Chevy volt owner doing the same thing and has tested it out. All you need is the connector adapter and the 50-ohm termination load. Install on the purple antenna connector. It stops the outgoing signal to Onstar but leaves your gps functioning just like Maverick described. I placed the order on amazon ($12 total) and will give it a shot once I pull the car out of it's hibernating spot.



here is the link to the two parts:
https://www.amazon.com/dp/B07PFLZ4HF...p_imgToDp&th=1
https://www.amazon.com/dp/B00BXUYDMM...hk_typ_imgToDp

Thanks for the parts link. Please report back if it works for you. Here is a link for a “stubby” connecter with no cable.

https://a.co/d/36QeI9L

[ChrisMal]

Looking forward to the report. Would be nice to have the mic back for changing music and such. Although I'm not sure how motivated I'll be to get back in that passenger footwell to put it back in.

[havelegs]

I see this question has been asked but there does not seem to be an answer. Why isn't just pulling the fuse good enough? When my LT1 was stolen, the fuse was removed and OnStar was unable to track the car. Why is it necessary to remove the module?

[arpad_m]

Originally Posted by havelegs

I see this question has been asked but there does not seem to be an answer. Why isn't just pulling the fuse good enough? When my LT1 was stolen, the fuse was removed and OnStar was unable to track the car. Why is it necessary to remove the module?

Because that takes out other functionality, too, so we are hoping there is a way to disable only the transmitter antenna and keep everything but OnStar functional.

[Curr]

Originally Posted by Rnovrit

Update:
I found some info on a Chevy volt owner doing the same thing and has tested it out. All you need is the connector adapter and the 50-ohm termination load. Install on the purple antenna connector. It stops the outgoing signal to Onstar but leaves your gps functioning just like Maverick described. I placed the order on amazon ($12 total) and will give it a shot once I pull the car out of it's hibernating spot.



here is the link to the two parts:
https://www.amazon.com/dp/B07PFLZ4HF...p_imgToDp&th=1
https://www.amazon.com/dp/B00BXUYDMM...hk_typ_imgToDp

Just know that doesn't stop the signal generation / transmission. That's done by the chips on the board. The terminators just effectively shortens the length of the antennae to the end of the terminator. So it's still putting out a signal, at it's normal strength (minus reflections), so if you get near enough to a receiver, it will still communicate, as shown by gatormaro's testing.

To kill the signal you either need to kill power to the chip generating the signal, or shield it enough where the signal strength can't be 'heard' by the receiving tower.

If I get some time in the next day or two I'm going to pull it, if not definitely on Saturday.

[jollymon]

Originally Posted by Curr

Just know that doesn't stop the signal generation / transmission. That's done by the chips on the board. The terminators just effectively shortens the length of the antennae to the end of the terminator. So it's still putting out a signal, at it's normal strength (minus reflections), so if you get near enough to a receiver, it will still communicate, as shown by gatormaro's testing.

To kill the signal you either need to kill power to the chip generating the signal, or shield it enough where the signal strength can't be 'heard' by the receiving tower.

If I get some time in the next day or two I'm going to pull it, if not definitely on Saturday.

If you have a correctly designed/made 50ohm termination (and the cable/adapter to it as well) it WILL NOT radiate. If either the coax cable, connectors, or 50ohm termination are not correctly made, it will radiate a little as mentioned above.

[havelegs]

Originally Posted by arpad_m

Because that takes out other functionality, too, so we are hoping there is a way to disable only the transmitter antenna and keep everything but OnStar functional.

Ok thank you

[Rnovrit]

Originally Posted by jollymon

If you have a correctly designed/made 50ohm termination (and the cable/adapter to it as well) it WILL NOT radiate. If either the coax cable, connectors, or 50ohm termination are not correctly made, it will radiate a little as mentioned above.

True on both accounts Jollymon and Curr. I added a roll of 1" copper tape (think Faraday cage) to my order to add a second layer to help prevent any signal from pushing through. Hope this all works.

[CalgaryZL1]

Originally Posted by jollymon

If you have a correctly designed/made 50ohm termination (and the cable/adapter to it as well) it WILL NOT radiate. If either the coax cable, connectors, or 50ohm termination are not correctly made, it will radiate a little as mentioned above.

This is why I suggest the non-cable adaptor, to reduce antennae possibilities coming off the module. At work we have long range radios in our trucks that do not work very well if the antennae is not the right calibration i.e. length

[arpad_m]

Silly question, because back in the day I barely passed the (brutally difficult) electromagnetic field theory exam at the university, but how do you guys know what the correct antenna length for maximum attenuation is? Did you do any calculations?

One product mentioned above has a longer cable, the other one is a stub, but they both have specific lengths, and wouldn't even an inch or two matter a lot at these frequencies?

[Curr]

Originally Posted by Rnovrit

True on both accounts Jollymon and Curr. I added a roll of 1" copper tape (think Faraday cage) to my order to add a second layer to help prevent any signal from pushing through. Hope this all works.

Stop the presses, copper tape probably not a good solution... read on.

Originally Posted by jollymon

If you have a correctly designed/made 50ohm termination (and the cable/adapter to it as well) it WILL NOT radiate. If either the coax cable, connectors, or 50ohm termination are not correctly made, it will radiate a little as mentioned above.

Ok, so I just spoke to an expert, and if you don't want to believe me, that's cool, but I know what I don't know, but I do know who to ask. This guy is "the guy" in our division (very large company, aerospace and defense sector). Patent holder, innovator in inertial guidance and telemetrics, and currently working on a lot of next-generation stuff that the "prime" defense contracting companies are very interested in. He's the real deal. Yes, I'm being purposely vague.

That said, the trace from the signal source, to the end of the PCB still counts as an antenna, and will absolutely radiate signal even "correctly terminated" (which we are just assuming it's 50 ohms...) which is probably why gatormaro saw limited connections occasionally.

He said that copper tape / shielding may not be a great idea due to it could actually increase the radiation pattern (my words mangling his explanation) and might not attenuate it at all. He explained to me some examples of antennas he'd built using layering of copper which helped propagate the waves instead of attenuate them.

Eccosorb, an very common energy isolation barrier, is perfect for this type of thing.

He also said, without looking at the board, in general, a good idea could be just AC coupling the signal to ground at it's origin, and at the edge of the pcb with something like 100pF to 1000pF cap.

So once I pull this thing and see what kind of space I have to play with, I'll have a better idea of what I'm going to try. But we have a tons of Eccosorb at work that I can probably snag some to try out.

[Curr]

Originally Posted by arpad_m

Silly question, because back in the day I barely passed the (brutally difficult) electromagnetic field theory exam at the university, but how do you guys know what the correct antenna length for maximum attenuation is? Did you do any calculations?

One product mentioned above has a longer cable, the other one is a stub, but they both have specific lengths, and wouldn't even an inch or two matter a lot at these frequencies?

I'd assume first thing you'd have to figure out what the signal frequency is...

Is the car using 4G? LTE?

Which network is it piggy-backing onto? AT&T? Verizon? Other?

Once you know that stuff then I'd assume you can back calculate your appropriate wavelength information?

Or course, I could be completely off base

Once again, I'm an EE, but I am *not* an antenna / e-mag / fields guy. But throw a rock here and I can hit 10 of them

So I think this might be why my friend said just AC coupling the signal to ground at the origin and edge of the PCB might be easiest.



EDIT:
Some quick Google'ing looks like OnStar uses AT&T 4G LTE network which looks to be from ~700MHz to ~2.5GHz.