Cell Phone Interference by Onboard Computer

Does anyone have any input on whether or not the Subaru onboard computers can reduce cell phone signal strength?

I have Motorola StarTac phones with handsfree kits in several cars.

In my Toyota I have the latest version handsfree kit which allows you to just insert the phone in the holder and everything hooks up automatically. No matter which of the two StarTacs I use everything is okay.

In my 94 SVX and 2001 Legacy I have the earlier version hands free where you have to attach a cable to the phone and then insert in a holder which in turn then engages the mic and speaker automatically. Since day one the signal strength drops by 2-3 bars in both cars on both StarTacs. Also swithced radios from stock to Pioneer but no change in cell performance.

All 3 cars had internal Terx glass mount antenna on upper right windshield area before today. I do not want to go the external antennae route.

I thought it might be coated glass but when I switched out the SVX windshield a few months ago I put in a non-coated one, at least that was the option I ordered. No chanage to cell signal strength. Also previously switched radios from stock to Pioneer but no change in cell performance.


I turned in my Toyota today and pulled the newer handsfree and switched with the one in the SVX and added a newer Andrews glass mount antenna in the same location. Old Terx was .75 inches by about 6 inches and the new Andrew is 3.5 x 3.5 inches square. Both antenna are made for Motorola with direct hook up, no adaptors required. The Andrews supposedly had better signal pulling. It did a little and I only lost 1-2 bars.

My local audiophile dealer mentioned that some car computers are not properly shielded for cell interference to signal strength. As both cars are Subarus I thought this might have some validity.

I tried hooking up the phone with it on and just bringinmg in to the car lost 1 bar then turning the ignition key to Accessory and not engage the computer and lost 1-2 bars. No chnage when I turned car on.

Doesanyone know if the computer is engaed in Accessory or just in the On position?

Any suggestions to test / resolve?