BTW, right now I'm using a temporary solution. I stripped the remains of the old antenna cable from it's copper shielding and routed it under the dash above the instrument cluster. The reception is pretty decent, I must say. Especially considering I didn't do any measurements to imiate a half-wavelength dipole and right now it is positioned parallel to wave polarization, so there is definitely room for improvement. But for now, I guess I found a good place to mount an internal antenna, invisible from outside and inside. It is above the lower level of the windshield and relatively far away from the body of the car and other big metal objects that can shield it.