A system for monitoring the pressure in a pneumatic tire supported on a wheel of a vehicle, the wheel being rotatable about an axis of rotation and defining a plane of rotation that is perpendicular to the axis of rotation. The system includes a housing mounted on the wheel of the vehicle and a sensor in the housing for measuring a pressure condition in the pneumatic tire. The system also includes a transmitter coupled to the sensor for generating a radio frequency output signal conveying the pressure condition measured by the sensor. The transmitter includes an antenna contained in the housing, where this antenna is configured to transmit the output signal according to a radial pattern. The system further includes an orientation mechanism operative to orient the housing during mounting of the housing to the wheel of the vehicle. The orientation mechanism may be further operative to orient the antenna within the housing. The orientation mechanism ensures that, once the housing is mounted to wheel of the vehicle, the output signal is transmitted substantially in the plane of rotation of the wheel of the vehicle.