| 摘要 |
PURPOSE:To achieve a position display with high accuracy, by switching the display to a position display operated based on a progressing direction and speed of a car, when the reception waves of navigation electromagnetic waves comes to a prescribed value or below. CONSTITUTION:In receiving a navigation electromagnetic wave with the intensity of electric field a prescribed value or more, contacts 8a and 8b of a switcher 8 are selected to the b-side. On the other hand, the navigation electromagnetic waves received on a reception antenna 1 is reproduced at a receiver 2 and given to a position detector 3, from which the electromagnetic waves are given to a display device 9 via the contact 8a as the position detection signal. Next, if either one of the navigation electromagnetic waves is weakened to the reception electric field intensity at a prescribed value or below, the contacts 8a and 8b of the switcher 8 are switched to the a-side. Thus, a position operator 7 takes a signal preset value from the detector 3 to an initial position to calculate the position of a car based on the signal toward the progressing direction from a magnetic compass 5 and a car speed signal from a car speed sensor 6, and the operation output is given to a display device 9 via the contact 8a. |
