Automobile antenna system

Claim 2

An automobile antenna system comprising: a main antenna provided on the rear portion of a vehicle body; a sub antenna provided to the rear of said main antenna; a high-frequency pickup provided forward of said main antenna in order to detect deflection of the output of said main antenna in advance; an antenna selecting signal generator which actuates a switch circuit so that said main antenna, the output level of which is predicted to dip after a predetermined lapse of time T, is changed over to said sub antenna, in which no dipping is occurring, for a period D during which the dipping in the output level occurrs, whereby the output level of said main antenna is maintained at a predetermined value or higher.

Claim 3

An automobile antenna system according to Claim 1, wherein said high-frequency pickup is provided in parallel to a marginal edge of said vehicle body or along a joint between adjacent flat vehicle panels.

Claim 4

An automobile antenna system according to Claim 2, wherein said high-frequency pickup is-provided along a front pillar of a vehicle body.

Claim 5

An automobile antenna system according to.Claim 1, wherein said main antenna and sub antenna are provided on the rear windshield of said vehicle body.

Claim 6

An automobile antenna system according to Claim 1, wherein said antenna selecting signal generator calculates said time T from the following formula: T = L 24 X 1/ vehicle speed wherein L 24 represents the distance between the position to which said high-frequency pickup is attached and the position to which said main antenna is attached, and the cutput level of said main antenna is predicted to dip after said time T has elapsed from the time when said high-frequency pickup detects in advance deflection of the output of said main antenna.

Claim 7

6 An automobile antenna system according to Claim 1, wherein said antenna selecting signal generator includes: a level comparator which outputs a mono pulse signal wl:n the output of said high-frequency pickup falls below th standard level L 0 ; a first pulse counter which is reset by said mono pulse signal and outputs a pulse signal every time said first pilse counter counts a count pulse generated by a vehicle speed pulse generator up to the number of pulses which ccssesponds to said time T; a first bistable multi vibrator which outputs a predetermined signal using the pulses produced by said level comparator and said first pulse counter as an ON signal and an OFF signal, respectively; a monostable multi vibrator which is driven by a negative voltage of the output signal from a differentiator which differentiates the output signal of said bistable multi vibrator; a second pulse counter which is reset by the output of said monostable multi vibrator and outputs a predetermined pulse signal every time said second pulse counter counts a count pulse generated by said vehicle speed pulse generator up to the number thereof which corresponds to said time D; and a second bistable multi vibrator which outputs a sub antenna selecting signal for a period T to T + D, using the outputs from said second pulse counter and said monostable multi vibrator as an ON signal and an OFF signal, respectively.

Claim 8

An automobile antenna system according to Claim 1, further comprising: a switch for outputting a predetermined drive signal when a transmission is set in the parking range or the reverse range; a first AND gate to which the outputs of said antenna selecting signal generator and said switch are input; a.second AND gate to which the output of said antenna selecting signal generator is input through an inverter and the output of a level discriminator which is produced when the output signal of an intermediate frequency amplifier of a receiver is below a predetermined value; and an OR circuit which calculates the outputs of said first and second AND gates on the basis of OR operation and outputs the calculated value as a selecting signal of said switch circuit; thereby enabling broadcast waves to be received by the antenna which is superior in receiving quality while said vehicle is being reversed or parked.