1. Field of the Invention
The present invention relates to a vehicular adaptor system which can adapt a portable telephone set to a vehicle having no vehicular telephone or to a vehicular telephone installed in a vehicle, used in a multiple carrier access system, such as a cellular mobile telephone system.
2. Description of the Related Art
Recently, portable telephones have become smaller in size and lighter in weight, i.e. convenient to carry. Accordingly, due to increased popularity, their numbers are increasing. A portable telephone can be considered a compact and light weight modification of the vehicular telephone due to its lower output power than the vehicular telephone. Since it is easily portable, it is used almost in the same way in the service area of the vehicular telephone. The portable telephone can be used in a vehicle; however, if it is used as it is, the shielding effect of the metal body of the vehicle decreases the radio frequency wave propagation, i.e. output power and receiving sensitivity, of the portable telephone, and may result in its operation being disabled. Therefore, a radio frequency booster/pre-amplifier is installed in the vehicle and a vehicular antenna is installed outside the vehicle.
A prior art vehicular adaptor system for a portable telephone set is hereinafter described with reference to a perspective view in FIG. 1. A portable telephone set 11 is composed of a main body of the portable telephone set and an antenna (not seen there due to being integrated in the main body). The main body includes an earphone, a speaker, a key board, and a display for displaying a call number dialed onto the key board, etc. When the portable telephone set 11 is rested in a cradle 12' of a vehicular adaptor 12, an end A.sub.4 of cradle 12' and an end A.sub.2 of portable telephone set 11 are electrically contacted so as to communicate control signals, audio signals and an adaptor signal informing the fact that the portable telephone set 11 is mounted on the adaptor, between the adaptor 12 and the portable telephone set 11. The antenna integrated in the main body of the portable telephone set 11 is coupled with a radio frequency coupler (not seen in the figure) integrated in a side A.sub.3 of cradle 12' so as to face the integrated antenna. Adaptor 12 communicates control signals of booster 13 and radio frequency signals to/from booster/pre-amplifier 13 by means of a control signal cable and a radio frequency cable. Adaptor 12 further communicates up-link/down-link data and audio signals to/from a remote control unit (referred to hereinafter as control unit) 14 by means of another cable.
Functions of the above-described adaptor system for the portable telephone are summarized as follows:
1. The portable telephone set brought into the vehicle is rested on vehicular adaptor 12. Then, a battery installed in the portable telephone set is charged by a charging circuit of the adaptor.
2. 0.6 watt output power of the portable telephone set is fed via vehicular adaptor 12 to radio frequency booster 13, wherein 0.6 watt is amplified up to 3 watt.
3. A radio frequency signal to be input to portable telephone set 11 is amplified so as to compensate for coupling losses at the radio frequency coupler, etc., and accordingly becomes the level as strong as a level of the portable telephone set when used outside the vehicle.
4. Control unit 14 is used in the same way as a vehicular telephone set, i.e. is used as a hand set for talking, for dialing a call number via its key board and for displaying the phone number, etc. thereon.
To use portable telephone 11 in a vehicle in which a vehicle telephone has been already installed, all of FIG. 1 adaptor system is independently required in addition, except for a commonly used vehicular antenna.
The problems of the prior art FIG. 1 adaptor system include the following:
(1) Having to control both of the control unit and the radio frequency power booster/pre-amplifier, the adaptor unit becomes complicated in configuration and large in size.
(2) For connecting the integrated antenna of the portable telephone set to the radio frequency booster/pre-amplifier, a radio frequency coupler is required in the adaptor, causing complicated structure and precise mechanism.
(3) The vehicular adaptor becomes large in size caused the system to become large and occupy a large space in the vehicle.
(4) A portable telephone set to be used in a vehicle already having a vehicle telephone installed thereon requires a considerable investment for the duplicated radio frequency circuits, as well as a large space therefor.