1.  Field of the Invention
This invention relates to a mobile radio telephone device which can be used in switching a portable antenna and an external antenna. 
2.  Prior Art
FIG.  1 is a block diagram showing the construction of a conventional mobile radio telephone device.  In FIG.  1, reference numeral 1 designates a radio telephone device body, 11 is a circuit of a radio telephone device for execution of predetermined operations such as modulation, demodulation and amplification, and 12 is a detachable portable antenna mounted on the body 1.  Reference numeral 13 designates power input terminals to which power is supplied when a power source portion 2 is mounted on the body, and 16 is an antenna input terminal.  Numeral 3 is a separate antenna to be mounted on the body 1 in plate of the portable antenna 12 and 4 is a separate battery.  Numeral 21 designates a battery mounted on power source 2. 
FIG.  2 is a block diagram showing a further embodiment of a conventional mobile radio telephone device.  In FIG.  2, numeral 17 designates an antenna change-over switch which detects the mounting of the antenna 3 to an antenna input terminal 18 to effect switching.  In this embodiment, the portable antenna 12 is designed so that it may not be removed from the radio telephone device body 1. 
The operation of the prior art device will be described hereinafter.  The mobile radio telephone device shown in FIG.  1 is used with the portable antenna 12 and the power source portion 2 mounted on the radio telephone device body 1.  In this case, radio waves received by the portable antenna 12 are inputted into the circuit 11 through the antenna input terminal 12, and signals outputted from the circuit 11 are delivered as radio waves for transmission from the portable antenna 12.  Power from the battery 21 is supplied to the circuit 11 through the power source input terminal 13.  When the device is used inside a vehicle, the transmission/receiving electric field signal level is lowered, and the antenna 3 is mounted on the antenna input terminal to strengthen the signal level. 
The mobile radio telephone device shown in FIG.  2 utilizes the power source portion 2 when in use as a remote handset.  When the device is used while being fixed to a vehicle, the portable antenna 12 remains mounted, and the antenna 3 fixed to the vehicle is connected to the antenna input terminal 18.  The antenna change-over switch 17 is then switched to the antenna 3 fixed to the vehicle. 
When the device is used while being fixed to the vehicle, the power source portion 2 can be removed, and as shown in FIGS.  1 and 2, it may be connected to the vehicle battery 4 to prevent consumption of power in the battery 21. 
As discussed above, when the conventional mobile radio telephone device is used in a vehicle, a separate antenna is required to be mounted on the device, or a complicated change-over switch must be provided within the radio telephone device body.  This construction has several disadvantages such as cumbersome handling and increased production costs.