Cordless telephone system

Claim 1

A cordless, two-way telephone system, including: a base station and a mobile unit; said base station including a first radio transmitter designed to operate in the range of 1.7 Mhz and a first radio receiver operable in the range of 27 Mhz; said first radio transmitter including: a power supply, a power cord coupled to said power supply and having at least first and second electrical conductors for connecting said power supply to a source of a.c. power, the length of said first conductor in said power cord being less than one-eighth of a wavelength in said range of 1.7 Mhz, said first conductor being maintained above ground potential, for signals in said 1.7 Mhz range, at its end coupled to said power supply, a source of modulatable R-F signals connected to said power supply and powered thereby; and an antenna coil coupled to said source of R-F signals, said antenna coil having first and second terminals; first means coupling said first terminal of said antenna coil to said first conductor, only, of said power cord; an antenna conductor spaced from said first and second conductors and having a length substantially less than one-eighth wavelength in said range of 1.7 Mhz; second means coupling said second terminal of said antenna coil to one end of said antenna conductor; said mobile unit including a second radio transmitter and a second radio receiver; said second radio receiver including a ferrite rod antenna, a first detector coupled to said ferrite rod antenna for producing I-F signals when said ferrite rod antenna is in the R-F field from said first radio transmitter; indicator means for indicating when the signal from said base station is below a level which permits communication between said base station and said mobile unit, said indicator means including rectifying means coupled to said first detector for rectifying the I-F signals therefrom, switching means responsive to the absence of adequate output from said rectifying means to enter a conducting state, a source of operating voltage, and an out-of-communication indicator connected between said source of operating voltage and said switching means and responsive to the conducting state of said switching means to emit light.