WO1992008310A1

WO1992008310A1 - Selectable cordless or corded telecommunications system

Info

Publication number: WO1992008310A1
Application number: PCT/US1990/006199
Authority: WO
Inventors: Michael K. Pedigo
Original assignee: Weiser Telecommunications, Inc.
Priority date: 1990-10-26
Filing date: 1990-10-26
Publication date: 1992-05-14

Abstract

A selectable cordless or corded telecommunication system (10) that consists of a telephone base unit (12) a cordless type handset (14) and an interface unit (16) that provides the interface between the telephone base unit and the handset. The system (10) allows the handset to be operated in either a corded audio mode: that is the handset is attached to the telephone base unit by a handset cable assembly (18); or in a cordless radio-link mode that is effected by removing the handset (14) from the handset cable assembly (18). A plurality of systems (10) can be operated within a single structure, such as an office building, without interference from each other.

Description

SELECTABLE CORDLESS OR CORDED TELECOMMUNICATION SYSTEM

TECHNICAL FIELD

The invention pertains to the general field of telephone systems and more particularly to a system that allows a plurality of cordless type handsets to be operated within a single structure, without interference, in either a corded audio mode or a cordless radio-link mode.

BACKGROUND ART The use of cordless telephone sets has gained wide acceptance over the last few years. Typically, a cordless telephone set consists of a telephone base unit and a cordless type handset that can be operated at a substantial distance from the base unit. communication between the base unit and the handset is by means of a radio link. Therefore, both the base unit and handset include transceiver circuits that are responsive to preselected radio frequency signals.

The cordless telephone has been found to have problems that are not found in conventional corded telephone sets. The foremost problem is that practically only one cordless telephone set can be used within a single structure because of interaction and interference between closely located sets. Even in those units that include selective frequencies and signal multiplexing the problem still exists. The problem has been partially avoided by having each telephone base unit, that shares a frequency channel, transmit at different time intervals together with a base station identification signal. Because of this problem the primary use and utility for cordl ess telephones has been l imi ted to househo l ds rather than office buildings and the like.

A search of the prior art did not disclose any patents that read directly on the claims of the instant invention however, the following U.S. patents were considered related:

PATENT NO, INVENTOR ISSUED

4,908,847 Hannon et al 13 March 1990 4,752,949 Steinbeck et al 21 June 1988 4,703,324 White 27 October 1987 4,669,108 Deinser 26 May 1987

The Hannon patent discloses a conversion kit that allows a standard telephone set to be converted to a cordless telephone. The kit consists of a two-piece adapter set where each piece consists of a radio transmitter/receiver and a modular telephone plug. The conversion is made by removing the handset telephone cord from the telephone base unit and replacing same with one of the adapters. one end of the adapter is plugged into the base unit and the other end is plugged into the handset. The transmitter portion of the telephone adapter plugged into the base unit transmits to the receiver portion of the adapter plugged into the handset and vice versa. Thus, effectively providing cordless telephone operation.

The Steinbeck patent discloses a method whereby a single cordless telephone set can be used in either a cordless or coded mode of operation. The conversion is made by respectively disconnecting or connecting a single-cord that includes conversion circuits between the telephone base unit and the cordless handset When the cord is installed, the conversion circuits disable the transmitting and receiving circuits in both the base unit and the handset. Thus, permitting the telephone signal to be transmitted between the two units through the cord.

The white patent discloses a cordless telephone communication system in which a base station can communicate with a plurality of battery-powered handsets by means of a duplex radio link. Synchronizing signals are transmitted at predetermined intervals on a signalling channel by the base unit to the portable battery powered receiver. Thus, the need to send separate station identification signals are avoided by transmitting the synchronising signals in accordance with a predetermined signaling sequence.

The Deinzer patent discloses a wireless hands-free conference telephone system. The system consists of a wireless transducer/transmitter for converting sound received into a first corresponding signal and radiating that sound from a position remote from the remainder of the telephone system. The system further includes a unitary control module that includes a receiver circuit for receiving the remotely radiated first corresponding signal. This signal is transferred via a f irst s ignal path to an output adapted for connection to the telephone.

DISCLOSURE OF THE INVENTION

The selectable cordless or corded telecommunication system consists of a cordless K-style handset and an interface unit that functions in combination with any telephone base unit that is connected to a telephone central office (TCO). The interface unit functions as the interface between the telephone base unit and the handset. several such systems, where each system is connected to a separate telephone line, can be operated within a single structure, such as an office building, a warehouse, etc. without interference from each other.

The system features two modes of operation - a corded audio mode or a cordless radio link mode. Thus, if a user commences a conversation at a particular work station and there is a need to move to another location while still conversing, the user merely disconnects one end of the handset cord and then may move away and still operate the handset up to a distance of 150 feet (46 meters). The cordless radio-link is full duplex and operates under Fee Rules 15.209 in the receive or transmit frequency bands of 336MHz to 399MHz and 411MHz to 607MHz.

The telephone base unit may be derived from any standard telephone set . The unit preferably includes a cradle that is used to accommodate the cordless K-style handset. The cradle includes a cradle hook switch that controls the activation of the telephone line and the handset, in a preferred embodiment, inaddition to the hook switch, the handset is also activated or deactivated by a magnetic detection circuit to assure that the transceiver circuits used when operating in the cordless mode are deactivated when the handset is placed in the cradle. This circuit consists of a permanent magnet that is attached to the telephone base unit and another magnet that is juxtapositioned on the handset over the magnet on the telephone base unit. when the handset is lifted from its cradle, the handset is activated when the magnetic detection circuit detects a loss of the magnetic field; conversely, when the handset is returned to its cradle, the magnetic field is reinstated and the handset is deactivated.

The cordless K-style handset features a single, hidden antenna, a rechargeable Nicad battery and a set of transceiver circuits. The circuits provide the means for interconnecting and processing all the incoming and outgoing telephone calls from the interface unit and allows the handset to operate in either its corded audio mode or its cordless radio-link mode.

The interface unit also includes a set of transceiver circuits that provide the means for interconnecting and processing all the incoming and outgoing telephone calls from the handset. Power to the interface unit is provided by a power cable assembly that is connected to an a-c to d-c power converter. The converter plugs directly into a public utility a-c receptacle and provides the d-c power required to operate the interface unit. The power from the cable assembly is applied to a voltage regulator and charge circuit that further regulates the input power and additionally, provides the power to recharge the battery in the handset. A battery charging light emitting diode (LED) is provided to indicate when the batteries are being charged.

in view of the above disclosure, it is the primary object of the invention to provide a telecommunication system that uses a standard telephone set to transmit and receive signals from a handset that can be operated in either a corded audio mode or a cordless radio link mode. in addition to the primary object, it is also an object of the invention to have a system that:

o can be used on all national and international telephone lines,

o compensates for various models of telephone sets and wiring configurations,

o that functions without requiring modifications or changes to the external utility telephone lines,

o utilizes standard telephone modular connectors for easy installation,

o is highly reliable and maintenance free, and o is cost effective from both a manufacturers and consumers point of view. BRIEF DESCRIPTION OF THE DRAWINGS

FIGURE 1 is a block diagram of the system in the standby mode.

FIGURE 2 is a block diagram of the system with the handset removed from the telephone base unit cradle and operating in the corded audio mode.

FIGURE 3 is a block diagram of the system with a handset being used that has a hidden antenna and that is disconnected from the handset cable assembly allowing operation in the cordless radio-link mode.

FIGURE 4A and 4B are continuity block diagrams of the cordless K-style handset transceiver circuits.

FIGURE 5A and 5B are continuity block diagram of the interface unit transceiver circuits.

BEST MODE FOR CARRY I NG OUT THE I NVENT ION

The best mode for carrying out the selectable cordless or corded telecommunication system 10 is presented in terms of a preferred embodiment that is designed to allow a plurality of systems to be operated within a single structure, such as an office building, without interference with each other.

The preferred embodiment, as shown in FIGURES 1 through 5 is comprised of two major elements: a cordless-type handset 14 and an interface unit 16. The two elements function in combination with a telephone base unit 12 to form the system 10 as shown in FIGURES 1-3. in the basic system configuration, the telephone base unit 12 is connected to a telephone central office (TCO) and the interface unit 16 is connected between the telephone base unit 12 and the handset 14.

The telephone base unit 12, which is a component of a standard telephone set, is designed to process all incoming and outgoing telephone calls. in its normal configuration, the telephone set includes a handset cradle 12a that has a cradle hook switch 12b that turns the power off to the telephone base unit when the handset is placed in the cradle (on hook) and turns the power on when the handset is lifted from its cradle (off hook). The switch is operational in the inventive system 10. The standard telephone set also includes a conventional handset that is typically connected to the telephone base unit 12 by a coiled handset cord that has a standard telephone modular plug 18a on each end. one end of the cord is attached to a mating handset receptacle on the handset and the other end to a mating handset input receptacle 12c located on the telephone base unit 12. The receptacle 12c serves as the input to the internal circuits in the unit 12.

in the system 10, the conventional handset is replaced by a cordless type handset and preferably by a cordless K-style handset 14 that is described infra. The replacement is simply made by attaching the handset 14 by means of a handset cable assembly 18 that includes standard telephone modular connectors 18a on each end. One end of the cable 18 is attached to a mating handset receptacle 14a on the handset 14 and the other end to a mating handset cable receptacle 16a on the interface unit 16 as shown in FIGURES 1-3. Preferably, as shown in FIGURE 1, the handset cable assembly consist of the coiled handset cord that is normally supplied with the standard telephone set. To continue the system 10 interconnections, an interface cable assembly 20 having modular connectors 18a on each end is attached on one end to the handset input receptacle 12c on the telephone base unit 12 and the other end to the telephone base unit receptacle 16b on the interface unit 16. Finally, to complete the system interconnection, a power cable assembly 22 is used. This cable has on one end a power receptacle 22a that connects to the power input plug 16X and the other end is connected to an a-c to d-c converter 22b. The converter is designed to directly plug into a public utility a-c receptacle and to supply the d-c power required to operate the interface unit 16.

The selectable cordless or corded telecommunication system 10 operates in a standby mode and two operational modes: a corded audio mode or a cordless radio-link mode, when the system 10 is in the standby mode the handset 14, as shown in FIGURE 1, is placed on the cradle 12a of the telephone base unit 12 where the cradle hook switch 12b is "on hook" thus, the system is deactivated, when in the corded audio mode, a shown in FIGURE 2, the handset 14 is lifted from its cradled position at which time the hook switch is placed "off hook" allowing the handset to become operational. To place the system 10 in the cordless radio-link mode, the cable assembly 18 is disconnected from either end, as shown in FIGURE 3, and operated. The cordless radio-link is full duplex and operates under FCC rules 15-209 in the receive or transmit frequency bands of 336MHz to 399MHz and 411MHz to 607MHZ. when operated in the cordless radio-link mode, the handset 14 may be used up to a distance of approximately 150 feet (46 meters) from the interface unit 16. A detailed description of the K-style handset 14 and interface unit 16 follows.

The cordless K-style handset 14 includes a handset receptacle 14a and is sized to fit into the handset cradle 12a on the telephone base unit 12 A circuit means consisting of a set of transceiver circuits, provides the means for interconnecting and processing all the incoming and outgoing telephone calls and allows the handset to operate in either the corded audio mode or the cordless radio-link mode.

The handset transceiver circuits, which are described with reference to FIGURES 4A and 4B, consist of a single antenna 14b that allows the radio-linked signals to be received from and transmitted to the interface unit 16. The antenna 14b may be of the telescoping type, as shown in FIGURE 2 but preferably is encased within the handset structure and is hidden from view as shown in FIGURES 1 and 3. The antenna is connected to an antenna matching network 14c that combines and matches the outgoing transmitted signals with the incoming received signals. The network allows the use of just one antenna for both transmitting and receiving. The output of the network 14c is applied through an input filter network 14d that filters the incoming received signals so that only the. desired frequency is passed. From the filter network 14d the processed signal is applied to a radio frequency (RF) amplifier 14e where the incoming RF signal is amplified to a usable level.

The handset includes a 300MHz local oscillator 14f that generates a reference signal. when this signal is combined with the incoming RF signal a lower frequency is produced which is more easily manipulated. The ampl ified RF s ignal from the RF ampl ifier 14e and the reference signal from the 300MHz oscillator are inputted to a mixer circuit 14g. The mixer produces a differential signal having a frequency equal to the difference between the two input signals. The output signal from the mixer is applied to the input of a frequency modulated (FM) receiver circuit 14h. The circuit 14h converts the FM signal from the telephone base unit 12 into an audio signal that is then applied to an earphone speaker 14i through which conversations are heard. The speaker 14i is driven by signals supplied through the wired path when the handset 14 is in the corded audio mode, when the system is in the cordless radio-link mode, the earphone speaker 14 i is similarly driven, however the speaker driving signals follow the circuit path of the radio link.

The FM receiver circuit 14h is partially controlled by a 48MHz crystal oscillator 14j and a 455KHz intermediate frequency circuit 14k. The circuit

14j generates a reference signal that is applied to the input of the circuit 14h and into an internal mixing circuit that produces an intermediate frequency; the circuit 14k, filters the intermediate frequency from the mixing circuit, in the FM receiver chip's external circuit is also located an automatic frequency control

(AFC) circuit 14m. This circuit adjusts the frequency of the 300MHz local oscillator 14f to compensate for any error that is detected by the FM receiver chip 14h.

When the cordless handset 14 is operated in its cordless radio-link mode, the transceiver circuits in the handset are powered by a power source 14P consisting of a set of internal rechargeable batteries that are preferably Niσad rechargeable batteries. The batteries are automatically recharged by a charging circuit 14q when the handset 14 is operating in its corded audio mode, that is when the handset cable assembly 18 is connected on both ends. in addition to the cable assembly 18 supplying the voltage for the battery charging circuit 14q it also provides the wired audio path when the handset is in its corded audio mode.

When the handset is placed in its cradle 12a on the telephone base unit, a cradle power switch 14r automatically turns off the power to the handset transceiver circuits. Preferably, the cradle power switch operates by a magnetic detection circuit 14s which consists of strategically placing a small permanent magnet on the cradle 12a. Likewise, a magnetic detector, such as a reed switch, is juxtaposition on the handset above the permanent magnet, when the handset 14 is lifted from the cradle, the handset is automatically activated upon the detection of the loss of the magnetic field, conversely, when the handset 14 is placed on the cradle, the detection of the magnetic field deactivates the handset.

The voice of the speaker using the handset 14 is picked-up by an electret microphone I4t. The audio signal from the microphone is applied to an audio amplifier 14U where the signal is amplified. If the handset is in its corded audio mode, that is, the handset cable assembly is connected, the amplified signal from the amplifier 14U is applied through the handset receptacle 14a onto the interface unit 16. If the handset is in its cordless radio-link mode, the amplified audio signal is applied to a 300MHz oscillator 14V that converts the audio signal to a frequency modulated RF signal. The RF signal is then applied to an RF amplifier 14W where the signal is amplified to an acceptable level for transmission to the interface unit via the antenna matching network 14c and the antenna 14b.

The interface unit 16, which provides the interface between the handset 14 and the telephone base unit 12, also includes a set of transceiver circuits that provide the means for interconnecting and processing the incoming and outgoing telephone calls. The transceiver circuits which are described with reference to FIGURES 5A and 5B, consists of a single antenna 16c that is used to both transmit and receive the radio-linked signals from the handset 14. The antenna in the preferred embodiment has a swivel base and is of the telescoping type. The antenna is connected to an antenna matching network 16d that combines and matches the outgoing transmitted signals with the incoming received signals. The network allows the use of just one antenna for both transmitting and receiving. The incoming received signals are filtered by an input filter network 16e so that only the desired frequency is passed. From the network the processed signal is applied to a radio frequency (RF) amplifier 16f that amplifies the signal to useable level.

The interface unit 16 also includes a 300MHz local oscillator 16g that generates a reference signal. when this signal is mixed with the amplified RF signal in a mixer circuit I6h a new signal is produced that has a frequency equal to the difference between the two inputted frequencies. The output signal from the mixer is applied to a frequency modulated (FM) narrowband receiver circuit 16i. The circuit 16i converts the FM radio signal from the handset 14 into an audio signal which is ultimately applied to the telephone base unit 12 for further transmission through the telephone lines.

The FM receiver includes an internal mixing circuit that is applied a reference signal generated by a 48MHz crystal oscillator 16J. A 455KH2 intermediate frequency circuit 16k is also connected to the FM receiver. This circuit filters the intermediate frequency signal produced by the internal mixing circuit in the FM receiver circuit I6i. An automatic frequency control (AFC) circuit 16m is connected between the FM receiver circuit 16i and the 300MHz local oscillator 16g. The circuit 16m adjusts the frequency of the 300MHz oscillator 16g to compensate for any error detected by the FM receive circuit 16i. Also controlled by the circuit 16i is a transmit disable circuit 16n. when the circuit 16n is triggered, it turns off the transmitter power when there is no incoming signal from the handset 14.

The output of the transmit disable circuit 16n is applied to a 300MHz transmit oscillator 16P and to an RF amplifier circuit 16q. The oscillator 16P converts the audio signal from the telephone base unit 12 to a frequency modulated RF signal. The RF amplifier circuit 16q amplifies the RF signal to an acceptable level to transmit to the handset 14 via the antenna matching network 16d and the antenna 16c.

At the internal connection of the telephone base unit receptacle 16b is located a handset matching switches and amplifiers network 16r. There are no industry standards for the telephone wiring connected to the handset. Therefore, the network iδr compensates for the voltage levels required by a specific telephone set and allows the wire pairs in the handset cord to be rearranged to make the handset 14 compatible with virtually any telephone base unit 12. The output of the network 16r is applied to a telephone receive audio amplifier 16s that amplifies the audio signal from the telephone line to an acceptable level for sending to the handset. The audio signal is sent either through the handset cable assembly 18 via the handset cable receptacle 16a or through the radio link circuits via the antenna 16c. The handset cable assembly 18, when attached to the handsetcable receptacle 16a, provides the wired audio path and also carries the voltage for the battery charging circuit 14q in the handset 14 through the speaker wires.

The audio signal from the handset 14 coming from either the radio link circuits or through the handset cable receptacle 16a via the handset cable assembly 18 is applied to a telephone transmit audio amplifier 16t. The amplifier adjusts the incoming signal to an acceptable level for sending through the telephone line. Finally, the interface circuit 16 includes a voltage regulator and charger circuit 16U. The circuit regulates the power used by the interface unit 16 and also supplies the power to charge the Niσad rechargeable batteries 14P in the handset 14. The circuit 16a may also include a circuit means (not shown) for illuminating a light emitting diode (LED) when the rechargeable batteries in the handset 14 are being charged.

while the invention has been described in complete detail and pictorially shown in the accompanying drawings, it is not to be limited to such details, since many changes and modifications may be made in the invention without departing from the spirit and the scope thereof. Hence, it is described to cover any and all modifications and forms which may come within the language and scope of the claims.

Claims

CLA I MS

1. A selectable cordless or corded telecommunication system, where a plurality of said systems can operated within a single structure without interference from each other, said system comprising:

a) a telephone base unit connected to a telephone central office, where said telephone base unit is a component of any telephone set,

b) a cordless type handset having circuit means for processing incoming and outgoing telephone calls, and

c) an interface unit connected between said telephone base unit and said handset where said interface unit has circuit means for processing incoming and outgoing telephone cal ls and to al low said handset to be operated in either a corded audio mode or a cordless radio-link mode.

2. A selectable cordless or corded telecommunication system, where a plurality of said systems can be operated within a single structure without interference from each other, sai d system compris ing :

a) a telephone base unit that is connected to a telephone central office (TCO) and designed to process all incoming and outgoing telephone calls, where said telephone base unit is a component of any telephone set and includes a handset receptacle and a handset cradle, b) a cordless type handset sized to fit into the handset cradle on said telephone base unit, where said handset comprises:

(1) circuit means to allow operation in either a corded audio mode or a cordless radio-link mode,

(2) circuit means for processing incoming and outgoing telephone calls,

(3) a power source,

(4) a handset receptacle,

c) an interface unit comprising:

(1) circuit means for interconnecting and processing incoming and outgoing telephone calls,

(2) a power input plug that is connected via a power cable assembly to a power source,

(3) a telephone base unit receptacle that is connected, via a base unit cable assembly, to the handset input receptacle on said telephone base unit, and

(4) a handset cable receptacle that may be connected via a handset cable assembly to the handset receptacle on said handset, where when the handset cable assembly is connected, said handset operates in its corded audio mode and conversely, when the handset cable assembly is disconnected said handset is automatically placed in its cordless radio-l ink mode,

3. The system as specified in claim 2 wherein the power source for said handset comprises a set of rechargeable batteries.

4. The system as pecified in claim 3 wherein said rechargeable batteries are Nicad rechargeable batteries.

5. The system as specified in claim 2 wherein said cordless radio-link mode is full duplex and operates in the receive or transmit frequency bands of 336MHZ to 399MHZ and 411MHZ to 607MHZ.

6. The system as specified in claim 2 wherein said interface unit is lowered by an a-c to d-c power converter that plugj into a public utility a-c receptacle and that supplies the d-c power required to operate said interface unit.

7. The system as specified in claim 2 wherein said interface unit further comprises a voltage regulator and charge circuit that regulates the power used by said interface circuit and supplies the power to recharge said rechargeable batteries in said handset.

8. The system as specified in claim 2 wherein the cradle on said telephone base unit includes a cradle hook switch that automatically turns off the power to said handset when said handset is placed on the cradle.

9. The system as specified in claim 2 further comprising a magnetic detection circuit that consists of having a small magnet strategically placed on the cradle and a magnetic detector placed on said handset such that when said handset is lifted from the cradle said handset power is automatically activated upon detection of the magnetic field loss and conversely, when said handset is placed on the cradle, the detection of magnetic field deactivates said handset.

10. A selectable cordless or corded telecommunication system, where a plurality of said system can be operated within a single structure without inference from each other, said system comprising:

a) a telephone base unit that is connected to a telephone central office (TCO) and designed to process all incoming and outgoing telephone calls, where said telephone base unit is a component of any telephone set and includes a handset input receptacle and a handset cradle, b) a K-style handset that operates in either a corded audio mode or a cordless radio- link mode where said handset is sized to fit into the handset cradle located on said telephone base unit, and includes a handset receptacle and a set of transceiver circuits that provide the means for interconnecting and processing incoming and outgoing telephone calls, where said transceiver circuits comprise:

1) an antenna for transmitting and receiving the radio-linked signals, 2) an antenna matching network that combines and matches the outgoing transmitted signals with the incoming received signals to allow the use of only one said antenna, 3) an input filter network that filters the incoming received signals so that only the desired frequency is passed,

4) a radio frequency (RF) amplifier that amplifies the incoming RF signal from said input filter to a usable level,

5) a 300MHz local oscillator that generates a reference signal which when combined with the incoming RF signal, produces a lower frequency signal which is more easily manipulated,

6) a mixer circuit that mixes the amplified RF signal from said RF amplifier with the reference signal from said 300MHz local oscillator to produce a differential signal having a frequency equal to the difference between the two input frequencies, 7) an earphone speaker through which conversations are heard, where said speaker is driven by signals supplied through the wired path when said handset is in the corded audio mode and through the radio link path when said handset is in the cordless radio-link mode,

8) a frequency modulated (FM) receiver circuit that converts the FM signal from said telephone base unit into an audio signal which can be heard through said earphone speaker,

9) a 48MHZ crystal oscillator that generates a reference signal that is applied to an internal mixing circuit in said FM receiver circuit, 10) an automatic frequency control (AFC) circuit which adjusts the frequency of said 300MHz local oscillator to compensate for any error detected by said FM receiver circuit,

11) a transmit disable circuit that when triggered by said FM receiver circuit turns off the transmitter power when there is no incoming signal from said handset,

12) a 300MHz transmit oscillator that converts the audio signal from said telephone base unit to a frequency modulated RF signal,

13) an RF amplifier that amplifies the RF signal from said 300MHz transmit oscillator to an acceptable level to transmit to said handset via said antenna matching circuit and said antenna,

14) a handset matching switches and amplifiers network located at the internal connection of the telephone base unit receptacle, where said network allows said interface unit to be connected to virtually any said telephone base unit by rearranging the wiring combinations and compensating for the voltage levels required by the telephone set,

15) a telephone receive audio amplifier that amplifies the audio signal from the telephone line to an acceptable level for sending to said handset where the signal is sent either through said handset cable assembly 17) a 300MHz oscillator that converts the audio signal from said audio amplifier to a frequency modulated RF signal,

18) an RF amplifier that amplifies the RF signal from said 300MHz oscillator to an acceptable level to transmit to said telephone base unit via the antenna matching network and the antenna and,

c) an interface unit having a set of transceiver circuits that provide the means for interconnecting and processing incoming and outgoing telephone calls, where said unit has a power input plug that is connected, via a power cable assembly, to a power source, a telephone base unit receptacle that connects, via a base unit cable assembly, to the handset input receptacle on said telephone base unit, and a handset cable receptacle that may be connected, via a handset cable assembly, to the handset receptacle on said handset, where when the handset cable assembly is connected, said handset operates in its corded audio mode and conversely, when the handset cable assembly is disconnected said handset is automatically placed in its cordless radio-link mode, where said transceiver circuits comprise:

1) an antenna for transmitting and receiving the radio-linked signals to and from said handset,

2) an antenna matching network that combines and matches the outgoing transmitted signals with the incoming received signals from said handset to allow just one antenna to be used for both transmitting and receiving, 3) an input filter network that filters the incoming received signals so that only the desired frequency is passed,

4) a radio frequency (RF) amplifier that amplifies the incoming RF signal from said input fi lter to a usable level,

5) a 300KHZ local oscillator that generates a reference signal,

6) a mixer circuit that mixes the amplified RF signal from said RF amplifier with the reference signal from said 300MHz local oscillator to produce a signal with a frequency equal to the difference between the two input frequencies,

7) a frequency modulated (FM) receiver circuit that receives the signal from the mixer circuit and converts the FM radio signal from said handset into an audio signal which is used by said telephone base unit to send through the telephone lines,

8) a 48MHz crystal oscillator that produces a reference signal that is appl ied to an internal mixing circuit in said FM receiver circuit,

9) a 455KHZ intermediate frequency circuit that filters the intermediate frequency signal produced by the internal mixing circuit in said FM receiver circuit, 10) an automatic frequency control (AFC) circuit which adjusts the frequency of said 300MHz local oscillator to compensate for any error detected by said FM receiver circuit,

13) an RF amplifier that amplifies the RF signal from said 300MHz transmit oscillator to a acceptable level to transmit to said handset via said antenna matching circuit and said antenna,

15) a telephone receive audio amplifier that amplifies the audio signal from the telephone line to an acceptable level for sending to said handset where the signal is sent either through said handset cable assembly via said handset cable receptacle or through the radio link via said antenna,

16) a telephone transmit audio amplifier that takes the audio signal from either the radio link circuits or said handset cable assembly and adjusts the incoming signal to an acceptable level for sending through the telephone line, and

17) a voltage regulator and charger circuit that regulates the power used by said interface unit and supplies the power to recharge said rechargeable batteries in said handset.

11. The system as specified in claim 10 wherein said telephone base unit may consist of any unit that forms a part of a standard telephone set.

12. The system as specified in claim 10 wherein said handset is designed to operate within a range of UP to 150 feet (46 meters).

13. The system as specified in claim 10 wherein said antenna on said handset is hidden from view.

14. The system as specified in claim 10 wherein said cordless radio-link mode is full duplex and operates in the receive or transmit frequency bands of

336MHz to 399MHZ and 411MHZ to 607MHZ.

15. The system as specified in claim 10 wherein said set of rechargeable batteries are comprised of

Niσad batteries where said batteries are automatically recharged when said handset is in the corded audio mode.

16. The system as specified in claim 10 wherein said interface unit further comprises circuit means for illuminating an LED indicator when the rechargeable batteries in said handset as being charged by the voltage regulator and charger circuit.

17. The system as specified in claim 10 wherein said cradle power switch operates by a magnetic detection circuit.

18. The system as specified in claim 17 wherein said magnetic detection circuit comprises:

a) a small magnet strategically placed on the cradle located on said telephone base unit,

and

b) a magnetic detector located on said handset such that when said handset is lifted from the cradle said handset power is automatically activated upon detection of the magnetic field loss, and, conversely, when said handset is placed on the cradle, the detection of the magnetic field then deactivates said handset.

19. The system as specified in claim 18 wherein said magnetic detector is comprised of a reed switch.

20. The system as specified in claim 10 wherein said power cable assembly includes an a-c to d-c power converter that plugs directly into a public utility a-c receptacle and that supplies the d-c power required to operate said interface unit.

21. The system as specified in claim 10 wherein said handset cable assembly consists of a standard coiled handset cord as used to connect a handset to a telephone base unit.