GB2370721A

GB2370721A - Cordless telephone with computer interface

Info

Publication number: GB2370721A
Application number: GB0125513A
Authority: GB
Inventors: Brian Kim; David C Nall; G Gerard Brennan; Mark E Gillis
Original assignee: ADVANCED AMERICAN TELEPHONES
Current assignee: ADVANCED AMERICAN TELEPHONES
Priority date: 2000-10-31
Filing date: 2001-10-24
Publication date: 2002-07-03
Also published as: DE10153265A1; GB0125513D0

Abstract

A cordless telephone device, for conducting telephone calls via either a digital data network, 311, or a public switched telephone network, 260. The device includes a base unit, 200, and a mobile unit, 100 or 110. The base, 200, and the mobile units, 100 or 110, each include transceivers enabling bidirectional radio communications, 150. The base unit, 200, can be connected with a computer, 300, to conduct telephone communications via a data network, 311, which the computer, 300, is connected, such as a voice over IP call (VoIP). The base unit, 200, includes an audio input (221) and an audio output (220) for connection to audio ports (320 and 321) of a sound card, 310, of the computer, 300, whereby voice signals exchanged during a VoIP call can be conveyed to and from the base unit, 200. The base unit, 200, may include a speaker through port (222), such that computer audio signals can be routed to powered loudspeakers, 400 and 401, when a telephone call is not in operation. Digital control data can also be exchanged between the base unit, 200, and an associated computer, 300, by utilising stereo audio connections between the base and computer, whereby one channel of the stereo connection carries audio signals, while the other channel carries modulated control data signals such as FSK.

Description

TITLE OF THE INVENTION

Cordless Telephone with Computer Interface BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates in general to telephone communications. In particular, the invention relates to a system for conducting telephone calls over either a public switched telephone net Boric, or a data communications network.

A 2. Background Art..

À.. As use of the Intemet becomes more prevalent and access to the Intemet becomes more available, many individuals are beginning to use the Intemet and like ... W computer data networks as an alternative to the conventional telephone system for lo, conducting bi-directional voice communications via the public switched telephone network (PTSN). Conducting a Telephone calls between two or more parties via an IPÀ; À. network such as the Internet, as opposed to via the PTSN, is commonly referred to as "voice over IP" (VolP).

A conventional telephone call conducted between two parties via the PTSN is of course made using a conventional telephone instrument, POTS, which is hard wire connected from the home or office to the telephone company switching equipment and ultimately to a POTS at the other party's location. Conducting a VolP call" between two parties via the Internet VolP is made by each party typically using a personal computer, (PC), though other "Internet appliance" products may be also be used. Instead of

speaking into a typical telephone handset having an integrated earpiece and mouthpiece, the computer user typically speaks into a dedicated microphone to speak to the other party and listens to the other party via the computer's conventional speakers. The microphone and speakers are connected by wires to the computer, and typically to the computer's sound card which provides audio input and audio output connections. Some prior art devices exist which replace the separate microphone and

speaker an angement and provide instead a head set worn upon the user's head which is hard wire connected to the computer.

To place a VolP call to another party a caller uses a PC running a software program designed specifically to provide VolP functionality. An example is Microsoft À- - 51 Corporation's NetMeeUng software product. To initiate an outgoing call, a user enters.

. in' into PC the address of the other user's computer wrth whom a conversation is desired. À À Assuming that the Called party is "on-line" and running the appropriate software, a data.

À connection between the two computers is established with the VolP software serving to: D _ :9 W facilitate the call. Each party to the conversation can speak into their microphone and. -. -.

À--e it; can hear the other party voice on their speakers. The computers process the spoken I'.

audio, and transmit it as a data signal to the one or more additional parties via a computer data network, such as the Intemet. Audio data received from other parties is processed and played audibly through speakers attached to the computer.

VolP calls can also be placed from a computer to a POTS telephone line by routing a call over a data network to remote computer that is configured with a POTS telephone line interface. The remote computer then initiates a POTS telephone call with the intended call recipient, and bidirectionally conveys voice signals between the

- computer data network and the POTS line over which the call is completed. In this way, a call can be placed to a POTS user with limited use of the conventional telephone network While multimedia computers are often equipped with speakers and a standalone microphone, these components often impose pefforrnance limitations in a VolP application. For example, the common positioning of the speakers and microphone often introduces uncontrolled feedback, which may create echoes in the audio path, in turn, disturbing the conversation. Also, many standalone microphones are highly susceptible to picking up background noise proximate the Calling party., contributing

further unwanted interference into the audio path. Furthermore, when a VolP . conference is conducted between a plurality of users, the VolP software running on the À (it). i' PC, such as Microsoft NetMeeting1 the combined feedback and background noise from À À

each party to the conversation often results in a highly objectionable level of noise and.

À - } interference that inhibits communications.

W A highly desirable aspect of VolP, and one which differs from conventional. -.

I-. telephone network communications, is that computer users typically pay flat rates for., access to the Intemet data network, as opposed to timed billing for telephone network access. Therefore, users who already have computer network connections can conduct unlimited VolP voice communications at no extra cost-a feature that can be particularly advantageous for placing long distance calls. Accordingly, VolP calls may be significantly longer in duration than a timed long distance telephone call given that such VolP communications are often thought of as essentially free. However, prior art

VolP hardware constrains a user to the immediate vicinity computer. For example, a

computers speakers and microphone are typically axed in position. Therefore, users are unable to move, for example, to different rooms in a house or office without interrupting the call.

In addition, to the extent that a VolP soflnNare package offers the user the ability to control the nature or characteristics of the communication, such as the volume level, the control can only be exercised by entering commands via the computer keyboard.

To the extent that the VolP software offers the user the ability to learn the identity of the Calling part inflating a VolP conversation, that infommation can only be learned by viewing the computer's monitor. Accordingly, if a user were to string together wires to extend the distance between the computer and the speaker and microphone, the user . 0.

Y controls for the VolP communication become out of reach.

À- 4 Further, a user may find that there are times when a VolP conversation is desirable and that there are times when a conventional telephone call using the PTSN.' it: is appropriate. To have this flexibility the user must maintain duplicate equipment 2 sometimes resulting in unnecessary clutter. If a user elects to use a headset to replace À;^ . !, À o n the computer speaker and microphone to conduct a VolP conversation the user must:.

re-cable the computer by detaching the speaker and microphone from the sound card on the rear of the PC and connect the headset, and then moreover, reverse the connections when the user wishes to use the PC's external speakers.

Accordingly it would be desirable to provide for the ability to conduct a VoiP conversation without being tied to a PC, to remotely control the operation of the VolP software, and to use the same base unit and handset/headset to conduct both a VolP conversation over the Intemet and a traditional telephone conversation over the PTSN,

as well as to use the PC audio capabilities without the need to reconfigure cable connections to the PC.

These and other desirable characteristics of the present invention will become apparent in light of the present specification and drawings.

SUMMARY OF THE INVENTION

The invention is defined in the claims to which reference is now directed. In a broad aspect, the invention provides apparatus to allow cordless telephone communications to be transmitted by a digital network, such as the Internet.

An embodiment of the

SUMMARY OF THE INVENTION

The invention allows telephonic communications to be conducted via a computer communications network without requiring that the user stay in the vicinity of a personal computer. A base unit and a self-powered mobile unit, such as a cordless telephone headset, are used in conjunction with a personal computer. The computer is utilized to set up a voice connection with another computer user. The audio signal transmitted by the other user is applied to a sound card within the computer. The sound card audio output port is then connected to an audio input port on the base unit. The base unit sends the audio input signal to the base unit transceiver for transmission to the mobile unit. Phi À..

w The mobile unit includes a wireless transceiver for receiving signals from and.

it À - transmuting signals to the base unit transceiver. The mobile unit further includes a speaker, which receives a signal from the receiver portion of the mobile unit transceiver, and a microphone, which supplies a signal to the transmitter portion of the mobile unit transceiver. Voice signals are transduced by the microphone, and subsequently À, À-. transmitted back to the base unit. The base unit receives the voice signals, and applies...

them to the base unit audio output port for subsequent transmission to the sound card audio input port Signals received by the sound card audio input port are subsequently digitized and transmitted to another computer via a digital data network.

To better mimic the audio characteristics of conventional public switched telephone systems, a feedback path can be provided in the base unit. The output of the base unit receiver portion can be attenuated, and subsequently mixed in to the base unit transmitter portion input.

Because computer users may desire to utilize their nonrival computer loudspeakers when telephonic communications are not being conducted, the base unit can be provided with a speaker port, to which speakers can be connected. When the mobile unit is not being utilized for a VolP call, a relay connects the base unit audio input port to the speaker port, such that the output of the computer sound card is routed through to the speakers.

The invention can also implement a bi-directional data communications link between the base unit and computer, without requiring any additional cabling or interconnection. This feature can be utilized to implement functionalRy such as the exchange of caller identification information between the base and computer, or .. advanced control of the base unit The voice signals transmitted between the base unit 0 and computer are conveyed on a first one of stereo audio channels on the audio input À.

and output ports. Both the base unit and computer include modulators and.

demodulators, such that the second of the stereo audio channels can be utilized for ' :' transmitting modulated data on the output ports, and receiving modulated data signals. À on the input ports. Both the base unit and computer also include microprocessors, À which process the conveyed data appropriately.

Finally, the base unit can also provide for communications with a conventional telephone network. Specifically, the base unit can include an interconnect, such that the transmitter and receiver portions of the base unit transceiver can be alternatively connected to the conventional telephone network connection, or to the base unit audio input and output ports for communications via the computer data network.

BRIEF DESCRIPTION OF THE DRAWINGS

fig. 1 of the drawings is a diagram of the connection of the present invention to a personal computer toward conducting a voice over IP communication.

Fig. 2 of the drawings is a diagram of the connection ports on the base unit of the present invention illustrating connection to a PC sound card and external speaker set.

Fig. 3 of the drawings is a schematic diagram of the base unit of the present invention providing for connection to the PC sound card as well as the public switched telephone network.

Fig. 4 of the drawings is a schematic diagram of the base unit of the present .. invention providing for connection to the PC sound card as well as the public switched i?. i," telephone network and further providing for the transfer of digital command data . between the PC and base unit '; .-i.i e-_ Jo id À -

À

[DETAILED DESCRIPTION OF THE DRAVVlNGS

While this invention is susceptible to embodiment in many different forms, there are shown in the drawings and will be described in detail herein several specific embodiments.

The present disclosure is to be considered as an exemplification of the principle of the

invention intended merely to explain and illustrate the invention, and is not intended to limit the invention in any way to embodiments illustrated.

The embodiment of Figure 1 includes computer system 300 with sound card 310 installed. Sound card 310 is a typical computer sound card which includes audio inputs and outputs. Computer 300 also includes data network connection 311. Network connection 311 can be one of a number of types of connections commonly employed 15} with personal computer systems, such as a telephone line modem connection to an intemet service provider, a cable modem, or a DSL line. Finally, computer 300 is also W connected to computer monitor 340, providing the user with a visual display. Computer system 300 is configured for the VolP communications. Specifically, it includes - i. W software enabling the initiation of a bi- directional audio communications link with one or CI more additional computers, and optionally with a subsequent POTS telephone line, via network connection 311.

Base unit 200 provides a wireless interface to a mobile communications device, which can be used for conducting telephonic communications. In the illustrated embodiment, a connection is established with cordless headset 100, which includes earpiece 101 and boom microphone 102. It is also contemplated that other user interfaces known in the art could be utilized, such as wireless telephone handset 110.

Cordless headset 100 and base unit 200 communicate via wireless communications

- channel 150. In the illustrated embodiment, base unit 200 provides flexible Voice communications via ether computer 300 and computer data network 320 or a conventional PSTN via connection 260. Moreover, the user can switch readily between communications methods while using a single common interface, cordless headset 100.

(:omputer 300 communicates with base unit 200 via soundcard 310. Figure 2 illustrates the connection between base unit 200 and sound card 310. Base unit 200 includes base audio input port 221, base audio output port 220 and speaker throughput port 222. Base audio input port 221 receives audio signals from computer 300 via connection 211 to sound card audio output 321. Base audio output port 220 transmits audio signals to computer 300 via connection 210 to sound card audio input 320. When computer 30Q is not used for VolP communications, it may be desirable to allow for: -

routing of computer audio signals to external powered speakers 400 and 401, without &.

- requiring the user to manually switch or reconfigure the soundcard audio connection c'-

211. Therefore, in the illustrated embodiment, speaker port 222 is provided on base.

id 200, and is connected to speakers 400 and 401 via connection 212.,...-

,.. Figure 3 illustrates the line interface circu try of base unit 200. Incoming audio signals are received from sound card 310 on audio input port 221. The audio signal on input 221 is applied to DPDT relay 230. When a VolP call is not being conducted, transceiver and control circuit 250 applies a signal to line 234, which places relay 230 into the illustrated position. In this position, audio signals received from sound card 310 are routed through to speaker port 222, such that they can be subsequently connected to powered loudspeakers. Thus, computer 300 can be easily used to listen to music or engage in over activities requiring sound without altering the computer cabling.

However, when a VolP call is initiated, control circuit 250 alters the Status of fine 234 such that relay 230 is switched into its alternate position. Computer 300 can then route incoming voice signals to the user through sound card 310, to base audio input 221. Signals applied to audio input 221 are passed through DC blocking capacitors 233a and 233b, and thereafter connected to the signal combiner comprised of resistors 231 and 232. This signal combiner joins the signals on the left and right stereo channels from audio input 221, and applies the composite audio signal to summing amplifier 240.

Users of public switched telephone networks are accustomed to hearing a certain to level of audio feedback from the telephone microphone into the telephone earpiece.

:.. However, when placing a VolP call, receive and transmit channels are typically independent, such that no feedback whatsoever occurs between the user's microphone Led and earpiece. As-a result, users of VolP communications systems often perceive that the \/olP telephone set sounds dead". Therefore, in order to provide users of Fit telephone VolP communications with a more familiar experience, alternate side tone ... path 270 is provided. Path 270 applies an attenuated copy of the outgoing signal on the base audio output channel to the summing amplifier 240, such that a controlled level of feedback is present on the user's headset. The output of summing amplifier 240 is then applied to buffer amplifier 246 before being input into transceiver and control circuit 250.

Transceiver 250 then broadcasts the audio signal via wireless communications link 150 to remote headset 100, where the audio signal is heard by the user on earphone 101.

During the telephonic communications, the user of headset 100 speaks into boom microphone 102. That audio signal is transmitted via wireless communication

- 150 to base unit 200. The signal is received and demodulated by transceiver and control circuit 250, before being applied to buffer ampirfier 247. Dunng the conduction of a VolP call, the output of amplifier 247 is applied to switch 274. Switch 274 is controlled by signal line 234 from control circuit 250. During placement of a VolP call, switch 274 is closed, such that the output of amplifier 247 is applied to the splitter comprised of resistor 242 and resistor 243, and passed through DC blocking capacitors 244a and 244b, such that the user's audio signal is present on both the left and right channels of stereo audio output 220.

Alternatively, the user of base 200 can utilize user interface 280 to select the public switched telephone network for routing of a telephone call, rather than the : À À

-1 computer data network When transceiver and control circus 250 detects the selection.

'.: OF of the PSTN, switch 274 and relay 230 are positioned into their illustrated states. Thus, the output of amplifier 247 is no longer connected to the audio output jack 220, and signals received by audio input 221 from sound card 310 are routed through to speaker LO jack 222 and, ultimately, speakers 400 and 401. Furthermore, switch 273 is placed into À. r I'd À.

its closed position. Thus, the output of amplifier 247 is applied to hybrid transformer 262 for coupling via switch and line interface 261 to the PSTN through RJ 11 jack 260.

Moreover, transceiver and control circuit 250 applies a signal to line 245 to close switch 275, such that the audio signal from the PSTN is transmitted to headset 100.

Specifically, the line signal on hybrid transformer 262 is applied to summing node 241.

Summing node 241 also receives the input of sidetone cancellation network 271, in order to reduce the feedback level of the user's own transmitted audio onto the headset input. The output of summing amplifier 271 is thereafter applied through switch 275 to

r summing ampirFier 240. Altemate sidetone path 270 is deactivated, because its input is eliminated by the opening of switch 274. The output of summing amplifier 240 is applied to buffer amplifier 246 before being transmitted to the wireless headset via transceiver and control circuit 250.

The above-described embodiment provides for the bi-directional communication of audio signals between the users of wireless headset 100 and computer 300.

Computer 300 can execute various software applications for telephony, such that high-

quality voice communications can be conveniently conducted over data network 320.

In an alternative embodiment, digital data communications can be enabled between computer 300 and base 200, and ultimately headset 100 without requiring Me. O Y additional interconnections. Such data communications can be used to provide..

À À e advanced functionality, such as the transmission of caller identification data between the base unit and the computer, for display on a base unit user interface andlor À; computer monitor 340. Additionally, the operation of the software/computer providing .. for the VolP conversation can be controlled remotely from base unit or headset 100 À..

without the need to actuate the computer keyboard. For example, using the handset or À À base unit the user can alter the volume or actuate other call functions, such as call waiting. The base unK incorporating bidirectional data transfer is illustrated in Figure 4.

Base unit 500 is interchangeable with base unit 200 in the diagram of Figure 1, so its operation will be explained in detail as if it were substituted for base 200 in Figure 1, and only to the extent that this operation differs from that of base 200.

Audio and data signals are received from computer 300 by base 500 on audio input port 521. Dunng the conduction of a VolP call, voice signals are received on a first one of the two stereo audio channels, and are coupled via line 529 to relay 530a.

Relay 530 is switched into its illustrated position, such that the voice signal is applied to line 531, and subsequently to summing amplifier 540. However, the second stereo audio channel on audio input 521 carries a modulated data signal via line! 28. In the illustrated embodiment, a frequency shift key data signal is utilized, although alternative modulation schemes such as DTMF or pulse coding could be employed as well. The FSK data signal is applied to relay 530b' and during placement of a VolP call, is subsequently applied to line 532. The modulated data signal received on conductor 532 À. I: is then routed to FSK demodulator 551. The demodulated data is then applied to I transceiver and control circuit 550, where an integral microprocessor processes the I E, data appropriately.

. - In the reverse direction, transceiver and control circuit 550 can send control data A to computer 300. Specifically, digital data is transmitted from circuit 550 to FSK A.' modulator 552. The output of modulator 552 is then applied to line 543, where it is conducted to a first one of the stereo channels on audio outport 520. The second stereo channel on audio outport 520 receives the users voice signal from line 542, analogously in the operation of base unit 200.

Computer 300 includes software which implements a FSK modem, such that audio signals received from base 500 at the sound card audio input 320 can be demodulated, and the resulting data can be processed accordingly. Similarly, computer 300 also includes software which implements a FSK modulator. Control data which

- - must be sent to base 500 is thereby modulated via software, and the modulated audio data signal is then applied to the appropriate stereo channel of audio output port 321 on sound card 310. Base unit 500 and computer 300 Hereby establish a bi-directional data link using the preexisting audio interconnect without a any additional cabling requirements. Thus, according to the foregoing alternative embodiment, a digital data command to, for example raise or lower the volume, can be initiated by the handset 100, transmitted to the base 500 and in turn transmitted to computer 300 where it is detected and acted upon by the computer. Conversely, the computer 300 can transmit digital data to base 500 to, for example, provide caller-id information to the user located.

it: À.-

remote from computer 300..

A:' The foregoing description and drawings merely explain and illustrate the invention

_ À À

and the invention is not limped thereto except insofar as the appended claims are so limited, inasmuch as Hose skilled in the art, having the present disclosure before them will

W be able to make mod ficaffons and variations therein without departing from the scope of..^ : - Àe the invention. À..

Claims

I claim:

1. A system for conducting voice communications via a digital dam network, the system comprising: a base unit capable of wireless communications, which base unit comprises: a first wireless transceiver, an input port which supplies a signal to a transmitter portion of 5 the first transceiver, and an output port which receives a signal from a receiver portion of the first transceiver; a mobile unit comprising: a second wireless transceiver that is capable of forming a bidirectional wireless communications link with the first wireless transceiver, :3 a speaker that receives a signal from the receiver portion of the transceiver, and a..

e - b microphone that supplies an audio signal to the transmitter portion of the transceiver,..

D i- and À-. a personal computer system in which a sound card is installed, the computer system further comprising a network communications connection to the digital data network, and software for digitally conducting voice communications with one or more.

.. additional computers connected to a data network on which a plurality of computers can À it, communicate, wherein the computer sound card includes an audio input port connected to the base unit audio output port and an audio out port connected to the base unit audio input port.

2. The system of claim 1, in which the mobile unit is a cordless telephone headset.

3. The system of claim 1, in which the base unit is further comprised of an attenuated feedback path from the receiver portion output to the transmitter portion input.

4. The system of claim 1, where the base unit is further comprised of a speaker output port, and a relay positioned between the audio input port and the speaker output port, which relay connects the input and speaker output ports when voice communications are not being conducted via the digital data network.

5. The system of claim 4, the system further comprising a set of powered . loudspeakers connected to the base speaker output port..

-

6. The system of claim 1, in which À - the base unit audio input and audio output ports are stereo; the sound card audio input and audio output ports are stereo; I,.*. the receiver portion of the base unit transceiver applies its output signal to a first 5 stereo channel of the base unit audio output port; the transmitter portion of the base unit transceiver receives its input signal from a first stereo channel of the base unit audio input port; the base unit is further comprised of a microprocessor control circuit, a modulator which receives digital data from the control circuit and applies a modulated output signal 10 to a second stereo channel of the base unK audio output port, and a demodulator which receives modulated digital data from a second stereo channel of the base unit audio

r input port and sends demodulated digital data to the microprocessor control circuit for appropriate processing; and the personal computer system includes a data modem which demodulates a 15 signal received on the second stereo channel of the sound card audio input for subsequent processing by the computer, and modulates data directed to the base unit, the modulated data signal being applied to the second stereo channel of the sound card audio output.

7. The system of claim 1, in which the base unit is further comprised of a telephone network interface for connection to a public switched telephone . .. network,. a switch, which can alternatively connect and disconnect the telephone network . 5 with the base unit transmitter portion input, and the base unit receiver portion output. '. ' it, W

8. The system of claim 6, in which the base unit is further comprised of. À,; ... a telephone network interface for connection to a public switched telephone: network, a switch, which can alternatively connect and disconnect the telephone network 5 with the base unit transmitter portion input, and the base unit receiver portion output.

9. A cordless telephone set for conducting voice communications via a personal computer, the set comprising:

- -. a mobile unit comprising: a wireless transceiver, a speaker that receives a signal from the receiver portion of the mobile unit transceiver, and a microphone that supplies 5 an audio signal to the transmitter portion of the mobile unit transceiver; a base unit capable of wireless communications, which base unit comprises: a wireless transceiver that is capable of forming a bi-directional wireless communications link with the mobile unit wireless transceiver, an audio input port which receives an audio signal from a personal computer for transmission by the transmitter portion of the

1 O base unit transceiver, and an audio output port which receives a signal from a receiver portion of the base unit transceiver for subsequent transmission to the personal computer; w:'. À Hi' whereby an external personal computer can utilize the base unit audio input and t:1 - I À " output ports for the conduction of voice communications.

. ... . 10. The cordless telephone set of claim 9, in which the mobile unit is a cordless W telephone headset.. I, ... B: À '

11. The cordless telephone set of claim 9, in which the base unit is further comprised of an attenuated feedback path from the receiver portion output to the transmitter portion input.

12. The cordless telephone set of claim 9, where the base unit is further comprised of a speaker port, and a relay positioned between the audio input port and the speaker ll

port, which relay connects the input and speaker ports when voice communications are not being conducted by the telephone set

13. The cordless telephone set of claim 9, in which the base unit audio input and audio output ports are stereo; the receiver portion of the base unit transceiver applies its output signal to a first stereo channel of the base unit audio output port; 5 the transmrtter portion of the base unit transceiver receives its input signal from a first stereo channel of the base unit audio input port; the base unit is further comprised of a microprocessor control circuit, a modulator.

... which receives digital data from the control circuit and applies a modulated output signal..

to a second stereo channel of the base unit audio output port, and a demodulator which jfip receives modulated digital data from a second stereo channel of the base unit audio.

input port and sends demodulated digital data to the microprocessor control circuit for . W appropriate processing; !. . whereby the base unit can receive and transmit digital control data via the audio input and output ports.

14. The cordless telephone set of claim 9, in which the base unit is further comprised of a telephone network interface for connection to a public switched telephone network,

-. 5 a switch, which can alternatively connect and disconnect the telephone network with the base unit transmr ter portion input, and the base unit receiver portion output.

15. Mine cordless telephone set of claim 14, in which the base unit is further comprised of.

a telephone network interface for connection to a public switched telephone network, S a switch, which can alternatively connect and disconnect the telephone network with the base unit transmitter portion input, and the base unit receiver portion output.

... À .a. .'.; &" *e In . W. 3: in À.^. .. ..,