RADIO COMMUNICATION SYSTEM

Abstract: A system for radio communication in at least one direction between a transmitter and a receiver. The signal connection of the transmitter or the receiver is coupled capacitively to a power supply conduit of an existing electrical network, the conduit serving as an antenna. The other unit, i.e. the receiver or the transmitter with its associated antenna, is placed at a distance from the conduit. The signal transfer is effected by electro-magnetic radiation between the conduit and the antenna being situated at a distance therefrom.

Description: Radio Communication System The invention relates to a radio communication system, i.e. a method and a device for radio communication in at least o direction between a transmitter and a receiver. The invention is based on a desire to accomplish a paging system, which can be used in a limited area with very simpl means, especially within a large building, such as an offic or a factory building, a hotel, a public building or the li In such a system it is a primary object to achieve a good co operation between the antennas of the transmitter and the receiver. Another object is to enable the use of an existing electrical network for the power supply of the transmitter or the receiver. As appears from the appended claims, according to the inven¬ tion, one uses an existing electrical supply network, e.g. a phase wire of an electrical supply system, as an antenna of one of the units, the electrical supply network being coupled capacitvely, e.g. by means of a capacitor, to the signal connection of the unit. In principle, the antenna of either the transmitter or the receiver may consist of such a existing wiring. In case of a paging system, a central transmitter is prefer¬ ably connected to the electrical network, which in this case serves partly as a power source for the electronic and indication equipment of the transmitter, partly as an antenna in that the signal amplifier output of the trans¬ mitter is 'capacitively coupled to a phase or neutral wire. A certain damping of the signals along the wire will of cour take place, but if the power output is of the magnitude of 50 W, sufficient electromagnetic radiation from the corre- sponding wire or wires can be obtained in the entire buil¬ ding or the like so that the transmitted radiation can be detected by means of portable, battery powered receiver units provided with ordinary ferrite antennas. Other possible applications are data communication, data collection and alarm systems. In the latter case, a number of different transmitters can emit radio signals which are detected by an electrical supply network, which serves as a receiver antenna and is capacitively coupled to an alarm centre. The transmitters as well as the central receiver ma in this case be powered either by the network or by batte¬ ries. The invention will be explained further below with referenc to the appended drawings which schematically illustrate an embodiment in the form of a paging system. Fig. 1 shows a simplified block diagram of a transmitter which is coupled to an electrical network, and a separate r ceiver; Fig. 2 shows an oscillator included in the transmitter; Fig. 3 shows an amplifier included in the transmitter; and Fig. 4 shows a power unit included in the transmitter. The upper part of Fig.l shows a transmitter and the lower part shows a receiver 2. According to the invention, the transmitter is coupled to an existing wiring network, namel an ordinary electrical supply system 3 having group wires comprising a protective earth 4, a neutral wire 5 and a pha wire 6. (220 V alternating voltage) . In the illustrated example, the transmitter 1 constitutes t central unit of a paging system and comprises a control de¬ vice 7 with a microphone 8, a FM-modulator 9, an oscillator an amplifier 11, a power device 12 and a match device 13, t latter being coupled to the amplifier output via a capacito OMPI The control device 7 is connected to the remaining transmitt portions 9-14 by means of a 7-wire cable 15, which partly secures the current supply from the power device 12, partly transmits coded information for addressing a paging device (receiver 2) , which information is transmitted via the devic 9-13 to be described further below. For this purpose, the co trol device is provided with the following means (not shown) and on-off switch, a set of keys for dialling a five-digit code number (e.g. in a 5-tone-CCIR-code) , a display for in- dicating the dialled code number,a transmitter key for emitti the coded information via the devices 9-13, a red light emit ting diode or the like for indicating that such information transmission is being performed, a green light emitting diod or the like for .indicating that transmission of speech is possible, and the microphone 8 (indicated in the figure). The signals from the control device are modulated in the FM-modulator 9 and are transferred to the oscillator 10, the circuits of which are illustrated in Fig. 2. Thus, the oscil lator comprises a s.c. synthesis oscillator consisting of a voltage controlled oscillator 16 (VCO) , a crystal controlled reference oscillator 17, a variable frequency divider 18 connected to the output of the VCO oscillator 16, and a phas comparator 19 connected to the frequence divider 18 and the reference oscillator 17, these components forming a phase- locked loop. The setting of a desired frequency is effected in the frequency divider 18. Thus, at the output of the oscil lator 10, a frequency modulated radio frequency signal is ob¬ tained, preferably having a carrier wave frequency of about 100 kHz and a modulation of about - 3 kHz. In principle, how¬ ever, a carrier wave frequency within the region 20 - 500 kHz can be used. The FM-modulated signal is transferred to the amplifier 11, which is illustrated schematically in Fig. 3. It consists of a power stage without transformer and of the push-pull type, working in class AB, The amplifier portion 19 is fed back via a band pass filter 20 tuned to the transmitter frequency This filter limits harmonics and other non-desired signals. The amplifier output is connected to the capacitor 14 which dimensioned to withstand rather high voltages and currents,e having a capacitance of about 1 μ F and designed to with- stand 600 V and 5A. Hereby, it is possible to connect the amplifier output to the existing electrical network 3. For an impedance match,a match device 13 having variable impedance inserted between the capacitor 14 and the electrical network connection 21, so that the load impedance can be adjusted the impedance of the amplifier 11, and an optimal energy transfer is ensured. The connection to the network also appears from Fig. 4, which shows a circuit diagram of the power device 12 of the transmitter. Thus, the signal output of the chain 9-13 is connected (capacitively via the capaci¬ tor 14) to a phase wire, supplied with 220 V alterating vol tage, by means of an ordinary plug which is connected to a protectively earthed electrical socket. By means of the same electrical socket, the drive power of the transmitter is provided. As appears from Fig. 4, the drive unit comprises for this purpose two separate transformers 22,23 and associated rectifiers 24,25 and capacitor filters 26,27. The upper power supply shown in Fig. 4 is connected, via a conduit 28-28, to the above mentioned on-off switch in the control device 7 and, via said switch, to a relay coil Re 1 in the lower power supply. The arrangement is such tha a transistor Trl, which is connected in series with the rel coil Rel, will conduct only if the plug is turned correctly, i.e. if the conduit F connected to the base of the transist is coupled to the phase wire of the electrical network. Sho the conduit F be coupled to the neutral wire instead, the transistor Trl remains non-conductive, which in turn results* in that a relay switch Rel in the upper power supply remains open. Both power supplies are mutually coupl also in that a relay coil Re2 in the upper supply controls a relay switch Re 2 in the other supply. OM In the lower power supply, there is another relay Re3 which is actuated by the above-mentioned transmitter key of the control device 7. When the conduits F,N and J have been con¬ nected correctly, i.e. to the phase, neutral and earth wires respectively, and all the relays Rel, Re2, Re3 are on, the upper power supply gives a stabilized d.c. voltage of 12 V to the control device 7, the modulator 9 and the oscillator 10, whereas the lower power supply supplies the power ampli- fier 11 with an unstabilized d.c. voltage of 40 V. If, on the other hand, no protective earth is available, or the plug is turned incorrectly, the power device 12 will not give any voltage at all. As illustrated in Fig. 1, the radio frequency signal is tran mitted via the connection (plug - socket) 21 to the phase wire 6 included in the electrical network, the phase wire being presumed to extend all around the building into its various parts. If certain groups are connected to the other two phases, a capacitive transfer coupling can be made so as to enable the signals to be distributed to the entire electr cal network in the building. The phase conductor 6 or conduc tors will hereby serve as an antenna and will radiate radio waves of the particular frequency of about 100 kHz, i.e. a relatively long wave radiation. Actually, a considerable damping occurs along the length of.the conduit counted from the connection 21, but nevertheless the radiated power has turned out to be sufficient for receiving and detecting by means of small, portable, battery driven paging receivers 2 within the entire building in question, since the electrical network normally branches into nearly all parts thereof and, consequently, the distance between a phase conductor 6 and a receiver 2' will be rather short, normally not exceeding 10 m Each receiver 2 comprises a ferrite antenna 29 tuned to the working frequency, a FM-receiver 30 connected to the antenna and, in two branches in parallel to each other, a decoder 31 for detecting the transmitted digit code (e.g. a CCIR-code) , possibly with an associated display 32, and a low fre¬ quency amplifier 33 having a loud-speaker 34 for speech trans mission. Furthermore, the receiver 2 comprises buttons or keys (not shown) for switching the units 30,31,33 on and off as well as switching over between visual indication on the display 32 and acoustic speech transmission via the loud¬ speaker 34. As mentioned above, the receivers 2 are battery powered, the batteries being preferably chargeable via the electrical network when the receivers are not in use as paging units, e.g. at night. As mentioned in the preamble, several applications are pos¬ sible within the scope of the inventive idea. The conduit network can consist of any electrical supply network. Furthe more, either a transmitter or a receiver, or an apparatus serving alteratively as transmitter and receiver, can be capacitively coupled to the wiring network functioning as an antenna. The signal modulation can be performed as de- sired, e.g. by frequency, phase, amplitude or frequency shift modulation. Even in other respects, various modifi¬ cations can be made by those skilled in the art within the scope of the claims. O PI Wlr -

Claims: C L A I M S 1. A method in radio communication in at least one directio between two units, one of which serving as a transmitter an providing a modulated radio frequency signal, whereas the otherunit serves as a receiver and demodulates the received signal, c h a r a c t e r i z e d in that the signal conne tion of one of the units is coupled capacitively to a power supply conduit of an existing electrical network, the con¬ duit serving as an antenna for said one unit, whereas the ot unit with its associated antenna is placed at a distance fr said conduit, and in that the radio frequency signal is tra mitted as electro-magnetic radiation between said conduit and said antenna being situated at a distance therefrom. 2. A method as defined in claim 1, c h a r a c t e r i z e in that the electrical network serves as an antenna as well as a power source for said one unit. 3. A method as ' defined in claims 1 or 2, c h a r a c t e r ¬ i z e d in that one or more phase wires are used as an antenna. 4. A method as defined in claims 2 or 3, c h a r a c t e r ¬ i z e d in that said one unit is connected to a protectivel earthed electrical socket by means of an ordinary plug, the unit being activated only if the plug is turned so that the signal transfer is effected via a phase conduit. 5. A device for radio communication in at least one direc¬ tion between two units (1,2) , one of which serving as a transmitter and comprising an oscillator (10) for providing a radio frequent carrier wave, a modulator (9) for signal modulation of the carrier wave, a power amplifier (11) for amplifying the signal modulated carrier wave, and an antenna coupled thereto, whereas the receiver (2) comprises an antenna (29) and a demodulating circuit (30) for demodula ting the received signal, c h a r a c t e r i z e d in that the signal connection (13) of one of the units (1) is adapted to be capacitively coupled to a power sup- ly con¬ duit of an existing electrical network (3) and serving as an antenna. 6. A device as defined in claim 5, c h a r a c t e r i z e d in that said one unit comprises a power device (12) which is connectable to the electrical network (3) . 7. A device as defined in claim 6, c h a r a c t e r i z e in that the power device (12) as well as the signal connec¬ tion is coupled to the electrical network (3) by means of a ordinary plug and a corresponding socket. 8. A device as defined in claim 7, c h a r a c t e r i z e in that the power device (12) comprises automatically ope¬ rating switching means (Rel, Re2) adapted to activate the unit only in case the plug is plugged into an electrical socket in such a way that the antenna connection (13) is coupled to a phase wire. ^tf

Inventors: BEUDAT ANDRE, HAMLIN INGE, BEUDAT, ANDRE, HAMLIN, INGE
Applicants: STOCKHOLM MOBILTELEFONSERVICE, MOBILTELEFONSERVICE I STOCKHOLM AB
Application year: 1982
Main classification: H04B3
IPC codes: H01Q1, H04B3, H04B5