| SE428513B | 1983-07-04 | |||
| US1930046A | 1933-10-10 | |||
| DE952989C | 1956-11-22 |
| 1. | A method of data communication by radio, for which purpose use is made of a standardized series interface (1) which, amongst other things, handles standardized TD (Transmitted Data), RD (Received Data), DCD (Data Carrier Detect) and RTS (Request To Send) signals, a transmitter (6) in which modulation takes place, a receiver (7) in which demodulation corresponding to the modulation takes place, and a common antenna (9) with a changeover switch (8), c h a r a c t e r i z e d in that, in conjunction with modulation, the crystal oscillator of the transmitter is modulated directLy with the TD signal of the series interface following voltage/frequency conversion, in •that, in conjunction with demodulation, the carrier wave and the level of the MF signal of the receiver (7) are detected in order to obtain the DCD signal of the series interface (1), and in that the Level of the LF signal of the receiver (7) is detected and filtered depending on the received DCD signal and the RTS signal of the transmitter in order to obtain the RD signal of the series interface (1). |
| 2. | A method according to Patent Claim 1, c h a r a c t er i zed in that the antenna change—over switch (8) is controlled by the RTS signal. |
| 3. | A method according to Patent Claim 1, c h a r a c t e r i zed in that the LF signal is sampled continuously, and in that the d.c. voltage value obtained from the sampling is able to influence the reference level in conjunction with the detection of the level of the LF signal. |
| 4. | An arrangement for data communication by radio comprising a standardized series interface (1) which at its contact pins (2—5) handles, amongst other things, standardized TD, RD, DCD and RTS signals, together with a transmitter (6) and a receiver (7), connected via an antenna changeover switch (8) to a common antenna (9), c ha ra ct e r i zed in that the TD pin (2) of the interface (1) is connected via a voltage / frequency converter (11) directly to the crystal oscillator of the transmitter (6), in that the MF signal output (12) of the receiver (7) is connected via a carrier wave and level detector (13, 14) to the DCD pin (5) of the interface (1), and in that the LF signal output (15) of the receiver (7) is connected to the RD pin (3) of the interface (1) via a level detector (16) and a filter (17), so arranged as to produce a reliable RD signal on the basis of the RTS signal of the transmitter and the DCD signal. |
| 5. | An arrangement according to Patent Claim A, c h a ra ct e r¬ z e d in that the arrangement includes a sampling circuit (18) connected to the LF signal output (15) of the receiver and so arranged as to monitor a d.c. voLtage level in the LF signal by means of which the reference level of the level detector (16) is regulated. |
The present invention relates to a method of data communication by radio, for which purpose use is made of a standardized series 5 interface which, amongst other things, handles standardized TD (Transmitted Data), RD (Received Data), DCD (Data Carrier Detect) and RTS (Request To Send) signals, a transmitter, a receiver and a common antenna with a change—over switch. The invention also relates to an arrangement for the execution of the method in
10 accordance with the invention, consisting of a standardized series interface which at its contact pins handles, amongst other things, standardized TD, RD, DCD and RTS signals, together with a transmitter and a receiver connected via an antenna change-over switch to a common antenna.
15
Conventional data communication by radio, in which binary characters are transmitted in the form of two different frequencies, makes use of a modem. This is supplied during transmission with a data signal in which the constituent ones and
20 zeros which have two standardized voltage levels are transformed into two different signal frequencies. These are fed into the transmitter part of the radio via its microphone input and, after amplification, are sent on to a modulator in the transmitter part.
25 The sequence described above takes place in reverse order during reception, that is to say the received signal is demodulated in the receiver so that a signal containing two signal frequencies is obtained from it, which frequencies are demodulated by the modem so that the original combination of two d.c. voltage levels
30 is reconstituted.
It will be appreciated that conventional data communication by radio involves double modulation and demodulation, which is in itself unnecessary since the radio is not being utilized to its 35 full capability, and in addition gives rise to the other serious disadvantages outlined below.
A modem of conventional and standardized design has a band width of 3.5 kHz, which is attributable to the fact that this is the band width which was selected in order to achieve satisfactory audibility from telephone communication in return for a 5 reasonable technical and financial input. The standard frequencies used for the binary characters *zero' and 'one' are 2100 Hz and 1700 Hz respectively. What this means, in conjunction with the.specified available band width, is that a conventional modem can permit a maximum of 1500 baud, which is a familiar fact 10 to experts. At these particular frequencies, this means that at least two periods are required in order to detect a character.
In addition a conventional modem has a number of in—built delays, so-called 'hand—shaking* routines, which are included in order to 15* increase the reliability of the transmission. These delays amount to 20-40 s, which is a comparatively long time for a 10-bit character, which is 2 ms at a rate of transmission of 4800 bits/s.
20 Other disadvantages are that a conventional modem is larger than a radio transmitter/receiver, requires a separate power supply, and represents a considerable cost.
The object of the present invention is to make available a method
25 of data communication by radio from which the disadvantages referred to above have been eliminated. In accordance with the invention this is achieved in that the crystal oscillator of the transmitter is modulated directly with the TD signal of the series interface after voltage/frequency conversion, that the
30 carrier wave and the level of the MF signal of the receiver are detected in order to obtain the DCD signal of the series interface, and that the level of the LF signal of the receiver is detected and filtered depending on the received DCD signal and its own RTS signal in order to obtain the RD signal of the series
35 interface.
An arrangement which operates by the method specified in the invention is characterized in that the TD pin of the interface is connected via a voltage/frequency converter directly to the crystal oscillator of the transmitter, in that the MF signal output of the receiver is connected via a carrier wave and level detector to the DCD pin of the interface, and in that the LF signal output of the receiver is connected to the RD pin of the interface .via a level detector and a filter, so arranged as to produce a reliable RD signal on the basis of the RTS and DCD signals.
The invention is described below in more detail with reference to the accompanying drawing, which, in the form of a block diagram, illustrates the construction cf an arrangement in accordance with the invention.
The following accepted abbreviations are used below in respect of signals which occur in a standardized series interface: TD = transmitted data RTS = request to send RD = received data DCD = data carrier detect.
The designation 1 is used in the drawing to indicate a standardized series interface which, at its contact pins 2, 3, 4, 5, handles, amongst other things, the above-mentioned signals. The designations 6 and 7 are used to indicate a transmitter and a receiver which are connected via an antenna change-over switch 8 to a common antenna 9. A frame 10 in the form of a broken line is used to indicate the characteristic features of the invention.
In accordance with the invention the TD pin 2 of the interface 1 is connected via a voltage/frequency converter 11 to the crystal oscillator of the transmitter 6, which is thus modulated directly with a voltage/frequency—converted TD signal. In addition the MF signal output 12 of the receiver 7 is connected to the DCD pin 5
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of the interface 1 via a carrier wave detector 13 and a level detector 14. What this means is that the DCD signal of the interface 1 is obtained after the detection of the carrier wave and the level of the MF signal of the receiver 7. In addition the 5 LF signal output 15 of the receiver 7 is connected via a level detector 16 and a filter 17 to the RD pin 3 of the interface 1. In this way the RD signal of the series interface 1 is obtained after the level of the LF signal of the receiver 7 has been detected and filtered depending on the DCD signal obtained in
10 accordance with the above and its own RTS signal. A sampling circuit 18 is connected to the LF signal output 15 of the receiver 7, which sampling circuit is so arranged as to monitor a d.c. voltage level in the LF signal by means of which the reference leveL of the level detector 16 is regulated. Finally
15 the antenna change—over switch 8 is connected to the RTS pin A of the series interface 1, that is to say it is controlled by the RTS signal.
Although self—evident, it should be mentioned that- all the
20 signals which pass the interface 1, which in reality consists of a plug—in contact with an appropriate number of contact pins, are standardized in accordance with the CCITT. Also omitted from the block diagram are signal level adjustments and similar which are obvious to an expert.
25
The following occurs during transmission: A data signal which is to be transmitted is fed via the TD pin 2 to the series interface 1. After voltage/frequency conversion in the converter 11, it is able to influence the crystal oscillator of the transmitter 6
30 directly. The RTS signal, which is a so-called *hand-shaking' signal at the pin A of the series interface 1, actuates the antenna change-over switch 8 so that the transmitter 6 is connected to the antenna 9. The aforementioned signal also actuates the filter 17 so that any signals from the receiver 7
35 are prevented from reaching the RD pin 3.
During reception the MF signal of the receiver 7 is taken out after the second IF filter of the receiver 7, is detected in the carrier wave detector 13, and has its LeveL detected after amplification and half-wave rectification in the detector 1A, which is preferably of the comparator type, when it constitutes the DCD signal of the receiver at the contact pin 5 of the series interface. The future RD signal is taken out in the form of an LF signal from the receiver 7 after the AF amplifier of the FM detector, and is sampled continuously in the sampling circuit 18, the d.c. voltage value of which is able to influence the reference level of the level detector 16, the output signal of which, after filtering in the filter 17, constitutes the aforementioned RD signal. In conjunction with filtering the RTS and DCD signals are used for controlling the filter 17.
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