GB1603159A

GB1603159A - System of transmitting a service channel in a radio relay system

Info

Publication number: GB1603159A
Application number: GB22929/78A
Authority: GB
Original assignee: Licentia Patent Verwaltungs GmbH; Licentia Oy
Current assignee: Licentia Patent Verwaltungs GmbH; Licentia Oy
Priority date: 1977-06-03
Filing date: 1978-05-26
Publication date: 1981-11-18
Also published as: BR7803522A; CA1101074A; CH630761A5; DE2725063C2; JPS543405A; FR2393478B1; DE2725063A1; SE7806456L; NL7805980A; NL189106C; NL189106B; SE442695B; FR2393478A1; YU128778A

Abstract

Each transmission or reception device of the service channel has a network with terminals for a receiver (Em) and a transmitter (Sd) and with outputs and inputs (FÜan, FÜab, HÖ, SP) for data and voice transmission devices. This network decouples the transmitter from the receiver and the inputs from the outputs for the data and voice signals. The network has a signal output which is connected to a bus (BUS) which interconnects all existing networks of this type. <IMAGE>

Description

(54) A SYSTEM OF TRANSMITTING A SERVICE CHANNEL IN A RADIO RELAY SYSTEM (71) We, LICENTIA PATENT VER WALTUNGS G.m.b.H., of 1 Theodor Stern-Kai, 6 Frankfurt/Main 70, Federal Republic of Germany, a German body corporate, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to a system of transmitting a service channel in a radio relay system in which the service channel is at the low frequency end of the transmission band.

Service telephone line devices are aids to intelligibility and run parallel to radio relay links. They facilitate service calls for the purpose of maintaining operation between the radio relay stations and their relay points. In order to make the intelligibility in the service channel as certain as possible, all of the operating devices have been separated from the transmission and the service channel has been modulated directly on to the radio signal transmitted. Such a method is very expensive since extensive additional devices are necessary chiefly because, not only are telephone conversations to take place via this service channel but signalling signals concerning operating conditions, switching signals to substitute devices, and also measured values, are to be transmitted.

The present invention seeks to simplify this system and to reduce its outlay.

According to the invention, there is provided a system for transmitting a service channel in a two way radio relay system in which the service channel is in the transmission band, wherein there is provided a net-work for each direction of transmission of the service channel, each network having connections for a receiver, a transmitter, and input and output connections for a data transmission device and a speech signal transmission device, each network isolating the transmitter from the receiver, and said input connections from said output connections, and wherein the networks are interconnected by a bus bar to which are applied signal outputs from each of the networks.

The service channel is preferably at the lower frequency end of the transmission band.

Preferably, each network comprises first and second operational amplifiers connected together, the service channel signal incoming from the receiver is supplied to the non-inverting input of the first operational amplifier, the output of which is connected: a) via a resistor to the bus bar (b) via a first voltage divider to the inverting input of the second oper ational amplifier and (c) via a second voltage divider to the inverting input of the first operational amplifier and the non-inverting input of the second operational amplifier is connected to the bus bar via a further resistor, the output of the second operational amplifier being connected to the transmitter.

In order to complete this system it is proposed that the network further comprises third and fourth operational amplifiers connected together, a signal incoming from the data transmission device or the speech signal transmission device at the respective input connection being supplied to the non-inverting input of the third operational amplifier, the output of which is connected:: fa) via a resistor to the bus bar, (b) via a third voltage divider to the inverting input of the fourth oper ational amplifier and (c) via a fourth voltage divider to the inverting input of the third operation al amplifier and the non-inverting input of the fourth operational amplifier is connected to the bus bar and its output is connected to the input of the data transmission device and to the speech signal transmission device via respective further resistors.

Filters may be connected in front of the hearing head and the speech head. The invention may be refined by connecting further transmitters with receivers to the bus bar.

This service channel system has been greatly simplified by connecting together the service channels at a bus bar and is capable of expansion in every respect. Owing to the use of operational amplifiers, insertion of the incoming conversion into the transmitter is completely suppressed.

This is achieved by means of negative feedback of the incoming conversation in the operational amplifier connected in front of the transmitter, by employing a connection to the inverting input of the operational amplifier.

The invention will now be described in greater detail, by way of example, with reference to the drawings, in which: Figure 1 shows the circuit arrangement of the network for a transmitter with a receiver; Figure 2 shows two networks for receivers/transmitters and data transmission device/speech apparatus, which networks are connected via a BUS-line, Figure 3 shows the circuit of a combination at a simple end point, and Figure 4 shows the circuit of a combination at a relay point with substitute devices.

In Figure 1, the incoming service channel from the receiver EM1 to one + input terminal of a first operational amplifier V1 is shown. The input resistor is R1. The output of the operational amplifier V1 is connected: 1. via a resistor R4 to the bus bar designated BUS 2. via a first voltage divider R5/R7 to the inverse input of a section operational amplifier V2 and 3. via a second voltage divider R2/R3 to the inverse input of the first operation al amplifier V1.

The transmitter input Sdl is connected to the output of the second operational amplifier V2. The first + input of this amplifier V2 is connected to the BUS-line via a resistor R8. The BUS-line is terminated by the resistor R9. The resistor R9 is dependent on the number n of networks which are similar and are connected to the BUS-line and is calculated at R9 = R4/n-1. In addition the input resistance of the amplifiers is neglected because REin > > R9.

If a conversation arrives from the receiver Eml, it would pass back to the transmitter Sdl via the output of the first operational amplifier V1 and the resistor R5 and via the second operational amplifier V2. The signal received from the receiver Eml is connected to the inverse input of the second operational amplifier V2 by the voltage divider R5/R7. Both signal parts which have been received from the BUS-line via the resistor R8 and via the voltage divider R5/R7 cancel each other out and become zero so that the transmitter Sdl does not receive any further signal portion from the received signal via the receiver Eml.

The voltage divider R2/R3 between the output and the inverse input of the first operational amplifier V1 and the resistor R6 between the output and the inverse input of the second operational amplifier V2 represent negative feedback which serves to control the entire amplification of the individual amplifiers and to stabilize the degree of amplification.

In Figure 2 two networks for a receiver/ transmitter on the one hand and a data transmission device with speech apparatus on the other hand are shown, these networks being connected together via a BUSline. Here it is a question of a receiver component in which the signal arriving in the receiver Em is supplied to the operational amplifier V1 at the terminal a via the terminal b of a multipoint connector (not shown in greater detail). The details of connecting elements of Figure 1 have been left out here. The output of the operational amplifier V2 is connected to the terminal d and is connected to the transmitter Sd. The BUS-line is connected to the terminal c.

Furthermore, the BUS-line is connected to further operational amplifiers V3 and V4 which are connected together. The incoming line to the data transmission device FUan (terminal e) and the speech head SP of the speech apparatus, which are each isolated via a resistor respectively, are connected to the first + input of the operational amplifier V3.

The output of the fourth operational amplifier V4 leads to the data transmission device FÜab (terminal ) and to the listening head HO of the speech apparatus, Both lines are also isolated via resistors.

Owing to the negative feedback in accordance with Figure 1, which is not shown in its details in Figure 2, the incoming conversations are prevented from being able to run back again into the transmitter. This is true both for the connection transmitter Sd/ receiver Em as well as for the listening and speech heads and for the data transmission device at the terminals Fijan and FÜab.

An embodiment is shown in Figure 3 in which the circuit of a simple terminal is shown. The circuit in the small boxes designated EM1 corresponds to the circuit arrangement in Figure 2 in its details. But here only the transmitter Sdl is added as a small box, whereby the transmitter Sdl is connected to the terminal d of the service channel.

Figure 4 shows the switching combination of devices at a relay point. Here the active devices are drawn in schematically on the left-hand side, comprising the receiver Eml which was shown and described in Figure 2, the transmitter Sdl, and moreover the opposite direction comprising the receiver Em2 and the transmitter Sd2 and on the right-hand side the reserve devices: receiver Eml', transmitter Sdl', receiver Em2' and transmitter Sd2'.

The switches S1 and S2 which are actuated together are electronically controllable switches which switch over to the reserve devices in each case when the active devices fail.

WHAT WE CLAIM IS: 1. A system for transmitting a service channel in a two way radio relay system in which the service channel is in the transmission band, wherein there is provided a network for each direction of transmission of the service channel, each network having connections for a receiver, a transmitter, and input and output connections for a data transmission device and a speech signal transmission device, each network isolating the transmitter from the receiver and said input connections from said output connections, and wherein the networks are interconnected by a bus bar to which are applied signal outputs from each of the networks.

2. A system according to claim 1 wherein the service channel is at the lower frequency end of the transmission band.

3. A system according to claim 1 or 2, wherein each network comprises first and second operational amplifiers connected together, the service channel signal incoming from the receiver is supplied to the non-inverting input of the first operational amplifier, the output of which is connected: (a) via a resistor to the bus bar (b) via a first voltage divider to the inverting input of the second oper ational amplifier and (c) via a second voltage divider to the inverting input of the first operational amplifier and the non-inverting input of the second operational amplifier is connected to the bus bar via a further resistor, the output of the second operational amplifier being connected to the transmitter.

4. A system according to any preceding claim wherein the network comprises third and fourth operational amplifiers connected together, a signal incoming from the data transmission device or the speech signal transmission device at the respective input connection being supplied to the noninverting input of the third operational amplifier the output of which is connected: (a) via a resistor to the bus bar (b) via a third voltage divider to the inverting input of the fourth oper ational amplifier and (c) via a fourth voltage divider to the inverting input of the third operation al amplifier and the non-inverting input of the fourth operational amplifier is connected to the bus bar and its output is connected to the input of the data transmission device and to the speech signal transmission device via respective further resistors.

5. A signal according to claim 4 wherein the non-inverting input of the third operational amplifier is connected to a speech head of the speech signal transmitting device and the output of the fourth operational amplifier is connected to a listening head of the speech signal transmission device.

6. A system according to claim 5, wherein filters are connected in front of the listening head and in front of the speech head.

7. A system according to claim 1, characterised in that further transmitters and receivers may be connected to the bus bar.

8. A system for transmitting a service channel in a two-way radio relay system substantially as described herein with reference to the drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. connected to the terminal d of the service channel. Figure 4 shows the switching combination of devices at a relay point. Here the active devices are drawn in schematically on the left-hand side, comprising the receiver Eml which was shown and described in Figure 2, the transmitter Sdl, and moreover the opposite direction comprising the receiver Em2 and the transmitter Sd2 and on the right-hand side the reserve devices: receiver Eml', transmitter Sdl', receiver Em2' and transmitter Sd2'. The switches S1 and S2 which are actuated together are electronically controllable switches which switch over to the reserve devices in each case when the active devices fail. WHAT WE CLAIM IS:

1. A system for transmitting a service channel in a two way radio relay system in which the service channel is in the transmission band, wherein there is provided a network for each direction of transmission of the service channel, each network having connections for a receiver, a transmitter, and input and output connections for a data transmission device and a speech signal transmission device, each network isolating the transmitter from the receiver and said input connections from said output connections, and wherein the networks are interconnected by a bus bar to which are applied signal outputs from each of the networks.