RADIO TRANSMITTING AND RECEIVING APPARATUS

Abstract: A simplex radio transmitting and receiving apparatus has a transmission blocking means which prevents selection of the transmitting mode of the apparatus while a signal of predetermined strength is being received by the apparatus at the time the press-to-talk key is operated. An over-ride circuit enables the blocking means to be disabled in an emergency or if another transmitter has been left operating in error. The over-ride circuit can be activated by, for example, repeated operation of the press-to-talk key, and ceases to operate when the key is released to return the apparatus to its receiving mode. Also disclosed is a transmission control means which can be used to modify existing transceivers to operate in accordance with the invention.

Description: RADIO TRANSMITTING Ar;D RECEIVING APPARATUS This invention relates to a radio transmitting and receiving apparatus and to a transmission control means for use in a radio transmitting and receiving apparatus. The apparatus is particularly applicable to aircraft voice communications. Aircraft air-to-ground and ground-to-air voice radio communications take place within the VHF band. Airlines are equipped with dual VHF transmitter/receivers ("transceivers") allowing a choice of any two of 720 channels spaced at 25 kHz in the range 118 to 136 MHz, and ground facilities communicate with aircraft on any single channel in that range. It is, therefore, quite normal to have as many as eight aircraft with their transceivers operating on a single VHF channel, i.e. that of a ground facility such as air traffic control. A problem which arises from such a situation is that if two transmitters operate at the same time on the same channel, any receivers tuned to that channel will receive either a jumble of words or a high pitched whistle. The operators of the two transmitters will be unaware that their transmissions are interfering one with the other. While this typically causes no more than a minor nuisance, with a request for each message to be repeated separately, it can cause messages to be misunderstood, with possibly disastrous consequences. To overcome this type of problem, it has been proposed to include blocking means arranged to prevent transmission of a signal by the apparatus while a signal of predetermined strength is being received by the apparatus. Apparatus of this type is disclosed in British Patent Specification No. 1 480 418 in the name of Budapesti Radiotechnikai Gyar. However, in an emergency, or where it is apparent that another transmitter has been left operating in error, some means of over-riding the operation of the blocking means is required. In Budapesti U.K. Patent Specification No. 1 480 4-18, reference is made to switching the apparatus to an operational mode in which the blocking means is made ineffective. It will be apparent that such a provision might well render the provision of a blocking control circuit in radio transceivers ineffective as a way of ov'.rcoming the original problem of preventing interfering sinltaneous transmissions, since it is possible that many transceivers would be left permanently switched to the o± > rational mode in which the blocking means is ineffectivH, either by oversight or even deliberately. This is particularly tru in the case of aircraft radio apparatus, where the inconvenience or even potential danger in having to operate a control on the transceiver set would dissuade aircrew from repeating the operation to cancel the over-ride their not required. Accordingly, the present invention provides a simplex radio transmitting and receiving apparatus, comprising a selector switch, operation of which causes the apparatus to change from a receiving mode into a transmitting mode, transmission blocking means arranged to prevent selection of the transmitting mode if a signal of predetermine-l strength is being received by the apparatus at the time the selector switch is operated, and an over-ride circuit whereby operation of the transmission blocking means may be selectively over-ridden to enable the transmitting mode to be selected, the improvement which comprises means for generating a control signal, means within said over-ride circuit responsive to said signal to initiate operation of-said over-ride circuit, and means within said over-ride circuit responsive to return of said selector switch to select the receiving mode of the apparatus to terminate operation of said over-ride circuit. The control signal can be generated by repeated operation of the selector switch, or press-to-talk button, for example within a predetermined time interval, or by operation of a separate over-ride switch. The blocking means may also be arranged to continue to prevent selection of the transmitting mode if the received signal ceases while the selector switch is being operated to select the transmitting mode, thereby preventing a user of the apparatus from gaining priority to transmit, when the existing transmission ceases, by holding the selector switch, or press-to-talk key, in the transmitting mode position The invention also provides a transmission control means for a simplex radio transmitting and receiving apparatus canprising: : a switching means connectable between the transmit press-switch and the transmitter control circuit of said apparatus; a detector connectable to the receiver circuit of said apparatus, the detector being operably connected to said switching means and arranged to detect receipt of a signal by the receiver, whereby when a signal is detected the detector causes the switching means to open the circuit between the press-switch and the transmitter circuit until said signal is no longer detected; and an over-ride circuit which comprises control signal detecting means, an over-ride control circuit, and mode-detecting means, the over-ride control circuit being activated by the control signal detecting means upon receipt of a control signal to over-ride operation of the switching means by the detector to close again the circuit between the press-switch and the transmitter circuit, the modedetecting means detecting the mode in which the apparatus is operating, and serving to de-activate the over-ride control circuit when a return to the receiving mode is detected. An advantage of the apparatus of the invention is that it can only be operated to over-ride the transmission blocking means until the over-riding transmission is finished. The apparatus cannot be left in an over-ride mode. The transmission control means of the invention can be readily installed in existing VHF transceivers and will not affect the operation of the VHF transceiver in any other way. As the necessary circuitry can be incorporated into a micro-electronic circuit, the additional weight of the modified radio is negligible, an important factor in aircraft. If the control means fails for any reason to operate, the radio reverts to its former state, operating as if the device were not present. Modification of a single unit gives the aircraft the advanges of the invention even if no other unit on any other aircraft has been modified, without affecting the operation of any other radio. Any modification can be made within a removable radio unit outside the aircraft, with no alteration to aircraft wiring. Retraining of aircraft crews is not necessary, since operation of the modified units is essentially the same as before modification. Reference is made to the drawing, which shows a circuit block diagram of part of an aircraft VHF radio apparatus in according with the invention. The transmission control means is shown as being operated to prevent operation of the transn!tter. The transmitter circuit of the apparatus is caused to operate by the closure of one of two press-switches 1 and 2, respectively the captain's and co-pilot's "press-to-talk" keys, which causes grounding of a line 3 from the transmitter circuit. In the line 3, a switciz 3 1evizG 4 is connected so as to be able to make or break the line 3 selectively. When the line 3 is broken, the "press-to-talk keys 1 and 2 are prevented from operating the transmitter. The switching device 4 includes a detector 4a connected through a line 5 to any convenient point in the "squelch" circuit of the receiver at which the voltage is increased in response to receipt of a radio signal of predetermined strength. The "squelch" circuit serves to suppress the amplification of signals below a predetermined level so that unwanted sound is not heard when the desired transmissions are not being received. The switching device 4 is thus arranged to operate when the "squelch" circuit allows a signal to pass to the amplifier, breaking the contact between the "press-to-talk" keys 1 and 2 and the transmitter circuit. An over-ride device 6 is connected to the switching device 4, and has a connection 7 to the common line from the keys 1 and 2. The over-ride device 6 is arranged to detect two or, if desired, a greater number of operations of either of the keys 1 and 2 and to cause re-set of the switching device 4 to close the line 3 on the second or last operation of-the key since the switching device 4 was activated to open the line 3. Thus, only if the *blocking" transmission from another transmitter continues will the second or final operation of the key serve to over-ride the switching device. If the transmission ends and re-starts after the first or penultimate operation of the key, further operations of the key will be necessary to over-ride the switching device 4. As an alternative, the over-ride device may be arranged to respond only to repeated operations of a key within a predetermined time interval. While the switching device 4 is represented in the diagram as an electro-mechanical relay, it will be appreciated that the switching may readily be effected electronically. Electronic circuits will also be suitable for the over-ride device 6. In aircraft radio, a 'sidetone' is fed by the apparatus to the captain's and co-pilot's headsets during transmission so that they may hear their transmission. It will be seen that if the transmitter is prevented from operating, the received signal will continue to be heard when speaking into the transmitted microphone, immediately indicating that the switching device has operated. Although the invention has been described with reference to VHF radios in aircraft ground/air and air/ground communications, it will be understood that the invention is applicable to other types of radio and to other uses than with aircraft.

Claims: CLAIMS 1. A simplex radio transmitting and receiving apparatus, comprising a selector switch (1,2), operation of which causes the apparatus to change from a receiving mode into a transmitting mode, transmission blocking means (4) arranged to prevent selection of the transmitting mode if a signal of predetermined strength is being received by the apparatus at the time the selector switch is operated, and over-ride means (6) whereby operation of the transmission control means may be selectively over-ridden to enable the transmitting mode to be selected, characterised in that the over-ride means (6) is adapted to operate upon receipt of a control signal and to cease to operate when the receiving mode of the apparatus is again selected. 2. Apparatus according to Claim 1, characterised in that the control signal is generated by repeated operation of the selector switch (1,2) within a predetermined time interval. 3. Apparatus according to Claim 1, characterised in that the control signal is generated by operation of a separate over-ride switch. 4. An apparatus according to Claim 1, 2 or 3, characterised in that the selector switch (1,2)is a spring-biassed press-switch. 5. Transmission control means for a simplex radio transmitting and receiving apparatus comprising a selector switch (1,2), operation of which causes the apparatus to change from a receiving mode into a transmitting mode, the control means comprising: a switching means (4) connectable between the selector switch and the transmitter control circuit of the apparatus; and a detector connectable to the receiver circuit of the apparatus and operably connected to the switching means, whereby, when the detector detects a received signal in the receiver circuit of a predetermined strength, the switching means is operated to open the circuit between the selector switch and the transmitter control circuit until the signal is no longer detected; ; characterised in that the control means also includes an over-ride circuit (6) which comprises control signal detecting means, an over-ride control circuit, and mode-detecting means, the over-ride control circuit being activated by the control signal detecting means upon receipt of a control signal to over-ride operation of the switching means by the detector to close again the circuit between the selector-switch and the transmitter circuit, the mode-detecting means detecting the mode in which the apparatus is operating, and serving to de-activate the over-ride control circuit when a return to the receiving mode is detected.

Inventors: CORRIGAN, NIGEL MATTHEW
Applicants: CORRIGAN, NIGEL MATTHEW
Application year: 1982
Main classification: H04B1
IPC codes: H04B1