GB2129656A - Radio transmitting and receiving apparatus - Google Patents

Abstract

A simplex radio transmitting and receiving apparatus, of the type comprising a power supply and radio transmitter 4 and receiver 5 circuits connected thereto, includes current monitoring means 40 between the power supply and the transmitter and receiver circuits to detect the higher current drawn when the transmitter circuit is operating and to operate a warning light 400 or buzzer, preferably after a suitable time delay, to warn that the transmitter is operating, thereby avoiding unintentional tranmissions blocking other tranmissions on the same frequency. <IMAGE>

Description

SPECIFICATION Radio transmitting and 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.

Aircraftair-to-grnund and ground-to-airvoice radio communications take place within the VHF band.

Airlines are equipped with VHF transmitter/receivers ("transceivers") allowing a choice of any of 720 channels spaced at 25 'Hz in the range 118to '88 136MHz, and ground facilities communicate with aircrafton 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 can arise in aircraft radio communications is the problem ofthe "stuck microphone", where a transmitter continues to operate, eitherthrough a fault orthrough the ,press-to-talk switch being inadveritantly pressed, thus interfering with or preventing the operation of other radio apparatus on the same frequency. The present invention prevents or reduces the risk of this problem occurring.

According to the invention, a sirnpie;: radio trans- misting and receiving apparatus comprises a power supply and radio transmitter and receiver circuits connected thereto, and current monitoring means between the power supply and the transmitter and receiver circuits, the current monitoring means being connected to warning means and being arranged to give a first output signal to the warning means when the current monitored corresponds to that required by activation of the transmitter circuit, and to give a second output signal to the warning means when the current monitored corresponds to that required by activation ofthe receiver circuit, the warning means including switching means responsive to the first output signal to operate a warning device.

Preferably, a delay circuit is provided between the switching means any the warning a'evice so thatthe warning device only operates after the afterthetransmission has been proceeded for a predetermined time. This avoids the danger of the operator becoming so accustomed to the warning device that he does not reactto it when the transmission time becomes extended. Typically, the warning device will be a light or an illuminable panel comparable with conventional warning devices within an aircraft cabin. Additionally, or alternatively, the warning device may comprise a sound generating device.

twill be seen that, by drawing the operator's attention to the fact that the transmitter is functioning, the apparatus will prevent inauvertant extended transmission which may interfere with other operators on the same frequency.

Reference is made to the drawing, which is a circuit diagram of an apparatus in according with the invention.

The apparatus comprises a transmitter circuit 4, a receiver circuit 5 and a transmit-enable circuit 3 arranged to select between a transmit mode, wherein the transmitter circuit 4 fu nctions while the receiver circuit is inoperative, and a receive mode, wherein the receiver circuit5 functions while the transmitter circuit is inoperative. Press4o-talkswitches 1 and 2 are operable by, for example, an aircraft's captain and co-pilot, to ground the line to the transmit-enable circuit 3, thus causing itto operate. Power is supplied to the transmitter and receiver circuits via line 43, which is connected to the current monitoring and warning circuit 40.

Line 42 is connected from the circuit 40to the power source for the transceiver, the aircraft 28 volt DC power supply. Thus, the circuitry 40 is connected between the power supply and the transceiver, and the transceiver supply current can be routed through a lowvalue resistor R41 (e.g. 0.01 ohms 5 watt 15 amp rating). The voltage drop across this resistor R41 is directly proportionai to the current through it and this voltage differential is detected and amplified by a differential amplifler44(SN7270N or equivalent) connected to either side of the low value resistor R41 through respective resistors R42 and R43 (each 1OOkD).

The output from the differential amplifier 44 is passed to a comrrlercially-available relay driver 45 (DS3886N or equivalent), for which resistors R46 (350) and R47 (2.5), connected respectively to ground and to the 28Vsupply, give a reference voltage.

In the receive mode of the transceiver, the voltage differmential across the low value resistor R41, amplified by the differential amplifier 44 is below the threshold, adjustably determined by the bridge formed by variable resistor R44 {1 ff) and fixed resistor R45 (1 ES}, to cause the relay driver 45 to energise the relay 20, which thus remains de-ener wised with the contacts 21 thereof open.The contacts 21 are interposed between a commercially-available time delay 24 (Series 6100-1402 by IMl-G Inc. Connedi- cut, U.S.A.) and ground, the time delay 24 being connected by a line 22 to a warning light 400 which in turn is connected to the power supply. Alternatively, an audible warning device may be used, or a combination ofthe two.

The power supply for the differential amplifier 44 and the relay driver 45 is a regulated power supply 25, of conventional design, connected to the 28 volt DC aircraft power supply via line 42.

When the transceiver is switched to the transit mode, the current th rough the resistor R41 increases, thus increasing the voltage differential across the differential amplifier 44.The output of the amplifier 44 is thereby raised to a level where the relay driver 45 is caused to energise the relay 20. The contacts 21 are therefore closed, supplying a ground signal which causesthetime delay 24 to operate and, after a predetermined time, to allow currentto flow in line 22, thereby operating the warning light 400.

In a simpler embodiment ofthe invention, the delay 24 is omitted, the connection to ground via contacts 21 taking the route effectively indicated by the broken line 23. In this simpler embodiment, the warning light will illuminate wheneverthe transmitter circuit of the transceiver is operating.

However, in most circumstances, itwill be preferred to incorporate the delay so that warning is only given when the transmission time becomes unduly extended. This may happen, for example, when a press-to-talk switch as hereinbefore described becomes stuck in a closed position, eitherthrough a fault in the switch, orthrough inadvertant pressure on the switch. Awarning will indicateto the operatorthatthe transmitter is operating and will enable him to take action promptly to prevent other transmissions on the same frequency being blocked.

Claims (3)

1. A simplex radio transmitting and receiving apparatus, comprising a power supply and radio transmitter and receiver circuits connected thereto, and current monitoring means between the power supply and the transmitter and receiver circuits, the current monitoring means being connected to warning means and being arranged to give a first output signal to the warning means when the current monitored corresponds to that required by activation ofthetransmittercircuit, and to give a second output signal to the warning means when the current monitored corresponds to that required by activation ofthe receiver circuit, the warning means including switching means responsive to the first output signal to operate a warning device.

2. An apparatus according to Claim 1,wherein a delay circuit is provided between the switching means and the warning device, whereby the warning device only operates afterthe transmitter has been operating fora predetermined time.

3. Asimplex radio transmitting and receiving apparatus, substantially as described with reference to the drawing.