Note: Descriptions are shown in the official language in which they were submitted.
--1--
RADIO TRANSMITTING AND RECEIVIMG 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.
S 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 kHæ
in the range 118 to 136 MHz, and ground facilities comm~nicate
10 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
15 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
20 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
25 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 Speciication No. 1 480 418
in the name of Budapesti Radiotechnikai Gyar. However, in an
emergency, or where it is apparent that another transmitter has
30 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. 1 480 418, reference is made to
switching the apparatus to an operational mode in which the
blocking means is made ineffective. It will be apparent that
35 such a provision might well render the provision of a blocking
control circuit in radio transceivers ineffective as a way of
7~
overcoming the origlnal problem of preventing interfering
simultaneous transmissions, since it is possible that many
transceivers would be left permanently switched to the
operational mode in which the blocking means is ineffective,
5 either by oversight or even deliberately. This is particularly
true 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 when not
10 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,
15 transmission blocking means 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 an over-ride circuit whereby operation of the
transmission blocking means may be selectively over-ridden to
20 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
30 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 e~isting
transmission ceases, by holding the selector switch, or
press-to-talk key, in the transmitting mode position.
-
--3--
The invention also provides a transmission control means
for a simplex radio transmitting and receiving apparatus
comprising:
a switching means connectable between the transmit
5 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
10 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 com~rises control signal
15 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
20 press-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.
An advantage of the apparatus of the invention is that it
25 can only be operated to over-ride the transmission blocking
means until the over-riding transmission is finishedO The
apparatus cannot be left in an over-ride mode.
The transmission control means of the invention can be
readily installed in existing V~l~ transceivers and will not
30 affect the operation of the VHF transceiver in any other way.
~s 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
35 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 uni~ on any
--4--
other aircraft has been modified, without affecting the
operation of any other radio. Any modification can be made
within a removable radio unit outsi~e the aircraft, with no
alteration to aircraft wiring. Retraining of aircraft crews is
5 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
10 is shown as being operated to prevent operation of the
transmitter. 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 causeslgrounding of a line 3 from
the transmitter circuit. In the line 3, a switching device 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 pre-determined
strength. The "squelch" circuit serves to suppress the
amplification of signals below a pre-determined 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
''~
1:
--5--
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, f~rther 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 ~ 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.
