GB2285199A - An alarm system for a radio transmitter - Google Patents

Abstract

An alarm system 40 for an unmanned radio transmitter installation for relaying a stereo radio signal from an associated radio station. The alarm system 40 has one or more sensors 41 to monitor a desired condition such as the fuel level in a fuel tank for an emergency generator at the installation. Means 43 is provided for stripping off the stereo pilot tone form the radio signal in response to a sensed alarm condition, the transmitter installation then broadcasting a mono radio signal. A tuner 31 provided at the radio station operates a warning lamp 46 upon reception of the mono radio signal. <IMAGE>

Description

"An Alarm System This invention relates to an alarm system for an unmanned radio transmitter installation.

It is technically preferable and usual for all radio stations to have their high power transmitters located at remote sites. These are in the main unmanned and automated in as much as possible. A problem with these remote transmitter installations is that a potentially serious emergency condition may not be noticed until it is too late or luck deems that routine checks uncover the condition.

Emergency conditions can arise in a number of situations.

For example, the electrical mains supply can fail, due to burglary, or automated switch over to a back-up transmitter.

For example, in one type of installation if the mains power supply fails an engine driven emergency electrical generator will cut in automatically to maintain power supply and to continue operation of the installation with only a five second delay. This will however have no delay when switching back to the mains electrical supply when this is restored. Therefore, there is no way to know in the radio station for how long the generator at the remote transmitter installation ran. There is the possibility of the fuel supply for the emergency generator running out as most maintenance is at relatively long intervals and power often fails during the night when it is less likely to be noticed by station personnel.

In the event of a break-in to the transmitter installation, various problems may arise such as the intruder may be injured, expensive equipment may be vandalised or stolen, or back-up batteries or generator start batteries may be stolen which would subsequently result in no emergency generator start during power failure.

An automatic switch over to a back-up transmitter arises when a fault develops in the main transmitter and the radio signal is automatically switched through a back-up transmitter immediately. This results in no loss of radio signal as it is very quick and therefore no one would know the station was running on its back-up until that failed and then there would be total outage with both transmitters inoperative, with no further spare transmitter. This is an extremely serious situation and can arise quite easily in totally automated installations.

Most modern transmitters are designed for automatic start up and power control and can run unattended for long periods without any difficulty. It is normal however, to carry out routine checks on the transmitter installation on a regular basis, however these checks may be two to three weeks apart. If the emergency generator began running a day or two after a check, then the generator could be running for a sufficiently long period to run out of fuel before the next check. Further, the back-up transmitter may be in operation for periods unknown to anyone in between checks. While ideally routine maintenance is carried out at regular intervals, this is not always possible due to outside factors, for example, pressure of other maintenance work, bad weather, etc.

A remote emergency warning system is therefore desirable to indicate to station personnel an emergency condition at the remote transmitter installation. It is possible to use a system known as Sub-carrier Audio (SCA) to encode telemetry about the conditions at the installation. This then is decoded at the studio control room at the radio station. However, the installation of an SCA system is relatively expensive and also uses the SCA part of the broadcast spectrum. This is not always legally permissible. Further, there is some indication that in future radio stations will use the SCA part of the broadcasting spectrum to give updated information on traffic, or on radio relay frequency changes, to automatically re-tune your radio to a relay of the listened-to station on a different frequency.Experiments are currently ongoing on this system known as Radio Data System and this will preclude the use of the SCA part of the broadcasting spectrum for site telemetry.

The present invention is directed towards overcoming these problems.

In its broadest sense the present invention relates to the use of the pilot tone associated with stereo radio signals for carrying information. The invention is particularly concerned with the monitoring of critical conditions at an unmanned radio transmitter station and relaying information concerning the monitored conditions to the radio station using the pilot tone.

According to the invention there is provided an alarm system for an unmanned radio transmitter station for relaying a radio signal from a radio station, the alarm system comprising sensing means to monitor a desired condition at the installation, and means to control the pilot tone in the radio signal transmitted from the installation in response to the sensed condition for regulating operation of an associated warning means.

In a preferred embodiment of the invention, the means to control the pilot tone is a filter operable to remove the pilot tone from the radio signal, and switching means associated with the filter which is operable to direct the radio signal through the filter in response to a sensed alarm condition.

In a further embodiment the sensing means has two or more alarm detectors connected to a pilot tone filter controller which is operable in response to a detected alarm to switch the pilot tone filter on and off in a coded manner associated with each alarm detector, the warning means having a decoder associated with the pilot tone filter controller for regulating operation of an alarm indicator associated with each alarm detector.

In another embodiment of the invention the warning means comprises a tuner operably connected to a visual and/or audible alarm indictor, the tuner controlling a relay operated normally open switch in an alarm indicator power supply circuit, the tuner operable to close the switch to operate the alarm indicator on detection of an altered or absent pilot tone in the radio signal broadcast from the transmitter installation.

In another embodiment a timer is provided associated with the pilot tone filter switching means to disengage the pilot tone filter after a preset time period.

In a further embodiment the alarm detector comprises a float switch for a fuel tank for an engine of an emergency electrical generator, the float switch operably connected to a relay operated switch for directing the radio signal through the pilot tone filter in response to detection of low fuel level in the fuel tank.

The invention will be more clearly understood from the following description of some embodiments thereof, given by way of example only with reference to the accompanying drawings in which: Fig. 1 is an illustration of a composite stereo radio signal; Fig. 2 is a diagrammatic illustration of a radio station and an associated remote transmitter installation; Fig. 3 is a diagrammatic illustration of an alarm detection portion of the alarm system; Fig. 4 is a diagrammatic illustration of a filter portion of an alarm system according to the invention; Fig. 5 is a diagrammatic illustration of an indicating portion of the alarm system; Fig. 6 is a diagrammatic illustration of another alarm system according to the invention; and Fig. 7 is a diagrammatic illustration of a further alarm system according to the invention.

Referring to the drawings, and initially to Figs 1 to 5 thereof, an alarm system according to the invention will be described.

Fig. 1 shows a composite stereo radio signal 1 comprising a mono audio signal 2, a pilot tone control signal 3, a stereo left hand audio signal 4 and right hand audio signal 5. A Sub-Carrier Audio (SCA) signal 6 may also be provided. This composite signal 1 is transmitted from a studio 10 by means of a UHF transmitter 11 to a remote unmanned radio transmitter installation 12 which is typically mounted on a mountain top for example. The installation 12 has a UHF receiver 14 and a VHF transmitter 15 in which the composite signal 1 is converted to VHF. When a stereo tuner receives the composite signal 1 from the transmitter 15, the tuner on detecting the pilot tone 3 separates the audio left signal 4 and audio right signal 5 for delivery to left and right speakers of the tuner respectively. If the pilot tone 3 is not detected the composite signal goes to both speakers.

According to the present invention an alarm detector 20 is provided at the installation 12. By way of example, in this case, the alarm detector is monitoring the condition of a fuel tank 21 containing fuel 22 for an engine which drives an emergency electrical generator (not shown). It will be appreciated, however that any other desirable condition at the installation may be monitored. A float switch 24 is provided within the fuel tank 21. When the fuel level within the fuel tank 21 falls to a predetermined level the float switch 24 operates a relay 26 which in turn operates a switch 28 (Fig. 4) to direct the signal 1 through a filter 30 for removal of the pilot tone 3 from the signal 1. A modified tuner 31 (Fig 5) within the studio 10, on detecting a monosignal only operates a relay 32 to illuminate a warning lamp 33.

Thus, studio personnel are alerted to the alarm condition at the remote transmitter installation 12. An engineer can then visit the transmitter installation 12 to correct the fault before possible shut-down of the transmitter installation 12 occurs.

It will be appreciated in its broadest sense the invention proposes the use of the pilot tone as a means of information transfer, in this particular case the information being the status monitoring of critical functions or conditions at a remote VHF transmitter site.

It must be accepted that any condition which threatens to put the transmitter off the air at short notice unknown to the station management or staff justifies some alteration to the station signal. Degradation would not be acceptable but a switch to mono from stereo for the time taken to correct the emergency or for very short intervals would be acceptable if the alternative is no output for an unknown length of time due to total shut-down of the remote transmitter installation resulting in at best loss of earnings and at worst possible injury to personnel or loss of life or damage to expensive equipment.

It is envisaged that the principle of altering the pilot tone could further be extended to include multiple telemetry from the remote transmitter installation for short bursts of stereo elimination. These bursts would be decoded and cause different appropriate indicators to let the station know which of a number of conditions have gone critical. An alarm system 40 of this type is shown diagrammatically in Fig. 6. Parts similar to those of the alarm system described with reference to Figs 1 to 5 are assigned the same reference numerals. In the alarm system 40 various inputs 41 from detectors monitoring desired conditions at the installation 12 are used to operate a filter controller 43 which causes the pilot tone filter 30 to switch on and off at a particular rate associated with the detected alarm.The tuner 31 at the studio has an associated decoder 45 which controls lighting of an associated alarm lamp 46 associated with the detected alarm condition.

Referring now to Fig. 7 there is illustrated a modified alarm system 50 which is largely similar to the alarm system of Figs. 2 to 5 and like parts are assigned the same reference numerals. In this case, two level sensors are provided in the fuel tank 21, namely a critical low level switch 52 which operates in similar fashion to the float switch described previously, and mounted above the critical level switch 52 is a low level indicator switch 54. When the fuel drops below the switch 54 this triggers a timer integrated circuit 55 which has a variable period i.e. the output can be held high from 0 to 5 minutes (greater or lesser if needed).An output from the timer 55 goes to an "OR" gate 56 which turns on the relay transistor to operate the relay 26, switching the composite radio signal through the filter 30 to strip off the pilot tone, thus holding the stereo off for the period of the delay in the timer integrated circuit 55. After the set time delay the timer integrated circuit 55 toggles back and the relay 26 is released thus returning the stereo signal. Within the radio station 10 the alarm lamp 33 will have illuminated for the period the relay 26 is held in, switching off when the relay 26 is released. If station personnel see the lamp 33 within the period it is on an engineer can be sent out to correct the fault.Even if the early warning signal is missed when the critical low level alarm 52 is actuated the relay 26 is held in permanently to maintain the indicator lamp 33 on until the fault condition is corrected.

It could also be arranged that when the warning lamp 33 is switched on initially in response to the switch 54 it remains on permanently until cancelled by station personnel, the time 55 effectively being used to switch on the lamp 33 and then cutting out to allow stereo broadcasting to resume.

It will be appreciated that instead of or in addition to the warning lamps an audible warning may be given.

Advantageously the use of the pilot tone for information transfer according to the invention does not use any extra band width. An alarm system based on the use of the pilot tone is relatively simple and inexpensive to produce and install.

The invention provides the use of the pilot tone of a composite signal to act as a vehicle for any kind of information transfer. The information may be transferred by eliminating the pilot tone. It is also possible to generate a modulated pilot tone at the remote transmitter installation, if the composite signal was to be generated at the remote transmitter installation by feeding left and right audio signals up the links to the stereo generator.

This opens up possibilities of amplitude modulation or other possible forms of modulation of the pilot tone which could again carry information.

The invention is not limited to the embodiments hereinbefore described, but may be varied in construction and detail.

Claims (7)

1. An alarm system for an unmanned radio transmitter installation for relaying a radio signal from a radio station, the alarm system comprising sensing means to monitor a desired condition at the installation, and means to control the pilot tone in the radio signal transmitted from the installation in response to the sensed condition for regulating operation of an associated warning means.

2. An alarm system as claimed in claim 1 wherein the means to control the pilot tone is a filter operable to remove the pilot tone from the radio signal, and switching means associated with the filter which is operable to direct the radio signal through the filter in response to a sensed alarm condition.

3. An alarm system as claimed in claim 2 wherein the sensing means has two or more alarm detectors connected to a pilot tone filter controller which is operable in response to a detected alarm to switch the pilot tone filter on and off in a coded manner associated with each alarm detector, the warning means having a decoder associated with the pilot tone filter controller for regulating operation of an alarm indicator associated with each alarm detector.

4. An alarm system as claimed in any preceding claim wherein the warning means comprises a tuner operably connected to a visual and/or audible alarm indicator, the turner controlling a relay operated normally open switch in an alarm indicator power supply circuit, the tuner operable to close the switch to operate the alarm indicator on detection of an altered or absent pilot tone in the radio signal broadcast from the transmitter installation.

5. An alarm system as claimed in any preceding claim wherein a timer is provided associated with the pilot tone filter switching means to disengage the pilot tone filter after a preset time period.

6. An alarm system as claimed in any of claims 2 to 5 wherein the alarm detector comprises a float switch for a fuel tank for an engine of an emergency electrical generator at the radio transmitter installation, the float switch operably connected to a relay operated switch for directing the radio signal through the pilot tone filter in response to detection of low fuel level in the fuel tank.

7. An alarm system substantially as hereinbefore described with reference to the accompanying drawings.