WO1997026633A1

WO1997026633A1 - Mobile telephone warning device

Info

Publication number: WO1997026633A1
Application number: PCT/SE1997/000034
Authority: WO
Inventors: Tonny Olsson
Original assignee: Duhs, Henry
Priority date: 1996-01-15
Filing date: 1997-01-14
Publication date: 1997-07-24
Also published as: SE505825C2; SE9600126D0; SE505825C3; AU1326397A; SE9600126L

Abstract

A mobile telephone warning device has a battery-operated (3) detector circuit of low current consumption which is comprised of a transistor switch (2-8, C1, C2, R1, R2, R3, D) that is operative in detecting radio frequency signals captured via an antenna (1). The transistor is connected regeneratively via a low-pass filter (5, 7, C1, C2, R1, R2, D), which enables the transistor to self-adjust its operating point and therewith obtain optimal sensitivity.

Description

MOBILE TELEPHONE WARNING DEVICE

The present invention relates to a mobile telephone warning device according to the preamble of Claim 1.

Mobile telephones are, in principal, a combined radio transmitter and radio receiver and are adapted to transmit signals on radio frequencies. The mobile telephone normally sends a radio signal to a link in the mobile telephone system informing the link of its availability for communication.

The problem with mobile telephones is that they are liable to interfere with sensitive equipment, for instance equipment in aircraft and in hospitals.

Mobile telephone warning devices are known in practice. When these devices sense the presence of an active mobile telephone, they trigger an alarm which clearly indicates to the owner of the telephone that the telephone should be switched off. A telephone warning device is, in principal, comprised of a radio receiver that is sensitive to the frequency range of the telephone itself and that triggers an alarm when sensing a signal level that exceeds a given threshold value.

Mobile telephone warning devices will preferably be easy to install, not require connection to the mains network when used in aircraft for instance, or in other mobile use, and will therefore preferably be battery operated. It is also necessary for the warning device to be operable over long periods of time, for instance over a twelve month period. Consequently, service routines (battery changes) will, in practice, be spaced several months apart, preferably twelve months apart.

However, known mobile telephone warning/detecting devices have a relatively high current consumption. These known devices should therefore be mains connected in practice, which limits their use. Accordingly, the object of the present invention is to provide an easily moved mobile telephone warning device that while being battery operated still has long maintenance intervals.

The inventive mobile telephone warning device is defined in the following claim 1.

Further developments of the inventive warning device are defined in the dependent claims.

The inventive warning device includes an antenna and a battery operated detector circuit which, through the medium of said antenna, detects the presence of an active mobile telephone by sensing a radio frequency output signal transmitted therefrom, while the detector circuit has an output whose output signal is operative in triggering an alarm when an output signal of mobile telephone frequency captured by the antenna exceeds a set bottom limit value. According to the invention, the detector circuit includes a transistor switch that is adapted to detect radio frequency signals and that is regenerativley coupled via a low-pass filter so as to self adjust its operating point, whereby the transistor switch obtains optimal sensitivity.

Because the detector/transistor switch constantly has optimal sensitivity, the current consumption is also minimised. It can thus be said that as a result of automatic amplification control, the detector acquires low current consumption so as to enable the device to be run on batteries even when long battery change periods are required or desirable.

The mobile telephone warning device will now be described with reference to an exemplifying embodiment thereof and also with reference to the accompanying drawings, in which a figure 1 illustrates schematically a detector circuit belonging to a mobile telephone warning device.

Shown in figure 1 is a circuit that includes two parallel conductor branches 7, 8 that are connected to one another at points 2 and 6. An output signal, referenced Ut, can be taken out at point 6. The circuit is supplied with current at point 6 from a current source 3 (battery) via a resistor R3. Arranged in the conductor 7 is a coil 5, a first capacitor Cl, a voltage divider comprised of resistors R1,R2, a second capacitor C2, and a diode D. The second conductor 8 includes a transistor 4. An antenna 1 is connected to the point 2.

The detector circuit illustrated in figure 1 is comprised of a transistor switch of low current consumption. The circuit detects radio frequency signals via the antenna 1, and includes a feed-back low-pass filter 5, 7, Cl, C2, Rl, R2, D, which enables the transistor to self-adjust its operating point. Optimal sensitivity is achieved in this way. The device includes a battery pack 3 and the capacitors Cl, C2 are charged when a voltage is applied to the circuit by the battery pack. The capacitor Cl therewith obtains a voltage of about 0.65 volt, whereby the same voltage will lie across the base 41 to the emitter 42 of the transistor 4. The voltage across the capacitor C2 is determined by (set with) the divider R1/R2. The voltage across R3 then becomes the difference between the supply voltage and the voltage across the transistor C2 minus the forward voltage across D. The current consumption is therewith obtained across R3. In this stable state, the detector is sensitive to alternating voltages delivered to the base of the transistor 4. The alternating voltage causes current consumption through the transistor 4 to increase, so that the voltage will fall to earth on the output. The output signal Ut activates an alarm, which may be an acoustic or an optical alarm for instance.

Claims

1. A mobile telephone warning device comprising an antenna (1) and a battery-operated (3) detector circuit (1-8, Rl, R2, R3, Cl, C2, D) that via the antenna (1) senses radio frequency output signals sent by an active mobile telephone, wherein the detector circuit has an output whose output signal (Ut) functions to trigger an alarm when the antenna (1) captures an output signal of mobile telephone frequency that exceeds a set bottom limit value, characterised in that the detector circuit includes a transistor switch that is regeneratively coupled through the medium of a low-pass filter (2-8, Cl, C2, D, Rl, R2, R3) for self-adjustment of its operating point.

2. A mobile telephone warning device according to claim 1, characterised in that the detector circuit includes two parallel conductor branches (7, 8), wherein one connection point (2) of the conductor branches (7, 8) is connected to the antenna (1) and the other connecting point (6) of said conductor branches (7, 8) is connected to a current supply battery (3) via a resistor (R3) , wherewith the detector output signal can be outputted at the second coupling point (6) between the branches (7, 8) ; in that when seen from the first connection point (2) one conductor branch (7) includes a coil (5), is connected to earth via a capacitor (Cl), includes a voltage divider (R1/R2), is connected to earth via a capacitor (C2), and includes a diode (D) that conducts towards the first point (2), whereas the second conductor branch (8) includes a transistor (4) whose emitter (42) is connected to earth, whose base (41) is connected to the first point (2), and whose collector (43) is connected to the second connecting point (6) .