FR2511565A1 - Transmission circuit for remote listening audio equipment - uses VHF oscillator modulated by AF signals to transmit to receiver in headset or loudspeaker - Google Patents

Abstract

Signals from various sources such as audio equipment are applied to a resistive network forming an electronic microphone circuit. A potentiometer allows the output level to be adjusted. The microphone output is applied through a capacitor (C7) to a choke which blocks HF components. The choke output is applied to the gate of an FET (T1) forming a VHF oscillator circuit whose frequency is adjusted by a capacitor (C8) across a tapped coil (L1,L2). The FET inter-electrode capacitances form part of the tuning circuit. The oscillator output is coupled through a capacitor (C1) to an antenna and its frequency is modualted by the low frequency signals applied through the microphone circuit. The oscillator transmits the modulating signals to receiver circuits in headphone sets. The arrangement is partic. intended for the hard of hearing.

Description

 The present invention relates to a device for remote listening and wireless in particular television, high fidelity chain, tape recorder, record player, this not limited to.

 Under certain conditions the aforementioned devices can have significant drawbacks in use.

 For example, a hearing-impaired person must, in order to have a correct hearing, adjust them to a noise level that is unacceptable to third parties.

 On the other hand, it may also sometimes be necessary to allow certain people in the same place to follow a television program or listen to a disc or magnetic tape without disturbing other people.

 This cannot be achieved with the devices currently offered on the market.

 The invention proposes to overcome these various disadvantages.

According to the invention, this result is obtained with a device allowing remote listening and without wires in particular of television, Hifi system, tape recorder, record player characterized in that it comprises in combination
- a frequency modulation receiver consisting of a wireless headset or a portable frequency modulation station,
- a frequency modulation transmitter connected to the headphone or loudspeaker outputs of the aforementioned devices.

 According to an advantageous characteristic of implementation, and in order to allow its adaptation indifferently to all possible sources, the transmitter will include a device for adjusting the modulation level.

 According to another characteristic of implementation, in the particular case of an audio-prosthetic use for the hearing impaired, the receiver headset with frequency modulation will be equipped with a balance system.

The receiver headsets usable for this application are the receiver headsets already existing in the trade
They will therefore not be described more precisely.

 It is also possible to use a portable frequency-modulated post as a receiver, allowing, for example, the recording of discs or cassettes at a desired location without having to carry the turntable or the tape recorder, or without having to adjust them to a level sound too high.

 The applications of the device according to the invention are multiple.

 The hearing impaired can adjust the sound level of the headphones to their best comfort, and this for each ear, without discomfort for those around them.

 In the same way, it is possible to follow for example a television program or other by suppressing the sound for the entourage.

 In all cases, it is of course possible from a single transmitter to use headphones for the user, which can be interesting for communities, with the additional possibility of listening to different programs.

 According to a more sophisticated variant of implementation, it will be possible to add to the transmitter assembly a microphone which may be plugged into any possible source.

 The applications of the micro transmitter are identical to those previously described, adding the following.

 It is possible to make a duplex link over short distances with two transmitters transmitting on different frequencies (application for games for example). This device can also be integrated into a noise-canceling headset.

The invention will be better understood with the aid of the following description of the electronic circuit of the transmitter, with reference to the appended drawings in which
- Figure I is a possible diagram of the circuit, with a micro transmitter;
- Figure 2 is a variant of the circuit of Figure 1, with removal of the microphone.

 The low frequency signals from the various sources (television, tape recorder, etc.) are applied to 11 inputs on the resistors Ri and R2 (see Figure 2).

 The Pi potentiometer allows you to adjust the level, in order to obtain a complete modulation of the transmitter.

 The resistors R3 and R4 make it possible to attack Tl under an almost constant impedance whatever that of the source.

 The low frequency signals are transmitted by C7 and the "Choke Self" with a Ti gate.

 The "Shock Self" blocks the high frequency component, present on the grid of T1 and thus prevents high frequency from being present on the input.

The oscillator consists of a field effect transistor T1, the inductors L1 and L2, the capacitors
C8, C3 and C5 as well as the inter-electrode capacities of T1.

 Resistors R5, R6 and R7 fix the polarization of T1.

 The C8 capacity allows you to adjust the frequency of the oscillator.

 It is this adjustable capacitor which makes it possible to adjust the emission frequency of the transmitter in the range from 88 to 104 MHz.

 Capacities C6 and C7 are used for decoupling.

 The high frequency present on the antenna is taken from the oscillator by C1.

 Frequency modulation is obtained by applying the low frequency signal to the T1 grid.

 The inter-electrode capacitances of T1 are part of the tuning of the oscillating circuit; as they are functions of the gate-source voltage, we obtain a high frequency frequency modulated by the low frequency signal.

 In Figure 1, the same circuit is shown in a variant with a microphone.

 The adjustment means integrated into the transmitter will allow a transmission frequency in the range of 88 to 104 MHz.

 The potentiometer P1 will adjust the frequency excursion determining the modulation according to the principle of frequency modulation.

 The user will reference the sound level of a set, which he will use on the headset. Then it changes the frequency to arrive at that of emission of the transmitter. It then adjusts the volume to a corresponding level to avoid over-modulation, resulting in distortion. Of course the transmitter will be fitted with a switch.

Claims (4)

1. Device allowing remote and wireless listening, in particular of television, stereo, tape recorder, record player, characterized in that it comprises in combination  - a frequency modulation receiver consisting of a wireless headset or a portable frequency modulation station,  - a frequency modulation transmitter connected to the outputs for headsets or speakers of the aforementioned devices. 2. Device according to claim 1, characterized in that the transmitter comprises a device for adjusting the modulation level. 3. Device according to any one of claims 1 and 2, characterized in that the frequency modulation receiver headset is equipped with a balance system. 4. Device according to any one of claims 1 to 3, characterized in that the transmitter comprises a microphone possibly connectable to the sources