WO1995025359A1

WO1995025359A1 - Battery-powered amplified television aerial

Info

Publication number: WO1995025359A1
Application number: PCT/IT1995/000037
Authority: WO
Inventors: Gianfranco Librandi
Original assignee: Tci Telecomunicazioni Italia S.R.L.
Priority date: 1994-03-15
Filing date: 1995-03-15
Publication date: 1995-09-21
Also published as: ITMI940480A0; IT1271745B; ITMI940480A1; TW257904B

Abstract

An amplified television aerial includes a dipole (1) for the UHF band, a pair of rods (2) for the VHF band and an amplifying section consisting in a double-stage amplifier (G1, G2), each of said amplifying stages including an ultra-low bias voltage transistor (TR1, TR2) operating on a voltage not greater than 3V, which is supplied by a pair of 1.5V AA batteries housed in a relevant compartment (4).

Description

"BATTERY-POWERED AMPLIFIED TELEVISION AERIAL "

The present invention relates to amplified TV aerials, and in particular to a battery-powered amplified aerial. It is known that amplified aerials are usually connected to the electrical network and supplied with 220V in order to carry out their amplifying function of the television signal. Owing to the ever increasing success of portable TV sets operating on a 12V supply, typically from the starter battery of a car, also specific aerials for said use on 12V have been developed. Eventually, completely independent TV sets, i.e. operating on the supply from standard batteries, have been made. However, battery- powered amplified aerials do not exist, whereby said TV sets, in order to be able to take advantage of the performance of an amplified aerial, are still bound to the electrical network or to the car battery, thus losing the practicality coming from their battery operation.

Therefore, the object of the present invention is to provide an amplified aerial capable of operating on a battery supply, in particular with two 1 ,5V batteries only.

A further object is the reduction in the cost and bulkiness of the aerial, whereby it can be easily coupled to a portable TV set.

These objects are achieved by means of an amplified aerial having the characteristics cited in claim 1.

It is apparent that the main advantage of the amplified aerial according to the present invention is to overcome the limitations of prior art amplified aerials, thus allowing the greatest freedom of use of the battery- powered portable TV sets.

A further advantage stems from its reduced bulkiness, which allows its use in any situation.

These and other advantages and characteristics of the amplified aerial according to the present invention will be apparent to those skilled in the art from the following detailed description of a preferred embodiment thereof referring to the annexed drawings wherein:

Fiq.1 is a block diagram illustrating the fundamental members which make up the present amplified aerial; and Fiq.2 is a circuit diagram relating to the aerial of fιg.1.

With reference to fig.1 , there is seen that an amplified aerial according to the present invention includes a conventional dipole 1 for the UHF band and a pair of rods 2 for the VHF band. While dipole 1 having a 75Ω impedance is directly connected to the amplifying section through a 470-860 MHz band-pass filter F1 , rods 2 require an impedance adapter T1 to adjust their 300Ω impedance to that of the amplifying section which is exactly 75Ω. A 45-230 MHz second band-pass filter F2 as well as a 88-108 MHz third notch filter F3 are arranged between said amplifying section and the T1 adapter in order to eliminate the interferences caused by the frequency modulation radio emissions on said band. The amplifying section of the aerial consists in a double-stage amplifier, a first input stage G1 and a second output stage G2, each of them providing a 15 dB gain. The UHF signal is applied to the inlet of the first stage G1 and thus amplified by 30 dB (in addition to 6 dB of the dipole), whereas the VHF signal is applied to point M between the two amplifier stages G1 and G2, whereby it is amplified by 15 dB by second stage G2 only.

The aerial of the present invention includes an automatic power-off device 3 which cuts the supply after 4 hours of continued use. This device allows to save the batteries in case the aerial is forgotten switched on. The aerial operating voltage is 3V when the supply comes from two AA batteries housed in a suitable compartment 4, whereas it is 12V if the aerial is connected, for example, to the starter battery of a car through a specific external socket 5. Said socket 5 is connected to the battery compartment 4 through an exclusion circuit 6, so that the insertion of a power jack into socket 5 automatically causes the disconnection of the batteries in order to prevent their damage by the 12V supply.

Referring now to fig.2, there is shown an example of a circuit which allows to employ electronic components operating on voltages not greater than 3V, which are usually applied in other fields such as, for example, vehicular telephony. In particular, these components consist in two ultra- low bias voltage transistors TR1 and TR2 (model S822T) and an integrated circuit 7 of the CMOS 74HC00D type containing four NAND gates, referred to as U1A-U1 D.

The use of a single integrated circuit allows to reduce cost and bulkiness, however it is necessary to couple it to some specific circuit elements in order to obtain the switch-on device with automatic timed power-off. Furthermore, the switching on and off are controlled by a single push-button P1 rather than by a more expensive double-throw switch or by two separate push-buttons.

Specifically, the elements allowing to perform this latter function are two pairs of resistors R8-R9 and R10-R11 and two capacitors C14, C15 arranged between the outputs of gates U1 B, U1C and one of the inputs to gates U1A and U1 D, respectively. Furthermore, the lines arriving to the other two inputs to gates U1A and U1D are provided with two diodes D3, D4 and other two capacitors C17, C18. As far as the timing for power-off is concerned, it is obtained by means of a capacitor C16 arranged in series with four ultra-high impedance resistors R13-R16 (10 MΩ each in the illustrated example). When capacitor C16 is sufficiently charged to generate the required voltage, it triggers the integrated circuit 7 which switches off the circuit. However, capacitor C16 must always be without charge when the circuit is switched on, because in case it would already be partially charged then the time required to reach the automatic power-off level would be shorter than desired. Therefore, the line connecting the output of the integrated circuit 7 to capacitor C16 includes a diode D5 which discharges the capacitor upon switching off of the circuit, either if it occurs in an automatic way or by a manual control through push-button P1.

Another peculiar problem of the battery-powered aerial of the present invention stems from its small size which obliges to locate the circuit, together with its power supply, between the signal input through dipole 1 and the two rods 2, and the output thereof through a coaxial cable connected to the J1 socket. In particular, in order to permit access to the battery compartment 4 from outside, the latter is positioned below the circuit in a central position and said position of the batteries causes a signal feedback problem. This occurs because in video amplifiers, due to the high frequency of the processed signal, any metallic body located between the input and the output causes a feedback of the output signal which interferes with the incoming one thus making it confused. Even if the positive pole of the batteries is isolated from their metallic body, the high- frequency video signal easily goes beyond said isolation and propagates back towards the input.

However, the signal confusion is not the only drawback caused by the feedback, in that the repeated firing of the feedback causes oscilla¬ tions between the input and output of the TR1 and TR2 transistors. Since these are ultra-low power transistors, the over-voltages generated by said oscillations cause the "burning" of the transistors after some firing cycles. In order to prevent these problems, an inductance L11 (of 5,5 μH in the example of fig.2) is inserted between the battery compartment 4 and the circuit "ground", through which the feedback takes place. This inductance L11 makes no opposition to the direct-current component of the supply, whereas it stops the high-frequency alternating components of the video signal tending to flow back to the input.

Nonetheless, this circuit arrangement is not sufficient to prevent completely the drawbacks, in that the problem of connecting the battery compartment 4 to the circuit still remains. This connection is conventionally carried out by means of two lengths of electric wire, each of them being welded at the ends to a pole of compartment 4 and to the circuit, respectively. However, even these short lengths of wire may take a position such as to form a "bridge" for the feedback passage of the video signal, thus jeopardizing the stopping effect carried out by inductance L11. In order to prevent this, the connection between the battery compartment 4 and the circuit is carried out by means of a pair of flexible sheets (not shown) almost S-shaped and preferably made of brass. Each sheet is welded at one end to a pole of compartment 4, and the other end is in contact with a conducting area of the circuit, such as a copper "pad". In this way, it is possible to arrange the connecting members for the circuit supply always in the same way, thus having the certainty that they can not cause the video signal feedback.

Finally, there is still a problem concerning the use of ultra-low power transistors. As in the case of the oscillations started by the feedback, the second transistor TR2 located near the output J1 may be damaged by the stray current flowing back from the TV set along the coaxial cable when the TV set is switched on. In order to prevent this drawback, an inductance L6 is arranged between the transistor TR2 and output J1.

The circuit arrangement of fig.2 is a mere example susceptible of changes, particularly concerning the values of resistance, inductance, capacity, etc. of the single members which make it up, as well as the arrangement of the additional members not cited in the description above.

Claims

1. An amplified television aerial comprising a dipole (1 ) for the UHF band, a pair of rods (2) for the VHF band and a circuit including an amplifying section consisting in a double-stage amplifier (G1 , G2), characterized in that each of said amplifying stages (G1 , G2) includes an ultra-low bias voltage transistor (TR1 , TR2) operating on a voltage not greater than 3V, said voltage being supplied by batteries housed in a relevant compartment (4).

2. A television aerial according to claim 1 , characterized in that an inductance (L11 ) is arranged between the battery compartment (4) and the circuit ground.

3. A television aerial according to claim 1 or 2, characterized in that the connection between the battery compartment (4) and the circuit is carried out by means of a pair of flexible metallic sheets, preferably made of brass, each sheet being welded at one end to a pole of the compartment (4) and the other end being in contact with a conducting area of the circuit, preferably a copper pad.

4. A television aerial according to any of the preceding claims, characterized in that an inductance (L6) is arranged between the second amplifying stage (G2) and the video signal output (J1 ).

5. A television aerial according to any of the preceding claims, characterized in that it includes a power-off timed device consisting in a CMOS-type integrated circuit (7) at the output of which a capacitor (C16) is connected in series to a plurality of ultra-high impedance resistors (R13- R16), the line connecting the output of the integrated circuit (7) to the capacitor (C16) including a diode (D5) connected in such a way as to discharge the capacitor (C16) upon switching off of the circuit.