Abstract:
A receiving antenna system for vehicles that eliminates interference in receiving signals. The interference detector is disposed within the receiver and generates and transmits an indicating signal, or a signal derived therefrom. Such signal can be formed in several different ways, and in the site of the antenna installation, it can be converted into a switching signal that only effects the switching condition in the antenna installation having a controllable switching circuit.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to antenna systems for motor vehicles. More particularly, it relates to a receiving antenna scanning diversity installation that detects and eliminates receiving interferences. 
     2. The Prior Art 
     In the scanning diversity antenna installation described in “Funkschau” (Radio Review) 8/1989 “Radio Reception From the Rear Windowpane”, the received signals of four ultra-short wave antennas formed by conductors printed on the rear windowpane of a vehicle are selected by a diversity processor. The diversity processor is mounted within the immediate proximity of the antenna installation, and has an output that is coupled to the antenna connection point. An antenna line connects the receiver to the antenna connection point. For detecting interference in high-frequency signals, the intermediate frequency signal present in the receiver is supplied to the diversity processor for distortion detection. The detector detects interferences with the received signal, and generates a signal that shifts the antenna selector switch to another switching position. The processor cyclically switches the antenna signals through to the receiver until a signal with sufficiently low interference has been found. The selection of the antenna signals is connected with change-over processes that lead to more or less audible interferences depending on the receiver. 
     One drawback with an arrangement of this type is that the interference detector is disposed at the site of the antenna installation. 
     The diversity processor operating according to the state of the art does not readily permit coordinated measures for mute-switching in the receiver. Another problem is the technical expenditure required for the introduction of an additional connection line between the diversity processor and the receiver. The additional line is needed when the change-over process pulses are supplied to the receiver during the change-over process for briefly switching the receiver mute. DE 44030612 describes a system by which change-over interferences can be avoided, however, such measures are very costly to implement. 
     SUMMARY OF THE INVENTION 
     The present invention provides a receiving antenna scanning diversity system that offers a greater number of antenna signals to the receiver for enhancing reception, while at the same time keeping the change-over interferences as low as possible. 
     According to the invention, the interference detector is incorporated into the receiver. This makes it possible to apply measures for suppressing audible noises associated with the change-over process, such as, for example, by switching the low-frequency amplifier mute during the change-over process. Overall, this permits superior tuning between the antenna installation and the receiver. Antenna diversity installations of the described type are expected to function together with different receivers. Generally, as a trade rule, the vehicle manufacturer specifies the antenna installation without making provision for any defined type of receiver that is optimized for such installation. 
     By incorporating the interference detector into the receiver, the present invention offers the receiver manufacturers the possibility to directly use an internally generated signal for indicating interference when a receiving interference occurs, without time delay. For example, to make the change-over process inaudible by switching to mute, or by soft mute-switching. It has been found, in practical application, that efficient suppression of change-over noise can be achieved only if the interference detection and the mute-switching measures are carefully harmonized with each other. The signal transmitted from the receiver to the antenna installation is, therefore, extremely simple and limited to logic signals. The logic signals can be interpreted simply on the side of the antenna installation, and will initiate a change-over process that will not generate any noticeable interferences. 
     Therefore, according to the present invention, when an interference is detected in the received signal, the receiver transmits to the antenna installation an indicating signal, or a signal derived therefrom. Such signal can be formed in several different ways, and in the site of the antenna installation, it can be converted into a switching signal that only effects the switching condition in the antenna installation having a controllable switching circuit. The change-over times are very short due to the availability of rapidly working electronic switches, and as such, further adaptation of the antenna installation with controllable switching circuit to any receiver specifically intended for such an installation, is not required. 
     It is therefore an object of the present invention to provide a receiving antenna scanning diversity system that offers a greater number of antenna signals to the receiver. 
     It is another object of the invention to provide a receiving antenna scanning diversity system that provides enhanced reception while keeping change-over interferences as low as possible. 
     It is a further object of the invention to provide a receiving antenna scanning diversity system that requires only one connection line between the antenna installation and the receiver. 
     Another object of the invention is to provide a receiving antenna scanning diversity system for vehicles that operates efficiently and reliably. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other objects and features of the present invention will become apparent from the following detailed description considered in connection with the accompanying drawings which disclose an embodiment of the present invention. It should be understood, however, that the drawings are designed for the purpose of illustration only and not as a definition of the limits of the invention. 
     In the drawings, wherein similar reference characters denote similar elements throughout the several views: 
     FIG. 1 is a schematic diagram of a first embodiment of the receiving-antenna scanning diversity system according to the invention; 
     FIG. 2 is a schematic diagram of a second embodiment of the receiving-antenna scanning diversity system according to the invention; 
     FIG. 3 is a schematic diagram of a third embodiment of the receiving-antenna scanning diversity system according to the invention; 
     FIG.  3   a  is a schematic diagram of an additional embodiment wherein a signal generator forms a signal bust for use as an indicating signal; 
     FIG. 4 is a schematic representation of the system according to a further embodiment of the invention; 
     FIG. 5 is a schematic representation of the receiving antenna system according to another embodiment of the invention; and 
     FIG. 6 is a schematic representation of the receiving antenna system according to another embodiment of the invention. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Turning now in detail to the drawings, FIG. 1 shows an antenna installation  21  with controllable switching circuit, and receiver  20  with an antenna line  12  connecting the receiver to antenna installation  21 . A separate signal line  24  is provided between receiver  20  and antenna installation  21  for transmitting an indicating signal  10 , or the control signals  26  derived therefrom, from receiver  20  to antenna installation  21 . 
     In the receiving antenna scanning diversity system according to FIG. 1, the occurrence of an interference is detected through the use of an indicating signal  10 , sent via signal line  24 , to antenna installation  21  having a controllable switching circuit ( 11 ,  5 ,  8 ) defined by switching circuit  11 , selector switches  5 , change-over switches  8 , control signals  9 , and in additional embodiments, selector circuits  13 . It is advantageous that only one additional line is required in connection with a large selection of antenna signals (i.e., signal line  24 ). Signal line  24  can be any suitable known type of conductor for transmitting logic signals, such as, for example, fiber optic conductors. 
     If, in relation to the geometric dimensions of the antenna installation  21 , the antennas A 1 , A 2 , A 3 . . . A n  are far removed from receiver  20 , it is preferable to avoid using several lines to connect antenna installation  21  with receiver  20 . This is particularly important, for example, with motor vehicles where a multi-antenna system is applied to their rear windowpane. In this case, only one antenna line  12 , carrying a receiving signal  23 , is required to connect antenna installation  21  with receiver  20  in the front part of the vehicle. Additional antenna lines would incur additional costs for suitable high-frequency plug connections. Furthermore, such plug connection represent additional error sources of the system, and thereby reduces operational safety. 
     In a simple case , indicating signal  10  can be designed as a signal  26  that is binary in configuration and which indicates the occurrence of the interference as long as the binary signal is present. In order to cause a particularly quick switching reaction in the controllable switching circuit ( 11 ,  5 ,  8 ) it is possible to make signal  26  a pulse signal from the response side of detector  18  by differentiation of indicating signal  10 . By forming a suitable pulse whose spectral energy, either does not form any contribution in the frequency range of the received signals, or whose duration in time is so short that it is physiologically not noticed, it is possible to transmit such pulse via antenna line  12  to antenna installation  21  with controllable switching circuit ( 11 ,  5 ,  8 ) without causing interference with the reception. 
     FIG. 3 shows antenna installation  21  having intermediate frequency signal  19 , which in the case of interference, is keyed up as a signal burst that is selectively transmitted via antenna line  12 , and by way of intermediate-frequency filters. 
     If the indicating signal is to be transmitted to the antenna installation  21  of the invention, for example, via a line carrying pre-applied DC voltage, or via another signal line  24 , it is possible, according to a further embodiment of the invention, to transmit such signal  26  as the envelope curve of a signal burst of high frequency, and to recover said envelope curve in the antenna installation  21  in order to trigger the change-over action. 
     The high-frequency oscillation for forming the burst can be formed by the intermediate-frequency signal  19  of receiver  20  itself. For obtaining such oscillation, signal  19  is supplied not only to interference detector  18 , but transmitted from receiver  20  to the antenna installation  21  also by way of an electronic switch  25  and signal line  24  (FIG.  3 ). 
     FIG.  3   a  shows an additional embodiment of the invention where a high frequency signal generator ( 27 ) is connected to interference detector  18  and produces a signal burst ( 28 ) of high frequency through analysis of said indicating signal ( 10 ) or control signal ( 26 ) derived therefrom. 
     In a particularly advantageous embodiment of the invention, which can be produced at a favorable cost, the high frequency antenna line  12  can be used at the same time as signal line  24 . In this case, it is necessary to protect the receiver input against indicating signal  10 , and against any interferences that may be caused by such signal. This is accomplished frequency-selectively using selection circuits  13 , which, on the receiver side, serve for coupling in the indicating signal  10 , and on the side of the antenna installation  21  for coupling out said signal. In the case of the transmission of signal  26  as a signal burst of intermediate-frequency for indicating interference, it is possible, and highly advantageous, to use standard intermediate-frequency filters for selection circuits  13 . 
     In the antenna installation  21 , signal  26  is filtered out of the receiving signal  23  and supplied to switching circuit  11  with the help of selection circuits  13 . The control signals  9  are generated on the output of switching circuit  11  and change the conditions of selector switches  5  and of the change-over switches  8  in the antenna installation  21 , whereby another receiving signal  23  is transmitted to the receiver  20 . The advantage of this arrangement lies in the free creatability by special programming of switching circuit  11 , permitting a defined cycle for forming the receiving signals supplied to the receiver. In the simplest form, the various switching positions of change-over switches  8  are cyclicly and repeatedly adjusted in a preset configuration. 
     FIGS. 4 to  6  show practical embodiments of the invention on examples of antenna installation  21  with controllable switching circuit ( 11 ,  5 ,  8 ,  13 ), which are substantially formed by the heating field  6  in windowpane  1  of a vehicle. In FIGS. 4 and 5, different antenna part connections  14  and  15  are produced by connections to the heating field, whereby the amplifiers  2   a  and  2   b  are connected to the two antenna part connections  15   a  and  15   b , respectively, for forming active antennas. The outputs of amplifiers  2   a  and  2   b  are connected to antenna selection switch  5 , by which one of the amplifier outputs is switched through to the antenna connection point  22 . The electronically controllable selector switch  5  is controlled by the switching circuit  11  via control signal  9  for the further formation of different receiving signals at the antenna connection site  22 . 
     FIG. 5 shows a modified version of the circuit of FIG. 4 where the electronically controllable selector  5  replaces the change-over switches in order to switch to different impedances  7 d 1 ,  7 d 2  and  7 d 3  to the antenna part connection  14   d . Electronically controllable selector  5  is grounded at a grounding point  3 . The different impedances  7 d 1 ,  7 d 2 ,  7 d 3 , etc. are preferably provided as reactances. 
     FIG. 6 shows an additional embodiment of the invention having at least one amplifier ( 2 ) with an input which is selectively coupled to second antenna part connection ( 15 ) thereby forming active antennas, and an output connected to antenna connection site ( 22 ). There are no selector switches ( 5 ) as in prior embodiments and antenna connections ( 14 ) are loaded with different impedances ( 7 ) via change over switches ( 8 ). 
     While several embodiments of the present invention have been shown and described, it is to be understood that many changes and modifications may be made there unto without departing from the spirit and scope of the invention as defined in the appended claims.