Method and circuit arrangement for receiving radio waves using a plurality of antennae.

p0001The invention relates to a method according to the preamble of the main claim.

p0002A method for receiving radio waves are already with multiple antennas are known in which from an antenna signal to an intermediate frequency signal is formed in each case, the intermediate frequency signals with respect to their level compared to each other and the one is selected with the highest level for further amplification and demodulation. In this case, a changeover switch is connected to the outputs of the tuning circuits (Tuner) is provided, which forwards the respective select signal to the intermediate frequency amplifier. In addition, the outputs are each connected to an auxiliary intermediate frequency amplifier. With the help of a respective amplitude demodulator connected to it a level of each corresponding voltage is then derived.

p0003In a comparison circuit corresponding to the levels of voltages are compared with each other. With the result of comparing the change-over switch is controlled. The system can come to a swing, since the input of the intermediate frequency amplifier loads the respective output of the tuning circuit, which decreases at the moment of switching on the output level of the respective tuning circuit, and then switches to the other antenna. The associated output amplifier is then charged again by the input resistance of the intermediate frequency amplifier, which leads back to a switching. At constant input levels, this process can be repeated continuously.

p0004Furthermore, level fluctuations can lead to switching, which are so small that they have to be no effect on the signal quality, so a switch would be unnecessary in.

p0005To avoid these disadvantages, it is known to provide the comparison circuit with hysteresis. However, it has been found that these known improvements not operate satisfactorily for nonlinearities of the relationship between the Pegelmeßspannung and the input level.

p0006The inventive method having the characterizing features of the main claim has the advantage that on the one hand the impact of the intermediate frequency amplifier can be largely counteracted precisely and that other hand on the Eingangspegelhub exactly matched hysteresis can be set, which is virtually independent of the absolute level of the field strength ,

p0007The measures specified in the dependent claims, advantageous circuitry for carrying out the disclosed in the main claim are possible.

p0008An embodiment of the invention is illustrated in the drawing with reference to several figures and explained in more detail in the following description. It shows:<ul><li>Fig. 1 is a block diagram of an arrangement for performing the method according to the invention and</li><li>Fig. 2 is a diagram showing the characteristic of a Pegelmeßschaltung.</li></ul>

p0009In the circuit arrangement of FIG. 1 signals of two antennas 1, 2 each having a tuning circuit (tuner) 3, 4 are fed. Both tuners are supplied by a tunable RF oscillator. 5 The signals present at the outputs of the tuner 3, 4, intermediate frequency signals are each a Pegelmeßschaltung 6, 7 which at its output a voltage is available which represents the level of the intermediate frequency signal or the field strength of the respective antenna.

p0010As Fig. 2 shows, the output voltage U_M the level measuring 6, 7 but not proportional to the input voltage U_ZF, Which is indicated by the dashed line, but has nonlinearities. This is shown in Fig. 2 by way of example as a solid line.

p0011The output voltages of both Pegelmeßschaltungen 6, 7 (Fig. 1) are supplied to a comparison circuit 8 which essentially consists of a differential amplifier 9 and a signal inverter 10. With the output signal of the differential amplifier 9, a changeover switch 11 is controlled, is connected to the respective one of the outputs of the tuner 3, 4 to the input of the intermediate frequency amplifier 12th The intermediate frequency amplifier 12 followed by other per se known circuits, the explanation thereof is not necessary for the understanding of the present invention. They are therefore not shown in FIG. 1.

p0012The Pegelmeßeinrichtungen 6, 7 each consist of an intermediate frequency amplifier 13, 14 with a controllable gain and a downstream amplitude demodulator 15, 16. In order to distinguish the intermediate frequency amplifiers 13, 14 from the intermediate frequency amplifier 12 they are hereinafter referred to as an auxiliary intermediate frequency amplifier. The auxiliary intermediate frequency amplifier 13, 14 can be carried out by the way simpler than the intermediate frequency amplifier 12, not so high requirements are imposed on them as the intermediate frequency amplifier 12, whose characteristics are essential for the reproduction quality of the receiving device.

p0013The control inputs 17, 18 of the auxiliary intermediate frequency amplifiers 13, 14 are connected to outputs of the comparison circuit 8 with a different polarity signal.

p0014In the illustrated position of the switch 11 it is assumed that the signal of antenna 1 is larger than the signal of antenna 2 is. In this case, the gain of the auxiliary intermediate frequency amplifier 13 is slightly made larger than that of the auxiliary intermediate frequency amplifier fourteenth

p0015Now sinks the output level of the tuner 3 in the output level of the tuner 4, takes place as long as no change when the difference is less than it is due to the different gain settings. Only when the output signal of the tuner 3 falls below this value, the output voltage of the comparator 9, which leads to a switching of the switch 11 changes. At the same time the gain of the auxiliary intermediate frequency amplifier 14 is increased and reduces the gain of the auxiliary intermediate frequency amplifier. 13 Thereby, again only a downshift to the tuner 3 be made when the output voltage of the tuner 4 is significantly smaller than the output voltage of the tuner third By a low level drop by the load at the output of the tuner 4 to the input resistance of the intermediate frequency amplifier 12 no downshift is caused. Nor cause small changes in the field strength for switching.

p0016In principle, only one of the auxiliary intermediate frequency amplifiers 13, 14, hysteresis may also be achieved by corresponding control of the gain. However, the control of both auxiliary intermediate frequency amplifier will often be preferable for reasons of symmetry.