Method and apparatus for suppressing undesired automatic transmitter change-over.

p0001The invention relates to a method for avoiding unwanted, automatic station changes in mobile radio receivers.

p0002Changing stations Are often made automatically when the reception quality of the selected station is no longer sufficient. Especially in the traffic mode, a transmitter search is started to set a stronger incident traffic information station at waste reception quality of a set traffic information station below a predetermined threshold. Such a radio receiver is described in the German Offenlegungsschrift DE-OS 34 16 917 in which case the reception quality is checked after every traffic announcement, and at a low reception quality, a new vote on a better receivable stations is carried out.

p0003In such receivers, it is also known that audible warnings when the Traffic Information mode a traffic information station can be received with sufficient quality.

p0004can process For broadcast receivers, the data signals to the Radio Data System (RDS), it is also known that prior to introducing the channel scan nor the alternative frequencies (AF's) that are tuning that as the same program or chain of stations set station belong, are checked to see whether such a frequency is receivable with aussreichender quality. Only if this is not the case a search is started.

p0005In the known procedures, however, a search is also the case of temporary disturbances began and dialed another program may, despite the originally set program can be received well after a short time, and thus the change is not necessary and the part of the user is undesirable.

p0006The object of the invention is therefore to avoid unwanted program change and warning signals in disorders that affect the entire frequency band.

p0007Disorders of the entire frequency band occur in car radio receivers, especially, when you drive through a tunnel, or when you are in an underground garage.

p0008An undesired channel search and / or the traffic to suppress a warning in such disorders, is prior to starting the channel scan, ie scanning, the purpose is the identification and setting of a transmitter, first a rapid, imperceptible to the user search started. This quick search takes place inaudibly and serves only to determine whether a station can be received. A tuning, ie mapping the reception quality to a frequency is not possible with the fast search and checking the quality of reception is limited to a quality such as reception field strength. If the reception quality in the entire frequency band below a predetermined limit, then the current tuning condition is maintained for a certain period and suppresses a station search and a warning tone in the Traffic Information mode. The rapid, imperceptible search with return to the initial state is repeated cyclically until back channels to be received.

p00091 shows an example of the timing of the tuning voltage (a), the reception quality (b) and the control signal for the mute mode (c).

p0010the reception field strength is here for the reception quality as an example given over the entire timeline. The reception may also be determined by other criteria, such as interference from multipath reception, RDS error rate, etc., or a combination of the individual quality characteristics. Only in the fast search, the review of the quality of reception is limited to a mark of quality.

p0011At time t_O is a transmitter of the frequency f₁ adjusted with the tuning U₁ which is received with sufficient quality. At time t₁ the reception quality falls below a predetermined threshold. With a short time delay a control signal is then output Sts for muting the time t₂ and it will be stored in memory alternative frequencies checked. In the illustrated case six alternative frequencies with tuning Uaf₁ to Uaf₆ be checked up to the time t₃. Assuming the case of that one with his car at a place where there is no reception or no sufficient reception quality is possible, as is the case generally in a tunnel or an underground car park, the reception quality is in Figure . 1b t₃ to time under the threshold e_th, In the inventive process not a normal scan with Stop is started at lower receivable transmitters at this point, which would be in vain and would possibly lead to a warning, but it is a fast, imperceptible search, of very short duration, started over the entire frequency band. For this, the tuning takes its highest value and drops linearly to the lowest value, which is reached at the time t₄. The linear decrease of the tuning voltage is shown here only as an example and can just as well be replaced by an increase or decrease of variable pitch.

p0012If the period t₃ to t₄ the reception quality the threshold E_th not reach or exceed, at the time the originally set tuning U₁ t₄ reinstated and the control signal Sts switches the mute shown in Fig. 1c again.

p0013For a predetermined time period now, the transmitter on the frequency f₁ remains set. If the reception quality during this period the threshold E_th does not exceed the time is started t₅ again with the Mute and checking the alternative frequencies.

p0014An advantageous further development of this approach is that is the period t₄ to t₅ the reception quality with a second, lower threshold compared and that, when falls below this threshold, the sound is muted with the control signal Sts. In this way, the reproduction of a highly disturbed program is prevented.

p0015A further advantageous embodiment of the invention is that when you turn the car radio, ie when switching through the A - / - off switch on the radio and also the automatic switch on the radio with the ignition, t₄ the period up t₅ takes longer because you in this case assumes that you are in an underground garage and leaving this underground lasts longer.

p0016Another embodiment of the invention arises when t₅ the time immediately begins fast scan imperceptible, without checking the alternative frequencies.

p0017To explain the execution of the described method 2 is a block diagram in Fig indicated, which comprises the following functional blocks.:

p0018The microcomputer unit MC controls the course of the inventive method and is connected to the display unit ON, which may be an optical or acoustic display. Further, the microcomputer MC is connected to the memory SP, which contains the tuning data for the alternative frequencies, and to the functional units AF, SSL and SL. The unit AF controls checking the alternative frequencies, while the units and SSL SL quick, imperceptible and control the tuning, the outputs of these units to the receiving part E lead and coordinate this. The received in this receiving portion signal in the amplifier V, which is controlled by the microcomputer MC, being only important for the invention control signal line Sts is for mute in the block diagram, strengthened. The reception quality is determined in function block EF and given an appropriate signal to the comparator K, where it E with the threshold_th is compared. The comparison result is evaluated in the microcomputer in the sense of the inventive method.

p0019A timer block T, which is connected to the microcomputer MC, and receives as its setting of this start and end time, the duration between the instants t₄ and t₅ controls.

p0020It should be noted that the block diagram of FIG. 2 contains only the inventively essential function blocks and compounds, and that individual functional blocks both hardware, as can also be embodied by a microcomputer program.