Automatic broadcast wave tuning device for RDS receiver

An automatic broadcast wave tuning device for a RDS receiver includes a controller to enforce the RDS receiver to receive the former broadcast wave by setting a forbidden flag under such conditions as being unable to receive a program identification code when a receiving signal level of the broadcast wave within the same broadcasting network is above a predetermined signal level, or in the case of being able to receive the program identification code when failing to meet up with that of the broadcasting station presently in contact. Hence, from the next automatic receiving frequency tuning, a control is provided for setting a frequency divisional ratio of the phase-locked loop circuit in order to select the best broadcast station of all by discriminating reception signal levels of the broadcast waves transmitted by all the broadcasting stations bearing no forbidden flag.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to an automatic broadcast wave tuning device and, 
more particularly, to an automatic broadcast wave tuning device for a 
radio data system (hereinafter referred to as RDS) receiver to receive RDS 
data wherein the radio receiver is controlled to tune in a broadcast wave 
bearing RDS data transmitted by a broadcasting station. 
2. Description of the Prior Art 
As a well known radio service, a radio data system (RDS) is common in 
Europe for providing broadcast wave listeners with a radio service. In 
such RDS, informative data relating to broadcast programs are transmitted 
simultaneously with the broadcast programs in a multiplex modulation from 
broadcasting stations and, upon receiving the broadcast waves, a desired 
broadcast program is selected by a broadcast wave listener based on 
demodulated data. 
The RDS is a data system standardized in the Europe Broadcasting Union 
(EBU), wherein the data relating to the broadcast such as broadcast 
programs and the like are coded into a two phase Differential Phase Shift 
Keying (DPSK) signal having a bit rate of 1187.5 bps, and these coded data 
are transmitted by frequency-modulating a sub-carrier in such that 
modulating a 57 KHz sub-carrier in accordance with a double-sideband 
carrier suppression amplitude modulation. 
In the RDS, the whole data are transmitted as a unit which is called a 
group consisting of 104 bits. One group in turn consists of four blocks, 
each of which consists of 26 bits. The data contained in each group are 
prescribed depending on their locations, whereby 16 bits of the first 
block always designate a program identification code (PI code), while in 
the second block, the first 5 bits designate a group-type code, the next 
one bit designates a traffic-program identification code (TP code), and 
the next succeeding 5 bits designate a program type code (PTY code). 
Further, the contents of the remaining are a traffic announcement 
identification code (TA code), program service name data (PS data) such as 
broadcasting station names, broadcasting network names and the like, and a 
list of alternative frequencies data (AF data) for identifying 
broadcasting network stations which broadcast the same program. 
In a motor vehicle-mounted RDS receiver, a poor reception is quite often 
encountered while listening to a broadcast during a motor vehicle travel. 
However, in the RDS broadcast, since the AF data of the broadcasting 
stations within the same broadcasting network, which stations are 
broadcasting the same broadcast program on different frequencies, are 
available as described above, it is possible to tune in another 
broadcasting station within the same broadcasting network having a greater 
signal level, or a stronger electric field strength, than that of the 
broadcasting station presently tuned in based on the AF data stored in a 
memory for chasing the same broadcast program. 
However, there has been a problem for causing faulty operation of the RDS 
receiver depending on a course of the motor vehicle such that the RDS 
receiver might come across a broadcasting station, out of but neighboring 
to the broadcasting network, having the AF data allocated to the same 
frequency as that of the broadcasting station within the broadcasting 
network, or the RDS receiver might tune in a wrong program as there are 
so-called non RDS broadcasting stations which are not capable of 
transmitting RDS data. This kind of faulty operation often happens when 
the motor vehicle is driven through many countries in Europe along the 
boundaries. 
Further, wrong AF data may have been stored in a memory due to an unknown 
reason in a duration of demodulating the received RDS data and this 
results in a problem for causing improper selection in the automatic 
tuning operation. A prior-art-type automatic tuning device is disclosed, 
for example, in the patent application laid-open No. 2-105731. 
It is therefore an object of this invention to eliminate the problems 
encountered by prior-art-type RDS receivers and to provide an automatic 
broadcast wave tuning device which is capable of preventing a RDS receiver 
from faulty operation. 
SUMMARY OF THE INVENTION 
An automatic broadcast wave tuning device for a RDS receiver embodying the 
present invention comprises an alternative frequencies data memory for 
storing at least one or more lists of alternative frequencies data being 
transmitted formerly by the broadcasting stations in contact and a 
controller. 
The controller provides a control for setting a frequency divisional ratio 
of a phase-locked loop in such a way as to enforce the RDS receiver back 
to receive the former broadcast wave by setting a forbidden flag for 
forbidding the receiving frequency from changing, within the same 
broadcasting network, under such conditions as being unable to receive a 
network identification code but a receiving signal level of a broadcast 
wave within the same broadcasting network is above a predetermined signal 
level, or to enforce the RDS receiver back to receive the former, 
immediately before, broadcast wave by setting the forbidden flag without 
discriminating the receiving signal level and forbid the RDS receiver from 
changing to receive a broadcast wave of the same network station having 
the forbidden flag while in case of being able to receive the broadcasting 
network identification codes but failing to meet up with that of the 
broadcasting station presently in contact. 
The controller in accordance with this invention checks, upon initiation of 
automatic tuning, program identification codes of the broadcasting 
stations, which are designated by the stored list of alternative 
frequencies data, starting from the broadcasting station presently in 
reception then to others. Whereby if the program identification code is 
detected to be wrong, it must be whether a wrong list of alternative 
frequencies data is stored in an alternative frequencies data memory or 
the stored list of alternative frequencies data must be the one assigned 
to a broadcasting station in another broadcasting network, thus setting up 
a forbidden flag, independently, to respective data in the stored list of 
alternative frequencies data. 
Further, if it is impossible to receive any of the program identification 
codes, since it is hard to determine whether the broadcasting station is a 
non RDS broadcasting station having no program identification code or the 
broadcasting station is a RDS broadcasting station but the broadcast wave 
from which is too weak to recognize the program identification code, it is 
determined whether or not the receiving signal level is at or above the 
predetermined signal level, whereas if it is, the broadcasting station is 
considered to be a non RDS broadcasting station and setting up a forbidden 
flag thereto. 
Accordingly, from the next operation for the automatic reception frequency 
tuning, provided is a control for setting a frequency divisional ratio of 
the phase-locked loop circuit in order to select the best broadcast 
station of the all by discriminating receiving signal levels of the 
broadcast waves transmitted by all the broadcasting stations bearing no 
forbidden flag.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
A preferred embodiment of this invention will now be described in detail by 
referring to the accompanying drawings. Referring to FIG. 1, there is 
shown a block diagram illustrating an automatic broadcast wave tuning 
device for a RDS receiver to implement the automatic turning operation in 
accordance with the present invention. 
In FIG. 1, an element 1 designates an antenna, FM multiplex broadcast waves 
received by the antenna 1 are fed to a front end 2 for selectively 
receiving a desired broadcast wave of an selected broadcasting station, 
and thereby the selected broadcast wave is converted into an intermediate 
frequency (IF) and fed to a frequency discriminator (FM detector) 3. 
The front end 2 is under the control of a phase-locked loop (hereinafter 
referred to as PLL) circuit 6 including a programmable frequency divider 
(will be described in detail hereinafter), a dividing ratio of which is 
controlled by a controller 10 for providing the tuning operation. 
A discriminated output of the frequency discriminator 3 is fed to a 
multiplex (hereinafter referred to as MPX) demodulator circuit 5 through a 
noise canceler (hereinafter referred to as NK) 4 for deriving a L (left) 
channel signal and a R (right) channel signal therefrom in case of a 
stereophonic broadcasting. 
A RDS data signal is extracted from the discriminated output of the 
frequency discriminator 3 by passing through a 57 KHz band-pass filter 8 
and fed to a RDS decoder 9 for decoding it into data readable by the 
controller 10. The controller 10 contains an AF memory 11, wherein 
obtained informative data relating to the broadcasting stations in contact 
(aforesaid data PI, AF, PS, TP, TA and the like) are stored. 
Further, there is provided a level detector 7 for detecting a received 
signal level (electric field strength level) based on the IF signal level 
fed from the frequency discriminator 3. The received signal level detected 
by the level detector 7 is then fed to the controller 10. 
In operation, FM multiplex broadcast waves received by the antenna 1 are 
fed to the front end 2, whereby a broadcast wave of a desired broadcasting 
station is selected and applied to the frequency discriminator 3 after 
being converted into the intermediate frequency. 
A discriminated output of the frequency discriminator 3 is fed to the MPX 
demodulator circuit 5 through the NK 4, and which discriminated output is 
then decoded for outputting the L and R channel audio signals therefrom in 
case of the stereophonic broadcasting. 
Further, the discriminated output of the frequency discriminator 3 is fed 
to the RDS decoder 9 through the 57 KHz band-pass filter 8, and thereby 
the discriminated output is decoded into data readable by the controller 
10. 
The controller 10 takes in the informative data PI, AF, PS, TP, TA and the 
like, and stores the AF data in the AF memory 11. 
The level detector 7 detects a received signal level (electric field 
strength level) based on the IF signal level fed from the frequency 
discriminator 3, and feeds a detected resultant to the controller 10. 
Operational steps to be implemented by the controller 10 of the automatic 
broadcast wave tuning device of FIG. 1 will be described by referring to 
the flowchart shown in FIG. 2. 
The following table 1 illustrates the data stored in the AF memory 11. 
TABLE 1 
______________________________________ 
AF frequency forbidden flag 
AF memory data storage area 
storage area 
______________________________________ 
No. 1 f.sub.1 0 
No. 2 f.sub.2 0 
No. 3 f.sub.3 1 
No. 4 f.sub.4 
. . 
. . 
.sup. No. N f.sub.N 
______________________________________ 
In the table 1 above, AF data lists are shown by characters of f.sub.1, 
f.sub.2, f.sub.3 . . . f.sub.n, whereby the AF data list f.sub.3, for 
example, is accompanied by a forbidden flag. It is assumed that data 
representing more than one broadcasting station are stored in the AF 
memory 11 at an AF frequency data storage area shown in the table 1. 
At step S1, the PI code of the broadcasting station presently tuned in is 
registered at the AF memory 11 contained in the controller 10 as being fed 
through the 57 KHz band-pass filter 8 and the RDS decoder 9, and all that 
the discriminated output of the frequency discriminator 3 is detected at 
the level detector 7 for deriving the received signal level therefrom and 
the derived signal level is also registered at the AF memory 11 in the 
controller 10. 
After registering the data at the AF memory 11 in the controller 10, the 
program goes to step S2. At step S2, one of the stored AF data with no 
forbidden flag is selected and read it from the AF memory 11, setting a 
frequency divisional ratio for the PLL circuit 6 based on the read out AF 
data, and then the front end 2 initiates the tune-in operation in 
accordance with the frequency divisional ratio being set for receiving the 
broadcast wave of the AF station that corresponds to the selected AF data. 
It is then determined, by comparison, at step S3 whether or not a received 
signal level of the AF station is greater than that of the former 
broadcasting station. If it is not, the program goes to step S7, whereas, 
if it is, it is then determined at step S4, after a predetermined period 
of time, whether or not the PI code of the AF station is detectable. If it 
is not, the program goes to step S9, whereas, if it is determined that the 
PI code is detectable at step S4, it is then checked at step S5 whether or 
not the detected PI code coincides with the PI code registered in the AF 
memory 11 at step S1. If it is not, the program goes to step S6, whereas, 
if it is, the program goes to step S8 for receiving the broadcast wave 
from the AF station, in other words, the reception of broadcast wave is 
switched from the former broadcasting station to a newly selected AF 
station. 
If it is determined at step S3 that the received signal level of the AF 
station is not greater than that of the former broadcasting station, or if 
it is determined at step S4 that the PI code of the AF station is not 
detectable and that the received signal level of the AF station is 
determined to be less than a predetermined signal level of V.sub.D at step 
S9, the program goes to step S7 for receiving the broadcast wave 
transmitted by the former broadcasting station without setting the 
forbidden flag to the corresponding AF data. That is a state of awaiting 
for the next chance. 
At step S9, if it is determined that the received signal level of the AF 
station detected at the signal level detector 7 is greater than the 
predetermined signal level V.sub.D, the program goes to step S6, and 
setting the forbidden flag to the corresponding AF data. 
In like way, if it is determined at step S5 that the PI code of the AF 
station is not the same as that of the data stored in the AF memory 11, 
the program goes to step S6, and writing the forbidden flag into the 
corresponding forbidden flag storage area (shown in the table 1) of the AF 
memory 11. 
Upon implementation of step S6 as described above, the program goes to step 
S7, whereby the RDS receiver is brought back to tune in the former 
broadcasting station. 
Accordingly, the AF data accompanying the forbidden flag will no longer be 
selected in the operational step of S2, thus preventing the malfunction of 
the automatic broadcast wave tuning device while in the tuning operation. 
In the embodiment described above, the received signal level of the AF 
station has been compared one after another with the signal level of the 
broadcasting station presently in reception, however, the present 
invention can be utilized in such an automatic system wherein a part or 
the whole frequencies that correspond to the stored AF data in the AF 
memory 11 may be checked successively for selecting the best broadcasting 
station to tune in. 
As it has been described above, in accordance with this invention, the 
forbidden flag is provided not only when it is determined that the 
received PI code is not identical with the one being stored while the AF 
station coincides with a RDS station in a different broadcasting network, 
but when it is assumed that the AF station is a non RDS station through 
the implementation of the operational step for determining whether or not 
the received signal level of the AF station is at or above the 
predetermined signal level in case of not receiving the PI code of the AF 
station. Therefore, it is possible to prevent the RDS receiver from 
causing malfunction in the operation against the RDS or non RDS 
broadcasting stations. 
It is to be understood by those skilled in the art that the foregoing 
descriptions relate only to preferred embodiment of the invention and that 
various changes and modifications may be made in the invention without 
departing from the spirit and scope thereof.