Pulse or digital communications – Receivers – Interference or noise reduction
Reexamination Certificate
1999-10-13
2001-08-07
Pham, Chi (Department: 2631)
Pulse or digital communications
Receivers
Interference or noise reduction
C375S347000, C455S140000
Reexamination Certificate
active
06272191
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an information receiving system, in particular to a broadcast receiving system, capable of receiving two kinds of information or broadcast radio waves. The broadcast receiving system may receive an FM radio broadcast and a FM multiplex broadcast for superimposedly displaying traffic information on a monitor displaying a road map. Furthermore the present invention relates to an information receiving method, in particular to a broadcast receiving method, using the inventive information receiving system.
2. Description of the Prior Art
In a system wherein an FM multiplex receiver and an FM radio are constructed by two tuners, basic function elements of the FM multiplex receiver
1
and the FM radio
2
are provided independently of each other as shown in FIG.
6
. Accordingly, there is no correlation between a tuning frequency (multiplex receiving frequency) f
0
of the FM multiplex receiver
1
and a tuning frequency (radio frequency) f
1
of the FM radio
2
.
Generally, in a superheterodyne receiver, though to a very small extent, local oscillation caused when a specific receiving frequency is selected is leaked as noise radio waves from an antenna or the like.
For example, when fIF in
FIG. 6
denotes an intermediate frequency of the FM multiplex receiver
1
and the relationship between the multiplex receiving frequency f
0
and the radio frequency f
1
is defined as f
0
−fIF=f
1
, if an electric field intensity from an FM radio station is weak, it is added onto a local oscillation frequency (f
0
−fIF) leading from the antenna of the FM multiplex receiver
1
, with the result that noise is included in the sounds from the FM radio
2
. In other words, the condition f
0
≠f
1
+fIF should be met, in order to avoid the generation of noise.
In order to mitigate the above problem, in a prior art system , an isolation buffer
3
is provided between the FM multiplex receiver
1
and the FM multiplex antenna, as shown in
FIG. 7
, to attenuate the local oscillation leaking from the FM multiplex receiver
1
, thereby reducing an influence on the FM radio
2
.
By attenuating the noise acting in a direction opposite to a normal direction by providing the isolation buffer
3
as described above, if the level of the local oscillation leaking from the FM multiplex receiver
1
is, for example, −60 dBm, the level of the noise leaking from the antenna is suppressed to −100 dBm or lower if the isolation level of the isolation buffer
3
is 40 dBm. As a result, the leakage of the local oscillation gives almost no influence on the FM radio
2
.
However, the external provision of the isolation buffer
3
complicates the system. Even if the isolation buffer
3
is provided in the FM multiplex receiver
1
, it similarly leads to a larger receiving system.
An object of the present invention is to provide an in formation receiving system capable of eliminating the influence of noise due to the leakage of local oscillation without additionally providing an isolation buffer, and an information receiving method using such a system.
SUMMARY OF THE INVENTION
According to the invention, there is provided an information or data receiving system, in particular for a broadcast receiving system, comprising a first information or data receiver for receiving a first information or data radio wave or electromagnetic wave, a second information or data receiver for receiving a second information or data radio wave or electromagnetic wave, and a control unit for controlling the first and second information receivers. The control unit has a function of discriminating whether or not the second information receiver is on. If the controller determines that the second information receiver is on, then the controller controls the tuning of the first information receiver to avoid having a tuning frequency of the first information receiver set to a specified frequency that is prohibited in cases when the second information receiver is on.
According to the present invention, whether or not the second information or broadcast receiver is on is discriminated. In the case that the second information or broadcast receiver is on, the tuning of the first information or broadcast receiver is controlled lest the tuning frequency of the first information or broadcast receiver should be set to the specified prohibited frequency. Accordingly, the generation of radio waves of the local oscillation from the first information or broadcast receiver, within a frequency band which adversely affects the second information or broadcast receiver can securely be prevented, thereby preventing radio wave noise from being induced in the second information or broadcast receiver. Particularly, since there is no need to provide an isolation buffer at the first information or broadcast receiver as in the prior art, the information or broadcast system is effectively prevented from becoming larger.
According to a preferred embodiment of the invention, the control unit may comprise storage means for storing, as a prohibited frequency, a first tuning frequency of the first information receiver which adversely affects or may affect the second information radio wave reception of the second information receiver, in particular by local oscillation generated during the reception of the first information radio wave. The control unit may also comprise discriminator means for discriminating whether or not the second information receiver is on. The control unit may further comprise a multiplex tuning controller for controlling the tuning of the first information receiver lest the tuning frequency of the first information receiver should be set to the prohibited frequency, in particular stored in the storage means, in the case that the second information receiver is on.
Preferably the control unit discriminates whether the tuning frequency (f
1
) has exceeded an upper limit frequency (fH), i.e. f
1
>fH and sets the tuning frequency to a lower limit frequency if this is the case, (i.e., in situations where a stepwise frequency change amount by which the tuning frequency is changed is positive). Alternatively or additionally, the control unit may discriminate whether the tuning frequency (f
1
) has exceeded a lower limit frequency (fL), i.e. f
1
<fL, and sets the tuning frequency to an upper limit frequency if this is the case, (i.e., in situations where a stepwise frequency change amount by which the tuning frequency is changed is negative). Thus it is avoided that the tuning frequency is set to a value outside of a desired range of frequencies, in particular the range of frequencies of the FM radio broadcast and/or of the FM multiplex broadcast.
Most preferably, the first information receiver is an FM multiplex receiver for receiving an FM multiplex information radio wave, in particular a FM multiplex broadcast radio wave including a traffic information, and the second information receiver is a radio for receiving at least an FM radio information radio wave, in particular an FM radio broadcast radio wave.
According to the invention, there is further provided an information receiving method. The broadcast receiving method may be for use in the information receiving system described above. The method may comprise a first discriminating whether or not the second information receiver is on. The method may then comprise a step of discriminating whether or not the tuning frequency of the first information receiver is equal to the prohibited frequency. The prohibited frequency may be stored in a storage means. The method may then include changing the tuning frequency in the case that the second information receiver is on. Finally the method may include varying the tuning frequency in the case that the tuning frequency is equal to the prohibited frequency, preferably stored in the storage means.
According to a preferred embodiment of the invention, the step of varying the tuning frequency is performed in a continuous and/or stepwise manner.
Pref
Bayard Emmanuel
Casella Anthony J.
Hespos Gerald E.
Pham Chi
Porco Michael J.
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