CA1093645A - Radio receiver employing premixing and digital display - Google Patents
Radio receiver employing premixing and digital displayInfo
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- CA1093645A CA1093645A CA280,868A CA280868A CA1093645A CA 1093645 A CA1093645 A CA 1093645A CA 280868 A CA280868 A CA 280868A CA 1093645 A CA1093645 A CA 1093645A
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- counter
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Abstract
ABSTRACT OF THE DISCLOSURE
A short wave broadcasting receiver which can receive accurately and stably the desired station is formed with a local oscillator which comprises a variable frequency oscill-ator, reference frequency oscillators, premixers and band pass filter, frequency converter and an 1F amplifier. By adding a frequency counter unit comprising a frequency counter block and digital display block, the received frequency can be digitally displayed stably and correctly by using a cheap low speed fre-quency counter.
A short wave broadcasting receiver which can receive accurately and stably the desired station is formed with a local oscillator which comprises a variable frequency oscill-ator, reference frequency oscillators, premixers and band pass filter, frequency converter and an 1F amplifier. By adding a frequency counter unit comprising a frequency counter block and digital display block, the received frequency can be digitally displayed stably and correctly by using a cheap low speed fre-quency counter.
Description
3~ 5 BACKGROUND OF THE INVENTION
..., . _ This inventian relates to a radio receiver, and more particularly to a radio receiver which can receive a signal of a desired frequency stably and accurately with a desirable characteristic of suppressing a spurious signal, and further to a radio receiver which can display the received frequency in digits by means of a frequency counter.
Generally, in short wave broadcasting, the carrier frequency uses a very wide frequency band from 3 MHz to 30 MHz, and there are broadcasting stations numbering 4000 to 5000 in the world. The minimum unit of the carrier frequency regulation of these stations is on the order of kilohertz.
Therefore, a receiver for receiving a short wave signal is required to receive the desired signal accurately and to con-tinue the receiving stably for a long time. However, con- ~ -ventional short wave radio receivers are not always satis-factory for the above requirements. It is often troublesome to tune the desired station accurately, and even when the receiver is accurately tuned to the desired station there is often a problem of drift of the received frequency.
As one of the method of improving the accuracy of tuning, there is a method of counting the oscillated frequency of a local oscillator digitally and displaying the nume~ral of the short wave frequency to be received. In such a short wave receiYer, the received frequency should be counted and displayed accurately and stably. In the prior art, for a superheterodyne radio recçiver, known to be one of the best methods of improving the display accuracy of the received frequency, the oscillated frequency of the local oscillator is directly counted and corrected with addition or subtraction of the intermediate frequency of e.g. 455 KHz, and then the received frequency is digitally displayed.
: - 2 -1093~;~5 However, conventionally there is a problem in this method as follows. That is, in receiving the signal of short wave band of 3 to 30 M~lz, although the frequency drift of the local oscillation frequency near to the lower end of the above band is comparatively small, for a higher frequency of that band it is difficult to hold stably the desired signal, which is once tuned accurately, for a long time. Further, in the case when a digital displaying device as described above is installed in a radio receiver, it becomes necessary to count the frequency up to a higher frequency. That is, although it depends on the intermediate frequency, in the case of 455 KHz intermediate frequency, it is necessary to count the frequency up to 30.455 KHz. This fact requires a high speed integrated circuit such as TTL for a radio receiver, and it is undesirable because of power consumption thereof and of heat generation in the set and spurious radiation.
For the problem described above, there is a method using a variable frequency oscillator having an oscillation frequency enough lower than the upper limit, e.g. 30 MHz, of the desired receiving frequencies and a reference frequency oscillator such as a crystal oscillator having a stable ref-erence oscillation frequency. The output signals of these two oscillators are mixed and passed through a band pass filter, and then there is provided a desired higher local oscillation frequency which is the sum or difference of these two oscil-lation frequencies. However, in this method it is very dif-ficult to take out only the desired local oscillation frequency because of difficulty of eliminating all of the spurious signals, i.e. higher harmonics of the two oscillation fre-quencies and cross modulation signals thereof, at the same time. In addition, there are further disadvantages that such a method requires many band pass filters and that in case of ~ - 3 -~g36~1~
displaying the received frequency by means of a digital counter a high speed presettable frequency counter, which is usually expensive, is required, as described hereinbefore.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an improved and novel radio receiver in which the problems described above can be eliminated and in which tuning is accurate and stable with less disturbance from spurious signals.
Another object of the present invention is to pro-vide a novel and improved multi-band radio receiver with a simple circuit configuration in which tuning is accurate and stable and eliminates spurious signals.
A further object of the present invention is to provide a radio receiver which can display the received frequency by means of a frequency counter of a comparatively low speed.
A further object of the present invention is to provide a radio receiver which can correct the error of in-dication in displaying the received frequency by means of a simple circuit.
These objects can be achieved according to the present invention by providing a radio receiver which comprises an input terminal to which a received signal having a frequency band centered about a frequency fO is applied; a variable fre-quency oscillator for producing a signal having an adjustable frequency f ; a first reference oscillator for producing a signal having a fixed frequency fRl which is higher than the upper limit of said frequency band of said received signal; a first premixer connected to said variable frequency oscillator and said first reference oscillator for mixing the signals of said variable frequency oscillator and said first reference oscillator;
3~
a first band pass filter connected to said first premixer for passing a frequency which is the algebraic sum of the frequency of said variable frequency oscillator and the frequency of said first reference oscillator; a second reference oscillator for producing a signal having a fixed frequency fR2; a second pre-mixer connected to said first band pass filter and said second ..
reference oscillator for mixing the signals of said first band pass filter and said second reference oscillator; a second band pass filter connected to said second premixer for passing a frequency which is the algebraic sum of the frequency passedby said first band pass filter and the frequency of said second reference oscillator; a frequency converter connected to said input terminal and said second band pass filter for mixing the signals of said input terminal and said second band pass filter and producing a signal at an intermediate frequency which is the difference of the frequency of said input terminal and the frequency of said second band pass filter; an intermediate fre-quency amplifier connected to said frequency converter for ampli-fying the signal of said frequency converter at the intermediate frequency; and wherein said variable frequency oscillator has a variable tuning circuit having a range of frequencies equal to twice the intermediate frequency.
The radio receiver can be one which can digitally display a received frequency fO, in which case it comprises:
an input terminal to which a received signal of frequency fO
. is applied; a local oscillator for producing a first signal having an adjustable frequency fl which has first constant frequency difference from said received signal of frequency fO and a second signal having an adjustable frequency f 1~
which has a second constant frequency difference from said received signal of frequency fO; a first frequency converter . - 5 -1(~93~i"S
connected to said input terminal and said local oscilla'cor for mixing the received signal of the input terminal and the first signal of the local oscillator and producing a signal at an intermediate frequency which is the algebraic sum of the fre- ~
quency of the received signal of the input terminal and the frequency of said first signal of said local oscillator; a first intermediate frequency amplifier connected to said local oscill-ator for amplifying the signal of said frequency converter at the intermediate frequency; a buffer amplifier connected to said local oscillator for amplifying said second signal of said local oscillator; a gate circuit connected to said buffer ampli-fier for passing the output signal of said buffer amplifier for a predetermined period; a lower digital frequency counter connec-ted to said gate circuit for counting the frequency of the out-put of said gate circuit and providing a digital output signalthereof; an upper digital frequency counter connected to said lower digit counter for counting the upper digits of the fre-quency of the output of said gate circuit and providing a digi-tal output signal thereof; a presetter connected only to said upper digit frequency counter for generating a digital signal representing said second constant frequency difference between the received frequency fO and the second signal of the local oscillator frequency fVl, and presetting that signal into the upper digit frequency counter for making the digital output signal of said upper digit frequency counter the sum of said preset digital signal and the upper digits of the count of the frequency of the output of said gate circuit; and a digital dis-play means connected to said lower digit frequency counter and said upper digit frequency for displaying the digital output signals thereof. The local oscillator can contain a variable frequency oscillator for producing a signal having an adjustable frequency of f l; a reference oscillator for producing a signal .~ - 6 -~J
3t~S
of fixed frequency equal to the algebraic sum of f and fl;
and a frequency conversion means connected to said variable frequency oscillator and said reference oscillator for mixing the signals thereof and for production of a signal of frequency ~1 -BRIEF DESCRIPTION OF THE DRAWINGS
These and other objects and the features of the present invention will be apparent from consideration of the following detailed description of an embodiment of the invention with the accompanying drawings, in which:
Fig. 1 is a block diagram of an embodiment of a radio receiver according to the present invention;
Fig. 2 is a circuit diagram of an embodiment of a first local oscillator of the invention used for the radio receiver shown in Fig. l; and Fig. 3 is a circuit diagram, partially in blocks, of a frequency counter unit used for a radio receiver accord-~- ing to the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Fig. 1 shows an embodiment of the present invention, a double-super heterodyne type short wave receiver which can display the received frequency in digits by means of a frequency counter. In Fig. 1, a signal received by an antenna desig-nated by a reference numeral 1 is applied to a radio frequency amplifier (RF Amp) 2. Said RF Amp 2 has a selection circuit for selecting the received signal of frequency f0, and the selected received signal of that frequency f0 is applied to an input terminal 4 of a first frequency converter (lst Freq. Conv.) 3. Said 1st Freq. Conv. 3 has another input f ~".
1(~93~'~5 terminal connected to an output terminal of a first local oscillator (lst Local Osc.) 5. The received signal of the frequency fQ and the output signal of a frequency fl of said 1st Local Osc. 5 are mixed by the 1st Freq. Conv. 3, and there is provided a signal of a first intermediate frequency (lst IF) f2 of the algebraic sum of these two frequencies =fo+fl) -A first intermediate frequency amplifier (lst IF
Amp.) 6 connected to the 1st Freq. Conv. 3 amplifies said 1st IF signal and provides its output signal to a second frequency converter (2nd Freq. Conv.) 7. Said 2nd Freq. Conv. 7 mixes the 1st IF signal and an output signal of frequency fv2 f a second local oscillator (2nd Local Osc.) 8, and a resultant signal of a second intermediate frequency f3 (f3=f2+fv2) is applied to a second intermediate frequency amplifier (2nd IF
Amp.) 9. Said 2nd IF Amp. 9 is connected to an amplitude modulation detector (AM Det.l 10, which is connected to an audio frequency amplifier (AF Amp.) 11 connected to a loud-speaker 12. Further, a frequency counter unit 13 composed of a frequency counter block 14 and a digital display block 15 is connected to a first variable frequency oscillator contained in the 1st Local Osc. 5. Said frequency counter unit 13 counts its oscillation frequency and digital displays the received frequency fO. As these blocks shown in Fig. 1, except the 1st Local Osc. and the frequency counter unit 13, can be realized by the suitable circuits which are well known to those skilled in the art, detailed description of the respective circuits are omitted herewith for simplification, Fig. 2 shows an embodiment of the 1st Local Osc. 5 used in Fig. 1 according to the invention. In Fig. 2, an oscillation frequency fVl of the first variable frequency oscillator (lst V.F.O.) 16 and its variable range ~fVl are 1C~93~5 arranged to be low and small so as to ensure sufficient Y ( 'g' fVl 5~9 MHZ, ~fvl=4 MHZ). As a first ref erence frequency oscillator (,lst R.F.O.) 18, a fixed oscillator of high stability such as a crystal oscillator is used, and its oscillation frequency fRl is arranged to be a frequency high than the upper limit of the receiving frequency band (e.g. fRl=60 MHz). The output signals of the frequencies fVl and fRl of these two oscillators are applied to a`first premixer 19 and mixed thereby. A first band pass filter (lst B.P.F.) 20 connected to the output terminal of said first premixer 19 passes through only a frequency component of fRl+f 1 (e.g. 65 to 69 MHZ) and provides a signal of that frequency to a second premixer 21.
A second reference frequency oscillator (2nd R.F.O.) 22 and a third reference frequency oscillator (3rd R.F.O.) 23 are stable fixed oscillators having oscillation frequencies fR2 and fR3, respectively (e.g. fR2+40MHz, fR3+48 MHz). Any one of the output signals of these 2nd R.F.O. 22 and 3rd R.F.O. 23 is selected by a first band switch 24 and provided to the second,premixer 21. When the 2nd R.F.O. is selected by the first band switch 24, in the second premixer 21 there is provided a frequency component fl'of a difference of the output signal frequency fRl+fvl f the 1st B.P.F. 20 and the oscillation frequency fR2 of the 2nd R.F.O. 22, i.e. fl=
fRl-fR2+fvl. A second band pass filter (2nd B.P.F.) 25 passes through cnly that frequency component fl=fRl-fR2+fvl (e.g.
fl=25 to 29 MHZ) and provides the output signal of the fre-quency. This output signal is selected by a second band switch 27 and provided to an output terminal 29. Said output terminal 29 is the output terminal of the 1st Local Osc. 5 described hereinbefore and connected to the 1st Freq. Conv. 3.
When the center frequency of the 1st IF Amp. 6 iS 2 MHZ, g 105~3~ S
in the case of the above example of the frequencies shown in the parentheses, the signals of short wave from 27 to 31 MHz can be satisfactorily received.
There is conventionally a so-called premix method used for amateur band receiver, in which one variable frequency oscillator and one reference frequency oscillator are used and a frequency of the algebraic sum of both the oscillation frequencies of them is generated as a local oscillation frequency. That is, the resulting frequency used could be 10 the sum frequency or the difference frequency. As the re-ceiving band of the amateur band receiver is comparatively narrow, in this case it is easy to separate the desired local oscillation signal and undesired spurious signal. On the other hand, as the receiving band of a short wave broadcasting receiver is wide, many spurious signals owing to premixing are caused at the output terminal of the local oscillator and so 7 it is difficult to use such a premix method for the short wave broadcasting receiver.
According to the present invention, as described 20 hereinbefore, as the oscillation frequency of the first variable frequency oscillator is once converted to the frequency higher than the receiving band by means of the first reference frequency oscillator, and after that down-converted by means of the second reference frequency oscillator, it becomes pos-sible to eliminate the spurious signals as described above.
Further, according to the present invention, as the oscil-lation frequency fVl f the first variable frequency oscil-lator can be made low, the short wave broadcasting signal can be received very stably. In addition, by counting said 30 frequency fVl, the received frequency f0 can be digitally displayed comparatively easily. If the frequency fV1 is higher, a high speed frequency counter of high cost is required.
1~93~ S
Usually, a short wave broadcasting receiver receives the signal by dividing the receiving band of about 3 to 30 MHz into suitable bands. In the above mentioned example, although the broadcasting wave of 27 to 31 MHz can be received as one receiving band, for receiving the broadcasting wave lower than 27 MHz many reference frequency oscillators and band pass filters as of the 3rd R.F.O. 23 and 3rd B.P.F. 26 are necessary.
However, according to the present invention, by arranging the frequency variable range ~fVl of the 1st V.F.O. 16 to twice of the center frequency of the 1st IF Amp. 6, the number of the required reference frequency oscillators and band pass filters can be reduced to a half. That is, as the center frequency of the 1st IF Amp. 6 is 2 MHz in the above example, the frequency variable range ~f 1 is made 4 MHz. Thus, there is provided a signal of frequency of 25 to 29 MHz at the output terminal 29 of the 1st Local Osc. 5. By this frequency, the broadcasting wave of not only the band of 27 to 31 MHz but also the band of 23 to 27 MHz can be received, because the center frequencies of these two bands are 2 MHz common to each -20 other.
Besides, there is another problem in prior art at digital displaying the received frequency with use of a digital counter. That is, it is necessary to use a presettable counter so as to correct the difference between the received frequency and the practically counted first local oscillation frequency.
The presettable counter has a higher speed and is more expen-sive as compared to a non-presettable counter. Further, the presettable counter to be used is required to be faster and so more expensive for a lower figure of the frequency to be counted and digital displayed. Further, in a conventional short wave broadcasting receiver, it is necessary to correct with the intermediate frequency of 455 KHz. According to the las3~i~s present invention, a radio receiver which can digitally display the received frequency can be provided without using a high speed presettable counter and so with a low cost.
Fig. 3 shows an embodiment of a frequency counter unit used for the radio receiver according to the invention.
An output terminal 17 of the first variable frequency oscil-lator 16 shown in Fig. 2 is connected to an input terminal 30 of a buffer amplifier 31 of Fig. 3. The output signal having the oscillation frequency fVl of the first variable frequency oscillator 16 is amplified by said buffer amplifier 31 and provided to a gate 34 in a gate circuit 32. If necessary, a driver 33 may be inserted between the buffer amplifier 31 and the gate 34. The period of the signal passing through the gate 34 is determined by a gate time generator 35 connected to the gate 34. The frequency of the signal passed through the gate 34 is counted by a lower digit frequency counter 36 connected to the gate 34. Said lower digit frequency counter 36 is a non-presettable counter and it counts the lower figure of the frequency fVl of the first variable frequency oscillator 16. An upper digit frequency counter 38 connected to a pre-setter 37 is a presettable counter, and a preset value thereof is decided by said presetter 37. Said upper digit frequency ~
counter 38 is connected to the lower digit frequency counter ' ~ ~ -36, and it counts the upper figure of the frequency fVl of the first variable frequency oscillator 16. The digital information of the outputs of these two counters are provided to a driver circuit 39 and then digital displayed by a display device 40 formed e.g. by light emitting diodes. As the blocks shown in Fig. 3 can be realized by suitable circuits which are well known to those skilled in the art, detailed descri-ption of the respective circuits are omitted therewith for simplification.
i 1093~;~S
According to the present inventlon, the received frequency fO is diyitally displĂ yed by using the first variable frequency oscillator having a variable tuning circuit for providing the oscillation frequency fVl which coincides with the received frequency fQ in the lower figure and by correcting for different upper figures by the presetter 37. Accordingly, it becomes possible to use the non-presettable counter 36 of low speed and low cost, as described hereinbefore, and so there is provided a short wave broadcasting receiver of low cost which can digitally display the received freq~ency.
Another feature of the present invention is the first local oscillator comprising a frequency synthesizer and the first variable frequency oscillator having the frequency fVl. The frequency synthesizer is connected to the variable frequency oscillator, and it provides the output signal of the frequency of fR+f 1 by shifting the above frequency fVl by a certain reference frequency fR. Therefore, in this case the above mentioned preset value of the presetter becomes the algebraic sum of that reference frequency fR and the center frequency fC of the 1st IF Amp. 6, i.e. fR+fC- Accordingly, degree of freedom for designing the frequency fC or fR becomes large. Further another feature of the present invention is that when the frequency syntheslzer as described above is not used, the 1st IF Amp. uses a tuning circuti having the center frequency f , which is an integral multiple of 100 KHz. By this, it easily becomes possible to use a non-presettable counter.
There is another problem~besides the above of ~sing the frequency counter in the radio receiver set. That is the problem of drift of the center frequency of the IF Amp. owing to e.g. temperature. By this frequency drift, there is caused an error between the practically received frequency and the 1~93~;'15 displayed frequency, Therefore, conventionally a high speed presettable counter of high cost which can preset the lowest figure is required. Another feature of the present invention is that such an error can be corrected simply. That is, ac-cording to the present invention, a double superheterodyne type is used as shown in Fig. 1, and the 2nd Local Osc. 8 has a variable tuning circuit, the frequency variable range of which is nearly equal to the band width of the 2nd IF Amp.
By this means, even when an error is caused in the center frequency of the 2nd IF Amp., it can be easily corrected by changing the oscillation frequency of the 2nd Local Osc.
'~,
..., . _ This inventian relates to a radio receiver, and more particularly to a radio receiver which can receive a signal of a desired frequency stably and accurately with a desirable characteristic of suppressing a spurious signal, and further to a radio receiver which can display the received frequency in digits by means of a frequency counter.
Generally, in short wave broadcasting, the carrier frequency uses a very wide frequency band from 3 MHz to 30 MHz, and there are broadcasting stations numbering 4000 to 5000 in the world. The minimum unit of the carrier frequency regulation of these stations is on the order of kilohertz.
Therefore, a receiver for receiving a short wave signal is required to receive the desired signal accurately and to con-tinue the receiving stably for a long time. However, con- ~ -ventional short wave radio receivers are not always satis-factory for the above requirements. It is often troublesome to tune the desired station accurately, and even when the receiver is accurately tuned to the desired station there is often a problem of drift of the received frequency.
As one of the method of improving the accuracy of tuning, there is a method of counting the oscillated frequency of a local oscillator digitally and displaying the nume~ral of the short wave frequency to be received. In such a short wave receiYer, the received frequency should be counted and displayed accurately and stably. In the prior art, for a superheterodyne radio recçiver, known to be one of the best methods of improving the display accuracy of the received frequency, the oscillated frequency of the local oscillator is directly counted and corrected with addition or subtraction of the intermediate frequency of e.g. 455 KHz, and then the received frequency is digitally displayed.
: - 2 -1093~;~5 However, conventionally there is a problem in this method as follows. That is, in receiving the signal of short wave band of 3 to 30 M~lz, although the frequency drift of the local oscillation frequency near to the lower end of the above band is comparatively small, for a higher frequency of that band it is difficult to hold stably the desired signal, which is once tuned accurately, for a long time. Further, in the case when a digital displaying device as described above is installed in a radio receiver, it becomes necessary to count the frequency up to a higher frequency. That is, although it depends on the intermediate frequency, in the case of 455 KHz intermediate frequency, it is necessary to count the frequency up to 30.455 KHz. This fact requires a high speed integrated circuit such as TTL for a radio receiver, and it is undesirable because of power consumption thereof and of heat generation in the set and spurious radiation.
For the problem described above, there is a method using a variable frequency oscillator having an oscillation frequency enough lower than the upper limit, e.g. 30 MHz, of the desired receiving frequencies and a reference frequency oscillator such as a crystal oscillator having a stable ref-erence oscillation frequency. The output signals of these two oscillators are mixed and passed through a band pass filter, and then there is provided a desired higher local oscillation frequency which is the sum or difference of these two oscil-lation frequencies. However, in this method it is very dif-ficult to take out only the desired local oscillation frequency because of difficulty of eliminating all of the spurious signals, i.e. higher harmonics of the two oscillation fre-quencies and cross modulation signals thereof, at the same time. In addition, there are further disadvantages that such a method requires many band pass filters and that in case of ~ - 3 -~g36~1~
displaying the received frequency by means of a digital counter a high speed presettable frequency counter, which is usually expensive, is required, as described hereinbefore.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an improved and novel radio receiver in which the problems described above can be eliminated and in which tuning is accurate and stable with less disturbance from spurious signals.
Another object of the present invention is to pro-vide a novel and improved multi-band radio receiver with a simple circuit configuration in which tuning is accurate and stable and eliminates spurious signals.
A further object of the present invention is to provide a radio receiver which can display the received frequency by means of a frequency counter of a comparatively low speed.
A further object of the present invention is to provide a radio receiver which can correct the error of in-dication in displaying the received frequency by means of a simple circuit.
These objects can be achieved according to the present invention by providing a radio receiver which comprises an input terminal to which a received signal having a frequency band centered about a frequency fO is applied; a variable fre-quency oscillator for producing a signal having an adjustable frequency f ; a first reference oscillator for producing a signal having a fixed frequency fRl which is higher than the upper limit of said frequency band of said received signal; a first premixer connected to said variable frequency oscillator and said first reference oscillator for mixing the signals of said variable frequency oscillator and said first reference oscillator;
3~
a first band pass filter connected to said first premixer for passing a frequency which is the algebraic sum of the frequency of said variable frequency oscillator and the frequency of said first reference oscillator; a second reference oscillator for producing a signal having a fixed frequency fR2; a second pre-mixer connected to said first band pass filter and said second ..
reference oscillator for mixing the signals of said first band pass filter and said second reference oscillator; a second band pass filter connected to said second premixer for passing a frequency which is the algebraic sum of the frequency passedby said first band pass filter and the frequency of said second reference oscillator; a frequency converter connected to said input terminal and said second band pass filter for mixing the signals of said input terminal and said second band pass filter and producing a signal at an intermediate frequency which is the difference of the frequency of said input terminal and the frequency of said second band pass filter; an intermediate fre-quency amplifier connected to said frequency converter for ampli-fying the signal of said frequency converter at the intermediate frequency; and wherein said variable frequency oscillator has a variable tuning circuit having a range of frequencies equal to twice the intermediate frequency.
The radio receiver can be one which can digitally display a received frequency fO, in which case it comprises:
an input terminal to which a received signal of frequency fO
. is applied; a local oscillator for producing a first signal having an adjustable frequency fl which has first constant frequency difference from said received signal of frequency fO and a second signal having an adjustable frequency f 1~
which has a second constant frequency difference from said received signal of frequency fO; a first frequency converter . - 5 -1(~93~i"S
connected to said input terminal and said local oscilla'cor for mixing the received signal of the input terminal and the first signal of the local oscillator and producing a signal at an intermediate frequency which is the algebraic sum of the fre- ~
quency of the received signal of the input terminal and the frequency of said first signal of said local oscillator; a first intermediate frequency amplifier connected to said local oscill-ator for amplifying the signal of said frequency converter at the intermediate frequency; a buffer amplifier connected to said local oscillator for amplifying said second signal of said local oscillator; a gate circuit connected to said buffer ampli-fier for passing the output signal of said buffer amplifier for a predetermined period; a lower digital frequency counter connec-ted to said gate circuit for counting the frequency of the out-put of said gate circuit and providing a digital output signalthereof; an upper digital frequency counter connected to said lower digit counter for counting the upper digits of the fre-quency of the output of said gate circuit and providing a digi-tal output signal thereof; a presetter connected only to said upper digit frequency counter for generating a digital signal representing said second constant frequency difference between the received frequency fO and the second signal of the local oscillator frequency fVl, and presetting that signal into the upper digit frequency counter for making the digital output signal of said upper digit frequency counter the sum of said preset digital signal and the upper digits of the count of the frequency of the output of said gate circuit; and a digital dis-play means connected to said lower digit frequency counter and said upper digit frequency for displaying the digital output signals thereof. The local oscillator can contain a variable frequency oscillator for producing a signal having an adjustable frequency of f l; a reference oscillator for producing a signal .~ - 6 -~J
3t~S
of fixed frequency equal to the algebraic sum of f and fl;
and a frequency conversion means connected to said variable frequency oscillator and said reference oscillator for mixing the signals thereof and for production of a signal of frequency ~1 -BRIEF DESCRIPTION OF THE DRAWINGS
These and other objects and the features of the present invention will be apparent from consideration of the following detailed description of an embodiment of the invention with the accompanying drawings, in which:
Fig. 1 is a block diagram of an embodiment of a radio receiver according to the present invention;
Fig. 2 is a circuit diagram of an embodiment of a first local oscillator of the invention used for the radio receiver shown in Fig. l; and Fig. 3 is a circuit diagram, partially in blocks, of a frequency counter unit used for a radio receiver accord-~- ing to the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Fig. 1 shows an embodiment of the present invention, a double-super heterodyne type short wave receiver which can display the received frequency in digits by means of a frequency counter. In Fig. 1, a signal received by an antenna desig-nated by a reference numeral 1 is applied to a radio frequency amplifier (RF Amp) 2. Said RF Amp 2 has a selection circuit for selecting the received signal of frequency f0, and the selected received signal of that frequency f0 is applied to an input terminal 4 of a first frequency converter (lst Freq. Conv.) 3. Said 1st Freq. Conv. 3 has another input f ~".
1(~93~'~5 terminal connected to an output terminal of a first local oscillator (lst Local Osc.) 5. The received signal of the frequency fQ and the output signal of a frequency fl of said 1st Local Osc. 5 are mixed by the 1st Freq. Conv. 3, and there is provided a signal of a first intermediate frequency (lst IF) f2 of the algebraic sum of these two frequencies =fo+fl) -A first intermediate frequency amplifier (lst IF
Amp.) 6 connected to the 1st Freq. Conv. 3 amplifies said 1st IF signal and provides its output signal to a second frequency converter (2nd Freq. Conv.) 7. Said 2nd Freq. Conv. 7 mixes the 1st IF signal and an output signal of frequency fv2 f a second local oscillator (2nd Local Osc.) 8, and a resultant signal of a second intermediate frequency f3 (f3=f2+fv2) is applied to a second intermediate frequency amplifier (2nd IF
Amp.) 9. Said 2nd IF Amp. 9 is connected to an amplitude modulation detector (AM Det.l 10, which is connected to an audio frequency amplifier (AF Amp.) 11 connected to a loud-speaker 12. Further, a frequency counter unit 13 composed of a frequency counter block 14 and a digital display block 15 is connected to a first variable frequency oscillator contained in the 1st Local Osc. 5. Said frequency counter unit 13 counts its oscillation frequency and digital displays the received frequency fO. As these blocks shown in Fig. 1, except the 1st Local Osc. and the frequency counter unit 13, can be realized by the suitable circuits which are well known to those skilled in the art, detailed description of the respective circuits are omitted herewith for simplification, Fig. 2 shows an embodiment of the 1st Local Osc. 5 used in Fig. 1 according to the invention. In Fig. 2, an oscillation frequency fVl of the first variable frequency oscillator (lst V.F.O.) 16 and its variable range ~fVl are 1C~93~5 arranged to be low and small so as to ensure sufficient Y ( 'g' fVl 5~9 MHZ, ~fvl=4 MHZ). As a first ref erence frequency oscillator (,lst R.F.O.) 18, a fixed oscillator of high stability such as a crystal oscillator is used, and its oscillation frequency fRl is arranged to be a frequency high than the upper limit of the receiving frequency band (e.g. fRl=60 MHz). The output signals of the frequencies fVl and fRl of these two oscillators are applied to a`first premixer 19 and mixed thereby. A first band pass filter (lst B.P.F.) 20 connected to the output terminal of said first premixer 19 passes through only a frequency component of fRl+f 1 (e.g. 65 to 69 MHZ) and provides a signal of that frequency to a second premixer 21.
A second reference frequency oscillator (2nd R.F.O.) 22 and a third reference frequency oscillator (3rd R.F.O.) 23 are stable fixed oscillators having oscillation frequencies fR2 and fR3, respectively (e.g. fR2+40MHz, fR3+48 MHz). Any one of the output signals of these 2nd R.F.O. 22 and 3rd R.F.O. 23 is selected by a first band switch 24 and provided to the second,premixer 21. When the 2nd R.F.O. is selected by the first band switch 24, in the second premixer 21 there is provided a frequency component fl'of a difference of the output signal frequency fRl+fvl f the 1st B.P.F. 20 and the oscillation frequency fR2 of the 2nd R.F.O. 22, i.e. fl=
fRl-fR2+fvl. A second band pass filter (2nd B.P.F.) 25 passes through cnly that frequency component fl=fRl-fR2+fvl (e.g.
fl=25 to 29 MHZ) and provides the output signal of the fre-quency. This output signal is selected by a second band switch 27 and provided to an output terminal 29. Said output terminal 29 is the output terminal of the 1st Local Osc. 5 described hereinbefore and connected to the 1st Freq. Conv. 3.
When the center frequency of the 1st IF Amp. 6 iS 2 MHZ, g 105~3~ S
in the case of the above example of the frequencies shown in the parentheses, the signals of short wave from 27 to 31 MHz can be satisfactorily received.
There is conventionally a so-called premix method used for amateur band receiver, in which one variable frequency oscillator and one reference frequency oscillator are used and a frequency of the algebraic sum of both the oscillation frequencies of them is generated as a local oscillation frequency. That is, the resulting frequency used could be 10 the sum frequency or the difference frequency. As the re-ceiving band of the amateur band receiver is comparatively narrow, in this case it is easy to separate the desired local oscillation signal and undesired spurious signal. On the other hand, as the receiving band of a short wave broadcasting receiver is wide, many spurious signals owing to premixing are caused at the output terminal of the local oscillator and so 7 it is difficult to use such a premix method for the short wave broadcasting receiver.
According to the present invention, as described 20 hereinbefore, as the oscillation frequency of the first variable frequency oscillator is once converted to the frequency higher than the receiving band by means of the first reference frequency oscillator, and after that down-converted by means of the second reference frequency oscillator, it becomes pos-sible to eliminate the spurious signals as described above.
Further, according to the present invention, as the oscil-lation frequency fVl f the first variable frequency oscil-lator can be made low, the short wave broadcasting signal can be received very stably. In addition, by counting said 30 frequency fVl, the received frequency f0 can be digitally displayed comparatively easily. If the frequency fV1 is higher, a high speed frequency counter of high cost is required.
1~93~ S
Usually, a short wave broadcasting receiver receives the signal by dividing the receiving band of about 3 to 30 MHz into suitable bands. In the above mentioned example, although the broadcasting wave of 27 to 31 MHz can be received as one receiving band, for receiving the broadcasting wave lower than 27 MHz many reference frequency oscillators and band pass filters as of the 3rd R.F.O. 23 and 3rd B.P.F. 26 are necessary.
However, according to the present invention, by arranging the frequency variable range ~fVl of the 1st V.F.O. 16 to twice of the center frequency of the 1st IF Amp. 6, the number of the required reference frequency oscillators and band pass filters can be reduced to a half. That is, as the center frequency of the 1st IF Amp. 6 is 2 MHz in the above example, the frequency variable range ~f 1 is made 4 MHz. Thus, there is provided a signal of frequency of 25 to 29 MHz at the output terminal 29 of the 1st Local Osc. 5. By this frequency, the broadcasting wave of not only the band of 27 to 31 MHz but also the band of 23 to 27 MHz can be received, because the center frequencies of these two bands are 2 MHz common to each -20 other.
Besides, there is another problem in prior art at digital displaying the received frequency with use of a digital counter. That is, it is necessary to use a presettable counter so as to correct the difference between the received frequency and the practically counted first local oscillation frequency.
The presettable counter has a higher speed and is more expen-sive as compared to a non-presettable counter. Further, the presettable counter to be used is required to be faster and so more expensive for a lower figure of the frequency to be counted and digital displayed. Further, in a conventional short wave broadcasting receiver, it is necessary to correct with the intermediate frequency of 455 KHz. According to the las3~i~s present invention, a radio receiver which can digitally display the received frequency can be provided without using a high speed presettable counter and so with a low cost.
Fig. 3 shows an embodiment of a frequency counter unit used for the radio receiver according to the invention.
An output terminal 17 of the first variable frequency oscil-lator 16 shown in Fig. 2 is connected to an input terminal 30 of a buffer amplifier 31 of Fig. 3. The output signal having the oscillation frequency fVl of the first variable frequency oscillator 16 is amplified by said buffer amplifier 31 and provided to a gate 34 in a gate circuit 32. If necessary, a driver 33 may be inserted between the buffer amplifier 31 and the gate 34. The period of the signal passing through the gate 34 is determined by a gate time generator 35 connected to the gate 34. The frequency of the signal passed through the gate 34 is counted by a lower digit frequency counter 36 connected to the gate 34. Said lower digit frequency counter 36 is a non-presettable counter and it counts the lower figure of the frequency fVl of the first variable frequency oscillator 16. An upper digit frequency counter 38 connected to a pre-setter 37 is a presettable counter, and a preset value thereof is decided by said presetter 37. Said upper digit frequency ~
counter 38 is connected to the lower digit frequency counter ' ~ ~ -36, and it counts the upper figure of the frequency fVl of the first variable frequency oscillator 16. The digital information of the outputs of these two counters are provided to a driver circuit 39 and then digital displayed by a display device 40 formed e.g. by light emitting diodes. As the blocks shown in Fig. 3 can be realized by suitable circuits which are well known to those skilled in the art, detailed descri-ption of the respective circuits are omitted therewith for simplification.
i 1093~;~S
According to the present inventlon, the received frequency fO is diyitally displĂ yed by using the first variable frequency oscillator having a variable tuning circuit for providing the oscillation frequency fVl which coincides with the received frequency fQ in the lower figure and by correcting for different upper figures by the presetter 37. Accordingly, it becomes possible to use the non-presettable counter 36 of low speed and low cost, as described hereinbefore, and so there is provided a short wave broadcasting receiver of low cost which can digitally display the received freq~ency.
Another feature of the present invention is the first local oscillator comprising a frequency synthesizer and the first variable frequency oscillator having the frequency fVl. The frequency synthesizer is connected to the variable frequency oscillator, and it provides the output signal of the frequency of fR+f 1 by shifting the above frequency fVl by a certain reference frequency fR. Therefore, in this case the above mentioned preset value of the presetter becomes the algebraic sum of that reference frequency fR and the center frequency fC of the 1st IF Amp. 6, i.e. fR+fC- Accordingly, degree of freedom for designing the frequency fC or fR becomes large. Further another feature of the present invention is that when the frequency syntheslzer as described above is not used, the 1st IF Amp. uses a tuning circuti having the center frequency f , which is an integral multiple of 100 KHz. By this, it easily becomes possible to use a non-presettable counter.
There is another problem~besides the above of ~sing the frequency counter in the radio receiver set. That is the problem of drift of the center frequency of the IF Amp. owing to e.g. temperature. By this frequency drift, there is caused an error between the practically received frequency and the 1~93~;'15 displayed frequency, Therefore, conventionally a high speed presettable counter of high cost which can preset the lowest figure is required. Another feature of the present invention is that such an error can be corrected simply. That is, ac-cording to the present invention, a double superheterodyne type is used as shown in Fig. 1, and the 2nd Local Osc. 8 has a variable tuning circuit, the frequency variable range of which is nearly equal to the band width of the 2nd IF Amp.
By this means, even when an error is caused in the center frequency of the 2nd IF Amp., it can be easily corrected by changing the oscillation frequency of the 2nd Local Osc.
'~,
Claims (3)
1. A radio receiver comprising:
an input terminal to which a received signal having a frequency band centered about a frequency fo is applied;
a variable frequency oscillator for produc-ing a signal having an adjustable frequency fv;
a first reference oscillator for producing a signal having a fixed frequency fR1 which is higher than the upper limit of said frequency band of said received signal;
a first premixer connected to said variable frequency oscillator and said first reference oscillator for mixing the signals of said variable frequency oscillator and said first reference oscillator;
a first band pass filter connected to said first premixer for passing a frequency which is the algebraic sum of the frequency of said variable frequency oscillator and the frequency of said first reference oscillator;
a second reference oscillator for producing a signal having a fixed frequency fR2;
a second premixer connected to said first band pass filter and said second reference oscillator for mix-ing the signals of said first band pass filter and said second reference oscillator;
a second band pass filter connected to said second premixer for passing a frequency which is the algebraic sum of the frequency passed by said first band pass filter and the frequency of said second reference oscillator;
a frequency converter connected to said in-put terminal and said second band pass filter for mixing the signals of said input terminal and said second band pass filter and producing a signal at an intermediate frequency which is the difference of the frequency of said input terminal and the frequency of said second band pass filter;
an intermediate frequency amplifier connected to said frequency converter for amplifying the signal of said frequency converter at the intermediate frequency ; and wherein said variable frequency oscillator has a variable tuning circuit having a range of frequencies equal to twice the intermediate frequency.
an input terminal to which a received signal having a frequency band centered about a frequency fo is applied;
a variable frequency oscillator for produc-ing a signal having an adjustable frequency fv;
a first reference oscillator for producing a signal having a fixed frequency fR1 which is higher than the upper limit of said frequency band of said received signal;
a first premixer connected to said variable frequency oscillator and said first reference oscillator for mixing the signals of said variable frequency oscillator and said first reference oscillator;
a first band pass filter connected to said first premixer for passing a frequency which is the algebraic sum of the frequency of said variable frequency oscillator and the frequency of said first reference oscillator;
a second reference oscillator for producing a signal having a fixed frequency fR2;
a second premixer connected to said first band pass filter and said second reference oscillator for mix-ing the signals of said first band pass filter and said second reference oscillator;
a second band pass filter connected to said second premixer for passing a frequency which is the algebraic sum of the frequency passed by said first band pass filter and the frequency of said second reference oscillator;
a frequency converter connected to said in-put terminal and said second band pass filter for mixing the signals of said input terminal and said second band pass filter and producing a signal at an intermediate frequency which is the difference of the frequency of said input terminal and the frequency of said second band pass filter;
an intermediate frequency amplifier connected to said frequency converter for amplifying the signal of said frequency converter at the intermediate frequency ; and wherein said variable frequency oscillator has a variable tuning circuit having a range of frequencies equal to twice the intermediate frequency.
2. A radio receiver which can digitally display a received frequency fo, comprising:
an input terminal to which a received signal of frequency fo is applied;
a first local oscillator for producing a first signal having an adjustable frequency f1 which has a con-stant frequency difference from said received signal of frequency fo and a second signal having an adjustable frequency fv1, which has a constant frequency difference from said received signal of frequency fo;
a first frequency converter connected to said input terminal and said first local oscillator for mixing the received signal of the input terminal and the first signal of the first local oscillator and producing a signal at an inter-mediate frequency which is the algebraic sum of the frequency of the received signal of the input terminal and the frequency of said first signal of said first local oscillator;
a first intermediate frequency amplifier connected to said first local oscillator for amplifying the signal of said first frequency converter at the intermediate frequency;
a buffer amplifier connected to said first local oscillator for amplifying said second signal of said first local oscillator;
a gate circuit connected to said buffer amplifier for passing the output signal of said buffer amplifier for a predetermined period;
a lower digital frequency counter connected to said gate circuit for counting the frequency of the output of said gate circuit and providing a digital output signal thereof;
an upper digital frequency counter connected to said lower digit counter for counting the upper digits of the frequency of the output of said gate circuit and providing a digital output signal thereof;
a presetter connected only to said upper digit frequency counter for generating a digital signal repre-senting said constant frequency difference between the received frequency fo and the second signal of the first local oscillator frequency fV1, and presetting that signal into the upper digit frequency counter for making the digital output signal of said upper digit frequency counter the sum of said preset digital signal and the upper digits of the count of the frequency of the output of said gate circuit; and a digital display means connected to said lower digit frequency counter and said upper digit frequency counter for displaying the digital output signals thereof.
an input terminal to which a received signal of frequency fo is applied;
a first local oscillator for producing a first signal having an adjustable frequency f1 which has a con-stant frequency difference from said received signal of frequency fo and a second signal having an adjustable frequency fv1, which has a constant frequency difference from said received signal of frequency fo;
a first frequency converter connected to said input terminal and said first local oscillator for mixing the received signal of the input terminal and the first signal of the first local oscillator and producing a signal at an inter-mediate frequency which is the algebraic sum of the frequency of the received signal of the input terminal and the frequency of said first signal of said first local oscillator;
a first intermediate frequency amplifier connected to said first local oscillator for amplifying the signal of said first frequency converter at the intermediate frequency;
a buffer amplifier connected to said first local oscillator for amplifying said second signal of said first local oscillator;
a gate circuit connected to said buffer amplifier for passing the output signal of said buffer amplifier for a predetermined period;
a lower digital frequency counter connected to said gate circuit for counting the frequency of the output of said gate circuit and providing a digital output signal thereof;
an upper digital frequency counter connected to said lower digit counter for counting the upper digits of the frequency of the output of said gate circuit and providing a digital output signal thereof;
a presetter connected only to said upper digit frequency counter for generating a digital signal repre-senting said constant frequency difference between the received frequency fo and the second signal of the first local oscillator frequency fV1, and presetting that signal into the upper digit frequency counter for making the digital output signal of said upper digit frequency counter the sum of said preset digital signal and the upper digits of the count of the frequency of the output of said gate circuit; and a digital display means connected to said lower digit frequency counter and said upper digit frequency counter for displaying the digital output signals thereof.
3. A radio receiver according to claim 2, wherein said first local oscillator contains:
a variable frequency oscillator for produc-ing a signal having an adjustable frequency of fv1;
a reference oscillator for producing a signal of fixed frequency equal to the algebraic sum of fv1 and f1; and a frequency conversion means connected to said variable frequency oscillator and said reference oscillator for mixing the signals thereof and for production of a signal of frequency f1.
a variable frequency oscillator for produc-ing a signal having an adjustable frequency of fv1;
a reference oscillator for producing a signal of fixed frequency equal to the algebraic sum of fv1 and f1; and a frequency conversion means connected to said variable frequency oscillator and said reference oscillator for mixing the signals thereof and for production of a signal of frequency f1.
Applications Claiming Priority (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP51-80510/1976 | 1976-07-06 | ||
| JP51-80509/1976 | 1976-07-06 | ||
| JP8051076A JPS535912A (en) | 1976-07-06 | 1976-07-06 | Radio receiver |
| JP8050976A JPS5847098B2 (en) | 1976-07-06 | 1976-07-06 | radio receiver |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1093645A true CA1093645A (en) | 1981-01-13 |
Family
ID=26421506
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA280,868A Expired CA1093645A (en) | 1976-07-06 | 1977-06-20 | Radio receiver employing premixing and digital display |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1093645A (en) |
-
1977
- 1977-06-20 CA CA280,868A patent/CA1093645A/en not_active Expired
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