JPS6031331Y2 - signal receiving device - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a signal receiving device that converts a received high frequency signal such as a television signal into an intermediate frequency signal and then converts it back into a predetermined high frequency signal to be used as a tuner in a conventional receiver. When supplying, the frequency of the above intermediate frequency signal (intermediate frequency)
By setting the frequency to a frequency located outside the frequency band of the intermediate frequency amplification circuit of a conventional receiver, it is possible to use a filter that is easy to manufacture and has an inexpensive configuration, and it is possible to sufficiently reduce beat interference. The object of the present invention is to provide a signal receiving device.

An example of a conventional signal receiving device that converts a received high frequency signal such as a television signal into an intermediate frequency signal and then converts it back into a predetermined high frequency signal and applies it to a tuner of a conventional receiver from an antenna terminal. A TV audio multiplex broadcast signal is received at the antenna terminal of a conventional television receiver that does not have a multiplex broadcast signal demodulation section, and the signal is converted into a television signal of an air channel in the area and applied to reproduce the image. There is a television audio multiplex broadcast transmitting/receiving adapter that has the function of displaying and demodulating multiplexed audio signals.With this type of adapter, the channel of a conventional television receiver can be simply fixed to an empty channel. There is no need to operate the adapter, and you can select the desired TV audio multiplex broadcast using a single tuner on the adapter.

Here, the video intermediate frequency ftp1 obtained by the tuner in the adapter is the video intermediate frequency f, g (for example, 58.75 MH) obtained by a conventional television receiver.
The same frequency as z) was selected.

However, due to errors in the circuit itself, in reality, the two video intermediate frequencies are not exactly the same, and there is a slight difference of about several hundred kilohertz, so the video intermediate frequency signal in the adapter is transferred to the high frequency of the empty channel. The input local oscillation frequency f of the RF converter for converting to a television signal.

A beat signal with a frequency that is the difference between □ and the video carrier frequency of the output high-frequency signal is generated in the mixing circuit of the television receiver, and this is not attenuated by about 50 dB or more than the signal level at the video intermediate frequency. In case,
Since the above-mentioned beat signal frequency is within the frequency band amplified by the video intermediate frequency amplification circuit of the television receiver, a significant beat disturbance occurs in the image.

Therefore, at the output part of the RF converter in the above adapter,
A filter circuit is inserted to attenuate the beat signal by 50 dB or more.

Here, as an example, due to the selectivity characteristics of a tuner in a conventional television receiver, the input high frequency signal frequency fRF2
The local oscillation frequency command molecule Lc input to the RF converter in the adapter is attenuated by 3QdB, and the output level of the video intermediate frequency ftp1 of the tuner in the adapter is set to a maximum of 105 dBμ and a minimum of 70 dBμ. Assuming that the output level of the input local oscillation frequency teaching molecule Lc is 115 dBμ, in order to attenuate the beat signal by 50 dB, the attenuation amount X of the filter circuit is 65 dB ("," 115-30-70-
X = -50) is required.

That is, this filter circuit has a video intermediate frequency f+p1
The level of local oscillation frequency fLc is set to 55 with respect to the level of
dB attenuation is required.

However, a filter circuit for obtaining an attenuation amount as large as 65 dB has the disadvantage that it is extremely large in size and expensive.

The present invention eliminates the above-mentioned drawbacks, and an embodiment thereof will be described below with reference to the drawings.

FIG. 1 shows a block system diagram of an embodiment in which the signal receiving apparatus according to the present invention is applied to receive television audio multiplex broadcasting, together with a block system diagram of a conventional television receiver.

In the figure, reference numeral 1 indicates an embodiment of the signal receiver device according to the present invention, which is equipped with a television audio multiplex broadcast reception function, and the block configuration itself shown in the figure is the same as that of the conventional television audio multiplex broadcast receiver adapter. - configuration, the present invention is characterized by the method of selecting the frequency of the local oscillation frequency fLt1, as will be described later.

This signal receiving device 1 is connected to an antenna terminal of a conventional television receiver 2.

The television audio multiplex broadcast radio waves that have entered the antenna 3 are thereby extracted as high-frequency signals, selectively tuned and amplified by the high-frequency amplification circuit 5 in the tuner 4, and then
The signal is supplied to the mixing circuit 6, where it is mixed (frequency converted) with the local oscillation frequency from the local oscillation circuit 7.

The mixing circuit 6 converts the high frequency signal frequency fRF1 of the desired channel from the frequency amplification circuit 5 and the local oscillation frequency antenna variablely output from the local oscillation circuit 7 according to the channel to be selected and received, as expressed by the following equation. It outputs an intermediate frequency signal having a constant video intermediate frequency fIp1 that is located outside the band for one channel from 54 MHz to 60 MHz in the overall frequency characteristic of the video intermediate frequency amplification circuit 21, which will be described later.

fI Pi” ft, tt f□
(1) The above-mentioned intermediate frequency signal is applied to the RF converter 15, which will be described later, and is also applied to the audio intermediate frequency amplification circuit 8, where the above-mentioned video intermediate frequency signal fl is 4
．． FM detection circuit 9 in which only the audio subcarrier obtained by frequency modulating the 5MH2 low carrier wave with a predetermined audio multiplexed signal is converted into an audio intermediate frequency signal with a carrier frequency of 4.5MH2.
and is subjected to FM detection here.

As is well known, the output signal of the FM detection circuit 9 is obtained by frequency modulating a direct wave main channel signal and a carrier wave having a frequency twice the horizontal scanning frequency of the television signal to be multiplexed with an audio signal. In order for the receiver to determine whether the subchannel signal and the multiplexed audio signal are dual audio broadcasting or stereo audio broadcasting, 922.5 is used in the case of dual audio broadcasting.
Hz control signal as a modulation signal, or in the case of stereo audio broadcasting, a 982.5H2 control signal as a modulation signal, and a control channel signal obtained by amplitude modulating a carrier wave with a frequency 35 times the horizontal scanning frequency. This frequency division multiplexed signal is supplied to a multiplexed signal demodulation circuit 10, where it is demodulated.

The signal demodulated by the multiplex signal demodulation circuit 10 is supplied to the speakers 13 and 14 via the low frequency amplifier circuits 11 and 12, and when receiving a stereo audio broadcast, the left channel signal from the speaker 13 and the right channel signal from the speaker 14 are simultaneously transmitted. On the other hand, when receiving a dual audio broadcast, the 2
A sound expansion signal for one of the types of sounds is selectively produced.

When receiving a conventional television broadcast rather than a television audio multiplex broadcast, no demodulated output is taken out from the multiplex signal demodulation circuit 10, and no sound is produced from the speakers 13 and 14.

On the other hand, the RF converter 15 is supplied with an intermediate frequency signal having a video intermediate frequency fI Pi from the tuner 4 and a constant local oscillation frequency fLc from the local oscillation circuit 16, and performs frequency conversion as shown by the following equation. Conduct, and always use high frequency television signals (of the sky channels in the area)
The signal is converted into a video carrier frequency fRF2) and supplied to the high frequency amplification circuit 18 in the tuner 17 from the antenna terminal of the conventional television receiver 2.

ftzp2=ft, c flpl (2) High-frequency television signal of an empty channel with a bandwidth of 6 MHz extracted from the high-frequency amplifier circuit 18 (to video carrier frequency, □)
is supplied to the mixing circuit 19, where it is mixed (frequency converted) with the local oscillation frequency fLt2 from the local oscillation circuit 20 so that the following equation holds, and the image intermediate frequency flF□(
Here, it is assumed to be an intermediate frequency signal having a frequency of 58, MH2).

flP□=fLt2−fRF□ (3
) As is well known, only the video intermediate frequency signal is extracted by the video intermediate frequency amplifying circuit 21 having the overall frequency characteristics as shown in FIG.
After being detected by the video amplifier circuit 23, the signal is applied to the cathode ray tube 24, where a reproduced image is displayed.

Note that when receiving conventional television broadcasting, the intermediate frequency signal branched and extracted from a part of the video intermediate frequency amplification circuit 21 is supplied to the audio intermediate frequency amplification circuit 25, where it is converted into a 4.5 MHz carrier wave. Only the audio intermediate frequency signal is separated and amplified, extracted, and supplied to the FM detection circuit 266.

The audio signal of the desired channel extracted by FM detection by the FM detection circuit 26 is amplified by the audio amplifier 27 and then applied to the speaker 28, thereby producing sound.

Next, an embodiment of how to select frequencies in the device of the present invention will be described in more detail.

As mentioned above, the video intermediate frequency f! The RP engineer has a total frequency characteristic of 54MHz for the video intermediate frequency amplification circuit 21.
It is assumed that the video intermediate frequency is a constant video intermediate frequency that is outside the band for one channel from 60 MHz (in this specification, this is also referred to as the frequency band of one intermediate frequency amplifier circuit), but for this reason, the local oscillation frequency In this embodiment, fLtl is, for example, a frequency f equal to the video intermediate frequency of 45.75 MHz, which is standardized for television receivers in the United States.
The value is selected to be output as IF1.

Here, if the empty channel of television broadcasting is now the second channel, the video carrier frequency fRF2 is 97.25 MHz of the second channel, so the local oscillation frequency fLC is 143 MHz (=97.25
+45.75).

Further, the video intermediate frequency f:+p2 is 58.75MHz
Therefore, the local oscillation frequency fL (2 is 1 from equation (3)
It becomes 56MHz (58,75+97.25).

Here, the beat signal frequency generated in the mixing circuit 19 is (f') in addition to the frequency flF2 expressed by equation (3).

A frequency component represented by -f RF2) is also generated, which becomes the beat signal described above.

However, according to this embodiment, this bee) signal (i
t, c-fRF2) is 45.75 MHz, and as can be seen from FIG. 2, it is approximately 40 to 50 dBI! due to the video intermediate frequency amplification circuit 21 in the next stage. degree, video intermediate frequency Lp2
is attenuated more than

Therefore, in order to attenuate the beat signal (fLc-9, □) at the output end of the video intermediate frequency amplification circuit 21 by 65 dB or more as described above, the filter circuit provided at the output section of the RF converter 15 must be The attenuation amount is 25dB (=
65-40), making it easier to manufacture and smaller in size than conventional filter circuits.

Also, the price can be reduced.

In addition, in the above embodiment, the video intermediate frequency F1
4, which is the video intermediate frequency of American television receivers.
The reason for selecting 5.75 MHz is that tuners and their production facilities for the United States can be used effectively, but the present invention is not limited to this. P□ may be outside the selectivity characteristic band of the video intermediate frequency amplification circuit 21, for example, approximately 49.75 MH2 or 62 MHz, which provides an attenuation of approximately 40 dB with respect to the video intermediate frequency f[F2.
．． Of course, it is also possible to set it to about 75MH2.

Further, in the above embodiment, for convenience of explanation, a case has been described in which the present invention is applied to a signal receiving apparatus having a TV audio multiplex broadcast reproduction section, but the present invention can also be applied to a VTR and other apparatuses.

Furthermore, the signals to be received are not limited to television signals.

As described above, the signal receiving device according to the present invention has the intermediate frequency fIP1 selected to be a frequency located outside the frequency band of the intermediate frequency amplification circuit of the receiver to which the high frequency signal fRF2 is supplied to the antenna terminal. Therefore, the intermediate frequency f■
The pH intermediate frequency signal is converted into a high frequency signal fR of a predetermined channel.
The attenuation amount of the filter circuit provided at the output part of the converter for converting into P2 can be made smaller than that of the conventional device. Therefore, this filter circuit can be manufactured easily and can be constructed at low cost. The circuit shape can be made smaller, and if the intermediate frequency f+p1 is selected as the intermediate frequency of a television receiver in the United States, tuners and production equipment for the United States can be used effectively.

[Brief explanation of the drawing]

Fig. 1 is a system diagram of a receiver in which the device of the present invention is applied to receive television audio multiplex broadcasts together with a conventional television receiver, and Fig. 2 shows the frequency characteristics of the main parts of Fig. 1. It is a figure showing an example. 1...Signal receiving device, 2...Conventional television receiver, 6,19...Mixing circuit, ?
, 16, 20...Local oscillation circuit, 15...
...RF converter, 21...Video intermediate frequency amplification circuit.

Claims (1)

[Scope of utility model registration request] Carrier frequency f of the desired channel obtained by selective reception
In a signal receiving device that converts a high frequency signal having RFI into an intermediate frequency signal having an intermediate frequency ftF1, and then converting it again into a high frequency signal having a high frequency carrier frequency fRF2 of a predetermined channel and applying it to an antenna terminal of a receiver. , a signal receiving device in which the intermediate frequency -'IF1 is selected to be a frequency located outside the frequency band of the intermediate frequency amplification circuit of the receiver.