JPH0251290B2 - - Google Patents

Description

[Detailed Description of the Invention] In satellite broadcasting, a carrier wave in the SHF band is FM-modulated with a television signal and transmitted. In this case, the modulation depth is about 3, which is much larger than about 1 in the case of FM radio broadcasting. In other words, the occupied bandwidth is
27MHz, whereas for radio it is several 100k
It is Hz.

In this way, in the case of television, if the occupied band is wide, a narrow band FM detector cannot be used, and moreover,
The disadvantage is that the AFC circuit configuration is complicated.

In view of these points, the present invention allows the use of a narrowband FM detector, simplifies the configuration of the AFC circuit, and allows the FM detector and AFC circuit to operate with signals of optimal frequencies.
This is an attempt to propose an FM television receiver.

An embodiment of the present invention will be described below with reference to the drawings. This example is a case where the present invention is applied to a television receiver for satellite broadcasting. In the figure, 1 is a microwave antenna (circularly polarized receiving antenna), 2 is an outdoor unit, and 3 is an indoor unit.

First, the outdoor unit 2 will be explained. High frequency signal in the SHF band from 11.7 to 12.0 GHz received by antenna 1 (wideband FM modulated television signal)
is supplied to the first mixer 4. On the other hand, the local oscillation signal of the first local oscillator 5 with an oscillation frequency of 2.7 GHz is supplied to the quadrupler 6 and converted into a local oscillation signal of 10.8 GHz, and then supplied to the mixer 4. A first intermediate frequency signal of 0.9 to 1.2 GHz is obtained from the mixer 4 and is supplied via a low noise amplifier 7 to an image rejection bandpass filter 8 of the indoor unit 3.

Next, the indoor unit 3 will be explained. The output of the filter 8 is passed through a first intermediate frequency amplifier 9 to
It is supplied to the second mixer 10. On the other hand, the local oscillation signal from the second local oscillator 11 is transmitted to the second mixer 10.
from which a second intermediate frequency signal having an intermediate frequency of 130 MHz is output. This second intermediate frequency signal is supplied via the second intermediate frequency amplifier 12 to a band pass filter 13 whose pass band center frequency is 130 MHz, and only the second intermediate frequency signal of 130 MHz is extracted. The output of the filter 13 is the limiter 14
supplied to

The present invention includes a mixer 10 to which a broadband high frequency FM modulated television signal is supplied, and a local oscillator 1 to supply the mixer 10 with a local oscillation signal according to the selected channel.
1, an intermediate frequency amplifier 12 to which the intermediate frequency FM modulated television signal from the mixer 10 is supplied, and an FM detector 24 to which the intermediate frequency FM modulated television signal from the intermediate frequency amplifier 12 is supplied.
In an FM television receiver, an intermediate frequency amplifier 12
a first frequency divider 15 to which an intermediate frequency FM modulated television signal is supplied and frequency-divided, and the frequency-divided output is supplied to the FM detector 24;
The second frequency divider 16 is supplied with a frequency-divided output, and the AFC circuit 17 is supplied with a frequency-divided output of the second frequency divider 16. , to control the oscillation frequency of the local oscillator 11.

The frequency divider circuit DV here consists of a first and a second frequency divider 15 and 16. A wideband FM modulated television signal, here the output of the limiter 14, is passed through a first frequency divider (n-ary counter) 15 with a frequency division ratio of 1/n (n=2, 3, 4,...) to an FM detector ( Ratio detector) 24 for FM detection. This FM detector 24 may be of narrow band type. Furthermore,
The divided output of the first frequency divider 15 is supplied to the AFC circuit 17 through the second frequency divider (m-ary counter) 16 with a frequency division ratio of 1/m (m = 2, 3, 4,...) .

The AFC circuit 17 is composed of a first-stage FM detector (ratio detector) 18 and a second-stage low-pass filter (active filter, preferably with a cut-off frequency of about 25 Hz or less, here 1 Hz) 20. 19 is a reference voltage source for the FM detector 18.

The output of the AFC circuit 17 is supplied to an adder 23 via a switch 21 which is normally on and turned off when a channel is selected. In the adder 23, the tuning signal generation circuit 2
Tuning signal from 2 and AFC from AFC circuit 17
The signals are added, and the added output is supplied to the variable capacitance diode of the second local oscillator 11 as an oscillation frequency control signal. Incidentally, the oscillator 11 may be a PLL (phase locked loop) synthesizer.

The detection output of the FM detector 24 is transmitted through a video filter (a low-pass filter that passes signals of 4.4MHz or less) 25, and a first audio filter (5.5MHz±
bandpass filter that passes 100kHz signals)
27 and 2nd audio filter (5.745MHz±
It is supplied to a bandpass filter 30 that passes the 100kHz signal. The output of the video filter 25 is connected to the video output terminal _TV via the variable gain amplifier 26.
supplied to The output of the first audio filter 27 is supplied to a variable gain audio FM detector 28 for detection, and the obtained first audio signal is supplied to the first audio output terminal T _A1 via an amplifier 29.
The output of the second audio filter 30 is supplied to a variable gain audio FM detector 31 for detection, and the obtained second audio signal is supplied via an amplifier 32 to a second audio output terminal T _A1 .

Next, the first and second frequency dividers 15, 16, FM
The operation of the detector 24 and the AFC circuit 17 will be explained. The frequency of the second intermediate frequency signal, i.e. the broadband FM modulated television signal, supplied to the first frequency divider 15 is expressed as F _I ±ΔF, where F _I
130MHz, ΔF is ±6MHz. Then, this television signal is divided into 1/n by the first frequency divider 15 and then supplied to the FM detector 24, and the frequency of this signal is expressed as F _I /n±ΔF/n. It turns out. Here, if n is 4, F _I /n is 32.5 MHz, ±ΔF/n ± 1.5 MHz. Therefore, by arbitrarily selecting n, a narrowband FM detector 24 can be used.

Further, the frequency of the signal supplied to the AFC circuit 17 is F _I /n·m±ΔF/n·m. Here, n is 4
, if m is 32, F _I /n・m is 1.0156MHz, ±ΔF/n・m is 0.047MHz, and the frequency deviation is extremely small, so this signal can be regarded as a single frequency signal. AFC becomes possible.

Further, by selecting the cutoff frequency of the filter of the AFC circuit 17 to be approximately 25 Hz or less, dispersion of SHF broadcasting can be removed.

Note that the output of the limiter 14 may be supplied to the AFC circuit 17 via a frequency divider with a frequency division ratio of 1/n·m.

Furthermore, the present invention is not limited to television receivers for satellite broadcasting and SHF broadcasting.

According to the present invention described above, a narrowband FM detector can be used, the configuration of the AFC circuit can be simplified, and the FM detector and AFC circuit can be operated with signals of optimal frequencies, respectively.
You can get an FM TV receiver.

[Brief explanation of drawings]

The figure is a block diagram showing one embodiment of the present invention. DV is a frequency dividing circuit, 15 and 16 are first and second frequency dividers, 17 is an AFC circuit, and 24 is an FM detector.

Claims (1)

[Claims] 1. A mixer to which a broadband high frequency FM modulated television signal is supplied, a local oscillator which supplies a local oscillation signal according to the channel selection to the mixer, and an intermediate frequency FM modulated television signal from the mixer. An FM television receiver having an intermediate frequency amplifier to which a modulated television signal is supplied, and an FM detector to which an intermediate frequency FM modulated television signal from the intermediate frequency amplifier is supplied; a first frequency divider to which an FM modulated television signal is supplied and frequency-divided and whose frequency-divided output is supplied to the FM detector; and a second frequency divider to which the frequency-divided output of the first frequency divider is supplied. a frequency divider, and an AFC to which the divided output of the second frequency divider is supplied.
1. An FM television receiver comprising: a circuit, wherein the oscillation frequency of the local oscillator is controlled by an AFC signal from the AFC circuit.