JPS60233982A - Method for converting frequency of catv - Google Patents

Abstract

PURPOSE:To attain plural frequency conversions with one local oscillator by adding or subtracting a local oscillating signal to/from a frequency of a superband and a mid band so as to form the result to be a VHF high channel frequency. CONSTITUTION:An input signal is switched by a selector switch SW1 and transmitted to a filter 1, which selects a signal f1 of the mid band of a television in an input signal (f), this signal is mixed with a local oscillating signal f0 from a local oscillator 3 by a mixe 2 so as to form a sum signal f1+f0, and similarly a difference signal f2-f0 is formed by a filter 4 and a mixer 5, then the both are used as the high channel VHF TV frequency, and the result is outputted via a selector switch SW2. In case of a conventional VHF television broadcast, the selector switches SW1, SW2 are thrown to the midposition and the signal is transmitted through a transmission line L1.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a frequency conversion method used in a CATV system.

The present invention is designed to convert mid-band signals and superband band signals into frequencies of the high channel band of TV VHF in multi-channel transmission of CATV systems. It is possible to convert the frequency of the oscillator and superband band signals using a common local oscillation signal.

(Prior Art) There are various frequency conversion methods used in CATV systems, but in order to convert two or more frequencies, usually a local oscillator is prepared for each frequency to be converted, and each oscillator is used to convert a different frequency. The local oscillation signal is oscillated and mixed with the input signal to convert it to the desired frequency.

(Problems to be Solved by the Invention) In the conventional frequency method described above, in order to convert two or more frequencies, a local oscillator must be prepared for each frequency to be converted, which makes the equipment complicated. The disadvantage is that the equipment costs increase accordingly. Moreover, as the equipment becomes more complex, failures are more likely to occur, and there is also the problem that maintenance and inspection become troublesome.

(Objective of the present invention) In order to solve these problems, the present invention makes it possible to convert the frequencies of multiple channels transmitted in a CATV system using one local oscillation frequency, and converts the frequencies of multiple channels one by one for each channel. Rather than converting them individually, each of the mid-band band and superband band, which includes many channels, is frequency-converted all at once.

(Means for Solving the Problems) In order to achieve the above object, the present invention switches the input signal with a selection switch SW and transmits it to the filter 1, and the filter 1 selects the input signal f from the mid-band band of the TV. The mixer 2 mixes the local oscillation signal fO generated from the local oscillator 3 with this signal so that the sum signal (f, +fo) of the two becomes the frequency of the high channel of the TV's VHF. In addition, the input signal is switched by the selection switch SW1 and transmitted to the filter 4, which selects the TV mid-band signal f2 from the input signal f, and adds the signal f2 generated from the local oscillator 3 to this signal by the mixer 5. The local oscillation signal fO is mixed so that the difference signal (fz-fo) between the two has the frequency of the high channel of the VHF TV.

Note that when the selection switch SW1 is in the intermediate position, the input signal f is directly transmitted from the transmission path L1 through the selection switch SW2 to the output terminal OUT, and normal VHF band television broadcasting is received on the television in each home.

In the figure, F is a filter that passes the signal of f, +fo, and +F2 is a filter that passes the signal of f2-fo.

(Example) In the present invention, the desired conversion frequency is set to 170 MHz to 222 MHz, which is the high channel frequency band of TV VHF.
Hz, 74 Luther l, 11OMHz ~ 162M
A device capable of selecting a frequency in the Hz mid-band was used, and 60 M) Iz was used as the local oscillation signal fO.

Under this condition, 1 10 selected by filter 1
A local oscillation signal fci of 60 MHz was mixed with a frequency of MHz-162 MHz, and a sum signal of both was obtained. As a result, it is clear from the following equation that the desired conversion frequency band is 17
Converted to frequencies from 0MHz to 222MHz.

110MHz+60MHz=170MHz162MHz
+60 MI (z = 222 MHz) Next, the desired conversion frequency is set to 170 MHz to 222 MHz, which is the high channel frequency band of TV VHF, as in the previous case, and the frequency in the superband band of 230 MHz to 282 MHz can be selected as filter 4. 60 MHz was used as the local oscillation signal fo.

Under this condition, 2 30 selected by filter 4
MHz ~ 282M) Iz (7) frequency to 60M) (Z
The local oscillation signal fo was mixed and a difference signal between the two was extracted. As a result, as is clear from the following equation, the frequency was converted to the desired conversion frequency band of 170 MHz to 222 MHz.

230MHz-60MHz=170MHz282MHz
-60MHz=222MHz Note that the local oscillation signal fO used in the present invention is not limited to 60MHz, but may be, for example, 54MHz.
z and others as appropriate.

(Effects of the Invention) The present invention as described above has the following various effects.

(a) Since two different frequencies are converted using one local oscillation signal fO, only one local oscillator is required, which simplifies the configuration of the converter and reduces costs.

(b) Since the frequency of the midband band and superband band is converted all at once, even though the frequency of multi-channel signals is converted, the transmission path of the input signal is L1 + L2 as shown in the figure. + Since only three L3s are required, the configuration of the CATV system becomes very simple.

(c) Since it converts the mid-band and super-band bands to the frequencies of the TV VHF high channel band, the signals transmitted in the mid-band and super-band bands must be received by existing televisions in each home. I can do it.

[Brief explanation of the drawing]

The figure is a block diagram for implementing the method of the present invention. 1.4 is a filter 2.5 is a mixer 3 is a local oscillator Applicant Keikyu Corporation Procedural Amendments Patent Application No. 1983-90486 2 Title of the invention 3 Relationship to the case of the person making the amendment Patent applicant address name Keihin Express Railway Co., Ltd. and 1 other person 5 Date of amendment order July 31, 1980 6 Subject of amendment Power of attorney;
All drawings are as attached (no changes in content). Procedural amendment 2 Title of the invention 3 Name of the person making the amendment Keikyu Corporation Haka1 person 5 Date of amendment order Initiator 6 Subject of amendment Column 7 for detailed explanation of the invention in the description Contents of the amendment Description 4 The entire text of the page will be corrected as shown in the attached sheet. (Make sure that (1+fo) is the frequency of the TV's VHF high channel, and select the input signal using the selection switch SW.
1, the filter 4 selects the television superband signal f2 from the input signal f, and mixer 5 adds the local oscillation signal fO generated from the local oscillator 3 to this signal. They are mixed so that the difference signal (F2-fa) between the two becomes the frequency of the high channel of the VHF TV. When the selection switch SW1 is in the intermediate position, the input signal f is transmitted through the transmission path to the output terminal 0, UT, through the selection switch SW2, and normal VHF band television broadcasting is received on the TV in each home. Ru. In the figure, F is a filter that passes the signal fl + fo, and F2 is a filter that passes the signal F2-fo. (Example)

Claims (3)

[Claims] (1) A local oscillation signal is mixed with the mid-band signal of the input signal so that the sum signal has the frequency of the high channel of the TV VHF, and the superband signal of the input signal is mixed with the local oscillation signal. A frequency conversion method for a television communal listening system, characterized in that a local oscillation signal and a local oscillation signal of the same frequency are mixed so that the difference signal has the frequency of a high channel of VHF of a television. (2) The frequency conversion method for a television communal listening system according to claim 1, wherein the frequency of the local oscillation signal is 60 MHz. (3) The frequency conversion method for a television communal listening system according to claim 1, wherein the frequency of the local oscillation signal is 54 MHz.