JPH0451114B2 - - Google Patents

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 super-band signals in multi-channel transmission of a CATV system to frequencies in the high-channel band of TV VHF. This allows signals to be frequency converted 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, making maintenance and inspection more troublesome.

(Objective of the present invention) In order to solve these problems, the present invention
It is possible to convert the multi-channel frequencies transmitted by a CATV system using one local oscillation frequency, and instead of converting the multi-channel frequencies individually for each channel, it is possible to convert the multi-channel frequencies transmitted by the CATV system into the mid-band band and superband band, which includes many channels. The frequency of each band is converted at once.

(Means for Solving the Problems) In order to achieve the above object, the present invention switches an input signal with a selection switch SW ₁ and transmits it to a filter 1. A band signal f ₁ is selected, and this signal is mixed with a local oscillation signal f ₀ generated from a local oscillator 3 by a mixer 2 to produce a sum signal of both (f ₁ +
f ₀ ) to the frequency of the TV's VHF Haitian channel, and also set the input signal selection switch to
SW ₁ is switched to transmit the signal to the filter 4, and the filter 4 selects the TV superband signal f ₂ from the input signal f, and mixer 5 adds the local oscillation signal generated from the local oscillator 3 to this signal. f ₀ is mixed so that the difference signal (f ₂ - _{f 0} ) between the two becomes the frequency of the Haitian channel of VHF television.

Note that when selection switch SW ₁ is in the intermediate position, input signal f is transferred from transmission path L ₁ to selection switch SW _2.
It is transmitted as it is to the output terminal OUT through the TV, and normal VHF band TV broadcasts are received on TVs in each home.

In the figure, F ₁ is a filter that passes the signal of f ₁ +f ₀ , and F ₂ is a filter that passes the signal of f ₂ −f ₀ .

(Example) In the present invention, the desired conversion frequency is
170MHz, the frequency band of the VHF Haiti channel
~222MHz and 110MHz as filter 1~
A device with a selectable mid-band frequency of 162 MHz was used, and 60 MHz was used as the local oscillation signal f ₀ .

Under this condition, the filter selected by filter 1
A local oscillation signal f ₀ of 60 MHz was mixed with a frequency of 110 MHz to 162 MHz, and a sum signal of both was obtained. As a result, as is clear from the following equation, the frequency was converted to the desired conversion frequency band of 170MHz to 222MHz.

110MHz + 60MHz = 170MHz 162MHz + 60MHz = 222MHz Next, set the desired conversion frequency to the frequency band of the TV VHF Haitian channel as in the previous case.
170MHz to 222MHz, as filter 4
A device that allows selection of frequencies in the superband band from 230 MHz to 282 MHz was used, and 60 MHz was used as the local oscillation signal f ₀ .

Under this condition, the filter selected by filter 4
A local oscillation signal f ₀ of 60 MHz was mixed with a frequency of 230 MHz to 282 MHz, 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 170MHz to 222MHz.

230MHz−60MHz=170MHz 282MHz−60MHz=222MHz Local oscillation signal f ₀ used in the present invention is 60MHz
However, the frequency is not limited to 54MHz, and may be selected as appropriate, such as 54MHz.

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

(b) Combine two different frequencies into one local oscillation signal f ₀
Since frequency conversion is performed using the converter, 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 the 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 L ₁ , as shown in the figure. CATV because only three L ₂ and L ₃ are required
The system configuration becomes very simple.

(c) Since it converts the mid-band and super-band bands to the frequencies of the television's VHF Haiti channel band, the signals transmitted in the mid-band and super-band bands cannot be received by existing televisions in each home. I can do it.

[Brief explanation of drawings]

The figure is a block diagram for implementing the method of the present invention. 1 and 4 are filters, 2 and 5 are mixers, and 3 is a local oscillator.

Claims (1)

[Claims] 1. A local oscillation signal is mixed with a mid-band signal of the input signal, and the sum signal is used as a television signal.
Set the frequency to the VHF Haiti channel,
A television characterized in that a local oscillation signal having the same frequency as the above-mentioned local oscillation signal is mixed with a superband signal of the input signal so that the difference signal has the frequency of the VHF Haitian channel of the television. Frequency conversion method for communal listening system. 2. The frequency conversion method for a television shared listening system according to claim 1, wherein the frequency of the local oscillation signal is 60MHz. 3. The frequency conversion method for a television shared listening system according to claim 1, wherein the frequency of the local oscillation signal is 54MHz.