JPS6329308Y2 - - Google Patents

Description

[Detailed description of the invention] This invention uses a fixed local oscillation frequency to
This invention relates to a CATV reception converter that converts a VHF band CATV broadcast channel into an equivalent number of UHF band channels.

FIG. 1 shows an example of the configuration of this converter for the US channel. in the US
CATV broadcast channels include conventional VHF broadcast channels 2 to 13 (low channel in the 54 to 88 MHz band and high channel in the 174 to 216 MHz band), as well as an intermediate band channel (120 to 174 MHz).
band) and superband channels (216-300MHz band). In Figure 1, CATV input terminal A
The CATV signal input from the distributor 1 is
Distributed to VHF output terminal B and internal converter circuit. Terminal B is connected to the VHF input of the television receiver so that it can receive the conventional VHF channel of the CATV signal. This is because the frequency arrangement of the low channel of the US channel and the 5th and 6th channels is irregular, and unlike other channels, when converted using a fixed local oscillation frequency, it deviates from the arrangement of the UHF reception channel band. on the other hand,
The signal distributed to the internal converter circuit is distributed over a passband (120-300MHz) from the lowest frequency of the intermediate band channel to the highest frequency of the superband channel.
band) and passes through a bandpass filter 2 with a broadband amplifier 3.
is amplified. The double-balanced mixer 4 mixes the amplified signal d and the output signal _LO of the fixed local oscillator 5 and converts it into an output signal i in the UHF band. The converted signal passes through a UHF bandpass filter 6, is amplified by a wideband amplifier 7, further passes through a UHF bandpass filter 8, and is output at a UHF output terminal C. this
The UHF output terminal is connected to the UHF input of the TV receiver, and the UHF tuner connects the CATV 120~
Receive channels in the 300MHz band.

With a converter configured like this, VHF band CATV
In order to be able to receive broadcast channels with the UHF tuner of a television receiver, the frequency conversion relationship is set as i = d + _LO (1). In a mixing circuit having such a fixed oscillation frequency _LO and a high-frequency wideband amplifier 3, due to the original characteristics of the mixing circuit, there is always a frequency relationship that causes beat disturbance that cannot be avoided in practice. Therefore, this point will be explained.

When the desired signal frequency d and the interference signal frequency u are in the same band, and the conversion output signal frequency i is above the local oscillation frequency _LO , the following interference relationship is experimentally unavoidable in practice. It becomes a hindrance.

(i) Relationship where u = i...(1) (ii) Relationship where the sum of u and d is i u+d=i...(3) (iii) 2 Relationship where the difference between _LO and u is i 2 _LO −u=i …(4) (iv) Relationship where 2u becomes i 2u=i …(5) Substituting the relationship in equation (1) into the above equation and solving for u, from equation (2) u=d+ _LO ...(6) From equation (3) u= _LO ...(7) From equation (4) u=-d+ _LO ...(8) From equation (5) u=1/2d+1/2 _LO ...(9 ) becomes. Here, as an example of this converter for the US channel, _LO is 590MHz, d and u are both
120~289MHz band (midband channel, VHF
FIG. 2 shows the relationship of beat interference when the frequency band is set to the Haitian channel and the band including the J to U channels of the superband channel. In Figure 2, the horizontal axis is d,
When the vertical axis is u, the signal existence area is indicated by D,
The straight lines showing the interference relationships of the above equations (6) to (9) can be expressed as (6) to (9). When the straight lines (6) to (9) do not intersect within the signal presence area, no beat disturbance occurs.
As can be seen from this relationship diagram, the signal presence area D
By setting _{the LO} appropriately, it is possible to suppress the occurrence of beat disturbance. In this case, it is best to set _{the LO} to the highest possible frequency.

However, from the relationship in equation (1), this _LO is the highest frequency in the signal existence region, that is, the maximum desired signal frequency.
It is constrained by the relationship between dmax and maximum conversion output frequency imax, imax=dmax+ _LO ...(10). In other words, once imax is determined, dmax can be determined by _LO . Here, if the maximum frequency of u is umax, then the relationship is as follows: umax=dmax (11). Furthermore, as can be seen from FIG. 2, the maximum desired signal frequency dmax at which no beat occurs is when the relationship of equation (8) holds, and is as follows: umax=-dmax+ _LO (12). From equations (10), (11), and (12), the relationship between dmax and imax must be dmax = 1/3imax (13). In other words, the maximum receiving frequency in the UHF band for US channels is 890MHz
Therefore, from equation (13), dmax≒296MHz...(14) In other words, when the converter of the method described so far receives a VHF band channel with a frequency of 296 MHz or higher, beat interference is generated by a specific interference signal within the same frequency band.
There is always a frequency relationship that makes it practically unusable.
Furthermore, in actual design, it is practically impossible to create a filter that can reliably attenuate frequencies above 296MHz.
The highest frequency of the interference signal frequency u is the highest frequency of the superband channel, 300 MHz. Therefore, in the case of the US channel, substitute imax=890MHz into equation (10), 890=dmax+ _LO ...(15) Substitute umax=300MHz into equation (11), 300=-dmax+ _LO ...(16) Therefore, solving equations (15) and (16) yields dmax=295MHz...(17) That is, even if _{the LO} is set to the maximum possible frequency, only the V channel (video carrier: 289.25 MHz, audio carrier: 293.75 MHz) of the superband channel can be received, and the W channel cannot be received. Note that _{the LO} at this time is 596MHz.

From the above, it was found that the reception frequency band of conventional converters is at most a little less than 300 MHz, but recently the CATV broadcast band in the United States is
Now it includes the 300MHz to 400MHz band, and it has become clear that it is no longer possible to receive the UHF channel on conventional television receivers using the conventional method.

The present invention focuses on the above points, and maintains the advantage of being able to select channels using the conventional TV receiver's channel selection mechanism, while being free from the effects of beat interference.
Can receive CATV channels up to 400MHz band
It provides a converter for CATV reception.

FIG. 3 shows its configuration. A CATV signal input from CATV input terminal A is distributed by distributor 1 to VHF output terminal B and an internal converter circuit. Terminal B has the same function as the conventional one, but the signal distributed to the internal converter circuit is transmitted from the lower frequency of the two intermediate band channels to the pass band of 400 MHz (to be more precise, 108 to 402 MHz). The signal passes through a bandpass filter 2 with a wideband band) and is amplified by a wideband amplifier 3. The double-balanced mixer 4 mixes the signal d (108~402MHz) and the output signal _LO1 (900MHz) of the first fixed local oscillator 5, and generates a first intermediate frequency signal _i1 (1008~402MHz) in the 1GHz band.
1302MHz). The converted signal passes through a first intermediate frequency bandpass filter 6 and is amplified by a 1 GHz band broadband amplifier 7. Here, specifically 900MHz
A filter 6 that sufficiently attenuates the first local oscillation frequency of
Use. Furthermore, i ₁ amplified by amplifier 7 is
Again through the bandpass filter 8 having the same band, the second
It is input to mixer 9. The second fixed oscillator 10 is
Oscillates the second fixed local oscillation frequency _LO2 of 448MHz,
Similarly added to 9. 9, the above i (1008~
1302MHz) and _LO2 (448MHz), and outputs a UHF band output signal _i2 (560~854MHz). Finally, this UHF band signal (560 to 854 MHz) is applied to the UHF output terminal C through a bandpass filter 11. This terminal C, like the conventional converter, is connected to the UHF input terminal of the television receiver, making it possible to receive CATV channels in the 108-402 MHz band and UHF channels in the 560-854 MHz band. That is, unlike the conventional single superheterodyne system, it is a fixed local oscillation double superheterodyne system.

Here, the beat disturbance relationship of the present double superheterodyne system will be described. First, the frequency conversion relationship in the first mixer (double balanced mixer) 4 is as follows: i ₁ =d+ _LO1 (18), which is similar to that of a conventional single superheterodyne. Therefore, the signal existence region
The relationship between the desired signal frequency d and the interference signal frequency u is illustrated in FIG. 4, assuming that the frequency is 108 to 402 MHz and _LO1 = 900 MHz. Here, the numbers of the straight lines indicating the interference relationship are the same as in the conventional case. As shown in FIG. 4, the interference relationship straight lines 6 to 9 do not fall within the signal existence region E, and no beat interference relationship exists. Next, the relationship of frequency conversion in the second mixer 9 is i ₂ = i ₁ − _LO2 (19). In this way, if the desired signal frequency i ₁ and the interference signal frequency u ₁ are in the same band, and the conversion output signal frequency i ₂ is above the local oscillation frequency _LO2 , the following interference relationship can be avoided in practice. It becomes an irreversible and obstructive relationship. That is, (v) the relationship where u ₁ becomes i ₂ u ₁ = i ₂ … (20) (vi) the relationship where the difference between i ₁ and u ₁ is i ₂ i ₁ − u ₁ = i ₂ … (21) u ₂ −i ₁ = i ₂ …(22) (vii) Relationship in which the difference between u ₁ and 2 _LO2 is i ₂ u ₁ −2 _LO = i ₂ …(23) 2 _LO −u ₁ = i ₂ …( 24) (viii) The relationship where 2u ₁ becomes i ₂ 2u ₁ = i ₂ ...(25) Substituting the relationship in equation (19) into equations (20) to (25) above and solving for u ₁ , we get ( From formula 20) u ₁ = i ₁ − _LO2 …(26) From formula (21) u ₁ = _LO2 …(27) From formula (22) u ₁ = 2i ₁ − _LO2 …(28) From formula (23) u ₁ = i ₁ + _LO2 … (29) From formula (24), u ₁ = −i ₁ + 3 _LO2 … (30) From formula (25), u ₁ = 1/2i ₁ −1/2 _LO2 … (31) Become.

Here, _LO2 is 448MHz, the desired signal frequency is the first intermediate frequency _i1 , and both _i1 and _u2 are 1008~
Figure 5 shows the beat disturbance relationship when the band is set to 1302MHz. In this figure 5, the horizontal axis is i ₁ ,
When the vertical axis is u ₁ , the signal existence region is indicated by F,
The interference relationship line of equations (26) to (31) above is (26) to
It can be expressed as (31). In other words, the disturbance relation line is
Since the signal does not enter the signal existence region F, there is no beat interference relationship. Furthermore, the first local oscillation frequency _LO1 is
900MHz and the second local oscillation frequency of 448MHz have no fundamental, harmonic, or difference frequencies within the d, i ₁ , and i ₂ bands, making it possible to obtain good reception. I can do it.

As mentioned above, by using double superheterodyne, which is different from conventional methods, CATV
Good reception up to 400MHz band. Furthermore, by incorporating the circuit of this converter inside the TV receiver, it can easily be used as a CATV receiver.

Note that this example uses equations (18) and (19),
Although this is an example of a double superheterodyne system, a double superheterodyne system using an up converter of i ₁ = _LO1 - d (32) and a down converter of i ₂ = _LO2 - _{i 1} (33) is also conceivable.

[Brief explanation of the drawing]

FIG. 1 is a block circuit diagram of a conventional CATV receiving converter, and FIG. 2 is a drawing showing the interference frequency relationship. Figure 3 shows the implementation of this invention.
This is a block circuit diagram of a CATV receiving converter, and FIGS. 4 and 5 are explanatory diagrams thereof. 4...First mixer, 5...First fixed oscillator, 9
...Second mixer, 10...Second fixed oscillator.

Claims (1)

[Scope of utility model registration request] It is for converting each channel of the VHF band used for CATV broadcasting into each channel of the UHF band, and converts the CATV channel signal of the VHF band into a first local oscillation signal of a constant frequency higher than that of the UHF band. a first converter that upconverts the output signal of the first converter to a frequency band sufficiently higher than the UHF band using a second local oscillation signal having a constant frequency higher than the frequency band of the output signal; A CATV reception converter consisting of a second converter that down-converts to the UHF band.