JPS59107642A - Tuner device for catv conversion - Google Patents

Abstract

PURPOSE:To prevent surely radiation from a space between shield cases by connecting a respective high frequency circuit contained in separate shield cases with a through-capacitor fitted with a cylindrical outer case. CONSTITUTION:The shield cases 40, 41 are constituted by sectioning an incorporated shield case with a pair of barriers 40a, 41a placed with a gap 42. The through-capacitor 43 is used to connect the 1st and the 2nd high frequency circuits contained in the cases 40, 41. The capacitor 43 is formed such that a cylindrical insulating section 45 is formed arount a lead 44 penetrating and an outer case 46 made of a conductive member is capsulated on the insulating section 45, and the outer case 46 is a cylindrical form longer than the gap 42. Since the shield at the gap 42 is attained sufficiently by using the capacitor 43 constituted above, unnecessary radiation from the gap 42 is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a tuner device for CATV conversion that receives a transmission signal of a CATV system, selects a channel, and supplies the selected channel to a television receiver.

[Technical background of the invention]

A general CATV (cable television) system distributes CATV signals from relay stations equipped with highly sensitive antennas and broadcasting stations that provide a variety of service information to each home through a wideband transmission line such as a coaxial cable. It is something. In order to receive this CATV signal with a general television receiver, a tuner device for CATV conversion is required. This CATV conversion tuner device selects a channel of a CATV signal, converts it to a vacant channel of a television receiver, and outputs it, and is usually constructed using a double super-hetero gain system.

Figure 1 shows the configuration of the block circuit, and shows CA transmitted from a relay station or broadcasting station via a transmission cable.
A TV signal is supplied to input terminal 11. This CATV
Shinzuki passes through the input bandpass filter 12 to the first mixer 13
will be supplied to This first mixer 13
A first tank circuit 15 that mixes the oscillation signal of the local oscillator 14 and the CATV signal to produce a first intermediate frequency signal, and controls the oscillation frequency of the first local oscillator 14.
The desired channel is selected from the CATV signal by adjusting the inductance.

Since the first intermediate frequency signal selected and extracted in this way is converted to a higher frequency than the CATV signal, the section from this input terminal 11 to the first mixer 13 is usually called an up section.

The first intermediate frequency signal output from the first mixer 13 of the up section is transmitted to an intermediate frequency signal which is composed of a first band filter 16, an intermediate frequency amplification circuit 17, and a second band filter 18, which constitute the down section at the subsequent stage. It is amplified by a frequency amplification circuit and supplied to a second mixer 19VC. This second mixer 19 mixes the oscillation signal of the second local oscillator 21 controlled by the second tank circuit 2o and the amplified first intermediate frequency code,
This is for extracting the second intermediate frequency signal, and the second tank circuit 2
0 and set the second intermediate frequency signal to an empty channel on the television receiver.

This set second intermediate frequency number is output from the output tuning circuit 22.
is supplied to the output terminal 23 via the output terminal 231/
This signal is supplied to an antenna input terminal of a television receiver (not shown) which is connected to a C-glue.

Since the second intermediate RDJ frequency signal output to the television receiver is converted to a lower frequency than the first intermediate frequency signal,
The section from the 21st band filter 16 to the output terminal 23 is called a down section.

Top = a Since both the up and down parts are high-frequency circuits, they must be carefully protected using a chassis as shown in Figure 2 to prevent their high-frequency components from leaking outside the tuner equipment and to prevent interference with each other. We are doing a lot of shielding. That is, this chassis consists of a first shield case 30 that accommodates the up section and a second shield case 3 that accommodates the down section, and the first and second cases 30.
31 is partitioned by a pair of partition walls 30a.

A gap 32 is set between 31 and 8 to effectively shield each other.

A feedthrough capacitor 33 as shown in FIG. 3 is used to connect the high frequency circuits housed in the shield cases 30 and 31 as described above.

This feed-through capacitor 33 has an exterior portion 35 insulated from a lead wire 34 passing through the interior, and one side of the exterior portion 35 is formed into a disk shape with a large diameter. That is, the connection between the up part and the down part is made using the shield case 30. as shown in FIG.
The through-type capacitors 33h and 33b are arranged in the partition walls 30m and 31h of the partition wall 31, respectively, so as to face each other, and the respective exterior parts 35b and 35b are connected to the partition wall 30a.
, 31 Solder to a. And bulkhead 30IL
, 31a, each lead wire 34a in the gap 32
Solder 36 to a J 4b, and connect the 5-lead wire 34a, J4b and the distance W30a.
1.91a, that is, a capacitance is provided between the wire and the ground, and the high frequency component riding on the first intermediate frequency signal flowing through the Leet ◆ wires 34h and 34b is pinosed to the ground.

[Problems with background technology]

However, even if the high frequency circuits are connected to each other using the feedthrough capacitor 33 as described above, the shield cases 30, 31
Due to insufficient shielding at gap 32, gap 35
High frequency components are radiated from the

In the CATV conversion tuner device using the tuple superhetero gain method, the oscillation signal of the second local oscillator 21 flows back to the first mixer 13 via the intermediate frequency amplification circuit, and the first mixer 13 There is a drawback that various unnecessary beat components are generated by mixing with the oscillation signal of the oscillator 14, and these unnecessary beat signals leak out from the input terminal 11 via the input band filter 12. Furthermore, since the output impedance of the first mixer 3 varies depending on the oscillation frequency of the 6-first local oscillator 14, it is difficult to match the impedance between the up section and the down section, resulting in a deterioration of the noise figure.

[Purpose of the invention]

This invention improves the above-mentioned drawbacks, and provides a CATV conversion tuner that reliably prevents radiation from occurring between the shield cases that shield each high-frequency circuit when connecting the high-frequency circuits to each other, and enables reception of high-quality images. The purpose is to provide equipment.

[Summary of the invention]

In other words, the CATV conversion tuner set according to the present invention"
The feedthrough capacitor 1 has a cylindrical exterior housing each high-frequency circuit housed in a separate shield case.
The external parts are grounded by soldering to each shield case.

[Embodiments of the invention]

Hereinafter, one embodiment of the present invention will be described with reference to the drawings.

FIG. 5 shows the shield case that houses the tuner unit taken out. The first high frequency circuit is housed in the first shield case 4o, and the second high frequency circuit is housed in the second shield case 41. do. The first and second shield cases 40 and 41 have a pair of partition walls 40a with a gap 42 between the integrated large shield cases,
It is divided into 41h. To connect the first high frequency circuit and the second high frequency circuit housed in the shield case 40 #4 J Vc, a feed-through capacitor 43 shown in FIG. 6 is used. This feedthrough capacitor 43 has a cylindrical insulating part 45 made of ceramic or the like formed on one lead wire 44, and this insulating part 45
An exterior part 46 made of a conductive material is attached to the
This exterior portion 46 has a cylindrical shape longer than the gap 42, with one pole side open and the other pole side open in a cylindrical shape with a smaller diameter. Insulating paint is filled between the exterior portion 46 and the lead wire 44 to fix the lead wire 44.

That is, in order to connect the first high frequency circuit and the high frequency circuit of the lower part 2, as shown in FIG. , the exterior part 46 of the feedthrough capacitor 43
An insertion opening with a diameter corresponding to the shape of
, 41h and fix it. Then, each high frequency circuit is connected to the lead wire 44 of the feedthrough capacitor 43.

Therefore, since the shielding in the gap 42 is sufficient, unnecessary radiation from the gap 42 can be prevented and the number of parts can be reduced.

Figure 8 shows the CA stored in the shield cases 4θ and 41.
This figure shows the configuration of a TV conversion tuner device, which is configured similarly to that explained in FIG.

The up section 47 converts the CATV signal into a first intermediate frequency signal, and the down section 48 converts the first intermediate frequency signal into a second intermediate frequency signal, and its configuration is the same as that in FIG. Therefore, the same parts are given the same reference numerals and the n(5?) is omitted. That is, the output signal of the up section 47 is supplied to the impedance current circuit 49 via the feedthrough capacitor 43.

The impedance matching circuit 49 is constituted by a low-pass filter circuit including a coil L and a capacitor C, and passes the blade signal from the up section 47 as it is and supplies it to the down section 48 .

FIG. 9 shows the principle of the impedance matching circuit 49. When a load of impedance Zt is connected to a power source of electromotive force E1 and internal impedance Zi, if we set Zi""R1+jX1 and Zz=Rz+jX4L, as is well known, The condition for matching the impedance to is R
This is when 4=R1 and Xt=-Xi are satisfied simultaneously. This is so-called conjugate e-matching.

FIG. 10 shows an impedance matching circuit of the shift section 10-47 and the down section 48 according to a Smith chart, where A indicates a constant conductance circle and B indicates a constant resistance circle. When the impedance matching circuit 50 is not connected,
Output impedances ZM and P of the up section 47 viewed from point M in Figure 8. The input impedance zpo of the down section 48 seen from the imaginary is at blue levels M and PoO, respectively.

At this time, if the output impedance ZM of the up section 4 is constant, the impedance at point M does not change, and the position conjugated and matched to this is Pi. Therefore, if the position of Po is moved to the position of Pi, the impedances will be matched.

First, when point Pc shown in FIG. 8 is grounded via capacitor C, point P is established. begins to move clockwise along the constant conductance circle A. At this time, the capacitance of the capacitor C is set so that Po stops at the position of Pc. Furthermore, point M and P. When a coil L is connected in series between the points P and P at the position Po. moves clockwise along constant resistance circle B. At this time P. The inductance of the coil L is set so that it stops at the order z1 of Pt. That is, if the coil L and capacitor C are set to appropriate values, the input impedance z, o of the down section 48 becomes the output impedance zM of the up section 47.
Impedance z to be combined and matched to
It becomes t.

Therefore, since the impedances are perfectly matched, the noise figure is reduced to a few degrees, and the matching circuit 49, that is, the low-pass filter circuit attenuates high frequency components higher than the first intermediate frequency, so that the oscillation signal of the second local oscillator 21 is Backflow can be almost completely prevented.

〔Effect of the invention〕

As described above, according to the present invention, even when high frequency circuits housed in each shield case are connected to each other, unnecessary radiation from the gap between the shield cases can be prevented. In this case, by further including an impedance matching circuit with low-pass characteristics in the gap connection part, it is possible to prevent the backflow of the oscillation signal from the second local oscillator, thereby preventing the generation and leakage of unnecessary beat components. You will be able to do this.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the configuration of the conventional tuner equipment for CATV conversion, Figure 2 is a diagram showing a case that houses the above-mentioned chisel device, and Figure 3 is a diagram showing the structure of the feed-through capacitor used in the above-mentioned case. FIG. 4 is a diagram showing the structure of the capacitor mounting in further detail; FIG. 5 is a diagram showing a shield case of a tuner device for CATV conversion according to an embodiment of the present invention; FIG. Figures 7 and 7 respectively show the structure of the feedthrough capacitor used in the case and how it is used, Figure 8 shows the configuration of the tuner section housed in the case, and Figure 9 explains the operation. 21... Second local oscillator, 40... First shield case, 41... Second shield case, 42...
13- Gap, 43... Feedthrough capacitor, 46... Exterior part, 47... Up part, 48... Down part, 49...
・Impedance matching circuit. Applicant's agent Patent attorney Takehiko Suzue 14-

Claims (2)

[Claims] (1) A first shield case that shields the first high frequency circuit and a second shield case that shields the second high frequency circuit are formed adjacent to each other with a pair of partition walls facing each other with a small gap, and The pair of bulkheads are connected through a cylindrical shield sheathing part that is longer than the width of the gap, and connected via a connecting part containing a lead wire inserted through the sheathing and a type capacitor to form the first shield. A tuner device for CATV conversion, characterized in that the first high frequency circuit and the second high frequency circuit are connected using the feedthrough capacitor without connecting the case and the second shield case. (2) The connecting portion of the first and second high-frequency circuits using the feedthrough capacitor is configured to include an impedance coupling circuit that performs conjugate matching between the output impedance and the input impedance and has low-pass characteristics. A tuner device for CATV conversion according to claim 1.