JPS643237Y2 - - Google Patents

Description

[Detailed description of the invention] The invention is used in a television receiver.
VHF tuners, especially discret type
Regarding input tuning circuit of VHF tuner.

Generally, a VHF tuner is provided with various trap circuits such as an IF trap 3, an FM trap 4, and an image trap 5 between an input terminal 1 and an input tuning circuit 2, as shown in FIG. like this
FIG. 2 shows the input tuning circuit 2 of the VHF tuner.
In FIG. 2, 6 is a first fixed contact spring connected to the trap 5, and 7 is a coupling capacitor.
A second fixed contact spring connected to the high frequency amplification circuit via Cb. These fixed contact springs 6,7
The first contacts S ₁₂ are paired for each channel.
-S ₅ and the second contacts S' ₁₂ -S' ₅ sequentially abut, thereby performing channel switching. L ₁₂ is the tuning coil of the 12th channel, the tuning coil L ₁₁ of the 11th channel and the tuning coil of the 10th channel.
_L10 is connected in series to the tuning coil _L12 of the twelfth channel. The same applies to the tuning coil L ₉ of the ninth channel, the tuning coil L ₈ of the eighth channel, and the tuning coil L ₇ of the seventh channel.
Further, the tuning coil L ₅ of the fifth channel is also connected in series with the tuning coil L ₆ of the sixth channel. Coil La common to each channel
The series circuit of capacitor Ca and capacitor Ca is Haiti channel (5th channel to 12th channel in West Germany)
At the time of reception, it constitutes a low channel (2nd to 4th channel in West Germany) or FM trap, and also operates for matching high channel signals. If this series circuit is represented by La' and the tuning coil of the receiving channel is represented by _L0 , the equivalent circuits of the 5th channel to the 12th channel are drawn as shown in FIG. Now, if this tuner is tuned to the _H frequency of the high channel, the selection characteristics for each interference signal _IF and _FM will be mostly determined by the trap circuit 3, which is provided before the input tuning circuit 2, as shown in FIG. 4, 5, etc. Therefore, for interference signals close to the high channel band, for example at a frequency of _H ± _IF (where _IF is the intermediate frequency), only the selectivity characteristics shown in Figure 5 can be obtained. The above-mentioned interfering signals cannot be completely blocked.

The present invention proposes a VHF tuner devised to eliminate these drawbacks.

The following will explain the embodiments shown in the drawings. As shown in FIG. 6, in the present invention, between the first contact point _S10 of the middle channel of the high band channel (the 10th channel in the illustration) and the first contact point _S9 of the 9th channel one level lower than that. A parallel trap circuit 8 consisting of a capacitor C _x0 and a coil L _x0 is connected to block interference signals of adjacent frequencies. Shang No.
A tuning coil L9 of the ninth channel is connected between the first contact _S10 of the tenth channel and the second contact _S'9 of the _ninth channel. With this configuration, the ninth to seventh channels have an equivalent circuit as shown in FIG. 7, and the parallel trap circuit 8 effectively removes the proximity interference signal. The selection characteristics at this time are shown in FIG. In Figure 8, _D is the frequency of the receiving channel, and solid line 9 is the trap circuit 8.
When the resonance point _Ui of is higher than the tuning frequency _D ,
Broken lines 10 indicate cases lower than _D. Proximity interference is removed from the 7th channel to the 9th channel as shown in Figure 6.
When the sixth channel and the fifth channel are not required, the first contact S ₆ of the sixth channel and the first contact S ₁₁ of the eleventh channel are short-circuited with a conductive wire 11 .

In the embodiment shown in FIG. 9, an auxiliary terminal 12 is further provided on the discrete plate (not shown) provided with the first and second contacts, and this auxiliary terminal 12 is connected to the second contact S' ₆ of the sixth channel. A tuning coil L ₆ of the sixth channel is connected between the two, and a capacitor is connected between the auxiliary terminal 12 and the first contact S ₆ of the sixth channel.
A second parallel trap 13 consisting of C _×1 and coil L _×1 is provided. Further, the shorting line 11 is connected to the auxiliary terminal 12. Therefore, the 9th channel~
Parallel trap circuit 8 when receiving the 7th channel
However, when receiving the sixth to fifth channels, the second parallel trap circuit 13 is inserted before each channel and works to block proximity interference signals.

In the embodiment of FIG. 10, the second trap circuit 13 is inserted between the first contact _S7 of the seventh channel and the first contact _S6 of the sixth channel. In addition, the tuning coil L 6 of the 6th channel is connected between the second contacts S' ₇ and S' ₆ of the 7th channel and _the 6th channel, and the capacitor Cy is connected between the first contact S ₈ of the 8th channel and the ground. ing. Therefore, when receiving channels from the 9th channel to the 7th channel, the equivalent circuit becomes as shown in FIG. 11, and its selection characteristics become as shown in FIG. 12. Further, the equivalent circuit when receiving channels 6 to 5 is shown in FIG. 13, and its special characteristic _is shown in _FIG. It coexists with

As described above, according to the present invention, since a parallel trap circuit is provided in the switching structure of the tuning coil in a discrete VHF tuner, it is possible to suitably remove interference signals close to the receiving channel, which is extremely effective.

[Brief explanation of the drawing]

Figure 1 is a block diagram for generally explaining the input side circuit of a VHF tuner, Figure 2 is a circuit diagram of the main parts of a conventional VHF tuner, Figure 3 is its equivalent circuit diagram, and Figure 4. and FIG. 5 are explanatory diagrams thereof. FIG. 6 is a circuit diagram of a main part of a VHF tuner embodying the present invention, FIG. 7 is an equivalent circuit diagram thereof, and FIG. 8 is a selection characteristic diagram thereof. FIG. 9 is a circuit diagram of a main part of another embodiment of the present invention. FIG. 10 is a circuit diagram of a main part of another embodiment of the present invention, and FIG.
FIG. 12, FIG. 13, and FIG. 14 are explanatory diagrams thereof. 1...Input terminal, 2...Input tuning circuit, 6, 7
...First and second fixed contact springs, 8, 13...Parallel trap circuit, _L12 to _L5 ...Tuning coil, _S12 to _S5 ...
...first contact, S' ₁₂ to S' ₅ ... second contact.

Claims (1)

[Scope of utility model registration request] An input tuning circuit having a pair of first and second contacts for each channel, each connected to the input terminal side and the output terminal side by a first and second fixed contact spring in order to switch the value of the tuning coil according to each channel. In a discret type VHF tuner, the first contact of the input tuning circuit corresponds to a channel in the middle of the VHF high band, and the first contact corresponds to a channel one channel higher than the channel. A parallel trap circuit for removing near-frequency interference consisting of a coil and a capacitor is connected between them, and between the first contact of the middle channel and the second contact of the channel one channel higher than the one channel higher. It is characterized by connecting a tuning coil of
VHF Chuyuna.