JPH0314843Y2 - - Google Patents

Description

[Detailed Description of the Invention] (a) Industrial Application Field The present invention relates to an antenna input circuit for a receiver, and particularly to an antenna input circuit for a receiver using a loop antenna.

(b) Conventional technology In recent years, low-impedance loop antennas have been used for reasons such as simplifying tracking adjustment and reducing the cost of the antenna itself compared to receivers using ferrite bar antennas. Receivers have been proposed (e.g. Jitsukaiaki
(See Publication No. 58-85828).

In such prior art, a desired frequency is selected by controlling a transistor in response to band switching and, for example, short-circuiting a long-wave band tuning winding when receiving a medium-wave band.

(c) Problems to be solved by the invention In the conventional technology such as that disclosed in Utility Model Application Publication No. 58-85828, when receiving a long wave band, the tuning winding of each input coil is connected in series, and the antenna winding is connected in a loop. Since they are each connected in series with the antenna, there is a problem in that image interference and spurious interference are induced in the medium wave resonant circuit.

(d) Means for solving the problem A loop antenna, a first input coil provided for first band broadcasting, a second input coil provided for second band broadcasting, and a variable antenna. An antenna input circuit for a receiver comprising a capacitive element, the primary windings of first and second input coils and a loop antenna are connected in series, and the secondary windings of the first and second input coils are connected in series. are connected in series, and the primary or secondary winding and the variable capacitance element are connected in parallel, respectively, and when receiving the first band, one of the second input coils is connected in parallel.
One switch means is provided to short-circuit the secondary winding of the first input coil when receiving the second band.

(e) Effect In the above configuration, when receiving the first band, the switch means shorts the primary winding of the second input coil, thereby transmitting the desired frequency signal selected by the first input coil to the subsequent high-frequency amplification. lead to the circuit,
Further, when receiving the second band, the switch means short-circuits the secondary winding of the first input coil, thereby guiding the desired frequency signal selected by the second input coil to the high-frequency amplification circuit in the subsequent stage. .

(f) Examples The figure shows an embodiment of the present invention.

In the figure, 1 is a loop antenna, 2 and 3 are input coils, and antenna windings 2a and 3a are connected in series with the loop antenna 1, and tuning windings 2b and 3b are connected in series, respectively. 4 and 5 are tuning windings 2
6 is a variable capacitance element connected in parallel to the series-connected tuning windings 2b and 3b, 7 is a coupling capacitor, and 8 is a field-effect transistor for amplification. , 9 is a gate resistor, 10 is a source resistor, 11 is a switch that is switched in response to band switching,
The long wave LW side terminal is connected to the connection point between the antenna windings 2a and 3a, the medium wave MW side terminal is connected to the connection point between the tuning windings 2b and 3b, and the common terminal COM is connected to the ground.

Next, the operation will be explained.

When a band switching switch (not shown) is set to the medium wave side in order to receive medium wave band broadcasting, the switch 11 is set to the medium wave MW side. The hot side of the tuned winding 3b is grounded, and the tuned winding 3b is short-circuited.

Therefore, when receiving medium-wave MW, the antenna winding 3a of the long-wave input coil 3 acts as a mere signal line, and the signal induced in the loop antenna 1 is transmitted via the antenna winding 3a of the long-wave input coil 3. The signal is led to the antenna winding 2a of the medium wave input coil 2, selects a desired frequency in a medium wave tuning circuit consisting of a tuning winding 2b, a trimmer capacitor 4 and a variable capacitance element 6, and is amplified by a transistor 8. and is guided to a high frequency amplification circuit (not shown).

At this time, the tuning winding 3b of the long-wave input coil 3
Since they are short-circuited, the tuning winding 3b does not affect the received signal.

Furthermore, when the band switching switch (not shown) is set to long wave LW in order to receive long wave band broadcasting, the switch 11 is set to long wave LW, so
The connection point between antenna windings 2a and 3a is grounded,
As a result, the antenna winding 2 of the medium wave input coil 2
a is shorted.

Therefore, when receiving long wave LW, medium wave input coil 2
No signal is supplied to the tuning winding 2b, which acts as a mere signal line, and the signal induced in the loop antenna 1 is transmitted to the antenna winding 3a of the long-wave input coil 3.
After selecting the desired frequency in a long-wave tuning circuit consisting of a tuning winding 3b, a trimmer capacitor 5, and a variable capacitance element 6, the voltage is applied to the transistor 8 via the tuning winding 2b, and the voltage is applied to the transistor 8. The signal is amplified and guided to a high frequency amplification circuit (not shown).

At this time, since the antenna winding 2a of the medium wave input coil 2 is short-circuited by the switch 11, the tuning winding 2b is also short-circuited, thereby preventing image interference and spurious interference from occurring.

In this embodiment, the case where medium wave and long wave band broadcasting is received has been described, but the present invention is not limited to this embodiment.

By the way, it goes without saying that an input coil having a tuning winding on the antenna side and a base winding on the secondary side may be used.

Furthermore, not only a mechanical switch but also an electronic switch such as a semiconductor switching element may be used.

(g) Effects of the invention According to the invention, a loop antenna, a first input coil provided corresponding to first band broadcasting,
An antenna input circuit for a receiver including a second input coil provided for second band broadcasting and a variable capacitance element, the antenna input circuit comprising primary windings of first and second input coils and a loop antenna. are connected in series, the secondary windings of the first and second input coils are connected in series, and the primary or secondary winding and the variable capacitance element are connected in parallel. One switch means is provided to short-circuit the primary windings of the two input coils, and to short-circuit the secondary winding of the first input coil when receiving the second band, so image interference and spurious noise can be eliminated with a simple configuration. Interference can be eliminated and good reception can be achieved.

[Brief explanation of drawings]

The figure shows an embodiment of the present invention. 1... Loop antenna, 2, 3... Input coil, 6... Variable capacitance element, 11... Switch.

Claims (1)

[Scope of utility model registration request] Antenna input of a receiver including a loop antenna, a first input coil provided for first band broadcasting, a second input coil provided for second band broadcasting, and a variable capacitance element. the circuit, wherein the primary windings of the first and second input coils and the loop antenna are connected in series, the secondary windings of the first and second input coils are connected in series, and the primary windings of the first and second input coils are connected in series; connecting the side or secondary windings and the variable capacitance element in parallel, and short-circuiting the primary winding of the second input coil when receiving the first band;
An antenna input circuit for a receiver, comprising one switch means for short-circuiting the secondary winding of the first input coil during second band reception.