JPS5846589Y2 - radio receiver - Google Patents

Description

[Detailed Description of the Invention] The present invention is a radio receiver, especially a double superheterodyne radio receiver, in which the first intermediate frequency is 10.7M.
The present invention relates to a radio receiver in which an FM intermediate frequency amplification circuit is also used as a shortwave first mixing circuit when the frequency is set to Hz.

In a conventional double superheterodyne radio receiver, when the first intermediate frequency is set to 10.7 MHz, the first mixing circuit for short waves must be configured with a dedicated transistor, or
As shown in FIG. 1, the FM intermediate frequency amplification circuit and the first mixing circuit for short waves were shared.

However, the former has an FM intermediate frequency amplification circuit and a shortwave first
If the mixed circuit is configured with separate transistors, the cost will increase.

In the latter case, as shown in FIG. 1, a switch S is connected to the emitter of the transistor Q1.

Since the FM bypass capacitor C1 and the short wave injection capacitor C2 are selectively connected, a switch S is connected between the emitter of the transistor Q1 and the FM bypass capacitor C1.

, and it is not possible to bypass the emitter of transistor Q with the shortest distance.

That is, the emitter of the transistor Q1, the TM bypass capacitor C1, and the switch S.

The length of the copper foil or lead wire on the printed circuit board between the two becomes extremely long, resulting in unstable circuitry and the need for one additional switch circuit.

In view of this, the present invention attempts to solve the above-mentioned drawbacks by using switching diodes.An embodiment of the present invention will be described below with reference to FIG.

Figure 2 shows the FM-shortwave selector switches 5i-t, 5l- in a double superheterodyne radio receiver.
2 and shortwave band selection switch 52-1, 52-2
and are used separately and independently as radio receivers.

Ql is an FM intermediate frequency amplification and short wave mixing transistor that serves both as an FM intermediate frequency amplification circuit and a first short wave mixing circuit, and is connected to the emitter of the transistor and the positive power supply path (ground).
A first capacitor C1' and a switching diode D are connected in series between 11 and 11, and the connection point 1 is connected to the FM side fixed contact F of the FM-short wave changeover switch 51-2 via a resistor R1.
Connected to M.

Further, the movable contact C01-2 of the switch 51-2 is connected to the emitter resistor R2 of the transistor Q1 and the negative power supply path 1.
2 is connected.

Q2 is a shortwave local oscillation transistor constituting the first shortwave local oscillation circuit, and the emitter of this transistor is connected to the resistor R3.
It is connected to the short wave side fixed contact SW of the switch 51-2 through the second and third capacitors C3 and C4.
The connection point 2 of the second and third capacitors C3 and C4 is connected to the emitter of the dual-purpose transistor Q1 through the movable contact CO2-1 of the shortwave band selection switch 51-2.
is connected to.

Each of the fixed contacts SW1 to SW4 of the switch 51-2 is connected to each shortwave band oscillation coil L1 to L4.

VC is a variable capacitor shared by each short wave band, and is selectively connected to the oscillation coils L1 to L4 for each short wave band via a second short wave band changeover switch 52-2.

51-1 is an FM/short wave changeover switch provided at the input end (base side) of the dual-purpose transistor Q1, and FT is an intermediate frequency transformer provided at the output side (collector side) of the transistor Q1.

The operation of the radio receiver configured in this manner will now be described.

(I) When receiving FM When receiving FM, switch 51-2 connects the positive power supply path (
A switching diode D and a resistor R1 are connected between the ground (ground) 12 and the negative power supply path 12, and the switching diode is forward biased and turned on, so that the emitter of the transistor Q1 is connected to the first capacitor C1. ', and the transistor Q1 operates for FM intermediate frequency amplification.

For example, even if there is no switching diode D, the emitter of the transistor Q1 passes through the second capacitor C3. For example, if the switch 52-1 is set to SW1, the emitter of the transistor Q1 passes through the capacitor C5 and connects to the primary tap of the oscillation coil L1. 3 to ground 11.

However, when receiving FM, shortwave band selection switch 5
The movable contact CO2-1 of 2-1 is located at an arbitrary position, and the variable capacitor VC has an arbitrary capacity.

Therefore, if the resonant circuit formed by any of the shortwave oscillation coils and the variable capacitor VC resonates at 10.7 MHz, the transistor Q2 cannot stably amplify 10.7 MHz.

On the other hand, in the circuit of the present invention, since the switching diode D is connected as described above, the emitter of the transistor Q1 is completely bypassed by the first capacitor C1'.

(II) During short wave reception When the short wave reception switch 51-2 is switched, the resistor R1 is disconnected from the negative power supply path 12, and the switching diode D is cut off.

Furthermore, since the resistor R1 is of the order of tens of magnitude and has a large Q, the bypass capacitor C1' is in an open state.

At this time, the short wave local oscillation transistor Q2 operates, and the 1
~ From the emitter of the transistor to the third second capacitor C4
, C3, the oscillation voltage is injected into the emitter of the dual-purpose transistor Q1, and the dual-purpose transistor Q1 operates as a short-wave mixed transistor.

In addition, in the experiment, capacitors c, ', and c3 were each 0.0.
4μF and 0.001μF, 10 as resistor R1
Ω was used.

As described above, the present invention does not require a mechanical switch between the emitter of the FM intermediate frequency amplification/short wave mixed transistor and the bypass capacitor, so a very stable and inexpensive circuit can be obtained, making it practical. It is.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a main part of a conventional radio receiver that serves as both an FM intermediate frequency amplification circuit and a short wave mixing circuit, and FIG. 2 is a circuit diagram of a main part of a radio receiver according to the present invention. Ql... FM intermediate frequency amplification and short wave mixed transistor, Q2... Short wave local oscillation transistor, 11.12... Positive and negative power supply path, CI'.
...First capacitor, D...Switching diode, 51-2...FM-short wave changeover switch, R2, R3...Emitter resistor, C3
, C4... Second and third capacitor, 52-1
...Shortwave band selection switch, L1 to L4
...Oscillation coil for each short wave band.

Claims (1)

[Scope of utility model registration request] A mixed transistor for FM intermediate frequency amplification and shortwave and a local oscillation transistor for shortwave are provided, and a first capacitor and a switching diode are connected in series between the emitter of the dual-purpose transistor and one power supply path. The movable contact of the switch is connected to the fixed contact on the FM side of the FM-shortwave changeover switch, and the movable contact of the switch is connected to the other power supply path that supplies forward bias to the emitter resistor of the dual-purpose transistor and the switching diode. The contacts are respectively connected to the emitter resistors of the short-wave local oscillation transistors, and a second
A third capacitor is connected in series, the connection point of both capacitors is connected to a movable contact of a shortwave band selection switch, and each fixed contact of the switch is connected to an oscillation coil for each shortwave band. Machine.