JPS5846591Y2 - Band switching circuit for AM-FM radio receiver with tape recorder - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a band switching circuit for an AM-FM radio receiver with a tape recorder.

Originally, in an AM-FM radio receiver with a tape recorder, switching of the radio tape recorder and AM-FM of the radio section
The M band switching was previously performed using separate switches, but recently AM-FMTape three-contact changeover switches have been used to reduce costs.

Figure 1 shows a three-circuit switch S for changing the band of radio section 1.
, -1,S, -2,S, and -6 are conventional examples.

51-2 is for switching the detection output. 51-1 is A when on FM
The secondary side 2' of all the M oscillation coils and the AMIFT 3 are grounded, and a voltage is supplied to the FM front end section 4.

During AM, the voltage supply to the FM front end section 4 is cut and the FMIFM ceramic filter 5 is short-circuited.

51-6, when receiving FM, the AMM human signal is sent to the FMI from the base winding (secondary winding) 6' of the AMM antenna coil 6.
It is guided to the FM path 19, 7.8, operates as a straight receiver, is demodulated, and is a shorting circuit for preventing interference in the FM signal.

9 is a tape recorder section, and 15 is a low frequency section.

Figure 2 also shows a 3-circuit switch S for band switching of radio section 1.
This is a conventional example using circuits 51-1, S]-2, S, and -6, and the operation of 51-1 is the same as that of the circuit shown in FIG.

51-2 is used to switch the detection output and to prevent interference of AMM input signals during FM reception.

That is, during FM reception, the base winding 6' of the AM antenna coil 6 is grounded through the AM detection filter converter C2 (approximately 0.022 μF) through 51-2, so the AMM input signal is guided to the FMIF stage. Interference is prevented without any interference.

Also, the AM detection output during AM reception is S, -2, R4, C3
is guided to the tape recorder section 9 through the tape recorder section 9.

51-6 is the radio section 1 when recording with the tape recorder section 9.
The detection output of the radio section 1 is short-circuited to ground to prevent noise from the IF amplification stage 19°7.8 of the radio section 1 from being mixed into the recording signal.

In the circuits shown in Figures 1 and 2, the radio band and tape recorder are switched using a three-contact changeover switch, but the number of band changeover switch circuits must be minimized to reduce costs. effect becomes smaller.

In view of this, the present invention aims to improve the cost efficiency by switching the bands of the radio section with a small number of switch circuits.An embodiment of the present invention will be described below with reference to FIG.

In FIG. 3, the same parts as in FIGS. 1 and 2 are designated by the same numbers as in FIGS. 1 and 2.

This invention is based on the three-circuit switch S shown in Figures 1 and 2.
t1. Sl 2. The operation performed using Sl 6 is performed using two circuits of switches.

That is, the radio section 1 includes an AM band front end section 1.
a first band selection switch 51- for selectively switching and supplying power to the 0 and FM band front end section 4;
1 and a second band changeover switch 51-2 for switching each detection output of AM and FM, and the second band changeover switch connects the movable terminal COM to the secondary winding of the AM antenna coil 6. Connect the FM side fixed terminal to the AM detection output terminal 12 and the Tape side fixed terminal to the AM and FM common detection output terminal 13 to the hot side terminal 11 of 6', and use the AM side fixed terminal as an idle terminal. There is.

Next, the operation of the AMFM radio receiver with tape recorder constructed in this way will be explained.

When receiving FM, the base winding 6' of the AM antenna coil 6
If the filter capacitor C2 (approximately 0.022 μF) of the AM detection circuit 18 is grounded through the switch 51-2, the AM large input signal will not be guided to the FMIF amplification stage 19, 7.8, and interference will occur. Prevented.

Furthermore, the AM detection output terminal 12 and the FM detection output terminal 14 are connected at a point 13, but when receiving FM, the AM detection output is short-circuited to ground at the base winding 6' of the AM antenna coil 60 through the switch 51-2. , are not guided to the low frequency section 15.

During FM reception, the 1M detection output is sent to the low frequency section 1 through C4.
5, but a part of it is grounded through R4 and C3.

Also, during AM reception, the AM detection output is guided to the low frequency section 15 through R4 and C3, but a part of it is guided to the low frequency section 15 through R5, R6, and R.
7, R,, D,, D2・FM detection transformer 16.16
It is grounded by the FM detection circuit 17, which is composed of ', etc.

By the way, the detection output of each band is 1M detection output < AM detection output (70 mv in FM < 150 mv in AM)
Therefore, it is necessary to match the levels of AM and FM.

In this invention, for AM-FM level matching, R4
Select a relatively high resistance value (10Kg or more) as the value of , and select an AM detection load resistance R3 (from 3 to 5, !Q).
By appropriately selecting , a part of the detection output is grounded at the time of each reception, which can be used as a signal loss for AM-FM level matching, making it possible to obtain the same characteristics as before. .

Furthermore, when recording with the tape recorder section 9, each detection output of the radio section 1 is short-circuited to ground through the switch 51-2 and the base winding 6' of the antenna coil 6.
There is no noise from the radio unit 1 mixed into the recorded signal.

As mentioned above, in conventional AM-FM radio receivers with tape recorders, three circuits of band selection switches were used in the radio section, but with the present invention, it is possible to use two circuits for band selection switches in the radio section. Therefore, it is possible to reduce costs.

[Brief explanation of the drawing]

1 and 2 are circuit diagrams showing a conventional AM-FM radio receiver with a tape recorder, and FIG. 3 is a circuit diagram showing an AM-FM radio receiver with a tape recorder according to the present invention. 1... Radio section, 4... FM front end section, 6... AM antenna coil, 6'.
...Secondary winding of AM antenna coil, 9...
... Tape recorder section, 10 ... AM front end section, 18 ... AM detection circuit, C2 ...
...Capacitor, S, -1, S, -2...
...First and second band selection switch.

Claims (1)

[Scope of utility model registration request] In an AM-FM radio receiver with a tape recorder, the radio section includes a first band selection switch that selectively switches the power to each front end section for the AM band and the FM band, and a first band selection switch for switching the detection output. A second band changeover switch is provided, and the second band changeover switch connects the movable terminal to the hot side of the secondary winding of the AM antenna coil.
The M side fixed terminal is connected to the AMM wave output terminal, the Ta and pe side fixed terminals are connected to the AM and FMM pass detection wave output terminals, respectively, and the AM side fixed terminal is used as an idle terminal, and the second band changeover switch is used to switch the FM During reception, the secondary winding of the AM antenna coil is grounded by the capacitor of the AM detection circuit, and during tape recorder operation, the AM
A band switching circuit for an AM-FM radio receiver with a tape recorder, characterized in that the detection output of each FM band is grounded through the secondary winding of the AM antenna coil.