JPS61242124A - Cross modulation preventing circuit for radio controlling receiver - Google Patents

Abstract

PURPOSE:To prevent the generation of cross modulation by applying the output of wave detection to a high frequency tuning circuit of a receiver for radio control from a secondary circuit of a different system. CONSTITUTION:A high frequency is converted by a mixing circuit 12 and then amplified by an intermediate frequency amplifying circuit 13 to undergo the envelope wave detection through a wave detecting circuit 14 and to be supplied to a high frequency attenuator 5. The attenuator 5 works when the output of wave detection reaches a fixed level and giving bypass to the high frequency flowing to a high frequency turning circuit 4. Thus the attenuator 5 is virtually put into the circuit 4 and the intensity of the high frequency supplied to a high frequency amplifying circuit 6. Thus the working points of the amplifying stages and the mixing stages set after the circuit 6 are kept at low levels. This prevents the generation of cross modulation, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a radio control receiver for preventing cross-modulation and desensitization under strong electric fields.

[Prior Art] Unlike general wireless communication, radio control is used under an extremely wide electric field range in which the electric field strength on the receiving side ranges from an extremely small electric field to a reinforcing electric field.

A particularly good example is radio control for models.

For example, when used on model airplanes, since the airplane is far away, it must work effectively even under a small electric field.
High sensitivity is required for the receiver. On the other hand, when landing, etc., the airplanes come very close to each other and enter into a reinforcing electric field. At that time, if several aircraft are flying at the same time, they will also be under the strong electric field of radio waves from other radio control transmitters, resulting in cross-modulation and sensitivity suppression at the receiver, causing radio control control signals to be It often causes disturbances and malfunctions. In this case, the risk of malfunction is particularly high if the receiver is highly sensitive.

In addition, many car radio controls are often operated at the same time over extremely short distances, and as a result, malfunctions have always occurred.

Furthermore, recently, it has become possible to allocate 13 waves in the 40882 band and 20kHz intervals in addition to the conventional radio waves for radio control (Ministry of Posts and Telecommunications Notification No. 895, 1982).
January 24th). Assuming a situation in which radio waves at 20 kHz intervals are detected under an extremely strong electric field, it can be said that the need for receivers to take sufficient measures is greater than ever.

For example, consider the case where 381s are flying simultaneously with the worst combination of frequencies that cause malfunctions in the table below. This table shows radio control air frequency allocation.

The table assumes a receiver in which the local oscillation frequency is set to a frequency lower than the receiving frequency by an intermediate frequency of 455 kHz. 40.770MHz and 40.83
Two radio waves with a 60kHz difference of 0HH2 are 40.7
40.830 when causing interference to a 108H2 receiver.
Two waves of MHz and 40.770MHz create a 60kHz beat, which affects the receiver's mixing circuit. In other words, the local oscillation frequency is 40.2 at 60kHz of the beat.
558Hz is added to create another local oscillator frequency of 40.315MHz, which is 40.770MHz.
Acts as a local oscillation frequency of z, and has an apparent value of 40.770
The receiver will be tuned to 8H2. Therefore, in addition to the original target signal, a signal due to the radio wave of 40.7708H2 is superimposed. This superimposed signal cannot be separated after the intermediate frequency amplification stage. The above example is
In the case of frequencies 60kHz apart, 40kHz2,
The same holds true for frequencies separated by 20 kHz.

Conventional AM radio control receivers use automatic volume controllers (AVC) and automatic gain controllers (AGC) to stabilize operation in strong and weak electric fields, as shown in Figure 2.
) is added. However, since it is controlled by the detection output received by itself, there is a limit to the effects that can be expected.
Furthermore, AVC and AGC are ineffective in FMM transmitters, and cannot prevent cross-modulation and desensitization that occur in reinforcing electric fields.

[Problems to be Solved by the Invention] The present invention solves the problems of the prior art and provides a high frequency tuning circuit for a radio control receiver in order to prevent malfunctions due to cross modulation and sensitivity suppression under strong electric fields. This invention provides a cross-modulation prevention circuit that applies a detection output from a sub-circuit of another system and automatically attenuates the current flowing through the tuned circuit to an extent that cross-modulation and sensitivity suppression do not occur. .

[Means for Solving the Problem] The first factor is a factor showing the configuration of the present invention. In the figure, (1) is a radio control receiver, (2 is a subcircuit, (3) is a receiving antenna, (4) is a high frequency tuning circuit, (
5) is a high frequency attenuator, (6) is a high frequency amplifier circuit, (7)
is a mixing circuit, (8) is an intermediate frequency amplification circuit 8, and (9) is a local oscillation circuit. In addition, (10) to (14) are subcircuits (2
Represents 1. (10) is a high frequency tuning circuit tuned to the same frequency as the high frequency tuning circuit (4), (11) is a high frequency amplifier circuit, (12) is a mixing circuit, (13) is an intermediate frequency amplifier circuit, and (14) is a high frequency tuning circuit. This is a detection circuit that performs envelope detection.

[Function] The function of the present invention will be explained using FIG. 1. (4) and (
6) to (9) are radio control receivers for receiving target signals.

In the sub-circuits (10) to (14), the high frequency tuning circuit (10) is tuned to the same frequency as the high frequency tuning circuit (4), and the high frequency tuning circuit (10) is tuned to the same frequency as the high frequency tuning circuit (4). Select. This selected high frequency (
It is thought that the radio waves (including those that directly enter the high-frequency circuit without passing through the antenna (3)) include those due to other strong electric fields that cause cross-modulation and suppression of sensitivity. These high frequencies are frequency-converted by a mixing circuit (12), amplified by an intermediate frequency amplification circuit (13), and then subjected to envelope detection by a detection circuit (14).

Therefore, the output of the detection circuit (14) is
) is roughly proportional to the high frequency intensity input from ).

The output from the detection circuit (14) enters a high frequency attenuator (5). The high frequency attenuator (S) operates when the detection output reaches a certain value or more, and bypasses the high frequency current flowing through the high frequency tuning circuit (4).

Thereby, it becomes as if an attenuator is inserted into the high frequency tuning circuit, and the intensity of the high frequency input to the high frequency amplifier circuit (6) can be lowered.

Therefore, the operating points of the amplification stages and mixing stages subsequent to the high-frequency amplification circuit (6) can be suppressed to a low level, and cross-modulation and the like can be prevented from occurring.

[Example] FIG. 2 is an example of a circuit actually constructed according to the block diagram of FIG. 1.

The portions surrounded by broken lines in FIG. 2 correspond to blocks labeled with the same numbers in FIG. 1.

In FIG. 2, the high frequency tuning circuit (4) and the high frequency tuning circuit (10) in FIG. 1 are coupled by a capacitor (C1) of small capacity (1 to 5 pF). This is to prevent the attenuation effect from reaching the high frequency tuning circuit (10) of the sub-circuit when the attenuator (5) operates. In the input stage of the sub-circuit, in order to reduce the loss of the high frequency tuning circuit (10),
A high frequency amplification FET (Q3) is used. For this reason, the loss in matching lance (January) is so small that it can be ignored.

If you use a transistor instead of an FET for high frequency amplification, use the matching transformer (■1) 2
It is sufficient to insert a coil on the next side and input the output of the coil to the transistor. The output of the FET (03) is passed through a matching transformer (T3), a high frequency amplification and mixing transistor (04), a matching transformer CT4), an intermediate frequency amplification transistor (Q5), and a matching transformer (■5). Detected by diode (0). Matching transformers (■3), (■4) and (■5) are inserted to improve the selectivity of the sub-circuits,
Ceramic filters can also be used.

The detection output is the capacitor (C2) that constitutes the time constant circuit.
and is supplied to the high frequency attenuator (5) through the resistor (R2). The time constant circuit can eliminate the effects of instantaneous fluctuations in electric field strength.

The detected output voltage obtained in this way is applied to the base of the transistor (Q6), and the detected output voltage is applied to the base of the transistor (Q6).
The transistor (Q6) becomes conductive only when the voltage exceeds the sum of the voltage (V, E-(1.5V)) and the operating voltage (0.5V) of the detection diode (0).

Therefore, in a weak electric field, a detection output that operates both the diode (0) and the transistor (06) cannot be obtained, and the high frequency attenuator (5) does not operate. In this case, the concave collector-emitter capacitance of the transistor (Q6) is the tuned circuit [T
Adds to the capacity of 2). Since the collector-emitter resistance of transistor (06) is very large, the Q of the tuned circuit is
will not decrease. Therefore, the high frequency tuning circuit (4
) does not deteriorate in selectivity.

If the electric field strength of the input radio wave exceeds about 60 dB, the transistor (06) reaches its operating point, and the high frequency is bypassed from the collector to the emitter of the transistor (Q6). The base power that enables this bypass is extremely weak, the residual voltage when conducting between the collector and emitter is extremely low compared to when a diode is used, and the resistance valve when conducting between the collector and emitter is low. These are the characteristics of the high frequency attenuator (5) according to the present invention.

Note that when an NPN transistor is used as the transistor (Q6), the polarity of the diode (D) may be reversed.

Figures 3a and 3b are examples in which the configuration of the high frequency attenuator (5) using a transistor (Q6) is changed. FIG. 3a shows an example in which the operating point of the transistor (06) is changed by applying a bias voltage from the resistor (R2), and the degree of attenuation can be adjusted. FIG. 3b shows an example in which a DC voltage is applied between the collector and emitter of an NPN transistor (Q6) so that the degree of attenuation can be adjusted.

FIG. 4 is an example in which the attenuation effect is roughly increased, and an attenuator using a transistor (07) is added.

Figure 5 shows 1. This is an example in which a straight type circuit, which is simpler than the case in FIG. 2, is used as the sub-circuit. That is, the frequency conversion circuit and intermediate frequency amplification circuit are omitted from the subcircuit shown in FIG. This subcircuit is intended to eliminate cross-modulation especially under strong electric fields, and is suitable when the sensitivity of the receiver is not so required, and is advantageous in terms of the area occupied by the receiver and the cost.

Although the 81 circuit in FIG. 5 has lower selectivity than the 01 circuit in FIG. 2, it can be expected to be more effective in suppressing radio waves of frequencies other than the target signal.

Next, a test example using the circuit shown in FIG. 2 will be shown.

In the radio control receiver using the circuit shown in Figure 2,
Approximately 100dB (100rV/g) (7) '
In the presence of R-field (!: radio waves), even when the field strength of the target radio wave was approximately 80 dB, it operated stably by eliminating cross-modulation and beat interference. Reception without the attenuator according to the present invention In the case of a 30dB, malfunctions still occurred even when the transmitter was brought close until the target radio wave reached 110dB.
This means that an improvement effect up to B was obtained.

[Effects of the Invention] In the present invention, an attenuator is added to the high frequency tuning circuit of a radio control transmitter, and the degree of attenuation by the attenuator is increased by the detection output of the receiver, thereby reducing the interference generated under strong electric fields. Modulation and sensitivity suppression can be suppressed, and safety in operating model airplanes and the like can be ensured.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a radio control receiver constituting the present invention, and FIGS. 2, 3a, 3b, 4, and 5 are circuit diagrams showing embodiments of the present invention. . (Main symbols in the drawings) (1) Radio control receiver (a: Sub circuit (4): High frequency tuning circuit (5): High frequency attenuator (6): High frequency amplification circuit; t73a decoy + 3b Figure 5 correction Procedures subject to this?In official document (spontaneous) October 24, 1985 1 Display of case 1985 Patent Application No. 83138 2 Name of invention Case of person who corrects intermodulation prevention circuit 3 of radio control receiver Relationship Patent Applicant Address 2-2-12 Eiwa, Higashiosaka-shi, Osaka Name Nippon Renri 11III1 Co., Ltd. Representative Fuekoku Kunfu 4th Director Rito 540 6 Contents of Amendment (1) Details?! Page I5 "As shown in Figure 2" in the bottom three lines
Delete. ('2J Correct the [resistance (R2) J on page 10, line 2] to 'resistance (R1) J'. (3) Correct 'transmitter' on line 7, page 13, to 'receiver'.

Claims (1)

[Claims] 1. When the detection output of the sub-circuit that detects the strength of the surrounding electric field exceeds a certain value, the detection output is applied to the high-frequency tuning circuit in the front stage of the high-frequency amplifier circuit of the radio control receiver. A cross-modulation prevention circuit for a radio control receiver having a high frequency attenuator for reducing high frequency input to the radio control receiver. 2. The high frequency attenuator is composed of a transistor,
2. The cross-modulation prevention circuit according to claim 1, wherein applying the detected output voltage causes the transistor to shunt the high-frequency current of the high-frequency tuning circuit. 3. The cross-modulation prevention circuit according to claim 1, wherein the sub-circuit is a superheterodyne receiver using an FET or a transistor in the first stage of a high-frequency amplifier circuit. 4. The cross-modulation prevention circuit according to claim 1, wherein the sub-circuit is a straight type receiver using an FET or a transistor in the first stage of a high-frequency amplifier circuit.