(the simplest walkie-talkie) is shown in Figure 1.
The radio intercom contains only three transistors. In the receiving mode, a supergenerative detector is implemented on VT1, and in the transmitting mode, the cascade on this serves as a master oscillator, emitting a carrier frequency into the antenna.
On transistors VT2, VT3 in the receiving mode serves as an amplifier of the low-frequency received signal, and in the transmitting mode it switches as an amplifier. DEM capsule, used as a microphone during transmission.
Details
Coil L1 is wound turn to turn on a frame with a diameter of 8 mm with an SCR core and has 9 turns of PEL wire with a diameter of 0.5 mm. Coil L2 is wound on top of it and has 3 turns of the same wire. Its diameter is 5 mm, it contains 60 turns of PEL wire with a diameter of 0.5 mm. The primary winding of the output transformer of a pocket transistor receiver can be used as inductor L4.
The radio station is designed for operation in a car, boat or stationary environment. It requires a constant voltage source of 12 - 15 V with at least 1 A. The communication range with a similar radio station is about 2 - 5 km in the city, up to 15 km on the highway and up to 30 km when operating in a stationary mode on a full-size antenna located on mast. The radio station operates with an antenna having a characteristic impedance of 75 ohms.
TECHNICAL CHARACTERISTICS OF CAR SV RADIO STATION
- Operating range................................................... ........................... 27 MHz.
- Transmitter output power at voltage
- Frequency modulation with deviation.................................................... .......2.5 kHz.
- Transmission current consumption, no more................................................... ......0.6 A.
- Receive current consumption, no more................................................... ......0.015 A.
- The sensitivity of the receiver with a signal-to-noise ratio is no worse than................1 µV.
- Selectivity in the adjacent channel at a detuning of ±10 kHz is no worse....... 36 dB.
12V power supply at 75 Ohm load............................................... ....................3 W.
The circuit of a pocket radio station (see Fig. 1) does not contain scarce elements, is easy to configure and simple to build. However, despite its simplicity, it has good characteristics. Receiver sensitivity is no worse than 10 μV, transmitter power is 250 mW, operating frequency is 27.14 MHz, communication radius in open areas is up to 1 km.
The transistorized pocket radio receiver is super-regenerative (VT2) and aperiodic (VT1). A useful signal is released at resistor R5, but it is much smaller with the suppression frequency of the super-regenerator. To suppress unnecessary noise and highlight the useful signal, the C12R7C13L7C14 filter is installed in the receiver. From it, the signal is supplied to resistor R13, which is a volume control, and then to audio frequency, made on transistors VT8, VT10, VT11.]
The transmitter of the pocket radio station is assembled on five transistors VT3-VT7 and is a push-pull self-oscillator, the signal of which is fed to the antenna through the coupling coil L2 and the matching circuit L1C3. Parallel connection of VT3, VT6 and VT4, VT7 allows you to increase the power transmitted to the transmitter antenna.
The use of portable radio microphones is usually associated with power supply problems, due to the need to regularly recharge batteries or change batteries. At the same time, autonomous power supply is not always necessary. The proposed radio microphone is designed to be powered by a voltage of 220 V, but differs from conventional circuits containing a network transformer or a quenching capacitor. Due to the low current consumption, it was possible to use quenching resistors, which have significantly smaller dimensions. The principle of a “network” radio microphone is shown in the figure below:
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The full-wave rectifier is assembled using diodes VD2 and VD3, voltage is supplied to it through quenching resistors R4, R5, and VD1 (about 8 V) is stabilized from the output of the rectifier.
Thanks to cascode connection
This receiver receives signals from AM and FM stations in the 27 MHz range. Despite the rather simple circuit, the receiver is highly sensitive and can be used as part of remote control systems, individual calling, security alarms, etc.
The circuit diagram of the receiver is shown in Fig. 1.
Rice. 1. 27 MHz receiver circuit
The high-frequency amplifier is assembled on a low-noise field tetrode type KP327A. The use of a field-effect transistor in UHF can significantly reduce the radiation of the local oscillator into the antenna. The antenna itself, together with inductor L1, capacitor C1 and the input capacitance of the transistor, form a filter tuned to the average frequency of the 27 MHz range. The frequency of self-oscillations (10...20 kHz) of the regenerator is suppressed by an active filter with a gain of about 20. The degree of feedback in the regenerator (VT2) is selected by variable resistor R5 until the highest quality reception of radio station signals is obtained.
Operational amplifier DA1 type K140UD6 is used as a low-frequency amplifier and active filter. High-impedance “TON” type telephones can be connected to the receiver output.
Details
Inductor L1 is wound with PEV-2 wire with a diameter of 0.4 mm on a frame with a diameter of 8 mm and contains 20 turns.
Coil L2 contains 2 turns of wire with a diameter of 0.1 mm, wound on top of coil L3.
Coil L3 contains 15 turns of wire with a diameter of 0.1 mm on a frame with a diameter of 8 mm.
Coil L4 contains 45...60 turns of PEV-2 wire with a diameter of 0.5 mm on a frame with a diameter of 10 mm.
A diagram of a simple homemade transistor receiver for working in a complex of radio control equipment. Frequency range 27 MHz.
Schematic diagram
Trimmer resistor R2 ensures that the desired operating point is set when tuning the receiver. Limiting resistor R1 prevents transistor VT1 from breaking down if the R2 slider is accidentally set to the uppermost position during tuning.
From the output of the low-pass filter R5C7, the detected signal is supplied to the input of the ULF, assembled on transistors VT2 and VT3. Direct connection of transistors covering the circuit with a deep negative DC coupling through resistor R7 provides good thermal stabilization of the position of the operating point.
Rice. 1. Schematic diagram of a homemade transistor superregenerator receiver for radio control at 27 MHz.
The total ULF gain in such a circuit can reach 1000-3000. The emitter follower on transistor VT4 provides decoupling of the receiver from subsequent stages.
Details and design
The printed circuit board is shown in Figure 2 and does not require any comments. All capacitors, except electrolytic C8 and C10, must be ceramic.
Rice. 2. Printed circuit board for a homemade radio control receiver with four transistors.
Trimmer resistor R2 can be either SPE-386 or RSh-bZMg. All transistors are either KT315 or KT3102 with any letter indices. The loop coil has 7 turns of wire with a diameter of 0.5 mm on a frame with a carbonyl iron trimmer core.
The diameter of the frame can be in the range of 5-9 mm. Choke L1 is standard 20-68 µH. A pin or flexible wire 20–40 cm long is used as an antenna.
Settings
The setup consists of setting the optimal super-regeneration mode using R2 and tuning the L2C5 circuit to resonance according to the signal from its transmitter. Capacitor Sb should have an initial capacitance of 15 pF. Its value is refined during the setup process until the maximum oscillations observed by the oscilloscope at the junction point of capacitors C7 and C9 are obtained.
Setting up the ULF comes down to setting a voltage of 4 V at the emitter of transistor VT4 by selecting the resistance of resistor R7, for which it is advisable to temporarily replace it with a variable one.
The connecting wires should be as short as possible to avoid interference with the VT2 base. If you don’t have an oscilloscope, you can connect high-impedance headphones (for example TON-2) to the receiver output and select the position of the R2 slider and the value of C6 based on the maximum volume of audible noise when the transmitter is turned off.
Then turn on the transmitter (meaning that it operates in amplitude modulation mode with signals from the output of the encoder), and adjust the input circuit to maximum volume. Sometimes after this it is useful to select the position of the potentiometer R2 slider.
Dnishchenko V. A. Remote control of models (500 schemes for radio amateurs).
This radio is designed for personal communications in the 27 MHz band. It has small dimensions and is quite simple, both in design and in repetition. The radio station has a ringing tone device, a speech signal compressor and a noise suppressor during reception. The signal from a condenser microphone with a built-in amplifier (MK1) is fed to operational amplifier M1, to its direct input. A voltage divider across resistors R2 and R3 is connected to this input, which creates half the supply voltage at this input, and thus allows the op-amp to operate with single-pole power supply.
Basic technical characteristics of the radio station:
- Transmitter output power minus; 0.5 W
- Receiver sensitivity at signal-to-noise ratio 10 dB minus; no worse than 1 µV/m
- Adjacent channel selectivity is no worse than 36 dB, and almost entirely depends on the parameters of the piezoceramic filter
- Selectivity for the mirror channel is no worse than minus; 26 db
- Rated output power of ultrasonic frequency minus; 60 mW
- The number of channels can be any, in this case minus; 4, according to the number of resonators available to the author
- Sound frequency range at level -3dB minus; 300...3000 Hz
- Allowable input signal value minus; from 0.3 µV to 100 mV
- Emission bandwidth at level 30 dB minus; no more than 11 kHz
- Frequency deviation at maximum modulation is about minus; 2.5 kHz
- Current consumption when receiving in silent mode minus; no more than 10 mA
- Current consumption during transmission minus; no more than 90 mA
- Supply voltage minus; 9B±B.
A circuit R7 C5 C6 is connected between the inverting input and output, which creates the desired gain and frequency response of the amplifier. This amplifier works as a speech signal compressor, compressing its dynamic range through a cascade on T1. The output voltage of the AF amplifier is detected by diodes D1 and D2 into a constant voltage, negative, which acts on transistor T1 and, with an increase in the level of the audio signal, increases the resistance of the channel of this transistor.
As a result, the bypassing of the inverting input by capacitor C6 is weakened and the negative feedback coefficient increases, which leads to a decrease in the gain of the op-amp. The output voltage of the op-amp, equal to half the supply voltage, is supplied through resistors R11 and R12 to the cathodes of varicaps D3. The modulating voltage of the AF changes at the cathode of the varicaps relative to this bias voltage. Circuit C4 R6 Kn1 generates a call signal; when the button contacts are closed, circuit R6 C4 is switched on between the output and direct input of the operational amplifier, switching it to generation mode.
Varicap matrix D3 is connected between one of the quartz resonators, which are selected by switch P1.1 when changing the frequency channel, and the common wire. Changing the capacitance of the varicap leads to some change in the frequency of the resonator. In this process, the inductance of coil L1 also plays a role.
Transistor T2 contains a master oscillator, the frequency in the collector circuit of which is determined by the switched on quartz resonator, inductance L1 and capacitance D3. Circuit L2 C13 in the collector circuit of this transistor is configured to the middle of the selected range and a frequency-modulated HF voltage with the frequency of the switched on channel is released in it. This voltage is supplied through the coupling coil L3 to the output stage, made on transistor T3.
The coil is included in the bias circuit based on this transistor - R17, R18, which creates the operating point of the output stage. An amplified and frequency-modulated RF voltage is released at the T3 collector. This voltage is then supplied to the antenna through the low-pass filter and extension coil. The low-pass filter on coil L4 and capacitors C16 and C17 serves to suppress harmonics and match the output impedance of the stage on T3 with the input impedance of the antenna; coil L5 introduces additional inductance into the antenna circuits and thus increases its equivalent length, approaching a quarter-wave.
As a result, the signal output to the antenna increases. Capacitor C19 prevents the failure of transistor T3 from accidental short circuit of the telescopic antenna with a common wire or power circuit.
The schematic diagram of the receiving path and the switching diagram of the “reception/transmission” modes is shown in Figure 2. In the position of switch P2 indicated in the diagram, the transmission modes are turned on, in the opposite position - the reception modes.
The signal from the antenna through switch P2.1 and capacitor C3 enters the input circuit - L1 C1, which is tuned to the middle of the selected range (the selected range means the frequency band from the channel with the minimum frequency to the channel with the maximum frequency, from among the selected transmitter resonators) .
The signal isolated by the circuit goes to a diode limiter on diodes D1 and D2 and then to a high-frequency amplifier on transistor T1. In the drain circuit of this transistor, circuit L3 C7 is turned on, configured, like the input circuit, to the middle of the selected range. This circuit is not completely connected to the drain T1, through the coupling coil L2. The signal from circuit L3 C7 through capacitor C8 is supplied to the gate of field-effect transistor T2, which serves as the second stage of the RF amplifier and mixer of the frequency converter.
The high amplification properties of the cascade are maintained due to the presence of capacitor C9, which shunts the negative feedback resistor H6 plus the relatively low connection between the transistor source and the local oscillator. The drain circuit of this transistor includes circuit L4 C10 tuned to an intermediate frequency of 465 kHz.
The radio station is assembled on an accessible element base, and is easy to manufacture and configure. It is designed to operate in the 27 MHz band on one fixed frequency, with AM. A schematic diagram of the receiving part of the radio station is shown in Figure 1. The radio path is assembled using a superheterodyne circuit with one frequency conversion. Transistor T1 is used as a high-frequency amplifier. The signal from the antenna is isolated by the input circuit L1 C2 and goes to the base of this transistor. The circuit is tuned to the frequency of the communication channel.Main technical characteristics:
1. Communication channel frequency - 27.045 MHz.
2. Intermediate frequency - 465 kHz.
3. The sensitivity of the radio receiving path is 2 µV.
4. Selectivity in the adjacent channel with a detuning of 9 kHz, no worse - 40 dB.
5. Transmitter power - 250 mW.
6. Modulation depth - 50%.
7. Current consumption during transmission is no more than 150 mA.
8. Current consumption when receiving in silent mode / maximum volume is no more than 12 mA/100 mA.
9. Supply voltage - 6V.
In the collector circuit of this transistor, a second circuit is switched on, which is also tuned to the channel frequency. The amplified RF voltage through the coupling coil L3 is supplied to the input of the frequency converter mixer. The coil is connected to the bias circuit of transistor T2. The emitter circuit of this transistor receives voltage from the local oscillator, which is located on the transmitter board (Fig. 2).
In the collector circuit of transistor T2, a complex of frequencies is distinguished, among which there is an intermediate frequency voltage - 465 kHz. This voltage is released by the piezoceramic filter PF1 and supplied to the intermediate frequency amplifier, which is made on the M1 chip. The K157XA2 microcircuit includes an intermediate frequency amplifier, an amplitude detector and an AGC system. The microcircuit is used for its intended purpose and is connected according to a standard circuit.
The AF voltage is supplied through resistor R10 and the volume control R12 to the transistor AF amplifier on transistors T3-T6. Dynamic loudspeaker Gr1 is turned on at the output. The receiving path is powered by a voltage of 6V and is turned on by switch B1.
Figure 2 shows the circuit of the transmitter and local oscillators. When making a 27 MHz radio station, even the simplest one, a radio amateur faces difficulties in purchasing quartz resonators, or microcircuits for a frequency synthesizer. Moreover, it is not profitable to use a synthesizer in such a simple radio station.
At the same time, in almost any locality, you can purchase 8.86 MHz resonators. They are used in PAL decoders for televisions. If we start the generator at the third harmonic, we get 26.58 MHz. This is exactly what is needed for the receiver's local oscillator: add 465 kHz, and we get a signal reception with a frequency of 27.045 MHz, this is exactly the frequency of one of the channels.
In order to use the same local oscillator for the transmitter, you need to make another frequency converter that would add the frequency of 26.58 MHz and 465 kHz, and output an IF of 27.045 MHz to the input of the transmitter power amplifier.
The local oscillator with a frequency of 26.58 MHz is made on transistor T1, circuit L1 C2 is tuned to the third harmonic of resonator K1 (Fig. 2). From the coupling coil L2, the local oscillator voltage is supplied to the receiving board, from the coil L3 to the converter on transistor T2. In the collector circuit of this transistor, a circuit tuned to a frequency of 27.045 MHz is included, and a signal with a frequency of 465 kHz from the local oscillator on transistor T4 is supplied to the emitter circuit.
The frequency of this local oscillator is determined by the resonance frequency of the piezoceramic filter PF 2, which here is exactly the same as in the IF path of the receiver. The result of the addition of these frequencies is isolated in the collector circuit T2, and goes to the output power amplifier on transistor T3.
This design uses basic amplitude modulation in the output stage. The signal from the dynamic microphone MK1 is fed to a two-stage AF amplifier using transistors T5 and T6. The cascades have capacitive couplings. From the collector T5 through the inductor Dr2, which serves to prevent the penetration of high-frequency voltage to the output of the microphone amplifier, the low-frequency signal is supplied to the base of transistor T3.
And it creates an additional displacement that changes in time with the sound signal. The gain of the output stage changes accordingly. In this way, amplitude modulation is carried out. The modulation depth can be set using variable resistor R7.
The modulated RF signal is isolated at the T3 collector. Circuit L4 C8 C9 serves to match the output impedance of the transmitter with the input impedance of the antenna, for which a 750 mm long telescopic rod is used, and to suppress harmonics of the main signal.
A wide variety of parts can be used in the radio station; it is important that the loop capacitors are ceramic and have a minimum TKE, for example KT-1 or KD. The rest are capacitors and resistors of any type. The quartz resonator is in a metal case, like those used in PAL decoders.
Transistors KT315 with any letter index, or KT312, KT316, KT3102, KT368. Instead of MP42 - MP16-MP26, MP39-MP42, instead of MP38-MP9-MP11, MP35-MP38. Diode D311 - KD503-KD522, D220-D223. The K157XA2 chip can be replaced with a K237XA2. Piezoelectric filters - the same ones used FP1P015, but you can use any at 465 kHz. In the transmitter, the KT603 transistor can be replaced with KT608, KT604, KT630. KT606 - on KT610, KT904, KT907, or use the same as T2, but take measures to remove heat.
Microphone - MD-1 or DEMSh can be any, and even a dynamic loudspeaker, the sound quality is worse. The coils are wound on frames from the color module of ZUSTST TVs. They are plastic and have a diameter of 5 mm, and a tuning core made of 400NN ferrite. The receiver coil L1 contains 13 turns of PEV-0.3 with taps from the 3rd and 7th turns, L2 is the same but without taps, L3 is on the same frame with L2 3 turns of the same wire.
Transmitter coils. L1 - 13 turns, L2 and L3 are placed on the same frame with L1, L2 - 1 turn, L3 - 4 turns PEV-0.3. L7 is the same as L1 of the receiver. L4 - 20 turns of the same wire. 1.5 - 130 turns of wire PEV-0.1, L6 on top of it, and has 10 turns, are wound on the same frame as the rest. Chokes Dr2 and Dr1 are wound on fixed resistors with a resistance of more than 50 kohms, they each have 100 turns of PEV-0.1 wire.
