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Schematic diagram of the radio receiver ocean 214

Today I am starting a series of articles “Legends Never Die”, in which I will try to talk a little about amazing and interesting things, to which the prefix “retro” is usually added these days.

Old..., this magic word, caressing the ear of every connoisseur of good things, has been irrepressibly exciting my imagination for the last couple of years. In search of interesting new products, I patrol city markets and thrift stores every weekend. About a month ago, the Ocean - 214 radio receiver, which I briefly mentioned in my blog, came into my networks.

This solid device from the end of the last century certainly aroused the envy of mere mortals, since it was not only made of wood, but also had an appropriate price.

The monthly salary of an ordinary engineer is a substantial sum for a small receiver.

And although I got this device for a much smaller amount (in terms of today's prices), its condition left much to be desired.

In addition, after five hours he stopped playing altogether.

Feeling a little sad, I gathered my willpower and got to work, deciding to bring the pensioner to his senses at all costs.

Restoration and repair of radio receiver Ocean - 214

To begin with, I started disassembling.

This process is not very labor-intensive, but very interesting.

Good sound quality is provided by only one speaker with a paper cone

While I was sorting it out, I encountered interesting feature- the receiver sometimes works, sometimes it doesn’t. Most likely, a bad contact has formed somewhere. The search began with a radio frequency unit,

therefore, it was during its rotation that interruptions in operation were observed.

Then I began inspecting the range shift knob.

It was then that the dog rummaged around - the power wire of the right backlight lamp had shorted.

After soldering, the receiver came to life and never turned off.

Having completed a successful renovation, I decided to concentrate on restoration. The plastic parts of the receiver were thoroughly washed and dried. To give them a factory shine, I decided to use a colorless shoe sponge.

I was quite satisfied with the result - the parts were free of whitish stains.

The wooden body was varnished in one layer.

Under no circumstances should you varnish the inner surface of the case, otherwise the receiver will lose all its sound properties.

The metal parts of the case were carefully processed with a soapy old toothbrush.

The transparent plastic windows were carefully wiped with a soft cloth for the monitor.

From USSR with love

On the threaded tip of the antenna,

I screwed on a new limit switch, given to me by Mitrofanich from the radio market.

As a result of assembly, the device acquired a solid appearance,

and pleased the household with such good sound that my favorite JVC EX-A1 respectfully asked permission to take a photo with the star.

The Nokia 7250i also sneaked in here unnoticed.

The rejuvenated pensioner coped with the move to another living space quite successfully, and even made a new friend.

Solid set for solid guys

Conclusion

So what do we have? Solid appearance, wonderful (albeit mono) signature “wooden” sound, extended VHF range, and not a second of regret about the transaction.

And if you look at the online auction molotok.ru,

then it becomes quite obvious - I invested my 422 rubles extremely successfully!

See you again, friends! And as a keepsake, a modest group photo.

Radio receiver of the 2nd complexity group with universal power supply “Ocean-214” contains a chassis with printed circuit boards and main blocks and assemblies. The receiver is structurally made according to the functional block principle. On the front and rear panels There are controls, sockets for connecting an external antenna, tape recorder, and headphones. The receiver provides DV, SV, five extended HF sub-bands and a VHF range. Power is supplied from elements of type 373 with a total voltage of 9 V or from the network through a rectifier.

1. VHF unit [A1]

The electrical circuit diagram of the Ocean-214 radio receiver (Fig. 1) uses a unified unit of the UKV-2-1C type [A1].

The signal from the whip telescopic antenna WA1 (points 20, 21 on the board [A3]) through the coupling capacitor C1 and the coupling coil L1 is fed into the input circuit L2, C2, C3, which provides initial suppression of the mirror channel and the forward channel. The input circuit is not tunable, therefore it is made broadband with a bandwidth of 2∆f 0.7, covering the entire VHF range from 65 to 108 MHz.

The input signal from the capacitive divider C2, SZ is fed to the input of the RF amplifier, assembled on transistor V1 according to the circuit with common base. Switching on with OB due to 100% OOS improves the characteristics of the cascade at high carrier frequencies of the VHF range, and the high output resistance of the transistor does not shunt the load circuit and does not reduce its quality factor. The load of the RF amplifier is the oscillatory circuit L3, C9, which is adjusted to the frequency of the received signal by a variable capacitor C9. Capacitors C7 and C8 ensure that the tuning limits fall within the standard boundaries of the VHF range. Resistors R1, R2, R4 determine the DC operating mode of the transistor.

Fig.1 VHF unit.

The frequency converter uses two transistors - VT3 (mixer) and TV4 (heterodyne). The local oscillator master circuit consists of coil L4, capacitor C19 and mating capacitors C18, C22, C23. To automatically adjust the frequency of the local oscillator, varicap V4 is used; the control (blocking) voltage of the APCG is supplied to the varicap through resistor R14 from the output of the fractional detector in the RF-IF block.

The local oscillator is powered through the decoupling filter R11, C17 from a separate stabilizer with a voltage of +4.2V. Resistors R6, R8, R10 determine the direct current mode of transistor V2, and capacitor C10 eliminates the negative feedback on alternating current. Since transistor V2 is connected in a circuit with OB due to C13, the obligatory PIC is formed by capacitor C12 from the collector to the emitter. The local oscillator oscillations through the coupling capacitor C15 are supplied to the base of the mixing transistor V3 along with the signal from the receiving station through its coupling capacitor C11..

The operating mode of the V3 mixer is set by standard piping elements R9, R7, R12, C16 and R13, C21. The load of the mixer is a dual-circuit bandpass filter (BCF) L5, C20 and L6, C24, tuned to the intermediate frequency of the FM path - 10.7 MHz. It provides adjacent channel selectivity.

The intermediate frequency signal from the L7 coupling coil is supplied to the base of transistor VT6 of the URCH-IF unit.

2. Block KSDV [A2]

Block KSDV [A2], consists of a drum range switch with a set printed circuit boards(7 pieces of strips) and magnetic antenna WA2 (Fig. 2).

The drum switch boards contain sets of replaceable coils and capacitors related to the input circuits (on the left in the diagram), the RF amplifier (in the middle) and the local oscillator (on the right). The board is connected to the circuit using 20 contact pads.

For example, let's look at the strips of the SV and HF-5 ranges; for the other ranges the differences are insignificant.

The input circuit of the CB range is formed by section C1.1 of the variable capacitor and the inductance coil L1 located on the ferrite rod of the magnetic antenna, while coil L3 is short-circuited. In the long-wave range, the inductance of the input circuit consists of series-connected coils L1 and L3. From the coupling coil L2 of the magnetic antenna, the signal through the contact group of the range switch (pins 13, 15) and the separating capacitor C9 is supplied to the base of the transistor V8 - the AM frequency tract.

Middle group elements on the SV-bar forms a load tunable resonant circuit of the RF amplifier, which ensures selectivity along side reception channels (mirror and direct transmission). It includes the second section of KPE C1.2 and the inductance of the coil L9.1. The tuning capacitor C12 is used to position the tunable circuit within the standard boundaries of the CB range. From the coupling coil L9.2 with the midpoint, the signal of the received station is fed to a balanced diode ring mixer V1…V4 [A3].

The right group of elements on the CB-bar forms the master circuit of the AM circuit local oscillator on transistor V9 [A3]. It consists of the third section of KPE C1.3, the inductance of the coil L10.2 and the mating capacitors C13, C14, C15. Resistors R4 and R5 select the required local oscillator mode for stable generation. From the coupling coil L10.1, the local oscillator signal is supplied to the balanced diode mixer V1…V4 [A3].

The switch strips for the HF range differ from those for the SW range only in the input circuits. For example, in the KV-5, the input circuit is formed by the inductance of the coil L11.1 and the first section of KPE C1.1. Capacitors C16, C17 are used to lay the input circuit within the standard range boundaries. From the communication coil L11.2, the signal is supplied to the base of the transistor V8 - the AM frequency tract [A3].

In the HF ranges, the input circuits, consisting of single circuits, have an autotransformer connection with the telescopic antenna WA1 through pin 16.

Fig.2 KSDV block

3. Block URCH - IF [A3]

The ARF-IF unit includes an AM frequency amplifier, an AM and FM amplifier, a frequency converter, AM and FM detectors, and a voltage stabilizer for powering the base circuits of the AM local oscillator.

The amplifier amplifier of the AM path is assembled on transistor V8 using a resonant circuit. To increase the stability of its operation, low-resistance resistors R11, R14 are included in the base and collector circuits of transistor V8. A filter consisting of a capacitor C14 and a corresponding coil L5, L8, or L12 [A2] is included in the emitter circuit in the ranges DV, SV, HF-5. This makes it possible to reduce the unevenness of the RF gain across the range, and also increases the selectivity of side reception channels. A single tunable circuit is connected to the collector circuit of transistor V8 through conductor 9 of the harness located on [A2].

The frequency converter is assembled according to a circuit with a separate local oscillator. The mixer is made using diodes V1...V4 according to a balanced ring circuit. He has balanced input for the signal: the resonant load circuits of the RF frequency control located on [A2] through points 7-6 of the board [A3] are connected to the horizontal diagonal of the bridge using diodes V1...V4. Circuit L2.2, C7, C8 tuned to the intermediate frequency of the AM signal 465 kHz is connected to the vertical diagonal of the bridge through the coupling coil L2.1 with the middle point. The local oscillator signal is supplied to the middle points of the communication coils connected to the diagonals of the mixer bridge L2.1 and L9.2 (for example, for the CB range in the module).

The conductivity of the diodes changes over time with the frequency of the local oscillator, as a result of which frequency components of the difference frequencies appear at the output of the mixer:

f pr = f g - f c

The local oscillator is made on transistor V9 according to an inductive three-point circuit. Capacitor C35 ensures that the transistor is switched on with alternating current. Resistors R24, R25, R22 set the DC mode, and low-resistance R20, R21 increase the stability of the cascade. The master circuit of the local oscillator is included in the PIC circuit between the collector and emitters.

The IF circuit with a balanced ring diode mixer is described in detail in the abstract T.5.3.

The amplifier-AM consists of three stages and is assembled on transistors V7, V10, V15. The load of the first stage is a five-link FSS: L4, C11; L6,C17; L8,C22; L10,C28; L11, SZZ, S34. The connection between the links is critical - through capacitors C16, C20, C25, C29.

The FSS is tuned to an intermediate frequency of 465 kHz, has a bandwidth of 9 kHz and provides full adjacent channel selectivity.

The load of the second stage is resistor (R31), the third stage is resonant (oscillatory circuit L14, C48).

The amplified intermediate frequency signal of 465 kHz is fed to the AM detector, made in a series circuit on diode V19, and the detector filter C50, R47, R48, C51 to suppress the carrier frequency f etc. After detection, the audio frequency signal from C51 is fed to the input of the ultrasonic audio frequency amplifier (block [A4]).

The receiver has automatic gain control AGC. From the collector of transistor V15, through a frequency-dependent chain R41, C46 and separating capacitor C45, voltage is supplied to diode V17, which, together with load resistor R42, forms a parallel-type AGC detector. An amplifier is made on transistor V16 direct current, which increases the efficiency of regulation. As the signal increases, the voltage detected by the AGC detector increases and transistor V16 opens, which leads to a decrease in the voltage at its collector relative to the emitter.

From collector V16 through chain R33, C36, R27, R26, which acts as an AGC filter with a time constant t AGC= 0.2 sec., the AGC control voltage is supplied to the base of V10 and reduces its initial base offset. At the same time, the slope of the transistor characteristic decreases and, as a consequence, the gain of the cascade, compensating for the increase in the signal amplitude at the receiver output. The mode of transistor V10 is set by resistor R26.

From the emitter V10, the enhanced AGC control voltage through the chain R23, C10, R8 "relay" is transmitted to the base of the transistor V7 and through the chain R18, C21, R16, R11 - to the base V8. Hence the AGC received the name ‘relay AGC’.

From emitter V7 through resistor R4, voltage is supplied to device PA1, which serves to indicate the receiver settings.

The FM amplifier is a four-stage one, made on transistors V6, V7, V10, V15, i.e., the same ones as the AM amplifier. Thus, the receiver uses a combined AM-FM amplifier circuit.

The signal from the output of the VHF unit (conductors 23 and 24 in the module harness) goes to the base of transistor V6, the load of which is circuit L3.1, C5. Diode V5 is designed to protect the path from overloads.

The load of the second stage on transistor V7 is a four-link FSS: L5, C15; L7,C19; L9,C27; L12,C32; tuned to an intermediate frequency of 10.7 MHz with a bandwidth of 200...250 kHz. The connection between the FSS links is capacitive through capacitors C18, C26, C31.

The third stage of the FM path on transistor V10 is made according to a resistor circuit.

The load of the fourth stage on transistor V15 is the oscillatory circuit L13.1, C47. Through the coupling coil L15, an intermediate frequency signal of 10.7 MHz is supplied to a frequency (fractional) detector assembled using diodes V20, V21 in a symmetrical circuit.

The fractional detector is described in detail in the abstract T.6.2.

The audio frequency signal is removed from the middle connection point of resistors R50, R56 and through an additional intermediate frequency filter R53, C59 and separating capacitor C57 is supplied to the input of the emitter follower V18, which acts as a matching stage. From its emitter load R46, through a special low-frequency distortion correction filter (LPD), introduced on the transmitting side to increase the noise immunity of high frequencies, the audio signal is sent to the low-frequency amplifier unit [A4].

Through the filter AFCГ R54,С60 with time constant t APCG= 01…0.2 sec. the voltage from the frequency detector is supplied to the varicap V4 of the VHF unit to automatically adjust the local oscillator frequency.

The APCG scheme is described in detail in the abstract T.7.2.

The receiver has two compensation-type stabilizers.

The primary on transistors V2, V8 [A4] ensures stabilization of the mains voltage rectified by the bridge circuit V4...V7 and filtered by capacitor C21. This voltage of 8.5 V powers the ultrasonic unit [A4].

To power the high-frequency blocks [A1] and [A3], an additional stabilizer is used on transistors V11, V14, V13 and zener diode V12 [A3]. It allows you to obtain a supply voltage of 4.4 V when the batteries are discharged from 9 to 5...6 V.

Emitter follower V18 serves to separate the AM and FM paths. When the VHF band is turned on (in the KSDV block [A2] contacts 3-18 are closed), the stabilized voltage from the collector V13 through the decoupling filter R19, C24, C23 is supplied to point 3 of the RF-IF board [A3]. From this point the voltage is 4.2 V across closed contacts 3 and 18 of the KSDV block [A2] enters the current 16 of the URCH-IF board [A3]. In this case, the supply voltage is supplied to the VHF unit, the first stage of the FM amplifier (V6) and to the emitter follower V18, the constant voltage on which is closed by the AM detector (diode V19).

Choke L1 in the HF-IF block serves to protect against mutual shunting of the input circuits of the AM and FM paths.

4. Ultrasound unit [A4]

The ultrasonic frequency unit [A4] consists of a preliminary stage on transistor V1, volume controls R1 and tone controls for low R10, C5 and high R7, C4, C6 audio frequencies and a power amplifier on a D1 chip of type K174UN7. Through the isolation capacitor C17, the amplified signal is supplied to loudspeaker B1. Block A4 also contains switches S1.1. (On scale backlight), S1.2 (On receiver), S1.3 (On and off AFC), as well as a rectifier on diodes V4-V7 and a rectified voltage stabilizer on transistor V2.

] >>> The Ocean-205 radio receiver is a further modification of the Ocean and Ocean-203 receivers discussed in § 3. Its schematic diagram is shown in Fig. 19 (insert), however, it does not show the circuit diagram of the HF-IF unit, since it practically does not differ from the corresponding circuit of the Ocean-203 receiver (minor changes are discussed below). For the HF-IF unit board, the diagram shows only contacts for connecting external circuits.

Rice. 19. Schematic diagram radio receiver "Ocean-205"
Range switch B - in position KBV ( P1), AM-FM switch ( B1) - in the AM position (VHF off), other switches AT 2-AT 5- in the off state. Magnetic antenna ( MA) is connected to the switch position IN: CB range - to contacts 15 , 17 planks P6, DV - 14 , 19 slats P7. Plank schemes P1, P2 And P3, P4 combined, the values of the elements of the strips are indicated in brackets P2 And P4(other denominations have no differences)

Signal from telescopic antenna through coupling capacitor C8 goes to the communication coil L1. To ensure the highest gain and lowest noise level, a wideband input circuit ( L2, C1, C2) is non-tunable and has an inductive coupling with the antenna. The contour stripe width is ~7.5 MHz with him constant tuning to the middle of the range (69.5 MHz). Connection between the input circuit and the emitter T1(UHF) - capacitive (divider from capacitors C1 And C2), which makes setting up the circuit more convenient.

UHF transistor ( T1) is connected according to a common base circuit, since such a connection does not require neutralization and provides a more uniform gain over the range. The UHF cascade has a single resonant circuit at the output >>> L3, C4, C6, C7 with autotransformer connection. Tuning it to the received frequency is associated with tuning the local oscillator circuit and is carried out by a two-section KPI block of variable capacitors ( C7 And S21). Resistor R12 is anti-parasitic. The load of the UHF circuit is the input resistance of the frequency converter, and the connection of this circuit with the transistor T2 carried out through a small capacitor C8. To reduce cascade overloads and local oscillator detuning with strong input signals, a limiting diode is connected in parallel to the UHF circuit D12 (D20), to which the blocking voltage from the stabilizer is applied.

The load of the converter is a bandpass IF filter, consisting of two connected circuits ( L5, C14 And L6, C18). The required bandwidth is provided by the magnitude of the coupling between the circuits. Using additional winding L7, inductively coupled to the coil L6, matching the output resistance of the frequency converter with the input resistance of the IF path is achieved.

A varicap is used to automatically adjust the frequency D13(D902), which is connected to the local oscillator circuit through capacitors C19 And S20. The control voltage to the varicap is supplied from the frequency detector through a resistor R52(installed between points A And B RF-IF boards, see fig. 17) and contact 27 (dot IN boards); contact 6 and resistor R10(VHF unit). This voltage acts on the varicap so that the difference between the frequencies of the local oscillator and the received signal approaches the nominal value of the intermediate frequency due to the fact that the capacitance of the varicap changes when the blocking voltage changes, and, consequently, the frequency of the local oscillator.

Rice. 17. Wiring diagram of the RF-IF board of the Ocean-203 radio receiver
The diagram does not show transistor screens T3, T4, T5, T8 And T9 and the position of the movable switch knives IN 1

Rice. 20. Wiring diagram of the board of the VHF radio receiver “Ocean-205”

Rice. 21. Wiring diagram of the ULF radio receiver board "Ocean-205"

Rice. 22. Wiring diagram of the rectifier board of the Ocean-205 radio receiver

The ULF receiver circuit is somewhat different from that discussed in § 3. The first two pre-amplification stages and the four-transistor ULF output stage are practically no different in their circuits from those discussed in § 3. In the one shown in Fig. 19 (see inset) in the bass amplifier circuit, the connection of the high tone controls has been changed ( R3) and low ( R2) sound frequencies. Their connection circuit is similar to that used in tube receivers. The entire amplifier is covered by deep negative feedback in direct and alternating currents to ensure high mode stability and a low level of nonlinear distortion.

Negative constant DC coupling is carried out from the ULF output to the emitter of the transistor T12 through a resistor R21. Positive feedback from the output through a resistor R24 supplied to transistor bases T14, T15(bass reflex). Using a variable resistor R20 the initial bias is set at the bases of these transistors and thereby the required value of the quiescent current of the output stage is selected. To reduce nonlinear distortions, AC feedback has been introduced - a chain R18, C12. The required frequency response is achieved by a capacitor feedback C13 connected between the base and collector of the transistor T13(type KT315B). Transistor based bias T12 set by a variable resistor R16. Chain R13, C10 acts as a filter,

The wiring diagram of the LF amplifier is shown in Fig. 21 (insert).

To power the receiver from a 127/220 V AC mains, it includes a power rectifier made according to a bridge circuit using four diodes D14-D17(D226), and a voltage stabilizer assembled according to a compensation circuit with a single-stage feedback amplifier. On a transistor T19(MP39) the cascade operates in DC amplifier mode, and on T18(P213A) - regulatory cascade. Feedback voltage is applied to the base of the transistor T19 from potentiometer R3, which is part of the divisor ( R3, R4), connected in parallel with the load.

As the output voltage increases (contacts 3 , 4 board) the base current increases T19, and with it the current of its collector. This leads to an increase in the voltage drop across the resistor R2 and reducing the base current T18, which in turn increases the resistance between the emitter and collector T18 and, accordingly, the voltage in the same area. As a result, the increase in output voltage is largely compensated. With help variable resistor R3 you can change the load voltage >>> from almost zero value to the value of the zener diode reference voltage D18(D814A). Stabilized voltage is removed from the emitter T18 and through switch contacts AT 3(“Network”) and AT 4(“On”) is supplied to the receiver circuit. Capacitor C1 reduces rectified voltage ripple. Circuit board circuit diagram of the rectifier unit ( Bn) is shown in Fig. 22 (insert).

The receiver power switch is located from the volume control potentiometer ( R1) to a special switch AT 4. Using a switch AT 5 The scale lighting is turned on and off (Fig. 23 on the inset).

Broadcasting receiver "Ocean-214".

Radio receiver of the 2nd complexity group with universal power supply “Ocean-214” contains a chassis with printed circuit boards and main blocks and assemblies. The receiver is structurally made according to the functional block principle. On the front and rear panels there are controls, sockets for connecting an external antenna, tape recorder, and headphones. The receiver provides DV, SV, five extended HF sub-bands and a VHF range. Power is supplied from elements of type 373 with a total voltage of 9 V or from the network through a rectifier.

1. VHF unit [A1]

The electrical circuit diagram of the Ocean-214 radio receiver (Fig. 1) uses a unified unit of the UKV-2-1C type [A1].

The input signal from the capacitive divider C2, SZ is fed to the input of the RF amplifier, assembled on transistor V1 according to a common base circuit. Switching on with OB due to 100% OOS improves the characteristics of the cascade at high carrier frequencies of the VHF range, and the high output resistance of the transistor does not shunt the load circuit and does not reduce its quality factor. The load of the RF amplifier is the oscillatory circuit L3, C9, which is adjusted to the frequency of the received signal by a variable capacitor C9. Capacitors C7 and C8 ensure that the tuning limits fall within the standard boundaries of the VHF range. Resistors R1, R2, R4 determine the DC operating mode of the transistor.

Fig.1 VHF unit.

The frequency converter uses two transistors - VT3 (mixer) and TV4 (heterodyne). The local oscillator master circuit consists of coil L4, capacitor C19 and mating capacitors C18, C22, C23. To automatically adjust the frequency of the local oscillator, a varicap V4 is used; the control (blocking) voltage of the APCG is supplied to the varicap through resistor R14 from the output of the fractional detector in the URF-IF block.

The intermediate frequency signal from the coupling coil L7 is supplied to the base of transistor VT6 of the RF-IF unit.

2. Block KSDV [A2]

The KSDV block [A2] consists of a drum band switch with a set of printed circuit boards (7 pieces of strips) and a magnetic antenna WA2 (Fig. 2).

For example, let's look at the strips of the SV and HF-5 ranges; for the other ranges the differences are insignificant.

The middle group of elements on the SV-bar forms a load tunable resonant circuit of the RF amplifier, which ensures selectivity along side reception channels (mirror and direct transmission). It includes the second section of KPE C1.2 and the inductance of the coil L9.1. The tuning capacitor C12 is used to position the tunable circuit within the standard boundaries of the CB range. From the coupling coil L9.2 with the midpoint, the signal of the received station is fed to a balanced diode ring mixer V1…V4 [A3].

In the HF ranges, the input circuits, consisting of single circuits, have an autotransformer connection with the telescopic antenna WA1 through pin 16.

Fig.2 KSDV block

3. Block URCH - IF [A3]

The frequency converter is assembled according to a circuit with a separate local oscillator. The mixer is made using diodes V1...V4 according to a balanced ring circuit. It has a symmetrical input for the signal: the resonant load circuits of the RF frequency control located on [A2] through points 7-6 of the board [A3] are connected to the horizontal diagonal of the bridge using diodes V1...V4. Circuit L2.2, C7, C8 tuned to the intermediate frequency of the AM signal 465 kHz is connected to the vertical diagonal of the bridge through the coupling coil L2.1 with the middle point. The local oscillator signal is supplied to the middle points of the communication coils connected to the diagonals of the mixer bridge L2.1 and L9.2 (for example, for the CB range in the module).

The conductivity of the diodes changes over time with the frequency of the local oscillator, as a result of which frequency components of the difference frequencies appear at the output of the mixer:

f pr = f g - f c

The IF circuit with a balanced ring diode mixer is described in detail in the abstract T.5.3.

The FSS is tuned to an intermediate frequency of 465 kHz, has a bandwidth of 9 kHz and provides full adjacent channel selectivity.

The load of the second stage is resistor (R31), the third stage is resonant (oscillatory circuit L14, C48).

The receiver has automatic gain control AGC. From the collector of transistor V15, through a frequency-dependent chain R41, C46 and separating capacitor C45, voltage is supplied to diode V17, which, together with load resistor R42, forms a parallel-type AGC detector. Transistor V16 is equipped with a direct current amplifier, which increases the efficiency of regulation. As the signal increases, the voltage detected by the AGC detector increases and transistor V16 opens, which leads to a decrease in the voltage at its collector relative to the emitter.

From emitter V7 through resistor R4, voltage is supplied to device PA1, which serves to indicate the receiver settings.

The FM amplifier is a four-stage one, made on transistors V6, V7, V10, V15, i.e., the same ones as the AM amplifier. Thus, the receiver uses a combined AM-FM amplifier circuit.

The signal from the output of the VHF unit (conductors 23 and 24 in the module harness) is supplied to the base of transistor V6, the load of which is circuit L3.1, C5. Diode V5 is designed to protect the path from overloads.

The third stage of the FM path on transistor V10 is made according to a resistor circuit.

The fractional detector is described in detail in the abstract T.6.2.

The APCG scheme is described in detail in the abstract T.7.2.

The receiver has two compensation-type stabilizers.

Emitter follower V18 serves to separate the AM and FM paths. When the VHF band is turned on (in the KSDV block [A2] contacts 3-18 are closed), the stabilized voltage from the collector V13 through the decoupling filter R19, C24, C23 is supplied to point 3 of the RF-IF board [A3]. From this point, a voltage of 4.2 V through closed contacts 3 and 18 of the KSDV block [A2] enters the current 16 of the RF-IF board [A3]. In this case, the supply voltage is supplied to the VHF unit, the first stage of the FM amplifier (V6) and to the emitter follower V18, the constant voltage on which is closed by the AM detector (diode V19).

Choke L1 in the HF-IF block serves to protect against mutual shunting of the input circuits of the AM and FM paths.

4. Ultrasound unit [A4]

Soviet receivers “Ocean”, “Meridian”, “Ukraine”, “Spidola”, once considered a symbol of abundance and prosperity, are now in demand, since radio broadcasting has not been carried out on the frequencies of their range for a long time.

It is possible to bring life back to such “superheterodyne” giants by retuning their VHF units to the upper VHF (FM) range.

Most receivers such as “Ocean”, “Meridian”, “Ukraine”, “Spidola” have unified blocks VHF. These units usually operate in the range 4.56 – 4.11 m (65.8 – 73.0 MHz). To tune such blocks to a higher frequency (88 - 108 MHz), you have to resort to reconfiguring the input circuit (L1, L2, C1, C2), the UHF circuit (L3, C4, C6, C7) and the local oscillator circuit (L4, C16, C17 , C21). In addition, it is necessary to pair the UHF and local oscillator circuits so that the local oscillator frequency is 10.7 MHz (intermediate frequency) higher than the frequency of the received radio station. This is achieved by adjusting the heterodyne and UHF circuits (fine adjustment - with capacitance C4).

However, to carry out all these operations, very precise and expensive instruments are required (broadband oscilloscope, VHF signal generator, etc.), as well as a certain supply of radio components (capacitors, circuits, cores, etc.).

For a simpler reconfiguration that does not require the presence of such parts, which I did on the Ocean-205 receiver, I removed capacitance C17 (18 pF) from the heterodyne circuit to increase its frequency and resoldered the antenna wire from pin “3” of the VHF unit to the emitter of the heterodyne transistor (aka mixer) T2 (GT 313 A).

Thus, the reconfigured VHF block takes the form:

The retuned VHF block works as follows: the received signal is sent to the input of the mixer and at the same time to the local oscillator, where an intermediate frequency (IF) signal is extracted from it, which is fed to pin “5” of the VHF block. Using a variable capacitor (VCA) C21, the heterodyne circuit is switched from one station to another.

When a receiver reconfigured in this way operates, a “Mirror Channel” effect is observed, which manifests itself in the form of double overlapping of the range (the same station is received at different positions of the control points). This is apparently caused by the fact that the local oscillator, due to its imprecise tuning, generates frequencies that can extract twice the IF from the same signal. In the first case, the IF is distinguished as the frequency difference Fsignal – Fheterodyne = 10.7 MHz, and in the second Fheterodyne – Fsignal = 10.7 MHz. In addition, it should be remembered that the retuned block does not have an input circuit (it is simply not used) and a UHF circuit that selects a signal of only one frequency (it is also not used). Only the local oscillator mixer works, to which the entire frequency band is supplied. Therefore, stations located close to each other (in frequency) will interrupt each other during reception, which complicates tuning the receiver. The APCG system (automatic adjustment of the local oscillator frequency) will also be useless, which will only work with powerful stations, and when receiving weak and remote stations, it is recommended to disable the APCG system and adjust the receiver manually. This is the “price” that you have to pay when abandoning the old VHF range.

In general, the FM receiver works satisfactorily.

The portable radio receiver "Ocean-214" has been produced by the Minsk Production Association "Horizon" since 1985. The radio receiver of the 2nd complexity group "Ocean-214" is designed for receiving radio broadcasting stations in the ranges of long, medium, short and ultra-short waves. The receiver has 8 bands: LW, MW, 5 HF and VHF. The receiver has auxiliary devices: smooth tone control for high and low sound frequencies, a switchable automatic frequency control system in the VHF range, a magnetic antenna for the DV and SV ranges, a tuning indicator, a telescopic rotating antenna in the HF and VHF ranges, scale illumination, built-in power supply from a 220 V network. The device has connectors for connecting: an external antenna, grounding, a tape recorder and a miniature telephone. Frequency range: LW - 148...285 kHz; NE - 525...1607 kHz; KV-5 - 3.95...5.95 MHz; KV4 - 5.95...6.20 MHz; KV3 - 7.1...7.3 MHz; HF2 - 9.50...9.77 MHz; KB1 - 11.7...12.1 MHz; VHF - 65.8...74.0 MHz. Sensitivity when receiving on an internal ferrite antenna, mV/m: in the LW range - 0.5, in the MW range 0.3. Sensitivity when receiving on a whip antenna, µV/m: in the range KB 85, VHF 20. Selectivity in the adjacent channel with a detuning of ±9 kHz in the ranges LW, SW 36 dB. Range of reproduced frequencies by sound pressure, Hz: in the ranges LW, NE, KB 125...4000, VHF 125...10000. The nominal output power of the receiver is 0.5 W, maximum 0.9...1.3 W. Power consumption when operating from electrical network 5 W. The receiver is powered by 6 373 elements. The operating time of the radio receiver when powered by batteries is ~ 120 hours (at average volume). Dimensions of the radio receiver are 358x256x122 mm. Weight without batteries 4.0 kg.

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