Indiscriminate reception on Alan 78 plus. P2.4. Schematic diagrams of radio station components

Vendor code: Barry ASC TXPR002

FM sensitivity at S/N 20 dB: 0.35 µV.
AM sensitivity at S/N 20 dB: 0.5 µV.
Supply voltage: 13.8 V or 24 V.
Current consumption 0.85 A at 24 V / 1.7 A at 13.8 V.

Overall dimensions: 125 x 175 x 40 mm.
Weight: 0.9 kg.
Gross weight: 1260 grams (measured at Viva-Telecom).

Radio station features:
Double nutrition.
7 display backlight colors.
Impulse noise filter.
Manual and automatic patented noise reduction.
Megaphone mode.

By promotional code MYCHOICEPRESIDENT When purchasing Barry and any President antenna, you will receive a 5% discount.

5,500 rub.

In stock: O K

Operating frequency range: 26.965-27.855 MHz.
Output power: 4 / 10 W.
Modulation types: AM / FM.

Sensitivity: 0.5 µV.
Sound speaker power: 1 W.

Overall dimensions: 105 x 102 x 24 mm. Weight: 295 grams (with microphone).
Operating temperature range: -20...+50 degrees. Celsius.


Gross weight: 658 grams (measured at Viva-Telecom).

RUB 3,850

In stock: O K

Compact CB car radio.

Operating frequency range: 26.965 - 27.405 MHz.
Output power: 4/8 W.
Modulation types: AM / FM.
Automatic/manual squelch.
Sensitivity: 0.5 µV.
Speaker power: 3 W (at 10% distortion).
Supply voltage: 12-14.5 V.
Overall dimensions: 108 x 25 x 122 mm. Weight: 450 grams (with microphone).
Operating temperature range: -10...+50 degrees. Celsius.
Areas of application: truckers, delivery services.
Communication range: 5-20 km (depending on the antenna used and the terrain).

Radio station features:
1. Quick removal from the mounting bracket.
2. Headset connector.

3,700 rub.

In stock: O K

Vendor code: TXPR001

16% discount

Compact car CB radio with automatic noise reduction function.

Operating frequency range: 26965-27405 kHz (40 channels).
Modulation types F3E(FM) and A3E(AM).
Transmitter power: 4 W (AM and FM).
Sensitivity at S/N 20 dB: 0.5 µV AM, 0.35 µV FM.
Supply voltage: 13.8 V.
Current consumption 1.7 A at 13.8 V.
Internal audio speaker power: 2.5 W.
Overall dimensions: 25 x 100 x 102 mm.
Weight: 0.32 kg.

Radio station features:
7 display backlight colors.
Impulse noise filter.
Manual and automatic noise reduction.
Roger Beep.
USB connector (5V, 2.1A) for charging smartphones and other devices.

6,630 rub.
RUB 5,590

In stock: O K

Car radio for work on the highway.

Frequency range: CB.
Transmitter output power, W: up to 8.
Number of channels: 135 (CE, DE, EE).
Receiver sensitivity, µV: (12 dB s/n FM, 10 dB s/n AM): 0.3 / 0.5.
Modulation type: AM / FM.
Supply voltage, V: 13.8.
Maximum current consumption, A: 2
Dimensions, mm: 42 x 140 x 130.
Weight, g: 600.
Blue display backlight, hybrid noise reduction (automatic combined with threshold).

RUB 3,950

In stock: O K

Radio station OPTIM-778 designed for two-way radio exchange in the CB range with frequency or amplitude modulation.
The radio station is intended for use both in a car and as a base radio station.

Operating frequency range: 25615-30105 kHz.
Modulation types F3E(FM) and A3E(AM).
Output power: up to 20 W (AM), up to 50 W (FM).
Overall dimensions: 158x48x165 mm.
Weight 1.1 kg.
Gross weight: 1596 grams (measured at Viva-Telecom).

Distinctive features of the radio station are:
1. High transmitter output power to increase range.
2. The presence of automatic spectral and manual threshold noise suppressors, indispensable for operation in the city and open areas.
3. Keys for quick transition to the “general auto call channel” and “emergency call channel”.
4. “ECHO” effect mode during transmission.
5. 8 non-volatile memory channels.
6. Protection against connection to a power source with reverse polarity.
7. Scanning modes, both across memory channels and within a grid with the ability to create a scanning sheet.
8. Filter for eliminating impulse noise (NB) and limiting high frequencies (HI-CUT).

The low level of nonlinear distortion in the receiving path has a positive effect on the quality of the received signal and ensures maximum radio communication range.
The radio station is built on a modern element base, which ensures high reliability and durability.
The capabilities of a radio station can only be fully realized when using high-quality and well-tuned antennas.

7,500 rub.

In stock: O K

USER MANUAL

For questions regarding purchase and repair

radio stations and antennas

27 MHz contact:

VORONEZH, POBEDA BOULEVARD 13

TEL. (47,

394077 Voronezh, b

10. WARRANTY CARD.

Equipment identification - Transceiver ALAN 78 PLUS

I hereby confirm acceptance of the packaged equipment suitable for use, and also confirm the acceptability of the warranty conditions.

Please fill in legibly with a ballpoint pen.

WARRANTY TERMS.

Warranty repairs are subject to the following conditions:

Transportation of a faulty product is at the customer's expense.

The warranty includes replacement of spare parts and repair work during the warranty period.

The client has the right to demand replacement of equipment if the equipment has been repaired 3 times during the warranty period and continues to fail.

The warranty also does not cover the following faults:

9. Technical characteristics.

9.1. General information.

9.2. Receiver.

(Superheterodyne, double frequency conversion)

9.3. Transmitter.

1. INTRODUCTION.

1.1. Your transceiver ALAN 78 PLUS purchased from a Voronezh company "CBC connection". For all questions related to the operation of the transceiver, you can consult by phone .

1.2. GlavGosSvyazNadzor of the Russian Federation allows the use of the radio station in 40 channels (frequencies) of the so-called “C” grid ( 26,965...27,405 MHz) and 40 channels (frequencies) of the so-called “D” grid ( 27,415...27,855 MHz) CB band (Citizen Band).

1.3. Radio communications in this range are regulated by section 4 of the “Rules for the sale, registration and operation of portable transceiver radio stations” issued by the State Inspectorate of Electrical Inspections.

PLEASE READ EXTRACTS FROM THIS DOCUMENT (SEE APPENDIX) BEFORE GOING ON AIR!

1.4. NEVER TURN ON THE TRANSCEIVER FOR TRANSMISSION WITHOUT AN ANTENNA!

FAILURE TO COMPLY WITH THIS RULE WILL REMAIN THE TRANSCEIVER OUT OF OPERATION.

1.5. Radio station ALAN 78 PLUS certified by the company “SOTSINTEKH” in the Ministry of Communications of the Russian Federation (certificate N O OS/1-RS-272 dated 06/29/95).

2. CAPABILITIES OF THE RADIO STATION.

ALAN 78 PLUS- a new modification and new design of the famous radio station. Has improved sensitivity characteristics that are stable across all 80 civil band channels. Mainly used for mobile communications. Precise frequency tuning and reliability are achieved by using 400 channel frequency synthesizer. Assembled from the best components on a durable printed circuit board, this high-quality product of modern circuitry will serve for a long time and without failure.

Additional control functions.

8. DRAWINGS.

7. APPENDIX.

FROM "RULES FOR SALE, REGISTRATION AND OPERATION OF PORTABLE

TRANSMITTING RADIO STATIONS".

4.6. When operating a radio station, its owner must have an operating permit issued by the State Health Inspectorate.

4.7. Radios should only be used for voice communications. It is strictly prohibited to use speech encryption devices in radio stations.

4.9. During radio communications, the license number for the right to operate the radio station is used as an identification signal. In radio communications it is necessary to communicate the identification signal at least once.

4.10. Radio communications should be conducted in discreet terms and in clear language. The duration of radio communication should be as short as possible. It is not recommended to use radio stations in transmission mode without radio traffic, as this leads to busy public channels.

4.12. It is prohibited to transmit information constituting official or state secrets.

3. TRANSCEIVER CONTROLS.

3.1. FRONT PANEL. (Fig. 1.).

6. Working with the transceiver.

6.1. Connect a microphone through the microphone jack.

6.2. Make sure the antenna is properly connected to the antenna connector.

6.3. The SQUELCH handle must be turned fully counterclockwise.

6.4. Turn on the device and adjust the volume.

6.5. Select a channel.

When transferring.

Press the PTT button and speak in a normal voice.

Upon admission.

Release the PTT button.

Typically the transceiver is located under the instrument panel above the transmission tunnel. Do not install the transceiver in the path of a heater or air conditioner. Select the optimal location for installing the transceiver and, using the mounting bracket, mark the holes for the mounting screws.

Before drilling holes, make sure you do not damage the vehicle's power cables. Secure the bracket with screws or self-tapping screws with spring washers. Connect the red wire with the transceiver power cable fuse holder to "+" power supply (best to the auxiliary contact of the ignition switch), and black - to "-" (to the car body). To connect the transceiver, you can use a cable with an adapter to a car cigarette lighter (not included). Install the antenna and connect it with a coaxial cable to the antenna jack of the transceiver. If you decide to use an additional speaker in your car, then install it in a convenient place and connect it to the socket EXT. SPKR.

Replacing the fuse

The fuse is released from the holder by pressing and turning the housing. Use only 2A fuses for replacement (one spare fuse is included with the transceiver).

Antenna installation.

Place the antenna as high as possible.

The longer the antenna, the better the transceiver will perform.

If possible, place the antenna in the center of your chosen surface.

The antenna cable should be located as far as possible from sources of interference such as ignition or measuring instruments.

Make sure the metal-to-metal grounding is secure.

Be careful not to damage the cable when installing the antenna.

Warning. To avoid damage, never turn on the transceiver without a proper antenna. Check the cable periodically.

3.2. Back panel (Fig.2).

3.3. MICROPHONE.

4. INFORMATION ON THE DISPLAY.

Your radio has a built-in LCD display that shows the channel number and operating mode.

Note: Due to its physical characteristics, LCD displays should not be exposed to extreme temperatures and humidity. If the unit is exposed to temperatures below -20°C or above 60°C, the LCD display may temporarily lose its functionality and, in some cases, be permanently damaged. Do not expose the radio to extreme conditions, such as leaving it in a closed car in direct sunlight or prolonged frost.

The LCD display has a preferred viewing direction where contrast is maximized. This direction depends on the temperature and condition of the batteries and is found empirically - by slightly changing the orientation of the radio station relative to the operator.

5. INSTALLING THE TRANSCEIVER.

Safety and ease of use are the main requirements that must be considered when installing any mobile radio equipment on a vehicle (boat). All transceiver controls must be accessible to the user so as not to interfere with driving. Make sure that the connecting cables do not interfere with the use of the brake, clutch and gas pedals. It is also necessary to take care of the comfort of passengers (for example, will there be enough legroom). An important requirement is also the speed and ease of removing the transceiver from its installation location when maintenance and configuration are necessary.

All modifications are made at your own peril and risk!

Good old Alan 78 Plus. This radio station is well known to everyone who is familiar with the civilian CB band. This is, one might say, a hit of past years. But everything flows, everything changes; in order to reduce costs, radio production is being transferred to China and the Philippines, which entails certain consequences for quality.

This happened with Alan 78 Plus. The production of the once well-designed and fairly decently functioning radio station was transferred to the Middle Kingdom, transferred from output components to a modern element base, but this did not reduce the problems. Let's start fixing them. I remind you that all modifications are made at your own peril and risk! Modern Alan 78 Plus Multi are quite unstable and require an extremely careful approach when modifying and repairing. Be extremely careful when performing operations. Some old problems of the Alan 78 Plus, which were described earlier on the Internet and Fido, have already been corrected in the new models, they do not interfere with life, so I did not consider them in the framework of this article.

Modulation improvements

I would like to start with an eternal problem. How we are heard during the broadcast. And although the Alans have very good modulation, as they say, “out of the box,” we will make it even better!

For fans of extremely loud modulation in AM, you can perform another operation to disable the AMC system. The peak power of the radio station after such modification will reach 16 watts, but at the same time, at loud sounds, people who use automatic noise suppressors will have problems receiving your broadcasts, since at loud sounds the noise suppressors for your pumped-up broadcast will close.

Improved intelligibility

If you are satisfied with the quality of reception, do not touch anything.

Refinement of the threshold noise suppressor

Like all other Alans, the Alan 78 Plus does not have hysteresis in the threshold noise suppressor, as a result of which in threshold states the system begins to hiccup, randomly open and close at high speed. The fix is ​​quite simple. You only need to add 2 parts, a capacitor and a resistor. The resistor value is selected according to the device, to obtain a hysteresis of 6-8 dB, or by ear, over the air.

If you do not have enough range of adjustments of the noise suppressor knob, then you need to replace one resistor and adjust the operation of the threshold noise suppressor with a trimming resistor.

In older versions, the squelch clicked when switching from transmitting to receiving, but in new versions of stations this glitch has already been corrected.

Improved backlight

If you, like me, are annoyed when the backlight of a radio station dims when it goes into transmission, then you can install a stabilizer to power the backlight LEDs. For this, a regular LM7809 is suitable, which is included in the standard way in the circuit instead of a primitive resistor.

Description and Review

Description of the radio stationALAN78

The backlit multifunction display and keypad lock will greatly simplify your use of the ALAN 78-plus radio. The ALAN78 plus radio has connectors for connecting an external speaker, a signal level measurement device and a six-pin microphone connector.

1. Appearance of the radio station

• Keyboard backlight
• Backlit multifunction display
• Compact microphone with Up/Down keys
• Jack for connecting an external signal level meter
• Keys for quick channel selection Quick Up/Quick Down
• External speaker connector
• Connector for connecting an external device for measuring signal level

2. EquipmentALAN7 8+

• Radio station ALAN
• Push-to-talk with clip fastening
• Car mounting bracket
• Power cord with fuse
• User manual.

3. Main declared functions.

• Frequency stability: +/- 0.001%
• Quick installation of emergency channel (9D)
• Quick channel selection Quick Up/Quick Down
• Possibility of using 40 grid frequencies "D" (27.415...27.855).
• 400 channel communication.
• Use of amplitude and frequency modulation.
• Has improved sensitivity characteristics

Radio station overviewALAN78Plus

The Alan 78 PLUS car radio is created on the basis of high technologies for mobile communications in the CB range. The Alan78PLUS mobile radio is a compact device with great capabilities.

Frequency grid for mobile radio Alan78 is generated by a PLL synthesizer based on modern technology using a minimum number of quartz resonators. This achieves high reliability and channel frequency accuracy for the Alan 78 plus car radio.

Compared to previous modifications, it has a wider range. The alan 78+ radio operates on 80 civil band channels. The receiver uses intermediate frequencies of 10.695 MHz and 455 KHz.

The high degree of automation of the alan 78+ is designed to ensure comfortable work. For those without on-air experience, operating the station is not difficult. The user is guided by the channel number and operating mode. For stable operation of the Alan 78 plus chip and the display, a temperature mode of -20 +60C is recommended.

For safety reasons, the radio is installed in a place protected from moisture and dust. When installing, consider the ability to easily remove the transceiver for configuration. If necessary, an alarm can be triggered. The radio station ALAN78 + is a modern transmitting and receiving equipment. The simplicity and reliability of using the device have made it one of the most popular models of car radios. The use of walkie-talkies of this type allows you to almost completely automate radio communication.

ATTENTION! Do not use the radio without an antenna connected to it!

Among the wide selection of antennas, you can purchase what you need in RADIOSILA stores!

Radio station ALAN 78+ can be purchased in our departments at Moscow , St. Petersburg , Yekaterinburg , Tyumen , Perm, Chelyabinsk, Ufa, Samara or order delivery to any location in Russia: Kazan,Novosibirsk , Nizhny Novgorod , Omsk , Rostov-on-Don , Volgograd , Krasnoyarsk , Saratov , Voronezh , Krasnodar , Izhevsk , Ulyanovsk , Barnaul , Irkutsk , Novokuznetsk , Orenburg , Kemerovo and other cities.

Alan 78+, alan 78+, ALAN 78+, Alan 78 plus, alan 78 plus, ALAN78+, Alan78+, alan78+, Alan 78+, Alan 78+, ALAN 78+, Alan 78 plus, Alan 78 plus, ALAN78+, Alan78+, 78+, 78 plus.

P2.1. Purpose

Mobile radio stations “YOSAN”, “ALAN 78 PLUS”, “ALAN 78 PLUS R” are designed for organizing two-way and multi-way radio communications in the so-called civil band (Citizen Band - CB).

This range is allocated for personal radio communications. In the Russian Federation, the CB range covers the frequency band 26.965–27.405 MHz (11 m). It allows the use of AM (26.965–27.110 MHz) and narrowband FM (27.110–27.405 MHz). Any operator has equal rights to use any frequency channel in this range. The frequency 27.065 MHz (9th channel) is recommended to be used as a security channel.

Radio stations - car. When using 1.2 m long whip antennas, they provide a communication range of 6–10 km. When communicating with a stationary correspondent, whose antenna length is longer (usually 3–4 m, which is close to 4) and the antenna is located high enough, the communication range can reach 15–18 km.

Radio stations have similar circuit design solutions. We will conduct the review on the basis of the ALAN 78 PLUS radio station, stipulating, if necessary, the features of other types of radio stations.

P2.2. Specifications

Received frequency range: 25.615–30.105 MHz (“ALAN”) and 26.065–28.305 MHz (“YOSAN”). The range is divided into subranges, designated by Latin letters. Each subband, in turn, contains 40 channels, each 10 kHz wide. Channels are spaced 10 kHz or 20 kHz apart. In table A2.1 presents the nominal frequencies of 40 channels of the main subband (D for “ALAN”, C for “YOSAN”), The nominal frequencies of 1 and 40 channels of each subband are given in Table. P2.2.

Operating mode: simplex.

Modulation type: AM and FM.

Transmitter output power: 4 W.

Maximum modulation depth of the transmitter signal at AM: 85–95%.

Maximum deviation of the transmitter signal at FM: 2.5 kHz.

Output impedance: 50 Ohm.

Sensitivity at an output S/N ratio of 20 dB: 0.5 µV.

Adjacent channel selectivity: at least 65 dB.

Selectivity in the mirror channel: no less than 65 dB.

Audio signal power into 8 ohm load: 2.0 W.

Harmonic distortion of the audio signal at the output: 8%.

Supply voltage: 13.2 V 15%.

Current consumption in receive mode: 250 mA.

Current consumption in transmit mode: 1100 mA.

Dimensions: 180 x 140 x 35 mm.

Weight: 850 g.

Operating temperature range: from –10 to +55 C.

Table A2.1

Nominal frequencies of D-band channels

Table A2.2

Subband boundaries

P2.3. Block diagram of the radio station

P2.3.1. General principles of construction

The logic of building a radio station is dictated by the following circumstances:

The requirement for rapid tuning from one frequency channel to another determines the need to use a frequency synthesizer (MF) as a carrier generator for the transmitter and a local oscillator for the receiver.

For untuned communication, it is necessary to ensure frequency instability of no worse than 10 –6, which is only possible with quartz frequency stabilization of the reference oscillator.

Taking into account the simplex operating mode, it is advisable to use the same midrange in the transmitter and receiver. For this, the frequencies of the local oscillator of the receiver and the transmitter carrier oscillator must be sufficiently close.

To ensure high attenuation in the adjacent and mirror channels, the receiver must be configured with double frequency conversion and a high value of the 1st IF. However, at high IF, the receiver local oscillator frequency differs significantly from the frequency of the received (and transmitted) signal, which contradicts the previous point.

IF values ​​should be standard.

For operational control and monitoring of the operation of the radio station, it is necessary to use a microcontroller.

To resolve the above requirements in a radio station, a simplified block diagram of which is shown in Fig. A2.1, the following construction principle is implemented.

The midrange in transmit and receive modes generates frequencies in a relatively narrow range of 12.8075–19.410 MHz, which facilitates the construction of a voltage-controlled oscillator (VCO) of the midrange.

The receiver is a superheterodyne with double frequency conversion. Nominal values ​​of intermediate frequencies: f IF1 =10.695 MHz, f IF2 =455 kHz. The receiver uses the bottom mate ( f 0 =f G1+ f PC1), i.e. the frequency of the 1st local oscillator (MF) is 10.695 MHz lower than the tuning frequency. The values ​​of the midrange frequencies in the receiving mode for the extreme operating frequencies of the ALAN radio station, as well as the extreme frequencies of the D subband (used for personal communications in the Russian Federation) are given in Table. P2.3.

The transmitter path contains a frequency doubler, so in transmission mode the MF generates frequencies f MF = f 0 /2. The frequency values ​​of the synthesizer in transmit mode are also presented in table. P2.3.

Table A2.3

MF frequency values ​​in transmit and receive modes

The radio station can operate with two types of modulation (AM and FM), which also affects the construction of the structural diagram. When operating in AM mode, collector modulation is carried out: in accordance with the change in the transmitted audio signal, the collector voltage of the two output stages of the transmitting path changes. In FM mode, the supply voltage to these stages remains unchanged. A modulating voltage is applied to the midrange VCO, changing its instantaneous frequency in accordance with the modulation law. The reception path contains two different amplifiers of the 2nd IF (UPCH-AM and UPCH-FM) and various detectors (AD and BL).

The change in reception-transmission and AM-FM modes is controlled by a microcontroller.

P2.3.2. Radio frequency synthesizer

The midrange is divided into two parts. The controller integrated circuit contains:

phase detector (PD);

divider with a constant division coefficient (Div1);

divider with variable division ratio (Div2);

active elements of the reference oscillator (OG).

External to the controller are the synthesizer nodes:

low pass filter (LPL);

tunable voltage controlled oscillator (VCO);

buffer amplifiers (BU1 and BU2);

quartz resonator (CVR) exhaust gas; f OG =4.5 MHz.

The basis of the frequency synthesizer is the PLL system. It is in the capture mode if the frequency values ​​of the signals arriving at both PD inputs are equal, i.e. condition is met

Where M And N– division coefficients of frequency dividers Del1 and Del2.

By selecting the appropriate frequency channel number, the operator sets the division coefficient N divider with variable division ratio Del2. As a result, after the end of transient processes in the PLL loop, the frequency at the VCO output takes the value

.

In AM receive mode and AM transmit mode, only one slowly varying voltage is applied to the VCO from the output of the PLL low-pass filter. In the FM transmission mode, in addition to this voltage, which ensures that the desired carrier frequency is obtained with high stability, a second control voltage is applied to the VCO from the output of the modulating signal amplifier of the FM path (MU-FM). The spectrum of this voltage is limited to the band of a standard telephone channel of 300–3400 Hz, and the level is set to ensure a maximum deviation of the midrange frequency of 1.25 kHz.

The PLL low-pass filter plays an important role in the operation of the midrange. The cutoff frequency of this filter is approximately 5 Hz, which ensures good spectral purity of the signal at the synthesizer output. On the other hand, the filter cutoff frequency is significantly lower than the minimum value of the modulating frequency (300 Hz). In FM mode, this makes it possible to establish the desired nominal frequency value and the required long-term stability of the midrange frequency while simultaneously changing the instantaneous frequency of the VCO in accordance with the modulation law.

Buffer amplifiers BU1 and BU2 provide isolation of the VCO from external influences and thereby increase short-term frequency stability.

P2.3.3. Transmission path

The midrange signal from the output of the buffer stage BU2 enters a frequency doubler (UDF), the collector circuit of which includes a double-circuit bandpass filter with a passband of approximately 25.5–30.3 MHz. Thus, a voltage is released at the output of the UDV with a frequency equal to twice the midrange frequency. The deviation of the FM signal when passing through the UDV doubles and becomes equal to 2.5 kHz.

Next, the signal is amplified by two preliminary power amplifier stages (UM1 and UM2) with a low-Q resonant load and goes to a powerful output stage (UM3). At the output of UM3, low-pass filters Prd and LPF are turned on. The cutoff frequency of the filters is approximately 31 MHz, which provides the required attenuation of side spectral components of the output signal (primarily harmonics of the carrier frequency), as well as matching the output resistance of the transistor of the last stage of the transmitter and the antenna. The low-pass filter is common to the transmitter and receiver.

In the AM transmission mode, the signal from the microphone is fed to the modulating signal amplifier of the AM path (MU-AM). The output of the MU-AM provides sufficient power of the modulating signal necessary to implement collector modulation in the output stages of the transmitter. In FM mode, UM2 and UM3 are supplied with a constant supply voltage.

P2.3.4. Reception path

The radio station's reception path is a superheterodyne receiver with double frequency conversion.

A low-pass filter (LPF) with a cutoff frequency of about 31 MHz is turned on at the receiver input. The main purpose of this filter in reception mode is to suppress interference with frequencies exceeding the frequency of the received signal.

From the output of the low-pass filter, the signal is supplied to a diode limiter (OCL), which serves to protect the transistor of the radio frequency amplifier (RFA) when the radio station is operating in transmit mode. The adjustable attenuator (Att1) is an element of the receiver's AGC system: its attenuation increases when strong signals are received. In addition, in transmit mode, like the limiter, it attenuates the transmitter signal at the input of the amplifier.

The bandpass filter (BPF) has a bandwidth of 25.5–30.3 MHz. It provides the required receiver attenuation on the mirror and other side channels. In addition, significant attenuation at frequencies above and below the operating range reduces the likelihood of nonlinear effects due to out-of-band interference (blocking, cross-modulation and intermodulation) occurring in the RF frequency range.

The transistor amplifier determines the high sensitivity of the receiver. It is made according to a resonant amplifier circuit, which, on the one hand, makes it possible to obtain the necessary gain of the cascade, and on the other, provides additional attenuation through the side channels.

From the output of the RF amplifier, an amplified signal with a frequency f C is supplied to the input of the 1st frequency converter (PrCh1). A signal from the 1st local oscillator with a frequency of f G1. The resulting combination product with a difference frequency f WITH - f G1 is distinguished by a piezoceramic lumped selectivity filter (FSI1), the central frequency of which is equal to the nominal value of the 1st IF ( f IF1 =10.695 MHz), and the bandwidth is approximately 15 kHz. The selectivity of this filter is not sufficient to provide the required adjacent channel attenuation. It primarily serves to suppress interference in the mirror channel caused by the second frequency conversion.

Attenuator Att2, like Att1, is an element of the AGC system.

Next, the signal undergoes another frequency conversion to PrCh2. Its inputs receive signals with a frequency f IF1 and f G2. The frequency of the 2nd local oscillator (G2) is stabilized by a quartz resonator: f G2 =10.24 MHz. The signal with the difference frequency generated in PrCh2 f PC1 – f G2 is allocated by the 2nd lumped selectivity filter (LSF2), the central frequency of which is equal to the nominal value of the 2nd IF (f IF2 = 455 kHz), and the passband is 10 kHz. The filter has a frequency response with good squareness and provides the required attenuation in the adjacent channel.

The IM is made according to a classic diode circuit. BH – quadrature with FM to PM conversion and subsequent detection by a phase detector based on an analog multiplier.

The radio station has a silent tuning system (BSN). It is used in FM mode, when, in the absence of a signal, strong noise is heard at the receiver output. Since the standby mode is usually much longer than the correspondent switches on, the noise at the output disturbs the operator.

The BSHN system passes the signal from the output of the preliminary ultrasonic sounder to the volume control (Reg) and then to the output ultrasonic sounder only when there is a useful signal at the output of the black hole. The BSN system consists of a noise signal amplifier (NS), a signal-to-noise analysis correlation circuit (AN) and a key (BSN Key). The operator can adjust the response threshold of the BShN system up to its complete shutdown.

The receiver's AGC system includes an amplitude detector (DAGC), a low-pass filter (LPF AGC) and two adjustable attenuators (Att1 and Att2).

P2.4. Schematic diagrams of radio station components

A radio station is a rather complex device. Therefore, below is a description not of the complete circuit diagram of the radio station, but of its two parts: the input stages of the receiver and the frequency synthesizer units.

P2.4.1. Schematic diagram of the receiver input stages

In Fig. A2.2 presents a schematic diagram of the receiver from the input of the limiter Ogr to the output of the attenuator Att2 (see Fig. A2.1).

The diode limiter is implemented on back-to-back diodes VD1 and VD2. When the input voltage exceeds 0.25–0.3 V, the diodes open and their resistance drops, which prevents further voltage growth.

Attenuator Att1 is made on transistor VT2, which shunts the input when a positive control voltage is applied to it U p from the AGC system (when receiving a strong signal) or from the controller chip (in transmit mode).

The PF bandpass filter is implemented on elements L2, L5–L7, L9, L11, C8, C9, C11–C13, C16, C17, C20–C22.

The radio frequency amplifier URCH is made on transistor VT1 according to a circuit with a common base. The load of the transistor is the resonant circuit formed by L4, C5–C7. Since the range of received frequencies is quite wide (25.615–30.105 MHz), the URF provides the possibility of discrete restructuring of the circuit using switched capacitors C6 and C7. These capacitors are connected using transistor switches S1 and S2 according to controller commands. Schematic diagrams of the keys in Fig. P2.2 are not shown.

Rice. P2.2. Schematic diagram of the receiver input stages

The frequency converter PrCh1 is made on field-effect transistors VT3 and VT4 according to a balanced circuit. The signal voltage is applied to the gates of the transistors, and the local oscillator to the sources. Diodes VD3 and VD4 reduce the level of higher-order combinational components in the drain circuit of transistors VT3 and VT4. The output of PrCh1 includes a matching circuit L10, C19 and a piezoceramic filter of concentrated selectivity FSI1 ZQ1. Resistor R9 and transistor VT5 form an adjustable attenuator Att2.

P2.4.2. Schematic diagram of midrange units

In Fig. P2.3 presents a schematic diagram of a voltage-controlled oscillator (VCO), two buffer amplifiers (BU1 and BU2), as well as a low-pass PLL. The remaining midrange units (FD, Del1, Del2, OG) are implemented on an integrated controller chip.

The VCO is assembled on transistor VT3. The oscillatory circuit of the VCO is formed by inductance L1, capacitances of varicaps VD1, VD2 and capacitors C10–C13, C15, C16. In this case, capacitors C15, C16 form a capacitive divider, creating positive feedback and ensuring self-excitation of the generator. Capacitors C7, C8, C14 are isolation capacitors; they do not affect the resonant frequency of the circuit.

Rice. P2.3. Schematic diagram of frequency synthesizer components

Switched capacitors C10–C13 are connected to the circuit using transistor switches S1–S4 according to commands from the controller. The need for these capacitors is due to the wide tuning range of the VCO (12.8075–19.41 MHz). Capacitors C10–C13 bring the VCO's natural frequency closer to the currently generated frequency.

The VCO frequency, and therefore the frequency at the midrange output, is set using a varicap VD2. The control voltage is supplied to it from the PD output through a two-stage low-pass filter PLL. The first link of the filter is formed by resistor R1, capacitance C1 and the input capacitance of the composite transistor VT1, VT2 connected in parallel to it, which, in turn, is increased by including capacitance C3 in the collector-base circuit. The second link of the low-pass filter is formed by resistor R6 and capacitance C6.

Varicap VD1 ensures that the VCO frequency changes in accordance with the modulation law when the transmitter operates in FM mode. The required deviation value is set by potentiometer R5 during the factory settings of the radio station.

The voltage generated by the VCO is removed from the emitter of transistor VT3 and supplied to two buffer amplifiers. BU1 is assembled on transistor VT4, connected according to a circuit with a common emitter. From its output, the signal goes to a divider with a variable division ratio, Div2. Thus, the midrange PLL loop is closed.

BU2 is implemented on transistor VT5, connected according to a circuit with a common collector. From its output, the signal goes to the UDV transmitter doubler and the 1st frequency converter of the PrCh1 receiver.

P2.5. Controls and monitoring of the radio station

The location of controls and monitoring of the ALAN 78 PLUS radio station is shown in Fig. P2.4.

Rice. P2.4. Controls of the radio station “ALAN 78 PLUS”

Numbers in Fig. P2.4 are marked:

1. CHANNEL switch. Selecting a frequency channel.

2. Multi-function display with the following indicators:

frequency channel number and letter designation of the subband;

“SIG” – the level of the received signal in the receiving mode or “PWR” – the power of the emitted signal in the transmitting mode;

“AM/FM” – information about working in AM or FM mode;

“RX/TX” – information about operation in receiving (RX) or transmitting (TX) mode;

“SCAN” – information about working in frequency channel scanning mode;

“EMG” – information about working on the security channel.

3. “EMG” button – automatic tuning to the security channel (9th channel of the main subband; frequency 27.065 MHz).

4 and 5. “Q.UP” and “Q.DOWN” buttons – stepwise change in tuning frequency by 10 channels up or down.

6. “AM/FM” button – select the type of modulation AM or FM.

7. “SCAN” button – automatic range scanning. The receiver changes from channel to channel. Scanning stops when tuning to a working channel.

8. “SQUELCH” regulator – adjusting the threshold of the silent tuning system.

9. “ON/OFF VOL” control – a combined volume control and radio switch.

10. “MIC” connector – connector for connecting a microphone headset.

On the microphone headset there is a button to turn on the transmitter (push-to-talk) and buttons for tuning to the next channel up and down in frequency (“UP” and “DOUN”).

On the rear panel of the radio there are jacks for connecting an antenna (“ANTENNA”), an external speaker (“EXT”), an external level meter (“S.METER”), as well as a power connector.

The controls for the ALAN 78 PLUS R and YOSAN radio stations are somewhat different from the reviewed ALAN 78 PLUS radio station.

The radio station “ALAN 78 PLUS R” does not have the “EMG”, “SCAN”, “Q.UP” and “Q.DOWN” buttons, however, there is a “DW” (Dual Watch) button, which makes it possible to control two reception channels at once (main and additional).

The YOSAN radio station has “SCAN” and “DW” buttons. In addition, there is a “MO/RF” button that changes the operating mode of the level indicator. In the first position, the indicator shows the level of the modulating signal (the inscription “MOD” is displayed on the indicator), in the second – the level of the received or emitted radio signal (in this case, the inscription “SRF” is displayed on the indicator).

The YOSAN radio station can serve as a megaphone. In this case, only the audio frequency amplifier of the radio station is used. To enter this mode, use the “PA” (Power Amplifier) ​​switch combined with the “SQUELCH” control. Megaphone mode only works when an external speaker is connected.