Wiring diagram for a varicap in a VHF receiver. VHF FM receiver with electronic tuning on the K174ХА34 (TDA7021) chip. Operating principle of a stereo receiver

Now we will make a real FM Radio based on two cheap chips TDA7000 and LM386. What is TDA7000 and how does it work. This is a real FM receiver, with a conventional local oscillator, mixer, limiting amplifier, and phase detector. The microcircuit also has automatic frequency control. But the noise reduction function is somewhat weak, to say the least. If necessary, connecting a 10K resistor from the power supply to pin 1 will disable the squelch.

Block diagram of the microcircuit

Block diagram of TDA7000 is used as for a normal FM receiver. Audio output is about 75 mV. For more details, see the documentation for 7000.

Schematic parts list

Chip IC1 TDA7000 FM Radio
Chip IC2 LM386 Audio amplifier
18-pin connector (for TDA7000)
8-pin connector (for LM386)

Ceramic capacitors:

0.001 uF x 1 pcs
0.01uF x 1 piece
0.1 uF x 4 pcs
0.0022 uF x 1 piece
0.0033 uF x 2 pcs
0.022 uF x 1 piece
150 pF x 1 piece
180 pF x 2 pcs
220 pF x 2 pcs
330 pF x 2 pcs

Electrolytic capacitors:

220µF or 470µF or 1000µF - x 2 pcs
4.7µF - X 1 piece

Other radioelements:

10K (or 20 kOhm) trim resistor
C1 - Ceramics
L1 - Adjustable coils for tuning radio stations
10 ohms 1/4W or 1/6 W x 1 pcs
22K, 1/4 or 1/6 W x 1 piece
Speaker 8 Ohm 1 Watt
9V battery power

By the way, Philips did not stop at the TDA7000 in its 18-pin DIP package. Next came the TDA7010T which is the surface mount version. It comes in 16-pin SMD form. Next comes the TDA7021T chip, which is also designed for surface mounting, but is already stereo compatible with the decoder. And finally, there is the TDA7088T, which is mono only, but has automatic tuning search and operates on just 3V power. Unfortunately, the TDA7000 is no longer in production, having been discontinued in December 2003. Although they were produced for quite a long time - a little over 20 years.

Assembling a radio receiver on a TDA7000 chip

Together with the TDA7000, you can use the LM386 bass amplifier for the audio channel. At first a transistor amplifier was made, but the chip has a higher gain. Now the sound is very good.

Due to the large number of music radio stations in the VHF bands, small-sized VHF radio receiver circuits are popular among radio amateurs. Such a receiver, especially one made by yourself, is always nice to take with you for a walk or on a trip.

In the magazines "Radio Amateur" and "Radio" last years Quite a few circuit diagrams of such radio receivers have been printed. Almost all of them are options for incorporating the popular K174XA34 and K174XA42 microcircuits.

However, these microcircuits are characterized by certain disadvantages due to low IF, unstable operation at the upper limits of the FM range, and a tendency to self-excitation. The need to use an external low-frequency amplifier increases the weight and size indicators and current consumption.

Abroad there is big class single-chip radio receivers, for example U251 OB, KA22425D, SХА1019М, СХА1191, descriptions of which I have not seen in magazines. The U251OB microcircuit from Telefunken is a representative of a class of single-chip VHF radio receivers that is little known to wide sections of radio amateurs. Unlike the well-known K174XA34 and K174XA42 microcircuits, this microcircuit has a number of advantages. The best sound quality and absence of specific interference is due to the standard 10.7 MHz IF. High sensitivity is ensured by an RF amplifier with a tunable resonant circuit. The advantages of the microcircuit are the presence of an audio amplifier, electronic volume and HF tone controls, indicator settings, a wide range of supply voltage and low current consumption.

Specifications

Received frequency range, MHz……………………………64..108

Sensitivity is no worse, µV………………………………………….. 5

Nominal output power at a load of 8 Ohms, W…0.1 Quiescent current, mA 10

The functionality of the receiver is maintained when the supply voltage is reduced to 1.8 V, the maximum supply voltage is 9 V.

The U251OB chip is manufactured in a package with 28 pins. The pitch between pins is 1.75 mm.

Schematic diagram receiver is shown in Fig. 1. Radio station signals received by the antenna are fed to the input of the radio frequency amplifier (pin 12 DA1). The load of this URCH is a tunable

oscillatory circuit L3, C13.2, C14. The signal from it is fed to the mixer as part of the microcircuit. It also receives local oscillator voltage, the circuit of which is L2, C13.1, C12. The reference voltage of 2.4 V from the internal stabilizer is supplied to pin 8 of the microcircuit. The use of KPE in small-sized receivers with low-voltage power supply, according to the author, is preferable to the use of tuning on varicaps. With KPE it is possible to cover the entire range of 64 ... 108 MHz without additional coils and switching elements, and also maintains stable tuning to the radio station until the batteries are deeply discharged. For those who want to introduce varicap settings into the receiver, I recommend turning to, where they are discussed various options turning on circuits. The 10.7 MHz IF signal from pin 14 of the microcircuit is allocated to the mixer load resistor R5, filtered by the piezoceramic filter ZQ1 and supplied to pin 17 (input of the intermediate frequency limiting amplifier). To detect frequency-modulated oscillations, it is used phase detector microcircuits. Its phase-shifting circuit L1, SZ, C4, tuned to a frequency of 10.7 MHz, is connected to pin 2. From the demodulator output (pin 23) through capacitor C8, the signal is fed to the input of the audio amplifier. Capacitor C9 compensates for audio signal distortion introduced on the transmitting side to improve the signal-to-noise ratio. Resistor R2 regulates the volume level, and resistor R4 regulates the level of high frequencies in the sound signal. Reinforced sound signal is supplied to pin 27, to which the dynamic head BA1 with a power of 0.25... 1 W is connected through capacitor C2. The R1C1 chain is connected to pin 1, and the capacitor C6 is connected to pin.3 feedback amplifier 34. The capacitor SY of the APCG system is connected to pin 6. Its capacitance must be within 2.7...4.7 pF, otherwise the operation of the automatic frequency control system will be disrupted. Pin 15 – AM-FM band switching signal input. It should be noted that the U2510B microcircuit allows you to implement a receiver of amplitude-modulated signals (LW, MW, KB) with an intermediate frequency of 455 or 465 kHz. To do this, you need to close pin 15 to the common wire, and connect the corresponding circuits to pins 5, 10, 16 of the microcircuit. When fine-tuning the radio station, the VD1 LED connected to pin 19 lights up. If during the process of tuning the receiver it becomes necessary to disable the APCG system, then it is enough to connect pin 22 to the common wire. Power filter capacitor C5 is connected to pin 25. As a capacitor C13, you can use a four-section KPE from a Chinese radio, and those sections are used that are used for tuning in the MF and HF ranges. In such KPE blocks there are four tuning capacitors located on top, one for each section. Approximately the limits for changing the capacitances of these sections are 3...200 pF. This allows you to cover the entire required range of received frequencies without additional switching.

Resistor R2 - any type with an inverse logarithmic characteristic of resistance change (group B). Its resistance can be in the range of 22... 100 kOhm. Resistor R4 is of any type of group A, its resistance can be in the range of 4.7...33 kOhm. Piezoceramic filter ZQ1 - standard, type FP1P6-1.2 or imported at a frequency of 10.7 MHz.

The U2510B microcircuit has almost complete analogues - SХА1019М and СХА1191М from SONY. The difference lies in the absence of the R1C1 chain in the latter (pin 1 is connected to the common wire) and the HF tone control (pin 18 remains free).

Coil L1 is wound on a standard frame with a diameter of 6 mm with an adjusted ferrite core and contains 10 turns of PEL-0.16 wire. The coil must be shielded. Coils L2 and L3 are frameless with an internal diameter of 4 mm, wound with PEL-0.5 wire. Coil L2 has 6 turns, L3 has 7 turns.

During development printed circuit board The elements of the local oscillator and RF amplifier circuits must be located as close as possible to the corresponding pins of the microcircuit. The paths that connect them must be made as short as possible and at least 2 mm wide.

If the installation was carried out without errors and serviceable elements were used, then when the power source is turned on, a characteristic noise should appear in the dynamic head, the volume of which should be regulated by resistor R2. By connecting the antenna, the receiver is tuned to a radio station. By rotating the core of coil L1, we achieve maximum sound volume of the received radio station without distortion. By stretching or compressing the turns of the heterodyne coil L2, as well as rotating the rotor of the adjusted capacitor (not shown in the diagram) located on the C13.1 KPI, the range is set within the required boundaries. Next, tune the receiver to a weak radio station and tune the resonant circuit of the RF amplifier. By rotating the rotor of the corresponding adjusted capacitor on KPE S13.2, maximum volume and minimum noise are achieved. Finally, the final pairing of the contours is performed. You need to connect a voltmeter to pin 23 and, by adjusting the RF circuit, achieve the maximum reading when receiving a radio station.

Literature

1. Polyakov V. About the operation of the receiver on the K174XA34 chip // Radio. 1999. No. 9. P. 19.

2. Polyatykin P. VHF receiver on the K174XA42A chip // Radio. 1999. No. 6. P. 20.

3. Gerasimov N. Dual-band VHF receiver // Radio. 1999. No. 8. P. 6.

4. Danilenko B. Domestic and foreign amplifiers, radios. Minsk: Belarus, 2000.

5. Microcircuits for audio and radio equipment. Directory. M.: DODEKA, 1997.

Scheme simple VHF radio receiver for the domestic 65.8-74 ​​MHz and the new 88-108 MHz frequency ranges with electronic tuning.

In the relatively recent past, a wired radio broadcasting network with subscriber loudspeakers was widely developed in our country. Today, radio listeners give preference to VHF FM radios, especially since the number of radio stations transmitting in the VHF-1 (65.8...74 MHz) and VHF-2 (88...108 MHz) bands is increasing every year.

The author of the published article talks about how outdated wired devices can be turned into VHF receivers.

If you still have a subscriber loudspeaker, then using its housing with a dynamic head you can easily manufacture the simple network speaker offered here without any special expenses. VHF radio receiver. This does not require scarce or expensive parts

As you know, one of the most complex components of a VHF receiver is the radio reception path. But with the advent of specialized microcircuits, for example, TDA7021 (domestic analogue of K174ХА34) and K174ХА42, it is not so difficult to manufacture such a unit.

Schematic diagram

The receiver consists of a radio frequency amplifier on transistor VT1, an FM signal processing unit on the DA1 chip, an AF power amplifier on transistors VT5 VT11 and a power supply.

The radio signal received by antenna WA1 through antenna socket XW1, capacitor C1 and coils L1 and L2 is supplied to the base of transistor VT1. The input oscillating circuit L1C3 is tuned to the middle of the VHF-2 range to ensure a slight increase in the frequency response in the high frequency range of the operating range.

This is necessary to compensate for the decrease in sensitivity with increasing frequency of the used microcircuit. The radio signal amplified by transistor VT1 is isolated on coil L3 and, through capacitor C8, enters the input of microcircuit DA1.

Rice. 1. Schematic diagram of a VHF receiver based on the K174XA34 chip (TDA7021).

The inclusion of the microcircuit is standard, it was given in R-1995 No. 10, 11. The setting indicator is made on transistors VT3, VT4 and LED HL4. The signal is supplied to it from pin 9 of the DA1 chip. The sensitivity threshold of the indicator is set using trimming resistor R4. When fine tuning to a station, the HL4 LED lights up.

Tuning into radio stations is carried out by changing resonant frequency oscillatory circuits of the local oscillator of the DA1 microcircuit. The circuit of the VHF-2 band includes coil L5 with varicaps VD3 VD4 of the VHF-1 band, coil L4 varicap VD2 and capacitor C22. Switching of the coils is carried out by switch SA1. Section SA1.2 through resistor R11 simultaneously with switching bands lights up one of the LEDs HL2 or HL3, signaling the activation of one or another VHF band.

The setting element in the receiver is the variable resistor R6. included in the voltage stabilizer circuit on the HL1 LED. From the engine of this resistor, the tuning voltage through resistor R9 is supplied to the varicaps VD2-VD4, changing their capacitance.

The RF frequency control unit and the DA1 microcircuit are powered through a voltage stabilizer on the transistor VT2 and the zener diode VD5. The HL1 LED also serves as an indicator that the receiver is connected to the network.

The audio frequency signal (AF) from pin 14 of the DA1 microcircuit through capacitor C23 and trimming resistor R10 is supplied to a buffer amplifier on transistor VT5. It increases the amplitude of the AF signal to the level required for operation of the power amplifier audio frequencies(UMZCH).

ULF and power supply

UMZCH is made according to push-pull circuit with direct connection between cascades on transistors VT6-VT11. At its input there is a volume control - variable resistor R18. The feedback circuit C33R26R27 serves to correct the frequency response of the amplifier, providing a more pleasant sound. The amplifier is loaded onto the dynamic head BA1 through capacitor C35.

Rice. 1. (Continued) ULF circuit and the receiver power supply.

The receiver's power supply is made on a step-down transformer T1 with a rectifier on a diode bridge VD9. Output voltage stabilized by a device based on transistor VT12 and zener diode VD8.

Details and design

Instead of the TDA7021 chip. As already noted in the receiver, you can use its domestic analogue - K174XA34. KT3127A, KT363, KT337, KT3123 with any letter indices can work as transistor VT1 in the URF.

The remaining transistors VTZ-VT6, VT8 are any of the KT3102, KT315 series; VT7-VT9 -KT361, KT3107. Transistor VT2 - any of the KT502, KT815 series; VT10 - KT814, KT816; VT11, VT12 - KT815, KT817 with any letter indices.

Rice. 2. Printed circuit board for VHF receiver.

In place of diodes VD1, VD7, you can install KD522B, KD521B. and VD6 - D2B. D9B. LEDs HL1-HL4 are suitable for any of the AL307 series or imported ones with the corresponding recommended parameters. Varicaps VD2-VD4 - KV109. KV132

with any letter indices. Zener diodes VD5 - KS162A, KS168A, KS 147A, VD8 D814D, KS512A, KS213Zh. It is advisable to use miniature ceramic capacitors in the VHF unit KD-1 KD-2, KM-4, K10-23; trimmers S1, SZ - KPK-MN. It is possible to use other types, for example, KT4-21, KT4-25, KT4-23, but this will require changing the design of the printed circuit board.

Rice. 3. Printed circuit board of the bass amplifier for the receiver.

Variable resistor R18 - SP-1, SPZ-ZO with functional characteristic B; R6 - with linear movement of the SPZ-23a engine, length 86 mm and resistance 10.100 kOhm (functional characteristic A) All trimming resistors SPZ-38, SPZ-27. Dynamic head BA1 - any power up to 3 W, for example 1GDSH-9, 1GDSH-11, 2GDSH-7, ZGDSH-22, etc.

Coil L1 has 3.5 turns of PEV 0.3 mm wire, L2 has 2.5 turns of PEV 0.1 mm wire, ordinary winding, and both are located on the same polystyrene frame with a diameter of 5 mm. Coil L3 has 20 turns of 0.5 mm PEV wire, wound turn to turn on a mandrel with a diameter of 2 mm.

The local oscillator coils are frameless, L4 has 7 turns of 0.8 mm PEV wire, its internal diameter is 6 mm, and the L5 coil has 5 turns of 0.5 mm PEV wire, its internal diameter is 4 mm.

A slide switch from an imported radio was used as the SA1 range switch, but you can use any suitable one, for example P2K.

Rice. 4. Power supply circuit board.

Power transformer T1 is used from imported network adapter, but applicable to any power of 5...10 W with a voltage on the secondary winding of 12... 15 V.

Most of the receiver parts are mounted on three printed circuit boards: radio frequency part - fig. 2, UMZCH - fig. 3 and power supply - Figure 4.

These boards are installed in a housing, which, as already mentioned, can be used as a housing subscriber loudspeaker, but you can also make a homemade one, as shown in the photo in the screensaver and in Fig. 5. An antenna socket and a block for installing a fuse are placed on the side walls of the housing.

The remaining controls and settings are on the front panel. The movement of the resistor R6 slider is carried out from the tuning knob through the vernier device. All connections between individual boards are made with flexible wiring. The VHF board is connected to the antenna socket with a piece of coaxial cable.

If the receiver is manufactured as a wall-mounted one, then on the rear wall of the housing (removable) it is necessary to provide holes for mounting on the wall.

Setting up the receiver

First, using trimming resistor R19, set half the supply voltage on the collectors of transistors VT10, VT11, selecting resistor R16 - also half the supply voltage on the collector of transistor VT5, using trimming resistor R2, the voltage drop across resistor R3 is equal to 0.5 V.

Then, setting the sliders of trimming resistors R4 and R10 to the middle position, they set the boundaries of the received ranges by stretching or compressing the turns of the local dyne coils L4 and L5. You may have to reduce or add one turn at a time.

Having tuned in to the radio station, set resistor R18 to the top position in the diagram and use tuning resistor R10 to set the maximum sound volume at which distortion is not yet noticeable. After this, the tuning resistor R4 ensures that the HL4 LED clearly lights up when finely tuning to a station and turns it off when it is out of tune.

The final adjustment procedure is to rotate the rotors of tuning capacitors C1 and C3 to achieve maximum sensitivity of the receiver when receiving weak signals from radio stations.

I. Potachin, Fokino, Bryansk region. R-06-2000.

Greetings! In this review I want to talk about a miniature receiver module operating in the VHF (FM) range at a frequency from 64 to 108 MHz. I came across a picture of this module on one of the specialized Internet resources, and I became curious to study it and test it.

I have a special awe for radios; I have loved collecting them since school. There were diagrams from the magazine “Radio”, and there were just construction kits. Every time I wanted to assemble a better receiver and smaller in size. The last thing I assembled was a design on the K174XA34 microcircuit. Then it seemed very “cool”, when in the mid-90s I first saw a working circuit in a radio store, I was impressed)) However, progress is moving forward, and today you can buy the hero of our review for “three kopecks”. Let's take a closer look at it.

View from above.

View from below.

For scale next to the coin.

The module itself is built on the AR1310 chip. I couldn’t find an exact datasheet for it, apparently it was made in China and its exact functional device not known. On the Internet you can only find wiring diagrams. A Google search reveals: "This is a highly integrated, single-chip, stereo FM radio receiver. The AR1310 supports the FM frequency range of 64-108 MHz, the chip includes all FM radio functions: low noise amplifier, mixer, oscillator and low-dropout stabilizer. Requires a minimum of external components. Has good quality audio signal and excellent reception quality. AR1310 does not require control microcontrollers and no additional software, except 5 buttons. Operating voltage 2.2 V to 3.6 V. consumption 15 mA, in sleep mode 16 uA ".

Description and specifications AR1310
- Reception of FM frequencies range 64 -108 MHz
- Low power consumption 15 mA, in sleep mode 16 uA
- Supports four tuning ranges
- Using inexpensive quartz resonator 32.768KHz.
- Built-in two-way auto search function
- Support electronic volume control
- Supports stereo or mono mode (when contacts 4 and 5 are closed, stereo mode is disabled)
- Built-in 32 Ohm Class AB headphone amplifier
- Does not require control microcontrollers
- Operating voltage 2.2V to 3.6V
- In SOP16 housing

Pinout and overall dimensions of the module.

AR1310 microcircuit pinout.

Connection diagram taken from the Internet.

So I made a diagram for connecting the module.

As you can see, the principle couldn’t be simpler. You will need: 5 tact buttons, a headphone jack and two 100K resistors. Capacitor C1 can be set to 100 nF, or 10 μF, or not at all. Capacitances C2 and C3 from 10 to 470 µF. As an antenna - a piece of wire (I took a MGTF 10 cm long, since the transmitting tower is in my neighboring yard). Ideally, you can calculate the length of the wire, for example at 100 MHz, by taking a quarter wave or one eighth. For one eighth it will be 37 cm.
I would like to make a remark regarding the diagram. AR1310 can operate in different bands (apparently for faster station search). This is selected by a combination of pins 14 and 15 of the microcircuit, connecting them to ground or power. In our case, both legs sit on VCC.

Let's start assembling. The first thing I encountered was the non-standard pin-to-pin pitch of the module. It is 2 mm, and it will not be possible to fit it into a standard breadboard. But it doesn’t matter, I took pieces of wire and just soldered them in the form of legs.


Looks good)) Instead breadboard I decided to use a piece of PCB, assembling an ordinary “fly”. In the end, this is the board we got. The dimensions can be significantly reduced by using the same LUT and smaller components. But I didn’t find any other parts, especially since this is a test bench for running.

After applying power, press the power button. The radio receiver worked immediately, without any debugging. I liked the fact that the search for stations works almost instantly (especially if there are many of them in the range). The transition from one station to another takes about 1 s. The volume level is very high, it is unpleasant to listen to at maximum. After turning off the button (sleep mode), it remembers the last station (if you do not completely turn off the power).
Sound quality testing (by ear) was carried out using Creative (32 Ohm) drop-type headphones and Philips vacuum-type headphones (17.5 Ohm). I liked the sound quality in both. No squeakiness, just enough low frequencies. I'm not much of an audiophile, but I was pleasantly pleased with the sound of the amplifier of this microcircuit. I couldn’t turn up the maximum volume in the Philips, the sound pressure level was painful.
I also measured the current consumption in sleep mode 16 μA and in working mode 16.9 mA (without connecting headphones).

When connecting a load of 32 Ohms, the current was 65.2 mA, and with a load of 17.5 Ohms - 97.3 mA.

In conclusion, I will say that this radio receiver module is quite suitable for domestic use. Even a schoolchild can assemble a ready-made radio. Among the “cons” (more likely not even cons, but features) I would like to note the non-standard pin spacing of the board and the lack of a display to display information.

I measured the current consumption (at a voltage of 3.3 V), as we see, the result is obvious. With a load of 32 Ohms - 17.6 mA, with 17.5 Ohms - 18.6 mA. This is a completely different matter!!! The current varied slightly depending on the volume level (within 2 - 3 mA). I corrected the diagram in the review.