I recently assembled a well-known FM radio receiver circuit using a specialized k174x34 chip with a simple amplifier on a TDA2003 chip, but a domestic analogue, k174un14, can also be used as a ULF.

The entire structure of a homemade receiver is placed on a printed circuit board, except for variable resistors, an antenna, a speaker and a power supply. The box from under the head of a JRC car tape recorder was used as a body, since it is a little longer than its analogues in length - about a centimeter and a little deeper, which is what we need. Download the PCB drawing in LAY format here.

The FM receiver accepts the entire range from 88 to 108 MHz. I managed to tune it to seven radio stations, which are switched by smooth rotation of the variable resistor “TUNING”, but of the seven radio stations only five are of good quality, which is nevertheless very good for such a simple circuit, especially considering that the station is located at a distance more than 80 kilometers.

The receiver is very loud, and especially high-quality sound is obtained when connecting large external speakers. If you are not satisfied with the amplifier circuit, then the ULF chip can be replaced with any other one or removed altogether if you listen to the radio through headphones. The antenna is a piece of meter-long wire, but it is better to add a small antenna amplifier to the circuit, called a UHF (high frequency amplifier).

The resistance of the “VOLUME” resistor does not have to be 33 kΩ, any value within 10-47 kΩ can be used. Coils: coil L1 - frameless, 8 turns, wound on a frame with 3mm PEL wire 0.55mm. This is what sets up the FM receiver. L2 - input circuit, wound with the same wire, to the same diameter, only it has 13 turns.

When setting up the receiver, you need to stretch or compress the L1 coil until you catch the entire FM range. But don't rush to stretch it. First try to catch stations with a fully compressed coil, as in my case. For example, I didn’t have to configure it at all.

The FM radio can be powered by an ordinary Chinese landline telephone power supply or another similar one, with a current of 0.05A (in the version without ULF) or 1A (with the TDA2003 chip). The KT315 transistor can be replaced with any similar one. When assembling the circuit without errors, the receiver starts working immediately.

This dual-band VHF radio receiver is designed to receive radio stations in the range 64...74 MHz and 88...108 MHz.

Advantages of this scheme.

• Ease of manufacture due to the use of a small number of parts, and therefore small sizes;
• Receiver power supply is from 3 to 6 V, with a current consumption of 20 mA;
• The microcircuit on which the receiver is built contains a high-frequency amplifier, a local oscillator, a mixer, an intermediate-frequency amplifier, a frequency demodulator, and a low-frequency pre-amplifier;
• Receiver sensitivity is no worse than 1 µV;

Making the receiver

Transistors VT2, VT3, VT4 act as a parametric stabilizer, through which voltage is supplied to the varicap VD1. Switching between ranges is carried out using switch SA1.

All coils are wound with PEL wire with a diameter of 0.25 to 0.51 mm on a mandrel with a diameter of 3 mm and contain L1 - four turns, L2 - seven turns, L3 - five turns.

The adjusting resistor should be used multi-turn SP3-36 for easier smooth adjustment of the range. Capacitors should be used type K10 or similar, polar K50-16b resistors type MLT. Varicap KV122A can be replaced with KV106A. Transistors VT2...VT4 with any letter index. The K174XA34 chip can be replaced with a TDA7021. switch type PD-9-2 or PD-9-1. The parts are mounted on single-sided fiberglass laminate with dimensions 60x40.

Setting up a dual-band VHF radio receiver

Adjustment by range is carried out by compressing or decompressing coils L2 (adjusts the range 64...74 MHz), L3 (adjusts the range 88...108 MHz). It is necessary to achieve overlapping ranges. After this, you need to fix them with hot glue, wax, paraffin or any other dielectric material. More precise adjustment of the range is carried out by selecting resistors R3 and R7. It is best to start adjusting from the range 88…108 MHz.

Audio amplifier for radio receiver

The circuit of a dual-band VHF radio receiver requires a final amplifier; below is a circuit of a simple low-frequency amplifier on the K174UN31 microcircuit.

Characteristics of the final amplifier for a dual-band VHF receiver
Reproducible frequency range 20…30000 Hz
Supply voltage 1.8…6.6 V
Current consumption 7 mA
Load resistance not less than 8 Ohms
Output power 1.2 W

This device is assembled on one-sided fiberglass with dimensions of 35x35 mm. With error-free assembly, the amplifier immediately starts working; you only need to set the gain we need using resistor R3. This can be done by ear; you need to achieve the absence of distortion at the maximum sound level.

That's all. If you have comments or suggestions regarding this article, please write to the site administrator.

List of used literature: Shelestov I.P. “Useful diagrams for radio amateurs”

What is an FM receiver? A radio receiver is an electronic device that receives radio waves and converts the information they carry into something useful for human perception. The receiver uses electronic filters to separate the desired RF signal from all other signals picked up by the antenna, an electronic amplifier to increase the signal power for further processing, and finally recovers the desired information through demodulation.

Of the radio waves, FM is the most popular. Frequency modulation is widely used for FM radio broadcasting. The advantage of frequency modulation is that it has a higher signal-to-noise ratio and therefore emits RF interference better than an amplitude modulation (AM) signal of equal strength. We hear the sound from the radio cleaner and richer.

FM frequency ranges

The VHF (Ultra Short Wave) range with FM (Frequency Modulation) in English FM (Frequency Modulation) has a length from 10 m to 0.1 mm - this corresponds to frequencies from 30 MHz to 3000 GHz.

A relatively small area is relevant for receiving broadcast radio stations:
VHF 64 - 75 MHz. This is our Soviet range. There are many VHF stations on it, but only in our country.

Japanese band from 76 to 90 MHz. Broadcasting is carried out in this range in the land of the rising sun.

FM - 88 - 108 MHz. - This is the Western version. Most receivers currently sold necessarily operate in this range. Often now receivers receive both our Soviet range and the Western one.

The VHF radio transmitter has a wide channel - 200 kHz. The maximum audio frequency transmitted in FM is 15 kHz, compared to 4.5 kHz in AM. This allows a much wider range of frequencies to be transmitted. Thus, the quality of FM transmission is significantly higher than AM.

Now about the receiver. Below is the electronics diagram for the FM receiver along with its working description.

List of components

• Chip: LM386
• Transistors: T1 BF494, T2 BF495
• Coil L contains 4 turns, Ф=0.7 mm on a 4 mm mandrel.
• Capacitors: C1 220nF
• C2 2.2 nf
• C 100 nf x 2 pcs
• C4.5 10 µF (25 V)
• C7 47 nF
• C8 220 uF (25 V)
• C9 100 uF (25 V) x 2 pcs
• Resistances:
• R 10 kOhm x 2 pcs
• R3 1 kOhm
• R4 10 Ohm
• Variable resistance 22kOhm
• Variable capacitance 22pf
• Speaker 8 ohm
• Switch
• Antenna
• Battery 6-9V

Description of the FM receiver circuit

Below is a diagram of a simple FM receiver. Minimum components to receive local FM station.

Transistors (T1,2), together with a 10k resistor (R1), a coil L, and a variable capacitor (VC) 22pF make up an RF oscillator (Colpitts oscillator).

The resonant frequency of this oscillator is set by the VC trimmer to the frequency of the transmitting station that we want to receive. That is, it must be tuned between 88 and 108 MHz FM band.

The information signal taken from the T2 collector is supplied to the low-frequency amplifier on LM386 through a 220nF separating capacitor (C1) and a 22 kOhm VR volume control.

FM receiver circuit diagram

Electrical circuit diagramFM receiver

Tuning to another station is carried out by changing the capacitance of a 22 pF variable capacitor. If you are using any other capacitor that has a larger capacitance, then try reducing the number of turns of the L coil to tune to the FM band (88-108 MHz).

Coil L has four turns of enameled copper wire, 0.7 mm in diameter. The coil is wound on a mandrel with a diameter of 4 mm. It can be wound on any cylindrical object (pencil or pen with a diameter of 4 mm).

If you want to receive a signal from VHF stations (64-75 MHz), then you need to wind 6 turns of the coil or increase the capacitance of the variable capacitor.

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 build a better and smaller receiver. 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 structure is 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 audio signal quality 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 technical characteristics of AR1310
- Reception of FM frequencies range 64 -108 MHz
- Low power consumption 15 mA, in sleep mode 16 uA
- Supports four tuning ranges
- Using an inexpensive 32.768KHz quartz resonator.
- 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 of a breadboard, I decided to use a piece of PCB, assembling a regular “fly board”. 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). 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. There is no squeakiness, a sufficient amount of 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.