VHF radio receiver according to the classical scheme. A simple direct amplification VHF receiver

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

In the magazines "Radio Amateur" and "Radio" in recent years, many diagrams of such radio receivers have been printed. Almost all of them are options for including 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 band, and a tendency to self-excitation. The need to use an external LF amplifier increases the weight and size and current consumption.

Abroad, there is a large class of single-chip radio receivers, for example, U251 OB, KA22425D, СХА1019М, 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 little known to the general public. Unlike the well-known K174XA34 and K174XA42 microcircuits, this microcircuit has a number of advantages. The best sound quality and the absence of specific interference are due to the standard 10.7 MHz IF. High sensitivity is provided by the URF with a tunable resonant circuit. The advantages of the microcircuit are the presence of an audio frequency amplifier, electronic volume and treble tone controls, indicator settings, a wide range of supply voltage and a small current consumption.

Specifications

Range of received frequencies, MHz…………………………… 64.. .108

Sensitivity not worse, µV………………………………………….. 5

Rated output power at a load of 8 ohms, W ... 0.1 Quiescent current, mA 10

The receiver remains operational when the supply voltage drops to 1.8 V, the maximum supply voltage is 9 V.

The U251OB chip is manufactured in a 28-pin package. The pitch between the leads is 1.75 mm.

The circuit diagram of the receiver is shown in fig. 1. The radio signals received by the antenna are fed to the input of the radio frequency amplifier (pin 12 DA1). The load of this URC 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 the local oscillator voltage, the circuit of which is L2, C13.1, C12. The reference voltage of 2.4 V from the internal stabilizer is applied to pin 8 of the microcircuit. The use of KPI in small-sized receivers with low-voltage power, according to the author, is preferable to using tuning on varicaps. With KPI, it is possible to cover the entire range of 64 ... 108 MHz without additional coils and switching elements, and it also maintains a stable tuning to the radio station until the batteries are deeply discharged. For those who want to enter the varicap setting into the receiver, I recommend that you refer to where various options turning circuits on. The 10.7 MHz IF signal from pin 14 of the microcircuit is allocated to the mixer load resistor R5, filtered by a piezoceramic filter ZQ1 and fed to pin 17 (the input of the intermediate frequency limiter amplifier). To detect frequency-modulated oscillations, a phase detector of the microcircuit is used. Its phase-shifting circuit L1, C3, 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 frequency amplifier. Capacitor C9 compensates for audio signal pre-distortion introduced at the transmitter side to improve the signal-to-noise ratio. Resistor R2 controls the volume level, and resistor R4 controls the level of high frequencies in the audio signal. An amplified sound signal is fed to pin 27, to which a dynamic head BA1 with a power of 0.25 ... 1 W is connected through capacitor C2. A chain R1C1 is connected to pin 1, and a capacitor C6 is connected to pin 3. feedback amplifier 34. Capacitor SU of the APCG system is connected to terminal 6. Its capacitance must be within 2.7 ... 4.7 pF, otherwise the operation of the auto-tuning system will be disrupted. Pin 15 - AM-FM range switching signal input. It should be noted that the U2510B chip allows you to implement a receiver of amplitude-modulated signals (LW, MW, KB) with an intermediate frequency value of 455 or 465 kHz. To do this, it is necessary to close pin 15 to a common wire, and connect the corresponding circuits to pins 5, 10, 16 of the microcircuit. When fine-tuning to the radio station, the VD1 LED connected to pin 19 lights up. If during the tuning process of the receiver it is necessary to turn off the APCG system, then it is enough to connect pin 22 to a common wire. Capacitor C5 of the power filter is connected to terminal 25. As a capacitor C13, you can use a four-section KPI from a Chinese radio, and those sections that are used for tuning in the CB and HF bands are used. In such KPI blocks, four trimmer capacitors are located on top, one for each section. Approximately the limits of 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 - 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 chip has almost complete analogues - СХА1019М and СХА1191М from SONY. The difference lies in the absence of the latter chain R1C1 (pin 1 is connected to a common wire) and the treble tone control (pin 18 remains free).

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

When designing a 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 tracks that connect them must be made as short as possible and at least 2 mm wide.

If the installation is completed without errors and serviceable elements are 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 the resistor R2. By connecting the antenna, the receiver is tuned to a radio station. By rotating the core of the L1 coil, they achieve the maximum sound volume of the received radio station in the absence of distortion. By stretching or compressing the turns of the L2 heterodyne coil, as well as rotating the rotor of a tuned capacitor (not shown in the diagram) located on the KPI C13.1, the range is laid within the required boundaries. Next, tune the receiver to a weak radio station, tune the resonant circuit of the URF. By rotating the rotor of the corresponding tuned capacitor on KPI C13.2, they achieve maximum volume and minimum noise. In conclusion, the final conjugation of the contours is performed. You need to connect a voltmeter to terminal 23 and, by adjusting the URF circuit, achieve the maximum reading when receiving a radio station.

Literature

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

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

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

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

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

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

The FM receiver receives the entire range from 88 to 108 MHz. I managed to tune it to seven radio stations that switch with a smooth rotation of the “SETUP” variable resistor, but out 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 at a distance over 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 or removed altogether if you listen to the radio through headphones. The antenna is a piece of meter wire, but it is better to add a small antenna amplifier to the circuit, called a UHF (high frequency amplifier).

The resistance of the resistor "VOLUME" does not have to be 33k, it can be any within 10-47k. Coils: coil L1 - frameless, 8 turns, wound on a 3mm frame with PEL wire 0.55mm. She tunes the FM receiver. L2 - input circuit, wound with the same wire, on the same diameter, only has 13 turns.

When tuning the receiver, it is necessary to stretch or compress the L1 coil until you catch the entire FM range. But do not rush to stretch it. First, try to catch stations with a fully compressed coil, as in my case. For example, I did not have to configure it at all.

The FM radio can be powered by an ordinary Chinese power supply for a landline phone or another similar one, with a current of 0.05A (in the version without VLF) or 1A (with a TDA2003 chip). The kt315 transistor can be replaced with any similar one. When assembling the circuit without errors, the receiver starts working immediately.

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

I have a special trepidation for radios, I like to collect them since school. There were schemes from the magazine "Radio", there were just designers. Every time I wanted to assemble the receiver better and smaller. The last thing I collected was the design on the K174XA34 chip. 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.

Bottom view.

For scale next to the coin.

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

Description and technical characteristics of AR1310
- FM frequency reception range 64 -108 MHz
- Low power consumption 15 mA, sleep mode 16 uA
- Support for four tuning ranges
- Using an inexpensive 32.768KHz quartz resonator.
- Built-in two-way automatic search function
- Support for electronic volume control
- Support for stereo or mono mode (when closing 4 and 5 pins, the stereo mode is turned off)
- 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.

Pinout of the AR1310 chip.

Wiring diagram taken from the Internet.

So I made a wiring diagram for the module.

As you can see, the principle is nowhere simpler. You will need: 5 tact buttons, a headphone jack and two 100K resistors. Capacitor C1 can be set to 100 nF, you can set it to 10 microfarads, or you can not set it at all. Capacitances C2 and C3 from 10 to 470 uF. As an antenna - a piece of wire (I took the MGTF 10 cm long, because the transmitting tower is in my neighboring yard). Ideally, you can calculate the length of the wire, for example at 100 MHz, taking a quarter wave or one eighth. For one eighth it will be 37 cm.
I would like to comment on the diagram. AR1310 can work in different ranges (apparently, for a faster search for stations). 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 a non-standard inter-output step of the module. It is 2 mm, and it will not work to put it in a standard breadboard. But it doesn't matter, taking pieces of wire, just soldered them in the form of legs.


Looks good)) Instead of a breadboard, I decided to use a piece of textolite, assembling the usual "fly". As a result, here is the board. Dimensions can be significantly reduced by using the same LUT and smaller components. But I didn’t find any other details, especially since this is a test bench for running in.

After applying power, press the power button. The radio receiver immediately earned, without any debugging. I liked the fact that the search for stations works almost instantly (especially if there are a lot of them in the range). The transition from one station to another is about 1 s. The volume level is very high, it is unpleasant to listen to the maximum. After turning off the button (sleep mode), remembers the last station (if you do not completely turn off the power).
Sound quality testing (by ear) was carried out with Creative (32 ohm) “drop” type headphones and Philips “vacuum” type headphones (17.5 ohm). And in those, and in others, I liked the sound quality. There is no squeakiness, a sufficient amount of low frequencies. A music lover from me is useless, but the sound of the amplifier of this microcircuit was pleasantly pleased. In Phillips, I could not unscrew the maximum volume, the sound pressure level was painful.
I also measured the current consumption in sleep mode 16 μA and in working 16.9 mA (without connecting headphones).

When connecting a load of 32 ohms, the current was 65.2 mA, 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 schoolboy can assemble a ready-made radio. Of the "minuses" (rather not even cons, but features), I note the non-standard pin-to-pin pitch of the board and the lack of a display for displaying information.

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