As you have already noticed, there is no variable capacitor in the circuit; it is replaced by a pair of varicaps and a variable resistance. In this receiver, the resistance needs to be a variable multi-turn, but in my case there is a tuning multi-turn resistor. The following types can be used:
Varicap KV109 can be used with any letter designation; I used KV109A (with a white dot). Varicap pinout (the leg on the marking side is the anode, and the leg on the side of the convex mark is the cathode):
If you look closely at the diagram, the elements marked 10.7 MHz differ from each other in the number of pins. An element with two terminals can be called a quartz resonator, but it is more correctly called a descriminator filter. An element with three terminals is a radio frequency filter. These elements are recommended to be used by companies Murata.
Coil L1 is wound in the amount of 11 turns, with a 0.5 mm wire, on a hollow frame (a drill can be used for winding) with a diameter of 2.5 mm. L2 – 10 turns, 0.5 mm wire, on the same frame. This receiver has a very low output power, which is only enough for a high-impedance (40-60 Ohm) earphone, so you need to use ULF.
The printed circuit board for this device is very simple; it can be drawn with a marker. The figure shows the device's printed circuit board, which can be
The simplest radio receivers are not suitable for catching the FM range, frequency modulation. Common people say: this is where the name comes from. In English we interpret the letter FM as frequency modulation. A clearly expressed meaning is important for readers to understand: the simplest radio receiver, assembled with your own hands from rubbish, will not accept FM. The question of necessity arises: the cell phone picks up the broadcast. Electronic equipment has a similar capability built into it. Far from civilization, people still want to catch broadcasts the old-fashioned way - they almost said with dental crowns - by constructing efficient devices for listening to their favorite programs. For free…
Detector simplest radio receiver: basics
The story touched on dental fillings for a reason. Steel (metal) is capable of converting ethereal waves into current, copying the simplest radio receiver, the jaw begins to vibrate, the bones of the ear detect the signal encrypted on the carrier. With amplitude modulation, the high frequency repeats the speaker's voice, music, and sound in scope. The useful signal contains a certain spectrum, which is difficult for a layman to understand; it is important that when adding the components, a certain law of time is obtained, following which the speaker of a simple radio receiver reproduces the broadcast. At the dips, the jaw bone freezes, silence reigns, and the ear hears the peaks. God forbid, of course, you should have a simple radio receiver.
The reverse piezoelectric effect changes the geometric dimensions of the bones according to the law of electromagnetic waves. A promising direction: a human radio receiver.
The Soviet Union was famous for launching a space rocket, ahead of the rest, for scientific research. Union times encouraged degrees. The luminaries have brought a lot of benefit here - designing radios - and earn decent money over the hill. The films promoted the smart, not the wealthy, it is not surprising that the magazines are full of various developments. A series of modern lessons on creating simple radios, available on YouTube, is based on magazines published in 1970. Let’s be careful not to deviate from traditions; we will describe our own vision of the situation in the amateur radio industry.
The concept of a personal electronic computer was developed by Soviet engineers. The party leadership recognized the idea as unpromising. Efforts have been devoted to building giant computer centers. It is too much for a worker to master a personal computer at home. Funny? Today you will encounter more amusing situations. Then they complain - America is shrouded in glory, printing dollars. AMD, Intel - have you heard? Made in USA.
Everyone can make a simple radio receiver with their own hands. An antenna is not needed, there is a good stable broadcast signal. The diode is soldered to the terminals of high-impedance headphones (discard computer ones), all that remains is to ground one end. To be fair, let’s say the trick will work with the good old Soviet-made D2, the taps are so massive that they will serve as an antenna. We get the earth in the simplest radio receiver by leaning one leg of the radio element against a heating radiator that has been stripped of paint. Otherwise, the decorative layer, being the dielectric of the capacitor formed by the leg and metal of the battery, will change the nature of the operation. Try it.
The authors of the video noticed: there seems to be a signal, represented by an unimaginable jumble of rustles and meaningful sounds. The simplest radio receiver lacks selectivity. Anyone can understand and understand the term. When we set up the receiver, we catch the desired wave. Remember, we discussed the spectrum. The air contains a bunch of waves at the same time, you will catch the one you need by narrowing the search range. There is selectivity in the simplest radio receiver. In practice, it is implemented by an oscillatory circuit. Known from physics lessons, it is formed by two elements:
- Capacitor (capacitance).
- Inductor.
Let's take a moment to study the details; the elements are equipped with reactance. Due to this, waves of different frequencies have unequal attenuation as they pass by. However, there is some resonance. For a capacitor, the reactance in the diagram is directed in one direction, for an inductance - in the other, and the frequency dependence is shown. Both impedances are subtracted. At a certain frequency, the components equalize, and the reactance of the circuit drops to zero. Resonance sets in. The selected frequency and adjacent harmonics pass through.
The physics course shows the process of choosing the bandwidth of a resonant circuit. Determined by the attenuation level (3 dB below maximum). Let us present the theory, guided by which a person can assemble a simple radio receiver with his own hands. In parallel with the first diode, a second one is added, connected oppositely. It is soldered in series to the headphones. The antenna is separated from the structure by a 100 pF capacitor. Let us note here: the diodes are endowed with pn-junction capacitance, minds apparently calculated the reception conditions, which capacitor is included in the simplest radio receiver endowed with selectivity.
We believe we will slightly deviate from the truth when we say: the range will affect the HF or SV regions. Multiple channels will be received. The simplest radio receiver is a purely passive design, devoid of an energy source; one should not expect great achievements.
A few words about why we discussed remote nooks where radio amateurs crave experiments. In nature, physicists have noticed the phenomena of refraction and diffraction, both of which allow radio waves to deviate from their direct course. Let's call the first rounding obstacles, the horizon moves away, giving way to broadcasting, the second - refraction by the atmosphere.
LW, SW and HF are caught at a considerable distance, the signal will be weak. Therefore, the simplest radio receiver discussed above is a touchstone.
The simplest radio receiver with amplification
In the considered design of the simplest radio receiver, low-impedance headphones cannot be used; the load resistance directly determines the level of transmitted power. Let's first improve the characteristics using a resonant circuit, then supplement the simplest radio receiver with a battery, creating a low-frequency amplifier:
- The selective circuit consists of a capacitor and inductor. The magazine recommends that the simplest radio receiver include a variable capacitor with an adjustment range of 25 - 150 pF; the inductance must be made according to the instructions. A ferromagnetic rod with a diameter of 8 mm is wound evenly with 120 turns, covering 5 cm of the core. A copper wire coated with varnish insulation with a diameter of 0.25 - 0.3 mm is suitable. We provided readers with the address of the resource where you can calculate the inductance by entering numbers. The audience can independently find, using Yandex, and calculate the number of mH of inductance. The formulas for calculating the resonant frequency are also well known, therefore, it is possible, remaining at the screen, to imagine the tuning channel of a simple radio receiver. The instructional video suggests making a variable coil. It is necessary to push the core inside the frame with wound coils of wire. The position of the ferrite determines the inductance. Calculate the range, using the help of the program, YouTube craftsmen offer, winding the coil, draw conclusions every 50 turns. Since there are about 8 taps, we conclude: the total number of revolutions exceeds 400. Change the inductance abruptly, fine-tune with the core. Add to this: the antenna for the radio is decoupled from the rest of the circuit with a 51 pF capacitor.
- The second point you need to know is that a bipolar transistor also has p-n junctions, and even two. It’s appropriate to use a collector instead of a diode. As for the emitter junction, it is grounded. DC power is then applied to the collector directly through the headphones. The operating point is not selected, so the result is somewhat unexpected; patience will be required until the radio receiver is perfected. The battery also greatly influences the choice. We consider the headphone resistance to be collector resistance, which determines the slope of the transistor's output characteristic. But these are subtleties, for example, the resonant circuit will also have to be rebuilt. Even with a simple diode replacement, let alone the introduction of a transistor. That is why it is recommended to conduct experiments gradually. And the simplest radio receiver without amplification will not work at all for many.
How to make a radio receiver that would allow the use of simple headphones. Connect via a transformer, similar to the one at the subscriber point. A tube radio differs from a semiconductor radio in that in any case it requires power to operate (filament filaments).
Vacuum devices take a long time to reach operating mode. Semiconductors are ready to accept immediately. Don't forget: germanium does not tolerate temperatures above 80 degrees Celsius. If necessary, provide cooling for the structure. At first, this is necessary until you select the size of the radiators. Use fans from a personal computer, processor coolers.
Bands are no longer relevant, the common and well-known microcircuit for the FM band 174ХА34 is also outdated, so we will consider independently creating a high-quality VHF receiver using a modern elementary base - specialized inexpensive microcircuits TEA5711 and TDA7050. The TEA5711T chip in this case is in a planar package.
Advantages of the microcircuit. Very wide supply voltage - from 2 to 12V. In our case, we take 2 AA batteries - 3 volts in total. The current consumption is 20mA, and the sensitivity in the FM range is only 2 µV. Three-pin piezoceramic filters are used here, which very effectively eliminates urban interference in the FM range.
The high-frequency part of the FM receiver is assembled on a Philips TEA5711 microcircuit. To improve selectivity, two series-connected bandpass filters are used. To increase the output level of the low-frequency signal, an amplifier based on a planar two-channel TDA7050 microcircuit is used. It allows you to reduce the supply voltage down to 1.6 volts - optimally 3V. In this case, the output power is about 0.2W. The winding data of the coils can be taken from
This simple FM receiver built on the TDA7000 integrated circuit with a minimum number of passive components. The receiver is quite sensitive over the entire range of received frequencies (88 - 108 MHz).
Description of FM receiver
The special feature of this TDA7000 FM radio is its voltage controlled oscillator. Instead of using a variable capacitor, you can adjust the frequency with a 100K variable resistor which changes the input voltage of the generator.
The advantage of using a variable resistor instead of a variable capacitor is obvious - capacitance pickup is eliminated when you touch it and the potentiometer can easily be installed in any convenient location of the receiver.
Specifications:
- Supply voltage: 2 - 10 volts
- Frequency range: 70 - 120MHz
- Current consumption: 8 mA
- Audio output: 75 mV
TDA7000 is an integrated circuit for mono FM portable radios. For its operation, a minimum body kit is required, which is important when creating miniature devices. The TDA7000 includes the following functions: RF input stage, mixer, local oscillator, intermediate frequency amplifier, phase demodulator, signal cutoff detector, and mute.
This circuit runs on just one 1.5 V battery. An ordinary earphone with a total impedance of 64 Ohms is used as an audio playback device. The battery power passes through the headphone jack, so you just need to pull the headphones out of the jack to turn off the receiver. The sensitivity of the receiver is sufficient that several high-quality HF and DV stations can be used on a 2-meter wire antenna.
Coil L1 is made on a ferrite core 100 mm long. The winding consists of 220 turns of PELSHO 0.15-0.2 wire. Winding is carried out in bulk on a paper sleeve 40 mm long. The tap must be made from 50 turns from the grounded end.
Receiver circuit with just one field-effect transistor
This version of the circuit of a simple single-transistor FM receiver works on the principle of a super-regenerator.
The input coil consists of seven turns of copper wire with a cross-section of 0.2 mm, wound on a 5 mm mandrel with a tap from the 2nd, and the second inductance contains 30 turns of 0.2 mm wire. The antenna is a standard telescopic one, powered by one Krona type battery, the current consumption is only 5 mA, so it will last for a long time. Tuning to a radio station is carried out by a variable capacitor. The sound at the output of the circuit is weak, so almost any homemade ULF will be suitable to amplify the signal.
The main advantage of this scheme in comparison with other types of receivers is the absence of any generators and therefore there is no high-frequency radiation in the receiving antenna.
The radio wave signal is received by the receiver antenna and is isolated by a resonant circuit on inductance L1 and capacitance C2 and then goes to the detector diode and is amplified.
FM receiver circuit using a transistor and LM386. |
I present to your attention a selection of simple FM receiver circuits for the range 87.5 to 108 MHz. These circuits are simple enough to be repeated, even for beginner radio amateurs, they are not large in size and can easily fit in your pocket.
Despite their simplicity, the circuits have high selectivity and a good signal-to-noise ratio and are quite enough for comfortable listening to radio stations
The basis of all these amateur radio circuits are specialized microcircuits such as: TDA7000, TDA7001, 174XA42 and others.
The receiver is designed to receive telegraph and telephone signals from amateur radio stations operating in the 40-meter range. The path is built according to a superheterodyne circuit with one frequency conversion. The receiver circuit is designed in such a way that a widely available element base is used, mainly transistors of the KT3102 type and 1N4148 diodes.
The input signal from the antenna system is fed to the input bandpass filter on two circuits T2-C13-C14 and TZ-C17-C15. The connection between the circuits is capacitor C16. This filter selects the signal within the range of 7 ... 7.1 MHz. If you want to work in a different range, you can adjust the circuit accordingly by replacing transformer coils and capacitors.
From the secondary winding of the HF transformer TZ, the primary winding of which is the second filter element, the signal goes to the amplifier stage on transistor VT4. The frequency converter is made using diodes VD4-VD7 in a ring circuit. The input signal is supplied to the primary winding of transformer T4, and the smooth range generator signal is supplied to the primary winding of transformer T6. The smooth range generator (VFO) is made using transistors VT1-VT3. The generator itself is assembled on transistor VT1. The generation frequency lies in the range of 2.085-2.185 MHz, this range is set by a loop system consisting of inductance L1, and a branched capacitive component of C8, C7, C6, C5, SZ, VD3.
Adjustment within the above limits is carried out by variable resistor R2, which is the tuning element. It regulates the constant voltage on the VD3 varicap, which is part of the circuit. The tuning voltage is stabilized using a zener diode VD1 and a diode VD2. During the installation process, overlap in the above frequency range is established by adjusting the capacitors SZ and Sb. If you want to work in a different range or with a different intermediate frequency, a corresponding restructuring of the GPA circuit is required. It’s not difficult to do this armed with a digital frequency meter.
The circuit is connected between the base and emitter (common minus) of transistor VT1. The PIC required to excite the generator is taken from a capacitive transformer between the base and emitter of the transistor, consisting of capacitors C9 and SY. RF is released at the emitter VT1 and goes to the amplifier-buffer stage on transistors VT2 and VT3.
The load is on the RF transformer T1. From its secondary winding, the GPA signal is supplied to the frequency converter. The intermediate frequency path is made using transistors VT5-VT7. The output impedance of the converter is low, so the first stage of the amplifier is made using a VT5 transistor according to a common-base circuit. From its collector, the amplified IF voltage is supplied to a three-section quartz filter at a frequency of 4.915 MHz. If there are no resonators for this frequency, you can use others, for example, at 4.43 MHz (from video equipment), but this will require changing the settings of the VFO and the quartz filter itself. The quartz filter here is unusual; it differs in that its bandwidth can be adjusted.
Receiver circuit. The adjustment is carried out by changing the containers connected between the filter sections and the common minus. For this, varicaps VD8 and VD9 are used. Their capacitances are regulated using a variable resistor R19, which changes the reverse DC voltage across them. The filter output is to the T7 RF transformer, and from it to the second stage of the amplifier, also with a common base. The demodulator is made on T9 and diodes VD10 and VD11. The reference frequency signal comes to it from the generator at VT8. It should have a quartz resonator the same as in a quartz filter. The low-frequency amplifier is made using VT9-VT11 transistors. The circuit is two-stage with a push-pull output stage. Resistor R33 regulates the volume.
The load can be both the speaker and headphones. Coils and transformers are wound on ferrite rings. For T1-T7, rings with an outer diameter of 10 mm are used (imported type T37 is possible). T1 - 1-2=16 vit., 3-4=8 vit., T2 - 1-2=3 vit., 3-4=30 vit., TZ - 1-2=30 vit., 3-4= 7 vit., T7 -1-2=15 vit., 3-4=3 vit. T4, TB, T9 - 10 turns of wire folded in three, solder the ends according to the numbers on the diagram. T5, T8 - 10 turns of wire folded in half, solder the ends according to the numbers on the diagram. L1, L2 - on rings with a diameter of 13 mm (imported type T50 is possible), - 44 turns. For all, you can use PEV wire 0.15-0.25 L3 and L4 - ready-made chokes 39 and 4.7 μH, respectively. KT3102E transistors can be replaced with other KT3102 or KT315. Transistor KT3107 - on KT361, but it is necessary that VT10 and VT11 have the same letter indices. 1N4148 diodes can be replaced with KD503. The installation was carried out in a three-dimensional manner on a piece of foil fiberglass laminate measuring 220x90 mm.
This article provides a description of three simple receivers with a fixed tuning to one of the local stations in the MF or LW range; these are extremely simplified receivers powered by a Krona battery, located in subscriber speaker housings containing a speaker and a transformer.
The schematic diagram of the receiver is shown in Figure 1A. Its input circuit is formed by coil L1, capacitor cl and an antenna connected to them. The circuit is tuned to a station by changing capacitance C1 or inductance Ll. The RF signal voltage from part of the coil turns is supplied to the diode VD1, which works as a detector. From variable resistor 81, which is the load of the detector and the volume control, low frequency voltage is supplied to the base VT1 for amplification. The negative bias voltage at the base of this transistor is created by the constant component of the detected signal. Transistor VT2 of the second stage of the low-frequency amplifier has a direct connection with the first stage.
The low-frequency oscillations amplified by it pass through the output transformer T1 to loudspeaker B1 and are converted into acoustic oscillations. The receiver circuit of the second option is shown in the figure. The receiver assembled according to this circuit differs from the first option only in that its low-frequency amplifier uses transistors of different conductivity types. Figure 1B shows a diagram of the third version of the receiver. Its distinctive feature is positive feedback carried out using the L2 coil, which significantly increases the sensitivity and selectivity of the receiver.
To power any receiver, a battery with a voltage of -9V is used, for example, “Krona” or made up of two 3336JI batteries or individual elements; it is important that there is enough space in the subscriber speaker housing in which the receiver is assembled. While there is no signal at the input, both transistors are almost closed and the current consumption of the receiver in rest mode does not exceed 0.2 Ma. The maximum current at the highest volume is 8-12 Ma. The antenna is any wire about five meters long, and the grounding is a pin driven into the ground. When choosing a receiver circuit, you need to take into account local conditions.
At a distance of about 100 km from the radio station, using the above antenna and grounding, loud-speaking reception by receivers is possible according to the first two options; up to 200 km - the scheme of the third option. If the distance to the station is no more than 30 km, you can get by with an antenna in the form of a wire 2 meters long and without grounding. The receivers are mounted by volumetric installation in the housings of subscriber loudspeakers. Remaking the loudspeaker comes down to installing a new volume control resistor combined with the power switch and installing sockets for the antenna and grounding, while the isolation transformer is used as T1.
Receiver circuit. The input circuit coil is wound on a piece of ferite rod with a diameter of 6 mm and a length of 80 mm. The coil is wound on a cardboard frame so that it can move along the rod with some friction. To receive DV radio stations, the coil must contain 350, with a tap from the middle, turns of PEV-2-0.12 wire. To operate in the CB range there must be 120 turns with a tap from the middle of the same wire; the feedback coil for the receiver of the third option is wound on a contour coil, it contains 8-15 turns. Transistors must be selected with a gain Vst of at least 50.
Transistors can be any germanium low-frequency of the appropriate structure. The transistor of the first stage must have the minimum possible reverse collector current. The role of a detector can be performed by any diode of the D18, D20, GD507 and other high-frequency series. The variable volume control resistor can be of any type, with a switch, with a resistance from 50 to 200 kilo-ohms. It is also possible to use a standard resistor of the subscriber loudspeaker; usually resistors with a resistance of 68 to 100 kohms are used. In this case, you will have to provide a separate power switch. A trimmer ceramic capacitor KPK-2 was used as a loop capacitor.
Receiver circuit. It is possible to use a variable capacitor with a solid or air dielectric. In this case, you can insert a tuning knob into the receiver, and if the capacitor has a sufficiently large overlap (in a two-section, you can connect two sections in parallel, the maximum capacity will double) you can receive stations in the LW and SW range with one medium-wave coil. Before tuning, you need to measure the current consumption from the power source with the antenna disconnected, and if it is more than one milliampere, replace the first transistor with a transistor with a lower reverse collector current. Then you need to connect the antenna and by rotating the rotor of the loop capacitor and moving the coil along the rod, tune the receiver to one of the powerful stations.
Converter for receiving signals in the 50 MHz range The IF-LF transceiver path is intended for use in the latter, superheterodyne circuit, with single frequency conversion. The intermediate frequency is chosen to be 4.43 MHz (quartz from video equipment is used)
Magnetic ferrite antennas are good for their small size and well-defined directivity. The antenna rod should be positioned horizontally and perpendicular to the direction of the radio. In other words, the antenna does not receive signals from the ends of the rod. In addition, they are insensitive to electrical interference, which is especially valuable in large cities, where the level of such interference is high.
The main elements of a magnetic antenna, designated in the diagrams by the letters MA or WA, are an inductor coil wound on a frame made of insulating material, and a core made of high-frequency ferromagnetic material (ferrite) with high magnetic permeability.
Receiver circuit. Non-standard detector |
Its circuit differs from the classical one, first of all, in a detector built on two diodes and a coupling capacitor, which allows you to select the optimal circuit load for the detector, and thereby obtain maximum sensitivity. With a further decrease in capacitance C3, the resonance curve of the circuit becomes even sharper, i.e., the selectivity increases, but the sensitivity decreases somewhat. The oscillating circuit itself consists of a coil and a variable capacitor. The inductance of the coil can also be varied within wide limits by moving the ferrite rod in and out.
