|
Arabic
Bengali
Chinese
English
French
German
Hebrew
Hindi
Italian
Japanese
Korean
Malay
Polish
Portuguese
Spanish
Turkish
Ukrainian
Vietnamese|
ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING A simple shortwave observer radio receiver. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / radio reception We offer the design of a simple heterodyne radio receiver for a range of 160 m. The receiver may be of interest to both beginner shortwave observers and more experienced radio athletes. Thanks to its economy and small dimensions, the receiver is particularly suitable for field work. To receive signals from amateur radio stations, conventional mass broadcasting receivers are unsuitable without their modernization so significant that it is easier to rebuild the receiver. It's not even their low sensitivity and overly wide bandwidth, but the fact that they are designed to receive amplitude-modulated (AM) signals. Amateurs, on the other hand, have long abandoned AM due to its low efficiency and use only telegraph (CW) or single-sideband modulation (SSB) on short waves (KB) with a speech signal. For this reason, the receiver must also be designed on completely different principles. In particular, it does not need an amplitude detector, and it is advisable to make the main amplification at low, audio frequencies, where it is much easier and cheaper. The CW signal is short and long bursts of an unmodulated carrier frequency lying in one of the amateur radio bands, in our case 1,8 ... 2 MHz (160 meters). In order for the signal to sound like a familiar Morse code melody, its high frequency must be converted down to the 3H range. This is done by a frequency converter installed at the receiver input (Fig. 1), immediately after the input filter Z1, containing a mixer U1 and a low-power auxiliary oscillator - local oscillator G1.
Let's say we want to receive a CW signal at 1900 kHz. By tuning the local oscillator to a frequency of 1901 kHz, we will receive signals of sum (3801 kHz) and difference (1 kHz) frequencies at the output of the mixer. We do not need the total frequency, but we will filter the signal of the difference, audio frequency (Z2), amplify it in UHF A1 and feed it to BF1 phones. As you can see, the receiver is really very simple. The SSB signal is the same sound, but with the spectrum transferred to the radio frequency region. On the low-frequency amateur bands (160, 80 and 40 meters), the spectrum of the SSB signal is also inverted (the lower sideband, LSB, is emitted). This means that with a carrier frequency of the SSB signal of 1900 kHz, its spectrum extends from 1897 to 1899,7 kHz, i.e. 1900 kHz - (0,3 .... 3 kHz). The suppressed upper sideband (USB) occupies the frequency band 1900,3...1903 kHz, as seen in the spectrogram (Fig. 2). The emitted LSB is marked with thick lines. To receive this signal, it is enough to tune the local oscillator exactly to a frequency of 1900 kHz.
The heterodyne receiver was invented at the dawn of radio engineering, approximately in 1903, when there were no lamps or other amplifying devices, but there were already antennas, telephones and undamped oscillation generators (arc, electric machine). For the next decade, exclusively heterodyne receivers were used for auditory reception of telegraph signals. Then the tube regenerator was invented, or the audion (1913), superheterodyne (1917), by the way, which got its name from the heterodyne receiver, AM began to be widely used, and heterodyne receivers were firmly and for a long time forgotten. Radio amateurs revived this technique in the 60-70s of the last century, proving in practice that a receiver with three or four transistors can receive radio stations from all continents, working no worse than large multi-tube devices. But the name has become different - the direct conversion receiver (Direct Conversion Receiver, DCR), which emphasized the fact of direct conversion (namely conversion, not detection) of the radio signal frequency into a low audio frequency. Referring again to fig. 1, we will explain the purpose of the filters. The input bandpass filter Z1 attenuates strong out-of-band signals from service and broadcast stations that can cause interference. Its bandwidth can be equal to the width of the amateur band, and if it is narrower, the filter is made tunable. It also weakens the side channels of reception, which are possible on the harmonics of the local oscillator. Filter Z2 is a low-pass filter that only passes the "telephone" audio band below about 3 kHz. The lowest frequencies, below 300 Hz, are sufficiently attenuated by coupling capacitors in the ultrasonic frequency converter. Filter Z2 determines the selectivity of the receiver: the signals of radio stations located further than 3 kHz from the local oscillator frequency create frequencies above 3 kHz at the mixer output, therefore, they will be effectively filtered in the low-pass filter. To the selectivity of the receiver is added the selectivity of telephones, which poorly reproduce frequencies above 2,5 ... differ in the audio range. There is nothing of this in AM receivers with a detector - it does not matter which signals to detect (it does not respond to the frequency), as a result, all signals that have passed through the radio path create interference. The disadvantages of a heterodyne receiver include two-way reception: in our example of CW reception, the interference signal at 1902 kHz will also give a difference frequency of 1 kHz and will be received. Sometimes such a hindrance can be eliminated. The fact is that two settings are possible for a signal with a frequency of 1900 kHz - the upper one (the local oscillator frequency is 1901 kHz) and the lower one (1899 kHz). If interference is audible at one setting, then it may not be at another. On the SSB signal, only one setting is possible - 1900 kHz, but all signals with frequencies of 1900 ... 1903 kHz will interfere (see Fig. 2) and cannot be eliminated. This drawback is significant only when receiving in "pile-up", when a lot of stations "huddled together" at close frequencies, hearing, for example, a rare "DX". With normal reception, when there are few stations and there are significant gaps between their frequencies, this drawback is completely invisible. The circuit diagram of the receiver is shown in fig. one.
The input signal from the antenna through a coupling capacitor C1 of a small capacitance is fed to a two-circuit band-pass filter. The first circuit of the L1C2C3C4.1 filter has a relatively high quality factor and, consequently, a narrow bandwidth, so it is tunable in frequency using one section of the dual KPI C4.1. The second circuit L2C7 does not need to be rebuilt, since it is heavily loaded with a mixer, its quality factor is lower, and the bandwidth is wider, so it does not rebuild and passes the entire frequency band of 1,8 ... 2 MHz. The receiver mixer is assembled on two diodes VD1 and VD2 connected in anti-parallel. Through the capacitor C8 (it is also included in the low-pass filter), the local oscillator voltage is supplied to the mixer from the tap of the coil L3. The local oscillator is tuned in the frequency band of 0,9 ... 1 MHz by another section of the KPI - C4.2. As you can see, the local oscillator frequency is half the signal frequency, which is necessary according to the very principle of the mixer. It works as follows. To open silicon diodes, a voltage of about 0,5 V is required, and the amplitude of the heterodyne voltage applied to the diodes barely reaches 0,55 ... 0,6 V. As a result, the diodes open in turn only at the peaks of the positive and negative half-waves of the heterodyne voltage, i.e. twice in a period. This is how the signal circuit is switched at twice the frequency of the local oscillator. The mixer is especially convenient for heterodyne receivers, since the local oscillator signal is practically not emitted by the antenna, being greatly attenuated by the input filter, and does not interfere with others (the first heterodyne receivers sinned in this, in which the local oscillator operated at the signal frequency and it was not easy to suppress its radiation), or its own reception. The local oscillator is made according to the "inductive three-point" scheme on the transistor VT1. Its circuit L3C6C5C4.2 is included in the collector circuit of the transistor, and the feedback signal is fed through the capacitor C9 to the emitter circuit. The required base bias current is set by resistor R1, shunted for high frequency currents by capacitor C10. The converter is designed in such a way that it does not require painstaking work on the selection of the optimal local oscillator voltage on the mixer diodes. This is facilitated by the easy operation of the local oscillator at a low collector-emitter voltage of the transistor (about 1,5 V) and a small collector current - less than 0,1 mA (pay attention to the large resistance of the resistor R2). Under these conditions, the local oscillator is easily energized, but as soon as the oscillation amplitude increases to about 0,55 V at the coil tap, the mixer diodes open at the oscillation peaks and bypass the local oscillator circuit, limiting further amplitude growth. The C8L4C11 LPF is a simple third-order U-shaped filter that provides 18 dB per octave slope (3x) above the XNUMX kHz cutoff frequency. The ultrasonic receiver is two-stage, it is assembled on low-noise transistors VT2 and VT3 of the KT3102 series with a high current transfer coefficient. To simplify the amplifier, a direct connection between the cascades is used. The resistances of the resistors are chosen so that the DC mode of the transistors is set automatically and depends little on temperature fluctuations and the supply voltage. The current of the transistor VT3, passing through the resistor R5, included in the emitter circuit, causes a voltage drop of about 0,5 V across it, sufficient to open the transistor VT2, the base of which is connected through the resistor R4 to the emitter VT3. As a result, opening, the transistor VT2 lowers the voltage at the base of VT3, preventing a further increase in its current. In other words, the UZCH is covered by 1% negative feedback (NFB) for direct current, which rigidly stabilizes its mode. This is facilitated by a relatively large (compared to generally accepted) resistance of the collector load VT3 - resistor R4 and small - resistor R15. OOS does not work on alternating current of sound frequencies, since they are closed through a high-capacity blocking capacitor C6. A variable resistor R3 is connected in series with it - the volume control. By introducing some resistance, we thereby create some OOS, which reduces the gain. This method of volume control is good because the regulator is installed in the already amplified signal circuit and does not require shielding. In addition, the introduced OOS reduces the already small signal distortion in the amplifier. The disadvantage is that the volume is not adjusted to zero, but this is usually not necessary. The phones are connected to the collector circuit of the VT3 transistor (through the XSXNUMX connector), both the alternating current of the signal and the direct current of the transistor flow through their coils, which additionally magnetizes the phones and improves their performance. Establishment of UZCH does not require. About the details. Start your selection with headphones. We need ordinary telephones of the electromagnetic system with tin membranes, necessarily high-resistance, with a total resistance to direct current of 3,2 ... 4,4 kOhm (they are not suitable for telephone sets - they are low-resistance). The author used TA-56m telephones with a resistance of 1600 ohms each (indicated on the case). Also suitable are TA-4, TON-2, TON-2m, still produced by the Oktava plant. Miniature headphones from players with low sensitivity cannot be used in this receiver. The telephone plug is replaced by a standard round three- or five-pin connector from sound reproducing equipment. A jumper is installed between pins 2 and 3 of the pin part of the connector, which serves to connect the GB1 power battery. When the phones are disconnected, the battery will turn off automatically. The former positive terminal of the telephone cord is connected to pin 2, this will ensure the addition of the magnetic fluxes created by the bias current and the permanent magnets of the telephones. The next critical detail is KPI. The author was lucky - he managed to find a small-sized dual KPI from a portable transistor receiver with a built-in ball vernier. You can use KPI without a vernier, while receiving CW stations will not cause problems, but fine tuning to SSB stations will be difficult, since the tuning density of 400 kHz per revolution is too big. Choose a maximum diameter setting knob or build your own vernier using a suitable pulley and cable. KPIs with air dielectric are better, but small-sized KPIs with a solid dielectric from transistor receivers are also suitable. Often they are already equipped with vernier pulleys. The capacitance of the capacitor is not critical, the necessary range overlap can be selected by "stretching" capacitors C3, C5 (their capacitances must be the same) and C2, C6 (the capacitances are also the same). The receiver coils are wound on standard three-section frames used in transistor receivers. If the frames have four sections, the section closest to the base is not used. The coils are evenly distributed in all three sections of the frame, the winding is carried out in bulk. The frames are equipped with ferrite trimmers with a diameter of 2,7 mm. A PEL wire with a diameter of 0,12-0,15 mm is suitable, but it is advisable to use PELSHO, and even better, a litz wire twisted from several (5-7) PEL 0,07-0,1 conductors or a finished litz wire in a silk braid, for example, LESHO 7x0,07. Coils L1 and L2 contain 70 turns each, L3 - 140 turns with a tap from the 40th turn, counting from the output connected to the common wire. The L4 low-pass filter coil is wound on a K10x7x4 ferrite ring with a magnetic permeability of 2000 and contains 240 turns of PEL or PELSHO 0,07-0,1 wire. Its winding in the absence of experience can result in a problem (the author wound it in less than an hour). Use a shuttle soldered from two pieces of copper wire about 10 cm long. At the ends, the wires are slightly parted, forming "forks" into which a thin winding wire is placed. It is better to fold it in half and wind 120 turns, then connect the beginning of one wire to the end of the other (an ohmmeter is needed to identify the leads). The resulting average output is not used. Coil L4 can be replaced by the primary winding of an output or transfer transformer from pocket receivers. If its inductance turns out to be too large and the cutoff frequency of the low-pass filter decreases, which will be noticeable by ear by attenuating the higher frequencies of the sound spectrum, the capacitance of capacitors C8 and C11 should be slightly reduced. In extreme cases, the coil can even be replaced with a resistor with a resistance of 2,7 ... 3,6 kOhm. In this case, the capacitance of capacitors C8 and C11 must be reduced by 2 ... 3 times, the selectivity and sensitivity of the receiver will decrease somewhat. The capacitors included in the circuits should be ceramic, mica or film capacitors with good capacitance stability. Miniature capacitors with irregular TKE (temperature coefficient of capacitance) are not suitable here, they are usually orange. Do not be afraid to use vintage capacitors of the KT, KD (ceramic tubular or disk) or KSO (pressed mica) types. The requirements for capacitors C8-C11 are less stringent, any ceramic or metal-paper (MBM) capacitors are suitable here, except for capacitors made of low-frequency ceramics of the TKE H70 and H90 groups (the capacitance of the latter can change almost 3 times with temperature fluctuations). There are no special requirements for other capacitors and resistors. The capacitance of the capacitor C12 can range from 0,1 to 1 microfarad, C13 - from 50 microfarads and above, C15 - from 20 to 100 microfarads. The variable resistor of the volume control is any small-sized, for example, type SPZ-4. It is permissible to use almost any high-frequency silicon diodes in the mixer, for example, the KD503, KD512, KD520-KD522 series. In addition to the transistor KT361B (VT1) indicated on the diagram, any of the KT361, KT3107 series is suitable. Transistors VT2, VT3 - any silicon with a current transfer ratio of 150 ... 200 or more. A flat six-volt battery was taken from a used Polaroid camera cassette. Other options are also possible: four galvanic cells in series connection, "Krona" battery. The current consumed by the receiver does not exceed 0,8 mA, so any power source will last for a long time, even with long daily listening to the air. The design of the receiver depends on the case that you can pick up. The author used a box for threads made of thick plastic (see the photo of the receiver in "Radio", 2003, No. 1) with dimensions of 160x80x40 mm. Actually, the entire receiver is mounted on the front panel, which also serves as a lid for the box. The panel must be cut from one-sided foil-coated getinax or fiberglass. It is advisable to choose a material with a beautiful non-foil surface (the author has black getinax). Holes are drilled in the panel for the antenna and ground jacks, KPI, volume control, then the foil is cleaned to a shine with fine sandpaper and washed with soap and water. The phone connector is installed on the bottom side wall of the box (Fig. 4).
The battery is placed on the bottom of the box and pressed through the cardboard lining with a bracket made of thin elastic brass or tin, resting against the side walls of the box. The battery terminals are made from ordinary mounting wires. Their stripped ends are inserted into the windows provided in the cardboard battery case before the battery is installed in the receiver. The negative terminal is soldered to the body of the telephone jack, the positive terminal is soldered to socket 2. The connector is connected to the receiver board with four twisted conductors of sufficient length. Installation of the mounted receiver. Those parts, one terminal of which is connected to a common wire, are soldered by this terminal (shortened to the minimum length) directly to the foil. Then the remaining output also serves as a mounting rack, to which the conclusions of other parts are soldered, in accordance with the diagram. It is even recommended to bend one of the connected conclusions in the form of a ringlet or a mounting petal. If the design of the part allows (capacitors of the KSO type, oxide), it is useful to fix its case on the board with a drop of glue. Other mounting petals are the conclusions of the KPI and the volume control. The spring output from the KPE rotor plates must be connected to the board foil with a separate conductor - this will save you from possible frequency jumps when rebuilding the receiver, since the electrical contact through the bearings is by no means the best. When installing the low-pass filter coil, a short piece of a single-core mounting wire is soldered to the board and bent perpendicular to the board. A thick cardboard or plastic washer, a coil, another of the same washer are put on it sequentially and everything is fixed with a drop of solder. The top end of the reference wire must be insulated to prevent a shorted loop. If the upper washer is made wider, then it is convenient to fix the terminals of capacitors C8 and C11 on it. Even without drilling holes, the output can be "melted" through the plastic with a soldering iron. Loop coil frames usually have four pins for PCB mounting. Three of them are soldered to the foil of the receiver board, the rest is used to secure the "hot" output of the coil and as a mounting tab. The distance between the axes of the coils L1 and L2 should be about 15 mm to obtain an optimal connection. If the receiver is supposed to be taken with you on hikes, when wet weather often happens, it is better to fill the turns of all coils with paraffin. For this, a soldering iron and a candle cinder are enough. The same applies to all cardboard insulating parts. An approximate arrangement of parts on the receiver board is shown in fig. 5.
The "instrument" version of the receiver design (for home use) is also possible, when the front panel is located vertically, the antenna jack is on the right, and the volume control is on the left. In this case, it is advisable to install the phone connector on the front panel on the left, next to the volume control, and make the case out of metal to protect against pickups created by other equipment standing on the table. For other receiver design options, the general rules should be observed: input circuits and circuits should not be located close to the local oscillator, it is better to place them on opposite sides of the KPI, the case of which will serve as a natural screen; do not place the heterodyne coil close to the edge of the board in order to exclude the influence of hands on the frequency; space the input and output circuits of the UZCH away to reduce the likelihood of its self-excitation. At the same time, the connecting wires should be short and run close to the plated surface of the board. It is better to do without connecting conductors at all, using only the conclusions of the parts. The more metal connected to a common wire in the structure, the better. It is easy to see from the illustrations that these rules are observed in the proposed design. Tuning the receiver is simple and comes down to setting the desired local oscillator frequency and tuning the input circuits for the maximum signal. But before turning on the receiver, carefully check the installation and eliminate the errors found. The operability of the ultrasonic frequency converter is verified by touching one of the terminals of the low-pass filter coil. A loud "growl" should be heard in the phones. In the operating mode, the noise from the first stage will be weakly heard. It is easiest to check the operation of the local oscillator and set its tuning range of 0,9 ... 1 MHz using any broadcasting receiver with a medium wave range. In this receiver, the local oscillator signal will be heard as a powerful radio station during transmission pauses. A receiver with a magnetic antenna must be placed nearby, and if the receiver has only a jack for connecting an external antenna (now such receivers are rare), then a piece of wire must be inserted into it, brought to the local oscillator coil. In the absence of generation, it is necessary to install a transistor VT1 with a high current transfer coefficient and / or solder a resistor R2 of lower resistance. You can refine the graduation of the scale of the auxiliary receiver using the signals of local radio stations, the frequencies of which are known. In the center of Russia - "Radio of Russia" (873 kHz), "Free Russia" (918 kHz), "Radio Church" (963 kHz), "Slavyanka" (990 kHz), "Resonance" or "People's Wave" (1017 kHz) . The same signals can also be used to calibrate the scale of our receiver. The technique is as follows: tune the auxiliary receiver to the frequency of the radio station, turn on the tuned receiver and change the frequency of its local oscillator with the tuning knob and the L3 coil trimmer until the local oscillator signal overlaps with the station signal. A whistle will be heard in the loudspeaker of the auxiliary receiver - the beats of two signals. Continuing to tune, lower its tone to zero beats and mark a point on the scale - here the tuning frequency of our receiver is exactly equal to twice the frequency of the radio station. If the signal of the station in the auxiliary receiver is completely clogged with the signal of our local oscillator, slightly increase the distance between the receivers. The last operation is setting up the input circuits. Connect an antenna with a length of at least 5 m, you can even indoor. Surely you will already receive some signals. Alternately rotate the coil trimmers L1 and L2 to achieve maximum reception volume. It is more convenient to finally adjust the input circuits in a section of the range free from radio stations, simply to the maximum of the air noise. It should be noted that the L2C7 loop trim has a slight effect on the LO frequency, but this does not matter when tuning for noise. You can make sure that the settings are correct by connecting and disconnecting the antenna: the ether noise should be many times greater than the internal noise of the receiver. Receiver test results. Its sensitivity, measured using a standard signal generator (GSS), turned out to be about 3 μV. This is not surprising given the high amplification of UHF (over 10) and the presence of sensitive telephones. The mixer of the receiver practically does not introduce its own noise, but there is no URF in it. It is preferable to listen to the broadcast in the evening and at night, when the range of 160 meters is "open" (there is a long-range passage of radio waves). In the daytime, you can only hear local stations if they work (and amateurs, knowing the conditions for the passage of radio waves, usually do not go on the air in this range during the day). Not currently having an antenna for the range of 160 meters, the author tested the receiver with a temporary wire antenna no more than 10 m long, including descent. It was stretched from the balcony to the roof railing and fixed there on a pole no more than 1,5 m high. Nevertheless, SSB stations of the European part of Russia from Karelia to the Volga region and the Krasnodar Territory, as well as Ukraine and Belarus, were confidently received. Stations of Spain and Siberia (I name only the most distant ones) were heard by telegraph. "Grounding" on a heating battery or a water pipe significantly increased the volume of reception. Thus, almost everything that can be heard on any other, much more complex receiver was received. Author: V.Polyakov (RA3AAE)
Artificial leather for touch emulation
15.04.2024 Petgugu Global cat litter
15.04.2024 The attractiveness of caring men
14.04.2024
▪ Men and women see differently ▪ Smartphone Gigabyte GSmart GX2 ▪ Vitamin B6 helps you remember dreams better ▪ Firefly Shine Synchronization
▪ section of the site Electrical safety, fire safety. Article selection ▪ Eldorado article. Popular expression ▪ article The name of which world-famous corporation arose due to a spelling mistake? Detailed answer ▪ article Klubnekamysh. Legends, cultivation, methods of application
Home page | Library | Articles | Website map | Site Reviews
www.diagram.com.ua |
See other articles Section 
Latest news of science and technology, new electronics:
All languages of this page