Operating frequency .................................................................. ...............27140 kHz;
Receiver sensitivity, not worse .................................. 5 µV;
UZCH power .................................................. ...................100 mW;
"Calling" frequency .............................................................. ......1.25 kHz.
The scheme of the receiver of the radio station is shown in fig. 1. It is made on the K174XA10 chip and does not have any features.
UHF is implemented on the VT1 transistor. The data of the receiver coils are given in Table. 1.
Table 1
Winding data of receiver coils
|
Coil |
frame, core |
Winding |
|
diam. 5 mm, with carbonyl core |
10 turns PEV-2 dia. 0.47mm |
|
|
2 turns PEV-2 dia. 0.47mm over L1 |
||
|
10 turns PEV-2 dia. 0.47mm |
||
|
60 + 60 turns of PEV-2 dia. 0.1 mm |
||
|
120 turns PEV-2 0 0.1 mm |
||
|
Over L6 10 turns of PEV-2 dia. 0.1 mm |
||
|
MLT-0.25 100 kOhm |
30 turns PEV-2 dia. 0.1 mm |
The dynamic head is placed in a separate case and is connected to the radio station with a flexible shielded wire, in the same case the "RX-TX" button is installed, which switches the radio station and the "Transmission" mode.
Switching is carried out by small-sized relays of the RES80 type with an operating voltage of 8 V. If desired, the output power can be increased by turning on an additional AF amplifier. The scheme of the transmitter of the radio station is shown in fig. 2. The data of the transmitter coils are given in Table. 2.
Rice. 1. 27 MHz radio receiver circuit
table 2
Winding data of transmitter coils
|
Coil |
frame, core |
Winding |
|
diam. 5 mm, with carbonyl trimmer |
10 turns PEV-2 dia. 0.47mm |
|
|
3 turns PEV-2 dia. 0.47mm over L1 |
||
|
13 turns of PEV-2 dia. 0.47 mm, branch from 6 to 9 turns, counting from below |
||
|
MLT-0.25 100 kOhm |
50 turns of PEV-2 dia. 0.1 mm |
|
|
Mandrel diam. 7 mm |
11 turns PEV-2 dia. 0.7mm |
The diagram of the switching unit is also shown in fig. 2. The "RX-TX" button is installed either on the front panel of the body of the portable radio station, or together with the BA1 loudspeaker in a separate case. On fig. 3 shows the supply voltage control circuit; it has small dimensions and is assembled by surface mounting, it is only necessary to set the threshold for the operation of the logic elements of the DD1 microcircuit by adjusting R1 and R2.
Rice. 2. The scheme of the transmitter of the radio station at 27 MHz
Rice. 3. 27 MHz radio voltage control circuit
This unit is especially necessary if the radio is powered by batteries located inside the case.
Coils L4, L5, L6, L7 of the receiver are placed in aluminum screens. You can use the IF circuit from transistor radios.
A detailed description of the radio station and installation are described in the magazine "Radio Amateur", No. 9, 1995.
Technical characteristics of the radio station:
Schematic diagram of the radio station is shown in the figure.
The signal from the WA1 antenna through the XS1 connector goes to the SB2 button, which switches the antenna and the power source of the radio station when switching from reception to transmission. In the circuit diagram, SB2 is shown in the radio receiving position.
In the receive mode, the received signal from the SB2 button is fed to the communication coil L1, and the radio supply voltage is also supplied there. The input circuit C1, L2 is tuned to the operating frequency of the radio station. In UHF, the full inclusion of the input circuit is used due to the large input resistance of the UHF VT1 field-effect transistor of the KP350B type. The UHF gain is set by resistors R1 and R2.
Fig.1
The UHF load is the circuit L3, C4, also tuned to the operating frequency. From the UHF output, the received, filtered and amplified signal is fed through the L4 communication coil to the DA1 chip of the K174XA42 type (its analogues are TDA7000, KC1066XF1). More information about this chip can be found in.
Pin 6 of the DA1 microcircuit receives an RF voltage from the local oscillator on the VT5 transistor. The input signal goes to pin 13. The output low-frequency signal from the volume control engine R5 goes to the ULF, made on a DA2 chip of the K174UN4A type, and from its output to the dynamic head BA1.
In the transmission mode, the SB2 button is transferred to the lower position according to the diagram, while the supply voltage is supplied to the microphone amplifier and the output stage of the transmitter. The master oscillator on the transistor VT5 is constantly running. In the transmission mode, the VD3 diode is closed, and the oscillator frequency on the VT5 transistor rises by the value of the intermediate frequency. Frequency adjustment over the range is performed by the core of the L5 coil, and its shift to an intermediate frequency is performed by capacitor C36.
In the circuit L7, C39, a signal is allocated with an operating frequency - in the transmit mode, and with a shift by the IF down - in the receive mode. From the coupling coil L6, the signal of the quartz oscillator is fed to the DA1 microcircuit, and from the collector of the transistor VT5 to the base of the transistor of the output stage of the VT6 transmitter of the KT646A type. The output stage of the transmitter operates in mode C, its load is a double P-filter on the elements L8, L9, C41 ... C44. The circuit L8, C42 is tuned to the second harmonic of the operating frequency. Further, the signal from the transmitter output through the SB2 button and the XS1 connector enters the WA1 antenna. A dynamic head BA1 with a resistance of 8 ... 50 Ohm is used as a microphone.
The microphone amplifier of the radio station is built on transistors VT2 and VT3. It slightly limits the low-frequency signal in amplitude, while expanding the signal spectrum. The low-frequency signal is fed to the low-pass filter, made on the transistor VT4 and elements C27 ... C29, R12, R13.
The filtered low-frequency signal from the resistor R19 is fed to the VD4 varicap of the KV109G type. Resistors R21 and R20 on the varicap set a constant voltage of +1.5 V. In the master oscillator, frequency modulation of the operating frequency is carried out in the transmission mode with a deviation of 2.3 ... 3 kHz.
SA1 is used to turn on the radio.
The printed circuit board of the radio station is made of double-sided foil fiberglass with a thickness of 1.5 mm, and the foil on the side of the installation of the elements is completely preserved and is removed by countersinking only under the leads that are not connected to a common wire.
The radio station uses resistors of the type MLT-0.125, S2-23, S2-33 or the like. Variable resistor R5 - type SP4-GM with a switch (SA1). Electrolytic capacitors - type K50-35, K50-41, K50-16 for an operating voltage of at least 6 V, the rest of the capacitors - types KM4, KM5, KM6, K10-17. Trimmer capacitor - KPKM type. Transistors VT3 and VT2 - type KT3102E (others can be used - KT315, KT342, KT358, etc.), VT5-KT368A, B, KT315, KT316, KT325, KT355, KT399, etc. Transistor VT6 - type KT646A, you can also use KT603, KT608, KT606, KT610, KT904, KT911, VD4 varicap - KV109, KV110, KV124, D901 with any letter index. When replacing components, be aware that the use of some of them will entail an increase in the dimensions of the radio station and power consumption.
Inductors L1, L2, L3, L4, L5, L6, L7 are wound on frames with a diameter of 5 mm with tuning cores from SB-9 or from intermediate frequency filters of SV-, LV-radio receivers. Coil L1 is wound on top of L2, L4 is wound on top of L3, and L6 is wound on top of L7. Coils L8 and L9 - frameless, on a mandrel with a diameter of 3 mm. Coils L10 and L11 - on ferrite rings of size K7x4x2 with a permeability of 300 ... 1000. All coils, except frameless ones, are wound with PEV-2 wire and impregnated with BF-2 glue. The winding data of the inductors are shown in the table. Frameless coils are wound with a wire with a diameter of 0.5 mm.
|
Number of turns |
Wire diameter, mm |
Frame diameter, mm |
|
Setting up a radio station start with the radio. By applying the supply voltage, the operation of the low-frequency amplifier of the DA2 microcircuit is checked. When a signal generator with a voltage of 100 mV and a frequency of 1 kHz is applied, the output voltage of about 1 V should be at pin 8. The volume control should be at maximum. Next, a voltage is applied with an operating frequency and a deviation of 3 kHz to the XS1 connector, and by rotating the cores, the circuits L2, C1 and L3, C4 are adjusted to the maximum volume. In this case, you may need to more accurately tune in to the operating frequency with a tuning capacitor C36. Then the sensitivity of the receiver is measured - it must be at least 0.2 μV with a signal-to-noise ratio of 3:1.
The setting of the transmitting path begins with the master oscillator. It usually starts working right away. The core of the L5 coil must be set to the operating frequency. Then, by rotating the core of the coil L7, its output signal is maximized, controlling the level on the collector of the transistor VT5 using an RF voltmeter. Then, by connecting a resistor with a resistance of 51 ohms and a power of 0.25 W as an antenna equivalent, stretching and compressing the turns of the coils L8 and L9 achieve the maximum output voltage on it, which should be at least 5 ... 7 V.
Tuning the modulator comes down to setting a voltage varicap of +1.5 V on the cathode. The low-frequency amplifier and filter start working immediately. It is only necessary to check the operation of the tone call generator by switching the SB1 button to the lower position according to the diagram.
The spiral antenna is wound on a polyethylene rod of a central dielectric from a RK-50 or RK-75 cable with a diameter of 7 ... 8 mm with a PEV-2 wire with a diameter of 0.5 mm, coil to coil, for a length of 160 mm. One end of this winding is fixed on the rod, the other is connected to the input of the radio station. The core and braid have been removed. From above, the antenna is wrapped with insulating tape, or a PVC tube of the appropriate diameter is put on it.
The antenna of the radio station is quite narrow-band, and requires tuning for effective operation. To tune, you need a simple resonant wavemeter to the desired frequency. By unwinding or winding the turns of the antenna winding, it is tuned to the maximum deviation of the arrow of the resonant wavemeter.
This completes the antenna setup.
Tests of this radio station showed that the communication range in open areas reaches 7 ... 8 km, and in densely built-up urban conditions - 2.5 ... 3 km.
For the purchase of printed circuit board drawings and assembly drawings, please contact the author by folding an envelope with a return address and Russian stamps into a letter.
Literature
Mini VHF FM Transmitter
A.Kichigin
RL 7/2000
I propose a radio microphone circuit (Fig. 1). Power - 1.5 V from the battery. Range - about 100 m, in line of sight. Consumption current - no more than 6 mA.
One flashlight battery is enough for 48 hours of continuous operation. The board (Fig. 2) is made of double-sided foil fiberglass. Coils L1 and L4 are wound on a plastic case of the transistor VT2 (KT368) (this transistor is not suitable in a metal case).
Coil L1 contains 1 turn of PEL wire 00.3 mm; L4-4 turns PEL 00.3 mm. Coil L2 is frameless, wound turn to turn on a mandrel 06 mm and contains 22 turns of PEL wire 0.6 mm. L3 is wound in bulk on a resistor of 100 ... 200 kOhm and contains 60 turns of PEL wire 00.11 mm. The battery is located directly on the board and is fixed with a brass plate, which is curved in the shape of the battery. It is inserted into the holes of the board and soldered from below. Pieces of wire are inserted into points X1 and X2 and soldered to obtain a negative battery contact. When setting up, you need to shift or stretch the turns of the coil L4, and, if necessary, and select the capacitor C5 to get the carrier into the desired range (30, 66, 108 MHz). Resistor R5 sets the required level of frequency deviation. After tuning to the required part of the range, the capacitors C7 and C8 achieve the maximum signal power.
For fixation and rigidity of the L4 coil, it is desirable to impregnate it with paraffin together with VT2.
This receiver receives AM and FM stations in the 27 MHz band. Despite the rather simple scheme, the receiver is highly sensitive and can be used as part of remote control systems, individual calls, burglar alarms, etc.
The circuit diagram of the receiver is shown in fig. 1.
Rice. 1. Receiver circuit at 27MHz
The high-frequency amplifier is assembled on a low-noise field tetrode of the KP327A type. The use of a field effect transistor in UHF can significantly reduce the radiation of the local oscillator to the antenna. The antenna itself, together with the inductor L1, capacitor C1 and the input capacitance of the transistor, form a filter tuned to the middle frequency of the 27 MHz range. The frequency of self-oscillations (10 ... 20 kHz) of the regenerator is suppressed by an active filter with a gain of about 20. The degree of feedback in the regenerator (VT2) is selected by a variable resistor R5 until the highest quality reception of radio signals is obtained.
An operational amplifier DA1 of the K140UD6 type is used as a low-frequency amplifier and an active filter. It is possible to connect high-resistance telephones of the “TON” type to the output of the receiver.
Details
The inductor L1 is wound with a PEV-2 wire with a diameter of 0.4 mm on a frame with a diameter of 8 mm and contains 20 turns.
Coil L2 contains 2 turns of wire with a diameter of 0.1 mm, wound over coil L3.
Coil L3 contains 15 turns of wire with a diameter of 0.1 mm on a frame with a diameter of 8 mm.
Coil L4 contains 45 ... 60 turns of PEV-2 wire with a diameter of 0.5 mm on a frame with a diameter of 10 mm.
A blog for beginner radio amateurs who want to make their first radio station with their own hands, master and understand how the receiver and transmitter work. The author introduces you to a simple radio designer for making the simplest radio station for the 50 MHz range with your own hands. This radio DOES NOT REQUIRE any permission or call sign to operate this radio. It is necessary to collect two radio stations. The practical application of radio stations will allow you to understand some of the subtleties of setting up equipment and antennas, as well as the passage of radio waves. Walkie-talkies allow you to conduct experiments to change or improve the circuit without a serious risk of damaging the elements. Radio stations have a reserve for modernization, which will significantly increase the reliability and range of radio communications. Radio stations operate with amplitude modulation in half-duplex mode. A real radio amateur is one who has assembled his own radio station at least once in his life!
Immediately warning. If you want to assemble a cheap walkie-talkie not for study or experimentation, then you have come to the wrong place. Buy this one right now LPD or a couple of these walkie-talkies because you won't be interested anymore.
When assembling a radio station, you must have experience in soldering components, skills in determining the ratings of components and mounting them on printed circuit boards by soldering. The tool for work is a low-power soldering iron with solder and rosin, wire cutters and a Phillips screwdriver.
The basis of the designer is a set of radio components JC986A, which includes all the necessary components (except for a 9V battery) to assemble one walkie-talkie in the range of radio telephones (frequencies around 49.8MHz). In total, you need to collect at least two walkie-talkies. All details of the designer are shown in the photo. The case is made soundly, but not from high-impact polystyrene. All plastic parts fit into place without any problems. The board withstood all the soldering and the elimination of installation errors, the tracks did not peel off. All tracks are covered with flux, soldering was carried out without problems. The completeness of the parts was complete.
Set (in polyethylene)
Kit details
Housing and plastic parts
Parts specification
Printed circuit board
PCB part side
walkie talkie speaker
Radio outline
The walkie-talkie diagram is attached and it is printed in Chinese style, like their characters. The meaning of the circuit is hidden in the drawing of the circuit. The author redrawn the diagram for a better understanding of its work. See photo.
The radio is controlled by two switches. The non-fixed switch S1 switches the mode of reception and transmission of the radio station (in the diagram, the switch is in the receive mode). Switch S2 supplies power to the radio. Transistor Q1 operates as a super-regenerative receiver. The RF signal to the receiver is supplied from the Ant antenna and the L1 coil to the C1T1C4 circuit. The reception frequency is mainly determined by this circuit. The resonance frequency of the circuit can be changed with a tuning core. When switch S1 is switched to the transmission mode, the receiver circuit switches to the RF oscillation generator mode at the receive frequency. A transformerless bass amplifier is assembled on transistors Q2-Q5. In the LF reception mode, the receiver signal through the chain R5, C10, C14 enters the VLF input and is amplified. The ULF load will be the SP speaker. In transmission mode, the speaker is connected by switch S1 to capacitor C14 (it becomes a microphone) and the ULF amplifies the signal from the speaker. The ULF load becomes the RF generator, which is supplied with an alternating voltage from the midpoint of the ULF amplifier through the limiting resistor R9. The AC voltage modulates the RF output signal to the antenna. The antenna is connected through an extension coil - choke L1. The board provides space for three more elements of the tone call during transmission - R10, C7 and a button (these parts are not included in the kit).
Step 1. After receiving the parcel, check the completeness of the body parts and radio components. Study the label. Resistor values are color-coded. Reading key is attached on the page. Do not confuse the L1 inductor with resistors, it is much larger. Small parts are best stored in a closed box. Examine the printed circuit board from the side of the parts to understand where to mount the parts.
Installation drawing board
The key to the resistor code
Step 2 We start soldering by installing resistors. We form the electrodes of the resistor. We solder it to the board and cut off the protruding electrodes with wire cutters. So we install all the elements with long electrodes. The location of each element is marked on the board. Be careful - don't make mistakes. Solder all the resistors in series. See photo.
Step 3. Solder the extension coil L1. See photo.
Step 4. Solder the capacitors. See photo.
Soldered resistors
Capacitors are soldered
Step 5 Solder the electrolytic capacitors. The elements have installation polarity. The correct installation of the negative electrode is shown in the photo.
Step 6. Solder the T1 loop coil, S1 switch. The metal case of the switch must be soldered to the board.
Correct installation on the board
Switch setting S1
Step 7. We solder the transistors, strictly adhering to the markings on the board. The position of the body of each specific transistor on the board is shown in the figure.
Step 8. From pieces of cut electrodes, solder jumper J1 to the board. See photo.
Collected Fee
Step 9. We check the correctness and quality of the installation of the elements. You can wash the board from flux residue with alcohol. We install a plastic switch key reception - transmission. We fix the board to the case with two self-tapping screws.
Step 10. Install the antenna. We install a plastic cap on top of the antenna. We solder the connection wire to the board to the antenna lobe. Solder the S2 switch with pieces of conductors from the parts. Check the operation of the power switch. The shift lever should move when the plastic knob is turned.
Checking the RDS setting of the receiver
We repeat these operations at a distance of 5 and 20 meters. The setting is best done outdoors. Do not forget, the radio stations are simple and the signal will be affected by objects directly located close to the antenna, and signal capture by the receiver may not work. It is very convenient to use a USB receiver when setting up the SDR. Watch the video. It will allow you to evaluate the signal strength, frequency, frequency stability and modulation quality. We assemble the case of the second radio station.
This completes the tuning of radio stations in such a circuit design. The communication range between radio stations in open areas is about 100 meters. But this is not the limit, with appropriate refinement or simply connecting the appropriate antennas, the communication range can easily be several kilometers. With interest in the topic, the author will publish part of the improvements. The station is interesting for its range and amplitude modulation. Interference by outsiders in your conversations is possible, but unlikely. The radiated power at the radio station's antenna is below the limits requiring authorization or registration.
The modern element base makes it possible to create radio-electronic devices with excellent technical characteristics, minimal dimensions and low power consumption.
Of course, for radio amateurs living far from large cities and regional centers, the possibility of acquiring foreign integrated circuits is practically not real, although they are relatively inexpensive. However, this does not mean that the design of devices using modern ICs should be stopped.
The attention of radio amateurs is offered a variant of a portable radio station, very similar to the Hummingbird radio station. Compared to Hummingbird, the described design has a higher output power, better sensitivity of the noise suppression system (SNR), and also uses a slightly different inclusion of the IC and transmitter transistors.
However, it should be noted that the characteristics of the radio station depend on many factors, therefore, when repeating the design, deviations of the values up or down from those indicated above are possible.
On fig. 1 shows a circuit diagram of the radio station. In the transmission mode, the signal from the BM1 microphone is fed to the stages of the DA1 MC2833R transmitter microcircuit. IC DA1 performs the functions of amplifying the low-frequency signal, limiting it, generating a high-frequency signal and modulating it.
The microcircuit also includes two transistors capable of operating at frequencies up to 200 MHz (according to passport data - up to 500 MHz). The signal from the RF amplifier (terminal 14 DA1) is fed to the base of the first transistor (terminal 13) through the resonant circuit L2, NW, on which the main signal of the transmitter (or harmonic, if a quartz resonator is used at a non-fundamental frequency) is selected.
In the collector circuit (pin 11), a resonant circuit L3, C8 is installed, tuned to the transmission frequency. From the coupling coil L4 through the coupling capacitor C10, the modulated signal of the operating frequency is fed to the line of amplifying stages on transistors VT1., VT2 and then through the double P-loop to the antenna WA1.
Rice. 1. Schematic diagram of a homemade radio station at 27 MHz, power 3 watts.
In the receive mode, the signal from the antenna WA1 through the capacitor C27 is fed to the communication coil L12. Now the second transistor of the DA1 chip performs the function of a resonant UHF receiver. The use of a bipolar transistor as a UHF, of course, cannot be considered the optimal solution. It would be better to use a field effect transistor (for example, KP307, KP350).
However, when developing the radio station, the goal was to create a design with the least number of parts, overall dimensions and cost. For lovers of experiments, we can recommend using the second transistor IC MC2833 as part of the transmitting path, and using a field-effect transistor as a UHF receiver.
Further, the received signal is fed to the multifunctional chip DA3, where the high-frequency signal with frequency modulation is completely converted into a low-frequency information signal. An adjustable noise suppression system is assembled on this IC. From the DA3 output (pin 9), through the volume control resistor R15, the low-frequency signal is fed to the ULF, made on the DA2 MC34119R IC.
Switch SA2 turns off the standby mode in cases where the signal of the received radio station is very low. Transistors VTZ and VT4 are used as an SPS amplifier.
When a received signal appears, the noise level is significantly reduced and the transistors put the DA3 chip into working condition. The rest of the time this IC is in the “off” state. This allows you to significantly reduce power consumption during standby reception.
The microcircuits are powered by integrated stabilizers DA4, DA5 78L06, so the radio station remains operational when the supply voltage drops to 6 ... , not providing communication at the proper distance.
One of the disadvantages of this design can be considered the need to select the quartz of the receiver and transmitter with an IF difference (usually 465 kHz, but 455 kHz is also possible). However, this gives a gain in the size of the device as a whole and improves frequency stability.
Tuning the radio station can be performed by a beginner. However, the radio station should be assembled in stages. That is, they set the elements of those cascades that will be tuned at the current time. This will avoid many problems in setting up the entire device. First, the operation of the receiver is checked, and then the transmitter.
1. Receiver:
2. Transmitter:
It should be remembered that the transmitter power amplifier must be tuned with an antenna or its equivalent connected! First, we set up the circuit L5, C11, and then the P-circuit. As a result, we adjust all the transmitter circuits (if necessary) until the maximum performance of the device used is reached and tune the UHF receiver circuits L11, C26 and L14, C28 into resonance. Now you can adjust the SNR with a variable resistor R23 according to the received transmitter signal.
In both modes (reception and transmission), it will be necessary to tune the RF circuits into resonance. By changing the inductance of the coil L1, it is necessary to set the operating frequency (according to the receiver). Resistor R9 adjust the gain of the microphone amplifier. The greater the resistance R9, the greater the gain. In receive mode, you should adjust the IF circuit according to the received signal (or pre-tune to the maximum noise level with the PN system turned off; and finally - according to the received signal). Then adjust the contours of the input UHF.
Finally, the P-loop is tuned to the maximum current in the antenna in transmit mode. It is better to make the adjustment with a non-resonant wavemeter according to the maximum deviation of the instrument pointer. The antenna can be used both telescopic and spiral. It all depends on the "taste" of the designer. Be sure to remember that without an antenna or with a poor-quality connection, you can damage the output transistor of the transmitter power amplifier, so its installation must be taken with all responsibility.
The SPS switch SA2 must not be connected between the base of the VTZ transistor and the common wire, but between the VTZ base and the right (according to the diagram) output of the DA5 stabilizer through a 68 kΩ resistor.
When the SA2 contacts are closed, the operating point of the VTZ transistor is shifted, which turns off the system and allows you to listen to weak signals under poor reception conditions.
To adjust the SNR response threshold, it is necessary to temporarily install a variable resistor with a resistance of 27 kOhm instead of resistor R22. The R23 resistor slider is placed in the middle position and, by rotating the temporary resistor slider, they find a position at which the SNR switches in the absence of a transmitter signal. Then, having measured the resistance of the temporary resistor, a constant resistor is soldered instead.
Improved transmitter power amplifier. To do this, the values of resistors R5 and R7 were changed, amounting to 1 kOhm each, and resistors R* 33 kOhm and R** 47 kOhm were added (Fig. 2). Since in this case the operation of the power amplifier stages occurs in class A, the quiescent current of the transistors increases. However, in this case, there is a noticeable increase in the gain and, accordingly, the signal transmitted to the antenna, which in turn increases the communication range.
Rice. 2. Refinement of the transmitter power amplifier, circuit.
Winding data of inductors are given in table. 1.
Inductors L6, L9, L10 are standard type D-0.1 with an inductance of 110 μH. The IF circuit coil is wound on the SB-12 core. Adjustment is made by rotating the core. Frameless coils L7, L8 of the P-circuit are tuned by stretching or compressing the turns.
If you could not find the MC34119R chip, do not despair. The silent tuning function can be performed on another widespread LM386 chip that does not have an “ON / OFF” input, or simply on transistors according to any known scheme. An example of using the LM386 IC as an ULF receiver is shown in fig. 3. In this case, the transistor VT4 and the resistor R20 are not installed, and points A, B and C, shown in fig. 1 are interconnected respectively.
Rice. 3. An example of using the LM386 IC as an ULF receiver.
Tab. 1. Winding data of inductors
| Coil | Frame diameter, mm | Core | Number of turns | Wire diameter, mm |
| L1 | 5 | from SB-12 (rigger) | 15 | 0,3 |
| L2, L3, L5, L11, L14 | 5 | from SB-12 (rigger) | 7 | 0,5 |
| L4 | over L3 | - | 3,75 | 0,5 |
| L12 | over L11 | - | 3,75 | 0,5 |
| L13 | over L14 | - | 3,75 | 0,5 |
| L7, L8 | 5,5 | - | 8 | 0,8 |
| L6, L9, L10 | - | standard choke D-0.1 | - | - |
| L15 | 4 | SB-12 (complete) | 80 | 0,1 |
The PCB drawings are mirrored (Fig. 4 and Fig. 5 - especially for the “printer” manufacturing method. The dimensions of the printed circuit boards: the transmitter and UHF receiver board 60x67.5 mm; the receiver board - 57.5x35 mm. The quality of the printed circuit boards at using the method below is pretty good.
1. In a graphic or text editor, select the required size of the printed circuit board drawing. We print it with the maximum consumption of toner on a laser printer on paper from any poster. Print on the back (white) side. The paper should have a glossy finish. Do not print on plain paper. You can’t touch the finished drawing with your hands - greasy spots will remain and the toner will not stick to the foil.
2. Cut out the printed pattern with a 2 cm border. We impose the resulting workpiece on a foil fiberglass treated with fine sandpaper, cut 7 ... 10 mm more than necessary on all sides (do not touch with your hands, otherwise the toner will not stick to the foil!), so that the toner is attached to the foil, and wrap the paper.
Rice. 4. Printed circuit board of the transmitter.
Rice. 5. Printed circuit board of the receiver.
We put it all on a hard surface and iron it for 1 minute. Time can be chosen experimentally. Then we let the fiberglass cool a little and lower it into very warm, but not hot water. After 20 minutes, carefully roll the paper into lumps until there is no paper left on the foil. In case the paper remains in some places, don't worry - the acid (or other pickling solution) will do the trick.
3. We lower the board into the etching solution. We poison. We wash. Cut to required size.
With careful observance of the above points, the accuracy will depend on the preparation of the surface of the fiberglass. Otherwise, the paper will peel off along with the toner.
