Schematic of a 430 MHz walkie-talkie. Radioamateur designs and sale of radio equipment. For the scheme "Experimental detector VHF-microwave receivers"

Transmitter at 430 MHz. designed to operate on the air in the range 430 ... 440 MHz. In conjunction with transmitters at 28 MHz and a converter for 430 MHz. it operates in AM, FM, SSB and CW modes on two parts of the band: 432 ... 434 and 434 ... 436 MHz. output power transmitter at a load of 75 ohms 5 watts. The supply voltage of the output stages is 27 V and preliminary - 10 V.

principled transmitter circuit at 430 MHz. shown in Fig.1. It consists of a balanced mixer and a linear power amplifier.

The balanced mixer is assembled on transistors V1 and V2. The emitters of these transistors are supplied with a local oscillator signal with a frequency of 404 or 406 MHz from the converter to 430 MHz., and to the base of the transistor V1-signal with a frequency of 28 ... 30 MHz from a transmitter at 28 MHz. At the output of the balanced mixer, the L1C4 circuit emits a signal with a frequency of 432 ... 434 or 434 ... 436 MHz. The mixer is balanced using resistor R5. Further, the signal from the mixer output is fed to a two-section filter formed by L2C7 and L3C8. The use of a balanced mixer and a two-stage filter in transmitter made it easy to solve the problem of suppressing the local oscillator signal and other conversion products by 40 ... 45 dB.

The linear power amplifier is five-stage, made on transistors V3-V7. Coordination between the two-section filters and the first stage was achieved by selecting the capacitance of the capacitor C9 and connecting this capacitor to the corresponding point of the coil L3. Coordination between the first and second stages depends on the capacitance of the capacitors C12 and C13, as well as the points of connection of these capacitors to the coil L5. Coordination between the second and third, third and fourth, fourth and fifth stages is performed using L-shaped communication circuits. Optimal matching is achieved by selecting capacitors C17, C21, C25 and changing the capacitance of trimmer capacitors C18, C22, C26. The output stage load is the L17C30 circuit. In this case, the capacitance between the output transmitter and housing is provided by the mounting capacity and high-frequency cable connected to socket X6. Feed-through capacitors and high-frequency capacitors of the KDU type are installed in the power circuits. Shielding between the stages and decoupling between them along the power circuits ensured reliable and stable operation of the transmitter.

Transmitter at 430 MHz. assembled on a silver-plated chassis measuring 211 x 57 x 32 mm, made of 1 mm thick brass sheet. The chassis is divided into compartments by partitions, on which feed-through capacitors are installed. The placement of elements in the chassis compartments is shown in fig. 2. Mounting transmitter volume. When performing installation, special attention is paid to the minimum length of the leads of the elements.

Figure 2. Transmitter at 430 MHz.

The following parts are used in the transmitter: fixed resistors of the MLT type with a power of 0.25 W; R17, R18 - 0.5 W; variable resistor R5 type SP5-2 or SP5-3; capacitors C1, C29 type KM-5; C2, C3, C5, C9, SP, C12, C14, C16, C17, C20, C21, C24, C25, C28 - KDU; C4, C7, C8, C13, SZO - KT2-17; C6, SU, C15, C19, C23, C27 - CFT; C18, C22, C26 - PDA-MP.
GT329A transistors can be replaced with GT329 or GTZZO transistors with any letter index, KT911A-KT911B transistors, KT610B - KT610A transistors.

Capacitors C6, CIO, C15, C19, C23, C27 are installed on the partitions, SP, C16, C20, C24, C28, C29 are soldered to the partitions and terminals of the through capacitors, C4, C7, C8, C13, C18, C22, C26, SZO mounted on the bottom of the chassis.
Coil L1 is made of PEV-2 1.3 wire 80 mm long. Before installation, the wire is given a C-shape. Coils L2, L3, L5 are also made of wire PEV-2 1.3. They contain one turn 0 10 mm each with a winding pitch of 5 mm, a ground lead 27 long, and a “hot” lead -11 mm. Lines L4, L6, L9, L13, L16 are pieces of PEV-2 0.8 wire 42 mm long. Before installation, they are given an arcuate shape. Lines L7, Lll, L14, L17 are made of silver-plated brass strip 1 mm thick, 4 mm wide and 48 mm long. Before installation, they are also given an arcuate shape. Coils L8, L12, L15 frameless, Ø 4 mm. They are wound with PEV-2 0.5 wire and contain four turns each.
Transistors V4-V7 are equipped with a common radiator. To install these transistors, appropriate holes are drilled in the bottom of the chassis and heatsink.
Collector currents of transmitter transistors in the absence of input signals are as follows: 2.5...3 mA (V1+V2); 4...5 mA (V3); 50....70 mA (V4); 40...60 mA (V5, V6); 30...50 mA (V7). If necessary, the transistor currents are adjusted by resistors R8, R11, R3, R16 and R18. The tuning resistor R5 is set in such a position that the voltages at the bases of transistors V1 and V2 are the same.

For settings Transmitter on 430 MHz. requires an RF generator tuned to 434 MHz, a wavemeter and a 75 ohm load. A load with a resistance of 75 ohms is connected to the output of the transmitter with a PK-75 cable with a length of at least 1 m. Then the base of the transistor V1 is shorted to the case and a signal with an amplitude of not more than 50 mV is sent from the RF generator to socket X2. All circuits are tuned to resonance using trimmer capacitors C4, C7, C8, C13, C18, C22, C26 and C30. The tuning frequency of the contours is controlled by a wavemeter. As the signal at the output of the transmitter increases, the input signal of the RF generator decreases. In the future, if necessary, capacitors C17, C21 and C25 are selected, the point of connection to the circuits of capacitors C9, C12, C14 and again all the circuits are tuned to resonance. At the next stage of the settings, remove the jumper from the base of the transistor V1, set the frequency to 405 MHz on the RF generator, and use the resistor R5 to balance the mixer according to the minimum signal at the transmitter output.

When input signals are applied to sockets X1 and X2 from a 28 MHz transmitter and a 490 MHz converter, the 430 MHz transmitter is tuned and checked with a wavemeter or spectrum analyzer. In this case, an RF generator is not needed.

In customized transmitter, when a signal with a frequency of 29 MHz with an amplitude of 300 mV is applied to the input X1 and a signal with a frequency of 404 or 406 MHz with an amplitude of 20 mV is applied to the input X2, the collector current of the transistor V7 should be about 350 mA. A smooth increase in the amplitude of the input signal with a frequency of 29 MHz should lead to a smooth increase in the collector current of the transistor V7. This will indicate the correct operation of the transmitter.

Transmitter at 430 MHz.

IN AND. humpbacked
Amateur VHF radio complexes

For the scheme "Super-regenerative receiver at 90 ... 150 MHz"

Radio reception Super-regenerative at 90 ... 150 MHz L1 - 2 turns, L2 - 4 turns on a frame with a diameter of 8 mm, PEL 0.8 wire. The inductor contains 60 turns of PEL 0.1 wire on a MLT 0.5 resistor. Variable capacitors with an air dielectric. - matching from a pocket radio. Mounting on "patch" according to the method of Zhutyaev. ("73 Magazine", Feb. 1974, p. 100) ...

For the circuit "Receiver on the chip TDA7000 (174XA42)"

Radio receptionRadio receiver on the microcircuit > TDA7000 (174XA42) / img / tda7000.gif The frequency range of the microcircuit is 1.5-150 MHz. printed circuit board side elements Literature: 1. K174XA42 - single-chip FM receiver. Radio N 1 1997 2. Single-chip FM receivers. Radio N 2 19973. Radio receivers on the K174XA42A chip. Radio N 5 1997....

For the scheme "Super-regenerative receiver at 144 MHz"

Radio receptionSuper-regenerative at 144 MHz as shown below scheme A super-regenerative receiver can operate as part of a simple portable radio station on the 144 MHz band. Scheme quite simple and has no special features. The receiver sensitivity is approximately 10...15 µV. scheme made on a printed circuit board. Unfortunately, I didn’t save the printed circuit board pattern after it was assembled (NB). The L1 coil contains 3 turns of “silver” with a diameter of 0.8 mm, frameless - on a mandrel with a diameter of 6 mm, winding length 4 mm. Dr1 - standard 25 μg. Dr2 - contains 250 turns of PEV 0.1 wire on an H1000 ferrite ring with a diameter of 8 mm. Transformer Tr - output from a transistor radio, if high-resistance telephones are used, then it is not needed. It is desirable to use more modern transistors ....

For the scheme "Experimental detector VHF-microwave receivers"

Radio receptionExperimental detector VHF-microwave receiversDetector for the range of 100-200 MHz Scheme The receiver, shown in Fig. 1, uses a tuned line in a case soldered from copper or foil-coated fiberglass. Coil L2 contains 4 turns of silver-plated wire. The inner diameter of the coil is 12 mm, the winding length is 12 mm. The withdrawal is made from the middle. Coil L1 is made in the form of a single turn over L2. Capacitor C2 is made of a copper plate measuring 25x50 mm with a Teflon gasket 0.125 mm thick. You can use a conventional RF reference capacitor. Receiver useful when setting up microwave equipment as a wavemeter. Radio amateur UA3ZNW turned the same one into direct conversion (Fig. 2). Capacitor C2 is the side of double-sided fiberglass from which the resonator was made. Triac ts112 and circuits on it When using a local oscillator and ULF from the book by V. Polyakov "Direct conversion receivers for amateur communications" (M. DOSAAF 1981, p. 64), this provided a significantly better reception than that given in the specified article with a two-transistor UHF on field-effect transistors KP303! The local oscillator was assembled on the wall of the resonator. At

For the circuit "VHF receiver with FM on a specialized microassembly KXA058"

For the scheme "Direct conversion receiver"

For the scheme "Simple KB receiver"

For the scheme "SIMPLE HF FM RECEIVER"

For the scheme "Theft indicator"

The proposed device consists of a miniature VHF transmitter, which is powered by a rechargeable battery, and an FM radio receiver with a prefix in the car owner's apartment. A miniature transmitter (Fig. 1) is installed before parking the car at night in such a place that it is not immediately detected by the hijacker. An FM receiver can be made by yourself according to any known scheme or used by an industrial one that has a VHF band. When the transmitter emits and stays in the "radio visibility" zone of the receiver, the hiss disappears at the output of the latter, and the transistor VT2 (Fig. 2) is closed, since there is no signal at the output of the FM receiver and there is no voltage on the secondary winding of the transformer T1. Transistor VT1 is open, relay K1 is on. When the car drives away a few meters, the power of the VHF transmitter becomes insufficient to trigger the receiver's squelch, resulting in noise. An alternating voltage appears at the output of the transformer T1, which is rectified by the VD1 diode and filtered by the capacitor C8. VT1 opens, relay K1 turns off and, with normally open contacts, turns on an audible alarm. If the hijacker has detected a VHF transmitter and disconnected the power, it will still beep. Yakovlev, Nizhnevartovsk...

It was manufactured using practically the same technology and on the same element base as the 1200 MHz beacon. Perhaps the only difference is that I still got the power amplifier line of our beloved MITSUBISHI company and put it in this beacon. Fortunately, 430 is not 1200 for you, buying the right piece of iron here or at 144 MHz is a couple of trifles.

"And why do you need them, these radio beacons?!"- the author has already answered this question in his article about beacon at 3579.5 kHz.

The radio beacon is assembled in a standard purchased silumin box measuring 110*60*30 mm. Attached to the side is a BNC-female connector, power and fan toggle switches, a smooth beacon power control and "+" and "-" terminals. A cooler consisting of an aluminum heatsink and a standard 50mm CPU fan is placed on top of the main body with thermal paste. At a power of less than 0.5 W, the fan can be turned off, the existing passive heatsink is enough anyway.

The circuitry and PCB of the VCO is exactly the same as the 1200 MHz radio beacon. But unlike him, the photo of the GUN with the still unsoldered screen has been preserved and I am happy to post it here:

In this photo, the little blue one on the right side of the board is a 27 nanohenry chip inductor.

The main, so to speak, "motherboard" board is drawn "from scratch" in Corel Draw and, together with the VCO board, is made by the method laser ironing technology.

Here is a photo of the finished beacon:

On the right in the penultimate photo you can see hermetically (well, almost hermetically :-)) a sealed double output P-filter.

The functions of the ATtiny2313 microcontroller are almost the same as in radio beacon at 1200 MHz. Only the division coefficients prescribed in the synthesizer and the modulating frequency of the tone telegraph differ: the latter was done on purpose so that without looking at the receiver screen one could say with confidence by ear what kind of beacon is heard there. A very, you know, useful "feature": if you, for example, have a portable radio station YAESU VX-7R (144/430) and KENWOOD TH-89A (430/1200), like mine (both with two receivers) and not I want to take the station out of my pocket to look at her face :)

Achieved results in audibility. They are very good. During the competition "Primorskaya Autumn - 2009" I received the signal of this beacon, being 85 km south of Vladivostok, on Cape Gamova. And the beacon, respectively, was located in Vladivostok and worked with a power of 1.5 watts on a "zigzag with a reflector" antenna turned to the north! Here is a piece of video from there:

On the recording, you can clearly hear how the portable is shutting up when Katya UB0LAE is transmitting with a frequency difference of 250 kHz. The distance to the beacon, let me remind you, is 85 km and the receiving antenna is a standard VX-7R pipette! A two-gun artillery turret cut by vandals-metal workers also gets into the frame.

Interesting features of the propagation of radio waves in the 430 MHz band, noticed thanks to this beacon:
There were none. The 430 MHz range occupies an intermediate position between 144 and 1200 MHz, but still looks more like 144. In other words, I did not notice any significant differences from 144 MHz, except that the reflections here are more pronounced than at 144 MHz, but worse than at 1200 MHz. Water vapor and fog also have a moderate effect (between 144 and 1200) on this band. And that's probably all.

There is a wide selection of multi-channel pocket radios on the 430 MHz band that do not require registration. The communication range of a set of radio stations is usually indicated in advertising as 3-5 km. In reality, such a range can only be obtained in line-of-sight conditions in the absence of interference. The actual output power of such a radio station is about 10 mW, therefore, in real conditions, the communication range is about 500 meters.

The low price allows using such a radio station as a small-signal path of a stationary transceiver, that is, a receiver and a modulator with a preamplifier, which is the radio station's own PA.

It is only necessary to make an additional power amplifier that amplifies the signal up to 5-6 W when powered from a mains source, which can be, for example, a laboratory power supply or a battery. In this case, using a well-matched antenna, you can get a real range in the countryside or over water of several tens of kilometers.

The circuit diagram of the power amplifier is shown in the figure. It uses relatively outdated high-frequency transistors, but therefore affordable, especially if you use parts from disassembled equipment.

The scheme is three-stage. The input signal from the output of the transmitter of the radio station is fed through the X1 connector to the first amplifying stage on VT1, which amplifies the input signal in power up to about 100 mW. The operation mode of the cascade is set by the resistor R1, which creates a bias voltage on the base. The load is the inductor L1, coordination with the second stage is carried out using the C4-L2-C5 circuit.

The power amplification stages on transistors VT2 and VT3 operate in the "AB" mode, with a small bias voltage at the bases, which helps the input signal open the transistors. The offset based on VT2 is set by the R4-R5 circuit. Load - choke L3. Coordination with the subsequent cascade using the L4-C7 circuit. The gain in the cascade on VT2 is up to about 1 watt.

Cascade on VT3 amplifies the signal up to 5-6W. The bias voltage is supplied to its base by the R6-R7 circuit, through the L5 inductor. The load is the inductor L6, and matching with the antenna using the L7-C10-C11 circuit.

The installation was carried out on a sheet of foil fiberglass with dimensions of 160x70 mm. Installation of printing-volumetric type. The arrangement of parts is almost like in the schematic diagram. All connections with a common minus are made by soldering to the foil, others - to the leads of the parts, or by means of areas cut out in the foil in the form of circles with a diameter of approximately 5 mm each.

To cut these circles, I use a steel tube with a diameter of about 6mm. One end of the tube is processed with a needle file so that the edge is uneven - with teeth like a file. I insert the opposite end of the tube into the drill chuck, and holding the board, I act with the notched end of the tube as a drill when drilling holes, but at low speeds and with very low feed, so as to only cut through the foil layer and nothing more. The result is very smooth, durable pads for mounting.

The reverse side of the board (on which there are no contact pads) is superimposed on an aluminum plate measuring 160x70x5 mm, which serves as a radiator and the lower part of the amplifier case. Seven holes need to be drilled in this platinum - four in the corners for fixing the board and three for the radiator bolts of the transistor cases. Screw everything with nuts of the appropriate size. Then, when the transistors and the radiator are installed, you can carry out the installation, guided by the circuit diagram.

In the end parts of the radiator plate, eight holes must be made for attaching the housing covers with M3 bolts, respectively, by cutting threads in these holes.

Coils are all frameless. The inductors L1, L3, L5 and L6 are the same; for their winding, a PEV-type wire with a diameter of 0.56-0.61 mm is used. As a mandrel I use a drill shank with a diameter of 2 mm. I wind a turn to turn 7 turns. Then, after cutting and tinning the leads, I pull the drill out of the coil. The resulting spring is a ready throttle.

Coils L2, L4, L7 are wound with silver-plated wire 0.8 mm (in extreme cases, you can use stripped and tinned PEV 0.76 instead of silver-plated wire). The mandrel is a drill shank with a diameter of 5 mm (after winding and cutting the coil leads, the drill is removed). Coil L2 - 2 turns with a pitch of 2 mm, L4 - 3 turns with a pitch of 2 mm, L7 - 2 turns with a pitch of 2 mm.

Establishment begins with setting the operating modes of transistors for direct current. Collector current VT1 should be 30 mA (set by selection of resistance R1). Collector current VT2 - 30 mA (selection of resistance R4), collector current VT3 - 50 mA (selection of resistance R7).

After setting the modes, you need to load the amplifier with the antenna with which it will work (or equivalent) and apply a signal from the radio station transmitter to the input. Capacitors C7 and C10 set to the minimum capacity. By controlling the collector current VT2, adjust the C4-L2-C5 circuit for the maximum collector current VT2. Then, monitor the VT3 collector current and adjust the L4-C7 circuit for the maximum VT3 collector current.

Adjust the output circuit L7-C10-C11 according to the maximum radiation of the antenna (or according to the maximum RF voltage on the dummy load).

In order not to break the collector circuits of transistors VT2 and VT3 to control the current when setting up the circuits, changes in collector currents can be viewed by the value of the DC voltage across resistors R3 and R8. Accordingly, the greater this constant voltage, the greater the collector current of the transistor.

The total current consumption by the amplifier during transmission reaches 630 mA. In standby mode (when receiving) - about 120 mA. The current is high, therefore, when working on reception, it is advisable to turn off the amplifier. So that the same switch can switch the radio station to receive and transmit and to switch the antenna between the receiver and transmitter, two relays can be used.

Place one near the input connector, and the other directly near the output connector. One relay will switch the input and the other the output. In addition, the free contacts of the relay that switches the input can be used to switch the radio to receive and transmit by connecting them in parallel with the corresponding button on the radio.

Amplifier housing covers consist of a 160x70x50mm U-shaped tin cover and two 70x50mm side covers. The side covers are drilled for the input and output connectors, as well as for the power supply connector. On the same caps, you can install a relay.

Since inexpensive 430 MHz handheld radios usually do not have an antenna connector, this connector will need to be installed. A similar amplifier can also be used in conjunction with so-called radio modules to increase the range of data transmission or alarm signals.

This spring, something was wrong with our access intercom, and being in a state of “premonition of its repair”, I remembered my long-standing desire to put a camera in it. And in this regard, I had a question - how to transfer the image to the apartment? Pulling wires is not really desirable. You can, of course, buy a wireless Chinese camera at 1.2 or 2.4 GHz, but then only I and those people who buy receivers can watch the signal, and they are quite expensive and they are not sold separately from the cameras. Of course, you can buy one receiver, and for the rest of the "subscribers" to separate the image with a cable, but this option also has its own problems ...

And then the idea came to my mind to create a low-power video transmitter, besides, I already had experience in creating such devices. Inspired by this idea, I began to study this topic on the Internet, hoping to find a diagram of something simple and universal until I came across the site www.vrtp.ru and specifically the forum topic dedicated to the 430 MHz transmitter (59 channel). The author under the nickname "CyLLlKA" has developed a small transmitter on the SAW resonator. I took the HF part of this scheme as a basis, since enough people in the forum repeated it with positive results. CyLLlKA and the rest of the guys (especially "mikhalych2" 🙂 did a great job debugging the above scheme. For which they have HUGE RESPECT!

Video transmitter circuit

The only thing I decided to change in this circuit is the modulator amplifier. Since I know from experience that such modulator amplifiers are very “capricious”, sensitive to input impedance and input signal level, as well as to the gain of transistors. And therefore I used the amplitude modulator circuit published in the collection "Encyclopedia of Electronic Circuits" Count and Shiitsa which he already collected and had experience in setting it up. That's what I did:

Scheme of an experimental video transmitter 430 MHz.

A small theoretical digression ...

What parts and tools are needed

I decided to assemble the video transmitter on SMD components, as I like to work with them and they are ideal for RF devices. They can be bought at the store or soldered from old boards. A good source of parts are boards from old car phones of various standards (NMT-450, GSM) Motorolla, Bosch, Siemens and the like. It is a valuable source of high quality inductors, RF transistors, quartz and other small items. So, to assemble the device you will need:

• Temperature controlled thin tip soldering iron, neutral flux, 0.25 mm thick solder, soft, fine flux brush;
• Foil fiberglass 1 mm thick (0.8 mm, 0.5 mm), ferric chloride for etching;
• Scalpel, tweezers, wire cutters;
• Magnifying glass (if necessary);
• A guide to labeling SMD components;
• RF transistors: BFR93A, 2SC3357(56), BFG135 or analogues close in parameters;
• LF transistors: BC847 (BCW60, others similar), BC327 or similar pnp, BCP56;
• SMD resistors (1206);
• SMD capacitors (0805);
• SAW resonator 420-450 MHz(0604 or in any other case);
• Enamelled wire diameter 0.3-0.35 mm.;
• Trimmer Resistors 1 kOhm, small;
• Stabilized power supply 6V;
• Tester;
• HF receiver, radio station;
• Oscilloscope, frequency meter - I did not use;
• Beer, coffee and sandwiches - depending on the time spent!

PCB manufacturing

The printed circuit board is the basis of any electronic device. I make boards using laser ironing technology (LUT). The description of this technology is on the Internet. We can say that this technology has changed the world of amateur radio. Now, in one evening, it has become possible to manufacture quite complex printed circuit boards at home. I will briefly describe the main points of this technology. We develop a printed circuit board anywhere - using special programs or vector editors. For example, I use the Visio program (a board drawing in Visio format). The resulting image of conductors on a printed circuit board is mirrored and printed on a laser printer on glossy (coated) paper (magazines).

We prepare foil fiberglass - we clean it with fine sandpaper and degrease it with alcohol or acetone. We impose a printed image of a printed circuit board on the prepared textolite - with a toner to copper foil and cover this entire “sandwich” with several sheets (of an old newspaper of 5-7 layers). I use an old paperback book for this process - I just put the board with the stencil inside. We heat the iron to the maximum and iron our “sandwich” by pressing hard enough! I do 2-3 sets of 15-20 seconds. After the first approach, it is necessary to control the position of the stencil on the foil - it should not slip ... During this procedure, the toner is melted and transferred from the surface of the paper to the copper foil. And due to the fact that the toner does not dissolve in water, we can use this process to make circuit boards.

After the board has cooled down, place it in a container with warm water for 15 minutes. As a result of this action, the paper gets wet, and we can gently roll it up with our fingers. Only translated tracks remain on the board. The board is ready for etching. We pickle in a hot saturated solution of ferric chloride to minimize the pickling time. We wash the board in running water and erase the toner with acetone - the board is ready for tinning.

In principle, high-quality tinning of printed circuit boards for high-frequency circuitry is possible only by chemical methods or by immersion in a melt, followed by “blowing off” the solder residues. But, if you do it carefully and not in a hurry, then at home you can do it efficiently. You will need a soldering iron, a good flux (neutral) and solder with a diameter of 0.25 mm. We cover the board with flux and warming up the tracks with a soldering iron tip, we begin their tinning using minimum amount of solder. "Thick" solder for such small boards is not very suitable. Excess solder quickly appears on the board. And attempts to remove them usually lead to overheating and flaking of the tracks.

I usually immediately I make 2-3 boards, especially if they are small and I strongly recommend this to you. Even if one board is damaged during pickling or tinning (this sometimes happens), there will always be a “strategic” reserve.

Mounting the device

There is nothing difficult in mounting SMD elements. There are several ways to solder them. I usually use the following: I place the element on the printed circuit board, hold the element with tweezers, apply flux to its contacts with a thin, soft brush. After that, I warm up one end, and it is soldered to the board due to tinning solder. After that, if necessary, I trim the element and then solder it using thin solder.

The board was designed for Murata's multi-turn variable resistors (blue), but during the installation process I found a couple of smaller "trimmers". I had to make a jumper and cut the board.

After completing the installation of the elements, the board is washed with a soft brush in warm water with Fairy or something similar. The result should be a device, as in the photo below or something similar.

Transmitter setup

Setting up the device consists of two steps. At the first stage, you need to make sure that the RF generator has started working and there is a “good” carrier frequency at the output of the device. To do this, apply power to the emitter of the transistor BCP56 and try to accept the carrier frequency (I have it 433.440 MHz) to the receiver or TV in channel search mode. Normally, an unmodulated carrier frequency is "displayed" on a TV with a black screen (not ripples). For tuning, I used a Yaesu VX-6 portable radio station - to control the carrier frequency in AM mode and in parallel with this I received a signal on the Icom IC-R3 in NTSC mode.

After the HF part of the device started working, I started debugging the modulator and gave it a signal from the DVD player. Matvey watched cartoons and I used Luntik to debug the device. To select the operating point of the BC327 transistor, I had to put a 1 K variable resistor in its base circuit and shunt it with a capacitor. After that, the modulator started working and a frequency modulated in amplitude appeared at the output of the device.

The current consumed by the device is 160-180mA. The quality of the video signal is like wired. Variable resistors in the video modulator allow you to configure it in almost all parameters (level, linearity and modulation depth). Signal power (approximated by wavemeter, approximately 100-150 mW). On the IC-R3, the signal is received in the yard, with a transmitter antenna length of 10 cm.

Gnativ Vasily.

March, 2009.