AM TRANSMITTER at 3 MHz
The transmitter consists of four stages. The author used almost all used parts, soldered at different timesfrom different techniques, and lay around in boxes for many years. The output power of the transmitter has not been measured, according to rough calculations it is about 5 Watts +/-, but most likely a plus. The master oscillator is assembled according to a classic three-point circuit, and despite its simplicity, it maintains a stable frequency. The buffer stage on VT2 is loaded on a broadband transformer, there was no desire to install circuits and then equalize the characteristic over the entire range, there are more brands and details extra , and here in one fell swoop, or rather with one transformer. The buffer stage is the load of a modulator assembled on an LM386 ULF chip. The author took the modulator circuit from Japanese radio amateurs, tested it and was satisfied. Well, the most important part is the final stage. It is assembled on a transistor taken from some Korean radio. The KT805BM in the first version did not live up to expectations and was disgracefully removed from the transmitter. As a result of the operation, the structure was not damaged, but the patriotic spirit of the author was tested. However, having inserted 2T921A into the design for testing, peace of mind was restored. Even more, there was pride in our defense industry. But it was decided to leave the “Korean” as the most optimal option, and it is easier to attach to the radiator. The operating mode of the cascade is set by resistor R12. Diode D4 serves to stabilize the quiescent current. It must be mounted on the radiator directly next to the output transistor. On the Korean transistor, the author slipped a diode directly under the transistor, since there was room there. It is advisable to coat the mounting location with heat-conducting paste.
Design details: a variable capacitor was installed with an air dielectric from a tube receiver. You can install almost any KPI, the main thing is that it covers the range of 2.8 - 3.2 MHz.
Coil L1 of the master oscillator has 80 turns of PEL wire - 0.32 with a tap from 20 turns. Coils L2; L3 are the same and have 20 turns of PEL wire - 0.6.
All coils are wound on frames with a diameter of 12 mm.
The author used a polystyrene frame from a spool of thread as frames.
Tr1 is wound on a ferrite ring with a diameter of 10 mm and a height of 5 mm. Twenty turns of folded and slightly twisted PELSHO wire - 0.25. Winding is carried out evenly throughout the entire ring.
Tr2 is wound on the same ring and contains 18 turns of PEL wire folded in three - 0.32.
L4 - 30 turns PELSHO - 0.25 on the same ring as Tr 1;2. For L4, you can use a ring with smaller dimensions.
ATTENTION:
Before you start setting up, you need to connect a 50 - 75 Ohm load to the transmitter output. The author used two connected parallel 100 Ohm resistors, 2 W each.
SETUP:
The setup begins by checking the power supply, having previously set the variable resistor R12 to the position of maximum resistance. By connecting an ammeter (multimeter) set to maximum between the circuit and the power source, usually 10 A supplies power. If the readings have not changed much, then you can proceed to the actual setup. Disconnect pin Tr1, which goes to C24 so that power from the modulator does not flow to the cascade. Connect a milliammeter between power supply +24 and the right terminal of transformer Tr2. We connect the power, and with resistor R12 we set the quiescent current of the output stage to about 30 mA. Then we restore all connections, monitor the signal with a frequency meter or receiver for generation. Then we set the middle of the range and use capacitors C19 - C21 to adjust the output filter to the maximum indicator readings. We connect the antenna, adjust C21 again and the setup is complete.
The transmitter is based on the S9-1449-1800 synthesizer. At the output of the synthesizer, an oscillating circuit with a coupling coil and a matching circuit for a wire antenna is installed, in the form of an inclined or horizontal multi-wire beam, 35-55 meters long, raised to a height of 20-30 meters. The output transistors of the synthesizer (KT608B) are powered through an emitter follower on the P701 transistor, which is connected at its base to the 140UD6 operational amplifier in the modulating signal circuit. That is, classical collector modulation with a regulating transistor takes place. The output power of such a transmitter in silent mode is 0.8 watts, when modulated by a sinusoidal signal (telephone power) - 1.2 W, at modulation peaks - up to 3 watts. This is enough to ensure reliable reception within a radius of 1.5 km in urban areas; for rural areas or for villages with low-rise buildings, the broadcast radius will be up to 3 kilometers. That is, this is a transmitter for college towns, holiday villages and villages, pioneer and student camps, remote military garrisons. It can also be successfully used to demonstrate radio broadcasting to schoolchildren and students in physics and radio engineering classes.
Schematic diagram radio transmitter
- drawing of the modulator board and output oscillatory circuit
However, for all its simplicity, this transmitter fully meets the quality standards for radio broadcast transmitters in accordance with GOST R 51742-2001.
The transmitter is powered by a network rectifier with a power transformer TN32-127/220-50 and a filter choke D16-0.08-0.8.
The front panel of the transmitter contains:
- power switch,
- two switches with 4 and 10 positions to set the nominal frequency of the synthesizer,
- variable capacitor knob for adjusting the output oscillating circuit,
- switch of turns of the extension coil (11 positions) of the antenna tuning circuit,
- toggle switch “setup-operation”, switching output power: 40% and 100%.
- blue LED - “Antenna current” indicator,
- red LED (lit in setup mode) - “Output stage current” indicator.
On the back panel there are:
- connector mains power 220 V, 50 Hz,
- two “tulips” - linear modulation signal input (stereo channel adder - inside),
- “Ground” terminal, for connection to the ground loop (required!) and to the counterweights,
- “Antenna 1” terminal for connecting an antenna less than a quarter wavelength,
- “Antenna 2” terminal for connecting an antenna with a length equal to or greater than a quarter wave.
Transmitter chassis dimensions: 220×110×120 mm.
AM signal transmitter
The XA994 microassembly is used in radio intercoms in the high and low frequency paths of the transmitter to generate and amplify HF signals
Radio microphone
The proposed device in conjunction with a radio broadcasting
VHF FM receiver can be used for wireless
transmission of voice messages over short distances or,
for example, as a baby monitor for remotely listening to noises and sounds in a children's room. The design feature is that the LC generator coil is made in the form of a printed circuit conductor.
Radio transmitter powered by 220 V network
This circuit, with a minimum of radio components, has fairly good characteristics:
high microphone sensitivity (you can hear the ticking of the wall clock in the room),
with an antenna length of 100 cm, the range is 500 meters (when using mobile phone with built-in FM radio).
L1 - 6 turns of copper wire, 0.5 mm in diameter
VD1 - zener diode, type KS168 (any other voltage 6.8V can be used)
VT1, VT2 - transistors, type KT315, maybe KT3102, KT368.
A correctly assembled circuit should work immediately, the entire setup consists of adjusting the frequency by compressing and expanding the turns of coil L1 and selecting resistance R7 (100 Ohm - 1 kOhm) to achieve maximum power.
C4 can be supplied with a larger capacity, in which case it will smooth out pulsations even better. The power supply should be separated from the transmitter with an aluminum screen.
Retro transmitter
The small-sized radio transmitter from Radio No. 9 - 1957 probably served as the prototype for the creation of the “toy of the 60s”. An interesting fact is that “the transmitter was also tested on the 80 and 40 meter amateur bands, where good results were obtained.” Radio amateurs who decide to repeat the design (given above or from the article published below), naturally, should not forget about the type of modulation that is in these AM transmitters ...
Simple radio microphone
The range of the radio microphone is more than 300 meters outdoors. Despite low voltage The 3V power supply of the radio microphone is quite powerful, the signal is confidently pressed from it to the radio receiver across 3 floors of the building. The frequency range of the radio microphone is from 87 to 108 MHz. Radio signal reception is possible on any FM radio receiver.
The coil (L1) is 3mm in diameter, has 5 turns of copper wire with a diameter of 0.61mm. The antenna length should be half or a quarter wavelength (for 100 MHz - 150 cm and 75 cm). By changing the width of the turns of coil L1, tune the radio microphone to the range from 87 to 108 MHz.
Source - http://www.hobby-hour.com/electronics/wireless_microphone.php
Simple CW transmitter
Transmitter output power is about 1 watt. Quartz is used from the RSIU station. Coils L1 and L2 are wound directly on the resonator body, the turns ratio is 5:1. To operate in the 3.5 MHz range, coil L1 must have an inductance of 25-29 µH, and for operation in the 7 MHz range - 7-8 µH. The tap is made from 1/3 to 1/5 of the turns of L1. The circuit is tuned by C2 and the antenna is tuned by C3. The circuit can be assembled using more modern transistors KT606, KT904, etc., by reversing the polarity of the power supply.
Simple QRP CW transmitter
VHF FM low power radio transmitter
In essence, this circuit can be classified as a radio microphone with an increased range of signal reception. The device is intended
to transmit an audio signal over a certain distance, using a frequency in the VHF-FM range 88-108 MHz. In this case, signal reception is possible on a VHF-FM broadcasting receiver operating in
corresponding frequency range. It should be noted that the output power of devices for this purpose is strictly regulated and cannot exceed 0.01 W. However, when setting up and fine-tuning this circuit, it is theoretically possible to reach 0.3-0.5 W.
Simple FM transmitter
The signal from the microphone is fed to the base of transistor VT1 through the isolation capacitor C1 (10 μF). VT1 acts as an AF amplifier and at the same time as an RF generator; as a result, we receive an FM signal at the transmitter output.
L1 - defines frequency range transmitter, the coil has a diameter of 7 mm, the wire diameter is 0.3...0.35 mm, the number of turns is 7, after winding the coil must be pulled out to a length of 15 mm. The collector of transistor VT1 is connected to antenna L2 (antenna), L2 has a winding diameter of 6 mm, the antenna is wound with a wire with a diameter of 0.35...0.5 mm. The antenna length is approximately 25...30cm. When winding, you should get a spring.
The transmitter range is 100 meters; when adjusting the transmitter range, compress or extend the L1 coil.
AM transmitter with a power of 25 W
Simple AM transmitter
A simple circuit of an AM HF transmitter on amateur band 3 MHz for a beginner radio amateur: detailed description works and devices
Proposed transmitter circuit does not contain scarce parts and is easily repeatable for beginning radio amateurs taking their first steps in this exciting, exciting hobby. The transmitter is assembled according to the classical design and has good characteristics. Many, or rather, all radio amateurs begin their journey with just such a transmitter.
It is advisable to start assembling our first radio station with a power supply, the diagram of which is shown in Figure 1:
picture 1:
The power supply transformer can be used from any old tube TV. The alternating voltage on winding II should be about 210 - 250 v, and on windings III and IV 6.3 v each. Since the load current of both the main rectifier and the additional one will flow through diode V1, it must have a maximum permissible rectified current twice as large as the other diodes.
Diodes can be taken of the modern type 10A05 (sample voltage 600V and current 10A) or, even better, with a voltage reserve - 10A10 (sample voltage 1000V, current 10A), when using more powerful lamps in the transmitter power amplifier, we need this reserve It can be useful.
Electrolytic capacitors C1 – 100 µF x 450V, C2, C3 – 30 µF x 1000V. If you don’t have capacitors with an operating voltage of 1000V in your arsenal, then you can make up 2 series-connected capacitors of 100 μF x 450V.
The power supply must be made in a separate case, this will reduce dimensions transmitter, as well as its weight, and in the future it will be possible to use it as a laboratory one, when assembling structures on lamps. Toggle switch S2 is installed on the front panel of the transmitter and is used to turn on the power when the power supply is under the table or on the far shelf, where you really don’t want to reach (can be excluded from the circuit).
Figure 2:
Modulator details:
C1 – 20mkfx300v, C7 – 20mkfx25v, R1 – 150k, R7 – 1.6k, V1 – D814A,
C2 – 120, C8 – 0.01, R2 – 33k, R8 – 1m variable, V2 – D226B,
C3 – 0.1, C9 – 50mkfh25v, R3 – 470k, R9 – 1m, V3 – D226B,
C4 – 100 µFx300V, C10 – 1 µF, R4 – 200k, R10 – 10k,
C5 – 4700, C11 – 470, R5 – 22k, R11 – 180,
C6 – 0.1, R6 – 100k, R12 – 100k – 1m
Electret microphone from a cassette recorder or telephone headset (tablet). The part of the circuit highlighted in red is necessary to power the microphone; if you intend to use only a dynamic microphone, then it can be removed from the design. Trimmer resistor R2 sets the voltage to + 3V. R8 – modulator volume control.
The output transformer is from a tube receiver or a TV of the TVZ type; you can also use vertical scan transformers TVK - 110LM2, for example.
The setting consists of measuring and, if necessary, adjusting the voltages at terminals (1) +60V, (6) +120V, (8) +1.5V of the 6N2P lamp and at terminals (3) +12V, (9) +190V 6P14P.
Figure 3:
Transmitter details.
C1 – 1 section gearbox 12x495, C10 – 0.01, R1 – 68k
C2 – 120, C11 – 2200, R2 – 120k
C3 – 1000, C12 – 6800, R3 – 5.1k
C4 – 1000, C13 – 0.01, R4 – 100k variable
C5 – 0.01, C14 – 0.01, R5 – 5.1k
C6 – 100, C15 – 0.01, R6 – 51
C7 – 0.01, C16 – 470 x 1000V, R7 – 220k variable
C8 – 4700, C17 – 12 x 495, R8 – 51
C9 – 0.01, R9 – 51
R10 – 51
The GPA coil L1 is wound on a frame with a diameter of 15 mm and contains 25 turns of 0.6 mm PEV wire. The inductor in the cathode of lamp L2 is factory-made and has an inductance of 460 μH. In my design, I used a choke from a TV, wound on an MLT - 0.5 resistor with a wire in a slot winding. Chokes L3 - L6 are wound between the cheeks on old-style VS-2 resistors and have 4 sections of 100 turns of PEL-2 wire with a diameter of 0.15 mm. Chokes L7 and L8 each have 4 turns of PEV wire with a diameter of 1 mm wound on top of resistors R8 and R9 MLT-2 with a resistance of 51 Ohms and serve to protect the final stage from self-excitation at high frequencies. The anode choke L9 is wound on a ceramic or fluoroplastic frame with a diameter of 15 - 18 mm and a length of 180 mm. PELSHO wire 0.35 turn to turn and has 200 turns, the last 30 turns in increments of 0.5 - 1 mm.
The L10 contour coil is wound on a ceramic, cardboard or wooden frame with a diameter of 50 mm and has 40 turns of PEL-2 wire with a diameter of 1 mm. When using a wooden frame, it should be well dried and varnished, otherwise, when exposed to high RF current, it will dry out, which will lead to deformation of the winding and possibly even a breakdown between the turns.
C17 is a double unit from a tube receiver with plates removed through one in a movable and fixed block.
Variable resistor R4 sets the bias on the control grid of the 6P15P lamp, and resistor R7 sets the bias for 6P36S lamps.
Relays can be of any type for a voltage of 12V with a gap between contacts of 1mm with a switching current of 5A.
Ammeter for current 100 mA,
The final stage is tuned to resonance using the minimum milliammeter readings.
The bias circuit is shown in Figure 4:
Figure 4:
Transformer T1, any step-down transformer 220v/12v with reverse connection. The secondary (step-down) winding is included in the filament circuit of the lamps, and the primary serves as a step-up winding. The output of the rectifier is about -120V and is used to set the bias of the lamps of the final stage of the transmitter.
Useful thing!
The figure above shows a diagram of the field strength indicator. This is a circuit of the simplest detector receiver, only instead of headphones, it has a microammeter, by which we can visually observe the signal level when tuning the transmitter to resonance.
The transmitter consists of the following blocks: master oscillator; buffer stage; output stage; modulator.
Master oscillator.
The master oscillator is assembled according to a capacitive three-point circuit using a 6P44S lamp. The contour coil is wound on a frame with a diameter of 20 mm, with a wire of 0.8 mm diameter, 40 turns. To achieve frequency stabilization in the control grid, it is necessary to use KSO capacitors of group G + -5%.
Buffer cascade
The buffer stage is designed to decouple the master oscillator from subsequent stages, which contributes to the stability of the generation frequency. In the same cascade, amplitude modulation of the carrier frequency occurs. The modulator must be a tube modulator that provides 200 volts or more at the output of the modulation transformer. 
Output stage
The Dr1 inductor is wound with 0.23-0.35 mm wire on a ceramic frame with a diameter of 10-15 mm, four sections of 80 turns per pile. Choke Dr2 is wound with three 0.5 mm wires on a thick ferrite rod. The chokes in the filament circuit are also wound on ferrite rods with 1.0-1.5 mm wire. The chokes are wound until the rod is completely filled, leaving room for its attachment. The contour coil is wound on a frame with a diameter of 50 mm with a 2.0 mm wire, the number of turns is 35-38
Modulator for AM transmitter
The modulator is a 4-stage low frequency amplifier. The microphone amplifier is made on one half of the 6N2P. The microphone used is an electret (tablet). C1 limits it by high frequencies to avoid excitement. Resistances R1 and R2 determine the voltage on the microphone (affects sensitivity); it should be within 1.5...3.0 V (depending on the type of microphone). Capacitor C3 prevents high DC voltage from reaching subsequent stages. Next comes a two-stage voltage amplifier. The signal comes to it from resistance R4 “volume”. Resistor R9 is a volume control for the line input (tape recorder, CD player, computer, etc.), and it is also a tone control for the microphone input. The audio power amplifier is assembled on a 6P3S. The amplifier is loaded onto a transformer, which you can wind yourself, the data is shown in the diagram. The power transformer from old Record and Vesna TVs (TS-180) also works well. When connecting to a transmitter, you may need to change the polarity of the secondary winding connection.
Antenna
The transmitter was loaded onto an "American" type antenna. Antenna length 48m made of 1.6mm wire. The transmitter was connected with a 1.0mm wire. The reduction is connected at a distance of 1/3 of the entire length.
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