This is one TV, Video Transmitter Circuit It can send video from DVD, camera, or other device to old TV in our house.
We do not need big parts or hard things.
Just small circuit and little care is all we need.
This type of circuit is good for fun or learning.
Circuit Working:
Parts List:
| Component | Description | Quantity |
|---|---|---|
| Resistors | All resistors are 1/4 W CFR | |
| 470Ω | 1 | |
| 100Ω | 1 | |
| 4.7k | 2 | |
| Preset 470Ω | 1 | |
| Capacitors | ||
| Ceramic 3.3pF | 1 | |
| Ceramic 2pF | 1 | |
| Ceramic 10pF | 1 | |
| Ceramic 100nF | 2 | |
| Electrolytic 100μF 16V | 2 | |
| Semiconductors | ||
| Transistor BFR91A | 1 | |
| Inductor Coil, air core, 2 turns, 3mm diameter using 0.5mm thick super enameled copper wire | 1 |
Main part of TV video transmitter is small oscillator using high frequency NPN transistor like BFR90, BFR91A, BFR92, or BFR93.
Here transistor is in small TO50 case.
Transistor make high frequency wave and it is in active part.
LC circuit has one coil and capacitor C1 and these set the frequency.
We can change coil and C1 to choose UHF frequency between 470 to 855 MHz.
This makes circuit send signal on one TV channel.
Antenna is a simple wire to about 5 cm and connect direct to oscillator to send RF signal in air.
Oscillator wave (carrier) is changed by video signal from camera or other source.
Wave become strong or weak and this is called amplitude modulation.
Circuit runs with 5 to 12V power and this power when ON makes oscillator send RF signal.
Potentiometer P1 controls how much video changes the wave and this is the modulation depth.
Adjust P1 to improve the picture.
After power ON then connect video source and turn coil or parts by hand to tune the circuit.
Then use old analog TV to find signal in UHF band with usually channel 37 to 50 with the range of 600 to 700 MHz and this is the tuning.
Formulas:
Here are easy formulas for TV Video Transmitter Circuit:
This circuit use LC formula to find frequency.
Resonant frequency (f) is:
f = 1 / 2π√LC
where:
- f is the working frequency of transmitter
- π is around 3.14159
- L is coil value is the inductance
- C is capacitor C1 value in capacitance
We can choose L and C value using circuit diagram to get right frequency.
This tell what channel our transmitter will work on.
This formulas help explain how frequency and modulation work in TV transmitter.
How to Build:
To build a TV, Video Transmitter Circuit following steps are required for connections:
- For coil and capacitor C1 values look at the circuit diagram and these two parts decide what frequency transmitter will use.
- Change coil and C1 to get frequency in UHF range from 470 to 855 MHz.
- For antenna just connect a wire about 5 cm means 2 inch long straight to oscillator.
- Give power to transmitter using 5 to 12V supply.
- Make live wires short to stop too much inductance and capacitance.
- To stop unwanted signals from parasitic effect put 100nF capacitor close to transistor.
- Also use 100uF electrolytic capacitors in parallel to block noise from 50 Hz to hundreds of MHz.
Caution:
- Know the legal rules before using UHF TV band for sending signal.
- In some countries this kind of broadcasting is not allowed.
- If someone has legal trouble from using this it is not writers fault.
- Do this project only under its countries laws and try it at ones own risk.
Conclusion:
TV, Video Transmitter Circuit design can change based on what we need or want to do.
There are also ready made transmitters for sale and these have sound, more channels, different frequencies and stronger signal.
Before using always check the local rules about radio frequency broadcasting.