Cable TV Amplifier Circuit uses small wire to send signal, but when signal goes far it become weak; like small radio, cable TV amplifier make signal strong again.
Also, this circuit helps people get better and clear picture.
Circuit Working:
Parts List:
| Components | Quantity |
|---|---|
| Resistors (All resistors are 1/4 watt) | |
| 680Ω | 1 |
| 820Ω | 1 |
| 75Ω | 1 |
| 100Ω | 1 |
| Capacitors | |
| Ceramic 0.01μF | 1 |
| Ceramic 0.0022μF | 2 |
| Semiconductors | |
| Transistors 2SC4308 | 2 |
| Connectors | |
| TV input | 1 |
| TV output | 1 |
This RF amplifier circuit is specially designed for cable TV applications because it can connect easily between two coaxial cables.
Also, input and output of both work good with 75 ohm cable.
Here, transistor T1 works in the main amplifier stage and transistor T2 operates as an emitter follower.
Bias get by 820 ohm and 75 ohm resistor and total gain of this amplifier is 22 dB, because transistor can not work with very high frequency which is only up to 2 GHz then this circuit works good till 150 MHz only.
So it is better to put in metal box and use 75 ohm coaxial wire only, also this amplifier uses around 20mA current.
Formula:
In high frequency circuit important thing is transistor gain bandwidth product (GBW) and we can find GBW by this formula:
GBW = Av × f−3dB
where:
- GBW is gain bandwidth
- Av is transistor voltage gain
- f−3dB is frequency where gain become 3dB lower
This formula give idea for rough calculations.
How to Build:
To build a Cable TV Amplifier Circuit follow the blow steps for connections:
Design of Circuit:
- First, check diagram for cable TV amplifier and put T1 and T2 transistor on PCB or breadboard like shown and then connect resistors and other parts same like diagram.
Soldering:
- Also, use soldering iron and carefully solder all parts on board and always check two times to stop short circuit.
Input and Output:
- Next, connect input and output coaxial cable to right place on circuit and use only 75Ω coaxial cable for good work.
Enclosure:
- Now, put full circuit inside metal box to block outside signal and also be sure the box have some airflow so it does not get too hot.
Power Supply (if needed):
- If amplifier need power then connect it same like shown in diagram and be sure voltage and current is correct for this circuit.
- First, switch ON amplifier, test it with cable TV signal and use tools like oscilloscope or signal tester to see if it works good.
Change and Adjust:
- The resistors 820Ω and 75Ω give feedback bias and we can adjust them to make amplifier work better.
Final Check:
- Also, at end be sure amplifier gives right gain and work in correct frequency range.
Safety Rules:
- Always follow safety rules when working with electric things and check all wires and solder and be sure nothing is loose or touching wrong.
Note:
- Also, making circuit need both skill and care and if anyone do not know about electronics well then ask for help from experienced person or expert.
Conclusion:
Finally, this Cable TV Amplifier Circuit help keep signal strong and clear; also this circuit is good for better TV picture when signal is weak.