Cable television channels run through using the thin lines.
These signals can get weaker as they travel greater distances.
A cable TV amplifier circuit works similarly to a little radio enhancing the power of the signals.
This helps ensure that viewers receive a clean signal.
Circuit Working:
Parts List:
| Component | 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 particularly developed for cable TV applications and can be easily installed between two coaxial wires.
Both input and output impedances are designed to work with 75Ω cables.
The T1 transistor is used in the main amplifier and transistor T2 acts as an emitter follower.
The feedback bias is calculated by 820Ω and 75Ω.
The total gain of this cable TV amplifier is 22dB.
Because of the inherent high frequency limitations of transistors up to 2GHz the amplifier works up to 150MHz.
Enclose it in a metal container and use 75Ω coaxial wires.
This cable TV amplifier circuits overall current usage is about 20mA.
Formula:
The following method are used to calculate a transistors gain bandwidth ratio (GBW) which is a key factor in circuits with large bandwidth frequencies.
GBW = Av × f − 3dB
where,
- GBW is the gain bandwidth product
- Av is the voltage gain of the transistor
- f−3d bandwidth of the circuit or frequency at which the gain drops by 3dB.
According to this formula a rough estimation of a transistors ability in amplifying signals at higher frequencies is obtained by multiplying its gain by the frequency at which the gain begins to drop off or the -3dB point for a specific transistor with a voltage gain of Av.
How to Build:
To build a Simple Cable TV Amplifier Circuit following steps are required for connections:
Gather Components:
- Gather all of the the necessary parts as mentioned in the above circuit diagram.
Circuit Design:
- Refer to the schematic design for the cable TV amplifier circuit.
- Place the T1 and T2 transistors on the PCB or protoboard as described in the circuit design.
- Connect the resistors and other components per the schematic.
Soldering:
- Use a soldering iron to carefully solder the components onto the board.
- To avoid short circuits always double check the connections.
Input and output connections:
- Connect the input and output coaxial cables to their proper spots on the circuit.
- Ensure the coaxial cables are 75Ω type.
Housing:
- To protect against external interference place the completed circuit within a metal enclosure.
- Make sure the case has sufficient ventilation to avoid overheating.
Power Supply (where applicable):
- If the amplifier requires a power supply connect it according the schematic.
- Ensure that the voltage and current requirements are satisfied.
- Turn on the amplifier and test it using a signal source such as a cable television supply.
- To check performance use suitable testing equipment such as an oscilloscope or signal analyzer.
Adjustment:
- To increase amplifiers performance adjust the biasing resistors 820Ω and 75Ω to provide the desired feedback bias.
Final Checks:
- Finally ensure the amplifier operates within the specified frequency range and generates the desired amount of gain.
Safety precautions:
- When working with electrical components it is necessary to follow every safety rules. Check all of the connections to verify there are no loose wires or soldering crossings.
Note:
Keep in mind that building electrical circuits requires a solid understanding of electronics as well as a knowledge of proper safety precautions.
If one is inexperienced with electronic construction get help from someone with experience or contact with an electronics expert.
Conclusion:
Simple Cable TV Amplifier Circuits play an essential role in maintaining signal quality and ensuring that customers receive clear and accurate television signals particularly when cable signals have to travel long distances or pass through several separation points in a distribution network.