Simple Booster Circuit for Cable Radio

Do you experience weak radio reception on your cable connection?

A device called a cable booster, or cable radio amplifier can help.

This electronic circuit strengthens the signals traveling through your cable wires.

Cable companies offer many channels but sometimes the signal gets weaker as it travels long distances or encounters interference.

This can make your radio sound fuzzy or unclear.

By using a cable booster, you can improve the signal strength and enjoy clear radio reception on your cable connection.

Circuit Working:

Parts List:

Utilizing this circuit enables the reception of local cable network transmissions on a portable VHF FM radio.

The ‘cable booster’ shares similarities with an antenna amplifier in both properties and design, featuring a two stage amplification using common RF transistors BF199.

In this setup the input is connected to the cable connection rather than an antenna.

The output, distinctively lacks a coaxial connection but includes a tuned circuit serving as impedance matching for a 1/4λ-antenna.

When appropriately tuned with trimmer C8 the amplified cable signal is emitted by the vertical antenna, easily receivable by a portable receiver within a three meter range.

While it’s feasible to construct the circuit on a prototyping board, for optimal performance utilizing the provided PCB layout is recommended given the inherent sensitivity of RF circuits.

During the design phase, essential connections were kept short and a spacious ground plane was incorporated.

Notably, capacitor C7 should be directly connected to the tap on L1 as illustrated in the photo.

The air cored coil, made of three turns of 1 mm enameled copper wire wound around an 8 mm diameter pencil is crucial to the construction.

To prevent signal interference and potential oscillation issues it is advised to keep the connecting wires from coax connector K1 to the PCB as short as possible.

Furthermore, enclosing the PCB in a metal casing is essential.

The power supply for the cable booster can be either a 9V battery or a compact regulated mains power supply with a modest current consumption of approximately 2.5 mA.

Formulas:

In order to ensure that the RF signal travels across the cable with enough power and clarity to reach the receiver, a booster circuit for cable radios must be designed.

For creating a booster circuit of this kind, keep in mind the following important factors and fundamental formula

The Low Noise Amplifiers (LNA) gain, which controls the signals amplification, is the crucial formula for the booster circuit.

G_dB ​= 10log_{10 ​^(G)}

where:

• G_dB​ is the gain in decibels (dB).
• G is the voltage gain of the LNA.

The resistors and capacitors employed in the LNAs design usually determine its gain G.

The datasheet for a lot of commercial LNAs includes the gain information.

How the formula works:

In a typical booster circuit, a commercial LNA with the right gain and low noise figure requirements suitable for cable radio frequencies like the Mini Circuits MAR 6 or something similar would be used.

In cable radio booster circuit design, the right LNA must be chosen, and a bandpass filter and impedance matching network may also be integrated.

The booster circuit enables dependable delivery of cable radio signals to the receiver, enhancing reception clarity and quality by efficiently boosting the RF signals and reducing noise.

How to Build:

Building the cable booster circuit involves several steps.

Prepare the PCB:

• Place the components on the PCB according to the provided layout.
• Solder the components onto the PCB starting with the lowest profile ones first.

Connect Components:

• Follow the schematic and the PCB layout to connect the components.
• Pay attention to the orientation of transistors, capacitors and the coaxial connector.

Prepare L1 Inductor:

• Wind three turns of 1 mm enameled copper wire around an 8mm diameter pencil.
• Solder L1 to the circuit connecting it as indicated.

Tune the Circuit:

• Adjust trimmer capacitor C8 to tune the circuit.
• Use a multimeter or an oscilloscope if available.
• Tune for optimal performance ensuring the amplified cable signal is radiated by the antenna.

Connect the Power Supply:

• Connect the power supply 9 V battery or regulated mains power supply to the circuit.

Enclose the PCB:

• Place the PCB in the metal enclosure to shield it from external interference.
• Ensure the coaxial connector is properly positioned in the enclosure.

Test the Circuit:

• Connect a portable VHF FM radio to the circuit using a cable.
• Power on the circuit and verify that you can receive local cable network stations on the radio.

Fine-Tune if Necessary:

• If needed, fine tune the circuit for optimal performance.

Note:

• Remember to follow safety precautions while working with electronic components, and double check your connections before applying power.
• If you are unsure or unfamiliar with electronics consider seeking assistance from someone with experience.

Conclusion:

The booster circuit usually includes components such as transistors, resistors, capacitors and inductors arranged in a specific configuration to achieve the desired amplification.

It may also incorporate features like impedance matching to optimize the transfer of signals between different components of the system.

In the context of cable radio a booster circuit for cable radio specifically amplifies the radio frequency RF signals associated with cable broadcasting.

This type of booster is employed to improve the reception quality of cable radio stations allowing listeners to enjoy better sound quality and reduce the likelihood of signal interference.

References:

Datasheet BF199