4-Way Active Antenna Splitter / Distribution Amplifier

Model: AS-4B (Buffered, 50Ω, 5V)

Distribute one antenna signal to four receivers — with zero interaction between them.

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📖 Overview

The AS-4B is a compact, four-port active antenna splitter designed to feed up to four receivers (scanners, SDRs, receivers, spectrum analyzers) from a single antenna without signal loss or cross-interference.

Unlike passive splitters, which introduce 6–8 dB of insertion loss, the AS-4B uses four independent BC547 emitter-follower buffer stages to isolate each output. This preserves signal strength and prevents one receiver from "pulling" the signal away from the others.

Ideal for:

• 🖥️ SDR enthusiasts running multiple dongles (RTL-SDR, Airspy, SDRplay)

• 📻 Scanner listeners monitoring multiple bands simultaneously

• 📶 Ham radio shacks with multiple receivers

• 🔬 Lab / test bench signal distribution

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✨ Key Features

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🔧 Technical Description

The AS-4B uses a common-emitter, emitter-follower topology optimized for 50Ω RF systems.

Signal Path

1. Input Stage: A 50Ω termination resistor matches the antenna feedline, while anti-parallel 1N4148 diodes clamp static and strong-signal surges to protect the transistors.

2. DC Blocking: A 100nF capacitor isolates the DC bias of the buffer stages from the antenna and termination.

3. Buffer Stages: Four identical BC547 emitter followers provide unity-gain buffering. Each stage has a low output impedance (~5Ω), enabling it to drive 50Ω loads without loss.

4. Isolation: Because each output has its own buffer, a mismatch or short on one output will not affect the others.

Power Supply

• Regulator: 78L05 (5V, 100mA)

• Input Voltage: 7V – 9V DC (9V recommended)

• Protection: Reverse-polarity diode (1N4001) on input

• Filtering: 470µF bulk + 100nF ceramic decoupling

Input Protection

The front-end features anti-parallel 1N4148 diodes to ground. If a strong signal or static discharge exceeds ~0.7V, the diodes clamp and dissipate the excess energy, protecting the sensitive BC547 transistors.

⚠️ Note: For high-RF environments (near broadcast towers), we recommend upgrading to BAT54S Schottky diodes for a lower clamp voltage (0.3V).

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📊 Performance (Typical)

Measured with 50Ω source and load, 5V supply, 25°C.

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🧰 What's Included

Kit Version:

• 1× AS-4B PCB (assembled SMD passives, through-hole actives)

• 4× BC547 transistors

• 1× 78L05 regulator

• 1× 1N4001 diode

• 2× 1N4148 diodes (input protection)

• All resistors, capacitors, and connectors

• Schematic + Bill of Materials

Assembled Version:

• Fully built and tested unit

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🧪 Applications

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📋 Disclaimer :

This device is intended for receive-only applications. Do not use it to transmit. Do not connect to a transmitter without proper isolation. The AS-4B is not lightning-protected — always use an external lightning arrestor for outdoor antennas.

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