RF Blocker Types: In-Band vs. Out-of-Band

This article explores the different types of RF blockers, specifically In-Band Blockers and Out-of-Band Blockers. We’ll delve into the distinctions between them and illustrate these differences with a diagram.

Introduction

An RF blocker, also known as an RF jammer, is a device designed to block or suppress radio frequency signals. Its purpose is to disrupt or block the transmission from a particular radio station or satellite within a specified frequency band.

By blocking these RF signals, the intended wireless signal becomes unreceivable or undecodable. While RF blockers aim to disrupt signals, receiver architectures are designed to counteract them, detecting and demodulating desired signals while removing unwanted RF interference.

Receivers employ techniques such as Automatic Gain Control (AGC) and power detection to effectively manage these blockage scenarios, and mitigate the mixer spurious signals and undesired products.

What is an RF Blocker?

• RF blockers are signals operating at radio frequencies with significantly larger magnitudes than the desired signal.
• These larger signals can easily jam a receiver.
• Blockers can generate frequencies that inter-modulate with other signals, leading to Intermodulation Distortion (IMD) products within the desired signal frequency range.
• There are two primary types of RF blockers: In-Band blockers and Out-of-Band blockers. Filtering out-of-band signals is generally easier than filtering in-band signals.

Figure-1: In-band blocker vs. Out-of-band blocker

In-Band Blocker

• An In-Band blocker is a signal that operates close to the desired frequency. These are strong carriers residing within the digital receiving band.
• They can create nonlinear distortion and interfere with weak RF carrier signals.
• In-band blockers are often mixed in the front-end part of a Direct Conversion Receiver, before the RF mixer, producing unwanted products at the baseband.
• Eliminating in-band blockers is typically only achievable at the end of the signal chain or in the digital domain.

Out-of-Band Blocker

• An Out-of-Band blocker is a signal that operates far away from the desired frequency. These are strong carriers residing outside of the digital receiving band.
• They can create nonlinear distortion and interfere with weak RF carrier signals.
• Out-of-band blockers can be more easily eliminated using filters, as they lie outside the desired frequency band.