1. Introduction

Duplexers provide critical frequency domain isolation between transmitter and receiver paths in repeater systems, typically achieving 80-100 dB of isolation. These passive filter networks enable full-duplex operation on a single antenna through precise cavity resonator design and coupling mechanisms optimized for specific frequency splits.

Duplexers are essential in amateur radio across multiple bands—2 meters, 220 MHz, 440 MHz, and 1.2 GHz—enabling repeaters to extend communication range and provide wide-area coverage. Without proper duplexer design, a repeater would be deaf to incoming signals or would destroy its own receiver with transmit energy.

This post demystifies duplexer operation, explores common types, and provides practical guidance for installation and troubleshooting. Whether you're maintaining a club repeater or designing a commercial system, understanding duplexer fundamentals will save you hours of debugging and improve system reliability.

Enhanced with practical examples and installation tips.

1. Introduction

Intermodulation (IM) interference plagues land mobile radio systems and RF engineers alike. It occurs when two or more signals mix in a non-linear device, creating new, unwanted signals that can disrupt communications. IM can degrade system performance, cause dropped calls, and even render entire channels unusable.

Understanding and controlling IM is essential for reliable RF system design and operation. This comprehensive guide explores prediction methods, detection techniques, and practical suppression strategies for RF engineers working with complex multi-transmitter environments.

Enhanced with signal math and forensic analysis methods.

1. Introduction

From WiFi routers to satellite links, RF engineering principles determine whether wireless systems succeed or fail. This comprehensive guide explores the fundamental physics and practical techniques that enable reliable communication across the electromagnetic spectrum.

RF technology constitutes the foundation of modern wireless communications, spanning applications from public safety radio systems to satellite communications and IoT infrastructure. This technical resource addresses fundamental electromagnetic principles, signal propagation characteristics, and system design considerations relevant to practicing engineers.

Topics covered include Maxwell's equations as applied to radio propagation, modulation theory, antenna characteristics, link budget calculations, and regulatory compliance. Mathematical formulations are presented alongside practical implementation examples from commercial and amateur radio systems.

Includes interactive calculators, design formulas, and reference specifications for system implementation.