High-power shortwave DRM transmitter in solid-state technology

Goran Pavlakovic,Silvio Hrabar

doi:10.1080/00051144.2018.1517439

Abstract

ABSTRACTDesign of high-power shortwave broadcast transmitters is one among the rare areas in the field of radiofrequency (RF) electronics, where the electron tube, as the main element for amplification of RF signal, is still in active use. The first successful attempts to replace the electron tube with solid-state components, primarily in the output stage amplifier modules for the Digital Radio Mondiale (DRM) shortwave broadcast transmitters have been published only recently. With the latest technology advancements in RF power transistors, it is now possible for commercially available RF power MOSFET transistors to be used for switching purposes at shortwave frequencies. Here, an architecture of a 10 kW shortwave broadcast transmitter with solid-state power amplifier modules in the RF output stage is proposed. Different implementations of the RF output stage that include power adding network from each amplifier module and the output matching network are analysed, both analytically and numerically. After choosing the optimal architecture, a prototype of a commercial shortwave DRM broadcast transmitter was designed and constructed, measured, tuned and tested at RIZ Transmitter factory Zagreb.

Highlights

With the advent of electron tube technology in the 1920s, power amplification of electrical signals has played a key function in radio broadcast systems
An attempt of introducing digital modulation techniques into the shortwave broadcast bands comes in the form of the Digital Radio Mondiale (DRM) standard that introduces Orthogonal Frequency Division Multiplexing (OFDM) modulation techniques in the existing Amplitude Modulation (AM) broadcast bands [12,13]
radio frequency (RF) exciter is capable of generating a dedicated pair of signals which are used to drive each of the power amplifier modules [18]

Summary

Introduction

With the advent of electron tube technology in the 1920s, power amplification of electrical signals has played a key function in radio broadcast systems. Those early years of broadcasting offered low efficiency, bulky transmitters. The electron tube is used only in the output stage, obtaining high-power amplitude-modulated RF signal in the shortwave band (3.9–26.1 MHz) with frequency auto-tuning systems. An attempt of introducing digital modulation techniques into the shortwave broadcast bands comes in the form of the Digital Radio Mondiale (DRM) standard that introduces Orthogonal Frequency Division Multiplexing (OFDM) modulation techniques in the existing Amplitude Modulation (AM) broadcast bands [12,13] Using this approach the audio quality on AM bands is the same as in FM bands [14,15]. We describe a possible architecture, give an insight in the fabricated RF output stage and present the preliminary experimental results of the prototyped novel shortwave DRM broadcast transmitter in solid-state technology

Basic architecture of high-power shortwave transmitter

Power amplifier module

Power combiner and output matching circuit

Solid-state 10 kW shortwave transmitter prototype

Findings

Conclusions