Overview

Over the years, advances in transistor technology have produced devices capable of considerable RF power in the HF range. These modern devices make possible today's compact, yet powerful, RF power amplifiers (PAs).

This chapter will consider the design of linear PAs for the 1.6-to 30-MHz range at power levels up to 1000 W. Only linear operation will be covered, as it is commonly used in most SSB transmitters. It also forms the basis of the more sophisticated applications covered in Chapter 13. The normal HF range, usually considered as 3.0 and 30 MHz, has been extended over recent years to the top of the AM broadcast band at 1600 kHz. This is a result of increased military and maritime usage, coupled with advances in solid-state technology.

Transistors with ever-increasing power dissipation capabilities have been developed, making high-power solid-state linear amplifiers practical. As few as eight output transistors are used in a Rockwell 1000-W (average) PA. Such amplifiers have replaced vacuum tube amplifiers at lower power levels and seriously challenge them at the > 1000-W level as component costs decrease, linearity improves and higher-power devices become available.

12.1 A Typical Solid-State HF PA

Figure 12.1 shows a block diagram of a typical solid-state HF PA. A high power system is shown in order to illustrate the combining of multiple output modules and their ancillary control systems. Multiple modules are usually required for output powers greater than 250 to 500 W. Depending on the types of devices used,...