1 Chelmsford Amateur Radio Society Intermediate Licence Course Murray Niman G6JYB Slide Set 4 (3) Technical Basics -2: Circuits Chelmsford Amateur Radio Society Intermediate Course (3) Technical Basics - 2 Circuits

2 Chelmsford Amateur Radio Society Intermediate Licence Course Murray Niman G6JYB Slide Set 4 (3) Technical Basics -2: Circuits Tuned Circuits Radios depend on the concept of tuned circuits. Tuned circuits are built from combinations of Inductors and Capacitors which have a self-resonant frequency. Tuned circuits are thus able to selectively pass or block frequencies in transmitters and receivers. They are the basis of tuners, filters, oscillators, ATUs etc.

3 Chelmsford Amateur Radio Society Intermediate Licence Course Murray Niman G6JYB Slide Set 4 (3) Technical Basics -2: Circuits Tuned Circuits - 2 Tuners, Filters etc depend on the concept of tuned circuits. Parallel Tuned - Reject Current Series Tuned Accept Current

4 Chelmsford Amateur Radio Society Intermediate Licence Course Murray Niman G6JYB Slide Set 4 (3) Technical Basics -2: Circuits Power Supplies Power Supplies convert AC Mains to DC via Transformers, Diodes and Capacitors Diodes Give DC Conversion Capacitors Store Energy and Smooth Waveform, but can still leave a ripple Transform Mains AC to lower Voltage

5 Chelmsford Amateur Radio Society Intermediate Licence Course Murray Niman G6JYB Slide Set 4 (3) Technical Basics -2: Circuits Power Efficiency Circuits consume more power than they output. Nothing is 100% efficient, and the waste is dissipated as heat. RF output power of an amplifier is less that the DC input power due to inefficiency - may only be 20-30% efficient. So a 50W PA may also generate 100W of heat, and need a total of 150W from a power supply Ambient and Internal Temperatures and Sound Mechanical Construction can be key factors in Circuit Reliability and Stability