Chelmsford Amateur Radio Society Intermediate Course (3) Technical Basics - 2 Circuits

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

Tuned Circuits

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Radios depend on the concept of tuned circuits.

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Tuned circuits are built from combinations of Inductors and Capacitors which have a self-resonant frequency.

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Tuned circuits are thus able to selectively pass or block frequencies in transmitters and receivers.

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They are the basis of tuners, filters, oscillators, ATUs etc.

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

Tuned Circuits - 2

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Tuners, Filters etc depend on the concept of tuned circuits.

Parallel Tuned Reject Current Series Tuned Accept Current

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

Power Supplies

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Power Supplies convert AC Mains to DC via Transformers, Diodes and Capacitors

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

Power Efficiency

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Circuits consume more power than they output. Nothing is 100% efficient, and the waste is dissipated as heat.

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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

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Ambient and Internal Temperatures and Sound Mechanical Construction can be key factors in Circuit Reliability and Stability

Chelmsford Amateur Radio Society Intermediate Licence Course Murray Niman G6JYB Slide Set 4 (3) Technical Basics -2: Circuits 5