Download Technical Basics - 2

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