Transcript Technical Basics

Chelmsford Amateur Radio Society
Foundation Course
(3) Technical Basics
Chelmsford Amateur Radio Society
Foundation Licence Course
Murray Niman G6JYB
Slide Set 3: v1.1, 15-Dec-2007
(3) Technical Basics
1
Electrical Units
Quantity
Voltage, V
Current, I
Resistance, R
Power, P
Frequency, f
Wavelength, 
Unit
Volt
Amp
Ohm
Watt
Hertz
Metre
Symbol
V
A

W
Hz
m
Note-1: Resistance is the opposition to current flow
Note-2: Voltage is sometimes referred to as Potential Difference
Chelmsford Amateur Radio Society
Foundation Licence Course
Murray Niman G6JYB
Slide Set 3: v1.1, 15-Dec-2007
(3) Technical Basics
2
Unit Prefixes
Factor
millionths
thousandths
thousands
millions
Prefix
micro
milli
kilo
Mega
Examples:
4.7k= 4700
1500mA = 1.5A
0.6MHz = 600kHz
Chelmsford Amateur Radio Society
Foundation Licence Course
Symbol
or u
m
k
M
Murray Niman G6JYB
Slide Set 3: v1.1, 15-Dec-2007
(3) Technical Basics
3
Power
P Watts
V Volts I Amps
Relates Power, P
Voltage, V
P=VxI V=P/I I=P/V
Chelmsford Amateur Radio Society
Foundation Licence Course
Murray Niman G6JYB
Current, I
Slide Set 3: v1.1, 15-Dec-2007
(3) Technical Basics
4
Ohms Law
V Volts
I Amps
R Ohms
Relates Voltage, V Current, I
Resistance, R
V=IxR I=V/R R=V/I
Chelmsford Amateur Radio Society
Foundation Licence Course
Murray Niman G6JYB
Slide Set 3: v1.1, 15-Dec-2007
(3) Technical Basics
5
DC & AC Power

• Batteries provide a source of DC power
• DC- Direct Current, flows in a single direction

AC - Alternating Current
• AC is easier to generate and transform
• Mains is 50Hz AC. Radio uses High Frequency AC
• Simple items such as Bulbs work with AC and DC, but many
electronic components are sensitive to the direction of current
Chelmsford Amateur Radio Society
Foundation Licence Course
Murray Niman G6JYB
Slide Set 3: v1.1, 15-Dec-2007
(3) Technical Basics
6
Frequency & Wavelength
• In air the velocity, v of radio waves is a constant ( ~3x108m/s)
• So if the frequency increases, the wavelength decreases, and
vice versa, determined by: v = fx
• A 1MHz to 1000MHz conversion chart, and frequency allocation
table is available
v
f
v m/s
f Hertz

Chelmsford Amateur Radio Society
Foundation Licence Course
Murray Niman G6JYB
 metres
Slide Set 3: v1.1, 15-Dec-2007
(3) Technical Basics
7
Circuit Symbols
• Also need to recognise symbols for
Switches, Earths, Crystals etc, etc
Antenna
Earth


+
Cell
Battery
-

Chelmsford Amateur Radio Society
Foundation Licence Course
Switch
SPST

Resistor
Fuse
Murray Niman G6JYB
Crystal
Loudspeaker
Lamp
Microphone
Slide Set 3: v1.1, 15-Dec-2007
(3) Technical Basics
8