Highfields Amateur Radio Club
Constructors Corner.

Component Recognition.
By Brian, MW0GKX.

Name.	Component Picture.	Unit.	Symbol.	Comments.
Fixed resistor.		Ohm.		A resistor of fixed value, it comes in many different packages depending upon the power handling ie the amount of watts of heat it can dissipate safely in its normal function.
Variable resistor.		Ohm.		A resistor of variable value and intended to be varied by the user.Also called a Potentiometer.
Preset variable resistor.		Ohm.		A resistor of variable value not intended to be varied by the user except when making adjustments to parts of a circuit that once adjusted remain untouched for most of the time. Enclosed and Skeleton types shown.
Name	Component Picture	Unit	Symbol	Comments
Fixed capacitor.		Farad		A capacitor of relatively small fixed value which can come in many different packages.
Variable capacitor.		Farad.		A capacitor of variable value and intended to be varied by the user - can be of various sizes depending upon the voltage potential that will be applied to the plates before flashover.
Preset variable capacitor.		Farad.		A capacitor of variable value not intended to be varied by the user except when making adjustments to parts of a circuit that once adjusted remain untouched for most of the time. Also called a trimming capacitor.
Electrolytic capacitor.		Farad.		A fixed value capacitor of large and very large capacitance, also know as a polarised capacitor. A smaller cased polarised capacitor is called a tantalum capacitor.
Name.	Component Picture.	Unit.	Symbol.	Comments.
Inductor.		Henry.		Basically a coil of wire (most often used when forming tuned circuits).
Inductor iron cored.		Henry.		The amount of inductance can be varied such as when adjusting a tuned circuit.
Variable Inductor.		Henry.		The one shown is a roller inductor from an antenna tuner.
Transformer.		kVA.		Two or more coils of wire in relatively close proximity to each other so that the magnetic field in one can induce a magnetic field in the other.
Name.	Component Picture.	Unit.	Symbol	Comments.
Diode.		Volts (max) & Amps (max).		A semi conductor which only allows current to pass in one direction.
Variable capacitance diode.				A reversed biased diode acts as a small variable capacitor. Varying the reverse voltage changes the capacitance. Although any ordinary diode may be used in this way, diodes manufactured specifically for this purpose can offer controlled and higher levels of capacitance.
Light emitting diode (LED).		N/A.		A semi conductor which only allows current to pass in one direction but illuminates due to the passing current.
Lamp.		Volts & Watts (sometimes Amps).		Come in all shapes, sizes and colours. Used for illumination and as statusmarkers.
Name.	Component Picture.	Unit.	Symbol.	Comments.
Valves (Tubes).		N/A.	Example.	These come in a variety of shapes, sizes and construction, glass being common. There are many types of valve: Diodes, Triodes and Pentodes to name just a few. For further information go to Wikipedia for an insight.
Transistors.		N/A.		These come in a variety of packages depending upon the current that they are to pass. It is important to be aware of the external connections: Emitter, Base & Collector or Gate, Drain & Source, as they are not the same on different transistors. Data sheets are available to indicate package type and what is called "pin out" configuration.
Field Effect Transistor FET.
Integrated circuits.		N/A.	Depends on type, usually a box with lots of connections	Usually found in a "many legged" plastic packaging and are several semi conductors all together in one package where some examples only need few other components to complete an operational circuit.
Crystals.		Hertz.		Crystals come in many different cases but all perform the same basic function to provide a fixed frequency for an oscillator.
Name.	Component Picture.	Unit.	Symbol.	Comments.
Microphones.		Ohms.		Microphones come in many different shapes and sizes the one shown is a small electret microphone such as may be used in a desk mic.
Loudspeaker.		Ohms & Watts.		Speakers come in many different sizes according to the frequency range and power they are to handle.
Earphone.		Ohms.		High impedence earphone.
Headphones.		Ohms.		Low impedence (usually) headphone.
Name.	Component Picture.	Unit.	Symbol.	Comments.
Cell.		Volts & Amps.		Usually around 1 - 2 Volts per cell.
Battery.		Volts & Amps.		A collection of cells connected in series to give more voltage.(Most cells can also be connected in paralell to give a higher current output. NB. DO NOT connect NiCad cells in paralell!).
Switch d.p.d.t.		Volts & Amps.		d.p.d.t = Double Pole Double Throw - this is change over switch that has 2 seperate sets of change over contacts.
Switch d.p.s.t.		Volts & Amps.		d.p.s.t = Double Pole Single Throw - this is a switch that can switch two separate lines on or off at the same time.
Switch s.p.d.t.		Volts & Amps.		s.p.d.t = Single Pole Double Throw - this is change over switch that has 1 set of change over contacts.
Switch s.p.s.t.		Volts & Amps.		s.p.s.t = Single Pole Single Throw - this is the standard on / off switch which can "make or break" a single circuit.
Fuse.		Volts & Amps		Come in all shapes and sizes. Do not be tempted to use a higher rating than listed on the equipment. They are a safety device. See: Fuses page for more info.
Name.			Symbol.
Antenna.
Earth.
Chassis Ground.