Highfields Amateur Radio Club
Constructors Corner.
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Component Recognition.
By Brian, MW0GKX.

NameSymbolComponent PictureUnit(s)Comments
Fixed
resistor
circuit symbol: fixed resistor Resistors Ohm Ω
& Watts
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
circuit symbol: resistor variable Variable resistor Ohm Ω A resistor of variable value and intended to be varied by the user. Also called a Potentiometer.
Preset
variable
resistor
circuit symbol: resistor preset Preset resistors Ohm Ω 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
Fixed capacitor circuit symbol: capacitor fixed Fixed capacitors Farad
sometimes Volt also
A capacitor of relatively small fixed value which can come in many different packages
Variable capacitor circuit symbol: variable capacitor 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
circuit symbol: variable capacitor preset trimmer 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 or trimmer capacitor
Electrolytic capacitor circuit symbol: electrolytic capacitor Electroylic capacitor Farad & Volts A fixed value capacitor of large and very large capacitance, also known as a polarised capacitor. A smaller cased polarised capacitor is called a Tantalum or Tantalum Bead capacitor. Must be inserted in the correct polarisation
Tantalum
Bead
capacitor
Tantalum Bead capacitor
Inductor circuit symbol: inductor Inductor Henry Basically a coil of wire (most often used when forming tuned circuits)
Inductor iron cored circuit symbol: adjustable inductor an adjustable inductor Henry The amount of inductance can be varied such as when adjusting a tuned circuit
Variable Inductor circuit symbol: variable inductor a variable inductor Henry The one shown is a roller or roller coaster inductor from an antenna tuner
Transformer circuit symbol: transformer 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
Diode
(Rectification)
circuit symbol: rectifier diode diodes Volts (max) & Amps (max) A semi conductor which only allows current to pass in one direction
Variable Capacitance Diode
Varicap Diode
circuit symbol: varicap diode Also called Varactor or Varicap.
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
Schottky Diode circuit symbol: schottky diode Also called hot carrier diode.
A semiconductor diode with a low forward voltage drop and a very fast switching action
Tunnel Diode circuit symbol: tunnel diode tunnel diode Volts (max) & Amps (max) Also called Esaki diode.
A diode which is capable of very fast operation, well into the microwave frequency region. Also relatively resistant to nuclear radiation, compared to other diodes
Zener Diode circuit symbol: zener diode zener diode Volts & Watts A type of diode that permits current not only in the forward direction like a normal diode, but also in the reverse direction if the voltage is larger than the breakdown voltage known as Zener knee voltage or Zener voltage
Photo Diode circuit symbol: photo diode Photo diode Volts (max) & Amps (max) Also called photosensitive diode.
A type of photodetector capable of converting light into either current or voltage, depending upon the mode of operation. Often looks like an LED
Light emitting diode (LED) circuit symbol: LED (light emmitting diode) Light emmitting diode Volts (max) & Amps (max) A semi conductor which only allows current to pass in one direction but illuminates due to the passing current. Available in a multitude of colours
Lamp circuit symbol: lamp Lamps Volts & Watts (or Amps) Come in all shapes, sizes and colours. Used for illumination and as status markers
Valves (Tubes) circuit symbol: a valve (typical, varies with type)
Example
valve N/A 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 circuit symbol: transistor 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, plus gain characteristics, max voltages and currents
Field Effect
Transistor
FET
circuit symbol: FET
Integrated circuits Depends on type, usually a box with lots of connections or may be shown as a series of triangles, each one being a part of the whole IC Integrated circuits N/A 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
Crystal circuit symbol: crystal (xtal) Crystals Hertz Crystals come in many different cases but all perform the same basic function to provide a fixed frequency for an oscillator
Microphones circuit symbol: microphone Microphone Ohms.Ω 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 circuit symbol: speaker Speaker Ohms Ω & Watts. Speakers come in many different sizes according to the frequency range and power they are designed to handle
Earphone circuit symbol: earphone earphone Ohms.Ω High impedence earphone
Headphones circuit symbol: headphones headphones Ohms.Ω Low impedence (usually) headphone
Cell circuit symbol: cell some cells Volts & Amps Usually around 1 - 3 Volts per cell
Battery circuit symbol: battery collection of cells connected in series 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 circuit symbol: dpdt switch dpdt switch 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 circuit symbol: dpst switch dpst switch 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 circuit symbol: spdt switch spdt switch Volts & Amps s.p.d.t = Single Pole Double Throw - this is a change over switch that has 1 set of change over contacts
Switch
s.p.s.t
circuit symbol: spst switch spst switch 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 circuit symbol: fuse fuses Volts & Amps Come in all shapes and sizes. Disconnects power to a circuit when an overload occurs. Do not be tempted to use a higher rating than listed on the equipment. They are a single use safety device. See: Fuses page for more info
Circuit Breaker circuit symbol: circuit breaker circuit breaker Volts & Amps Sometimes called a Resettable Fuse. Disconnects power to a circuit when an overload occurs. Automatic resettable fuses use temperature to reset, a thermal strip bends during overload, breaking contact and, as it cools, resets, whether the overlaod has been cleared or not. Manual types reset via a button once overload is removed. Do not be tempted to use a higher rating than listed on the equipment. They are a safety device
Thermal Fuse circuit symbol: thermal fuse thermal fuses Volts (max), Amps (max) & Temp Disconnects power to a circuit when higher than normal temperature occurs. Often mounted in contact with a heat sensitive component, clampped to a heatsink or integral with protected component (some "Wall Wart" transformers have them made into the transformer). Do not be tempted to use a higher temperature rating than original as fire could result. They are a safety device
NameSymbol
Antenna circuit symbol: antenna
Earth circuit symbol: earth
Chassis Ground circuit symbol: chasis ground

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