Bredhurst Receiving and Transmitting Society
Technical Basics Part 1
Whilst this is not the start of the Technical Basics Syllabus we have found it easier to introduce the Technical side of Amateur Radio by starting with the ELECTRON the basis of all electrical theory then all else follows.
Welcome to the electronics parts of the course. The word electronics comes from the word electron and an electron is defined in the "Oxford" dictionary as :-
An electron is a stable elementary particle with indivisible charge of negative electricity, found in all atoms and acting as carrier of electricity in solids.
What that means to you and I is that the electron forms the basis of all electrical theory and has a negative charge and therefore is attracted to anything with a positive charge.
Electrons can flow easily in some materials that are called conductors and not flow easily in others which are called insulators. An example of a conductor is a piece of copper wire and an insulator is plastic such as you often find around the out side of a wire so that your fingers are "insulated" from the wire carrying electrons.
This following could be a big learning jump for you - so take it slowly and anything you do not understand let your course tutor know - they should be able to explain it further - so that you have it clear in your mind from the start.
We are now going to look at the parts of the syllabus but are changing the order to help introduce you to the subject of electronics.
that a battery provides Potential Difference ( Voltage ) at
its terminals and that a circuit is needed to allow current to
Cells and batteries
A battery provide a potential difference (a voltage) at its terminals. One terminal is marked POSITIVE and the other NEGATIVE and the battery will provide DC DIRECT CURRENT when connected into a circuit.
Up to this moment you probably thought that the picture above shows a battery. In terms of going into a shop and asking for a battery you would still be right, but for the course you have to know that the picture above shows a single cell and that a battery is a number of cell either linked in series or parallel.
What does series and parallel mean ? Ok I will come back to that in a minute.
First let me tell you about a cell. One end is marked + and is the "positive" end and the other is often but not always marked - and is the "negative" end. The positive end is often the one with a protruding pip.
It is from the negative end that electrons are in abundance and they are all trying to reach the positive end. If you were to link a wire from the negative end to the positive end then electrons would flow. What you would have created is what is called a "CIRCUIT" between the positive and the negative terminals.
It would not do any good purpose except what we call flatten the battery, when all the spare electrons have flowed down the wire to the positive end. Even with a battery shown above if the wire is not thick enough it could get hot and thus burn your fingers.
NEVER connect a wire from the positive terminal to the negative terminal of any cell or battery else a fire could result. Such connection is called a "short circuit".
In the battery we have said that there is an abundance of electrons trying to leave the negative terminal and reach the positive terminal. We could also say that there is an opportunity for a current to flow if a wire was connected (or the "potential" for a current to flow if a wire was connected). The word potential is taken further in electronics and added to the word "difference" and we say that there is a POTENTIAL DIFFERENCE between the negative and positive terminals and the greater the number of electrons trying to make the journey the larger the potential.
The potential difference is measured in volts. Thus it is also said that a battery supplies a voltage.
Series and parallel
Linked in Parallel
What does series and parallel mean? It is the way batteries can be connected together. Let us explain further below.
You are now aware that a cell has two terminals one + and one -.
If we had three cells and joined all the + together and then joined all the - together we would have the cells in parallel. See diagram below.
Remember that a combination of 2 or more cells forms a battery.
Linked in Series
If we had three cells and joined the - of one cell to the + of the next and the - of that cell to the + of the third cell the cells would be arranged in series.
You might like to remember that linked in SERIES is just like a STRING of SAUSAGES you can buy at the supermarket ;- each join only to the next one.
Remember that a combination of 2 or more cells forms a battery.
CIRCUIT DIAGRAM SYMBOLS
These circuit diagram symbols will be introduced to you bit by bit (as necessary).
The two drawings above are representations of parallel and series batteries but they took a great number of lines to draw and there is an easier way by the use of what are called "circuit diagrams symbols" to represent the batteries.
Above is the circuit symbol of a cell and the second one is annotated to show the positive and negative terminals. In circuit diagrams the annotation is not used but is given here for you to learn. The positive side is the longer of the two lines.
The batteries shown above could therefore have been drawn as follows:-
|For there to be a circuit in
which current will flow there must be an unbroken path between
one battery terminal and the other.
3b.5 Recall that the polarity of a battery is not relevant if a filament bulb is used but that electronic circuits can be damaged by the wrong polarity.
Polarity of a battery + and -
A battery has two terminals to which you could connect wires. One is marked + and one marked - . The + indicated the positive terminal and the - the negative terminal.
There are very few electronic components that are NOT said to be "polarity sensitive".
What does polarity sensitive mean ? This means that if a positive terminal of a battery ( the one marked with a + ) is connected to where the negative terminal ( the one marked with a - ) should be connected and the negative connected to the positive terminal DISASTER will occur in most circumstances and the components ruined or a fire could occur !! So if you connected a battery the wrong way round in a portable battery radio not only would it not work when the battery is connected the wrong way round it will almost certainly not work when then connected the right way round.
remind you of hat you read earlier and hope that it
is now clear in your mind !
HOWEVER --- A filament lamp such as a torch bulb - relies upon the battery pushing an electric current through the filament in the bulb to shine BUT the bulb do not mind which way round the terminals of the bulbs are connected to a battery. It is therefore safe to connect either terminal of the battery to either of the wire leads from the bulb.
A lamp (bulb) does not mind which way round the electron are pushed by the battery
Why does it not matter which way round they are connected ? It is because the filament bulb is just a special piece of wire inside a glass holder and like any other piece or wire it can be connected which ever way round happens first!
Identify the circuit symbols shown in Table 1 below.
The origin of some of the text on this page is from the RSGB with additions by the web master