Narrow-bandwidth Television Association
Basic Electronics' theory
The prospect of learning about electronic circuit construction, testing and
theory of the equipment they are building daunt many people starting out.
Hopefully through a series of articles on this site the beginner will feel more
comfortable attempting to build NBTV equipment. Where possible I will include
links to other sites offering similar tutorials. NBTV is a hobby in which no
'off the shelf' equipment is available and therefore has to be 'home brewed'.
Luckily there are several proven designs around. Many of these have an
associated printed circuit board making construction easier and more reliable.
Projects without these boards will need to be constructed on breadboard or
stripboard, which we will cover later.
Printed circuit board, PCB
To the beginner a printed circuit board
populated with various components will seem a maze of multi legged blocks plus
strange devices with wires out each end and coloured mass between them. There
are many types of components but these normally fall into predefined categories.
In order to miniaturise the size of electronic assemblies for the mass market
the manufacturer will employ surface mount technology where all the components
are soldered directly to the board using a series of 'pads' on each component
connection. Larger versions of these devices are still available for the home
Passive and active
We divide our components into two classes; the first is passive components and
the second active. The active class is then sub divided into both analogue and
digital. The passive components consist of the following: - Resistors These we
can draw an anlogy to a water tap or valve in electronic circuits, they restrict
current flow, we can therefore use them to attenuate signals. Resistors are
available in different ohmic values and dissipation (watts) as the circuit
dictates. Most of our circuits will be using ¼ watt resistors and are
identified by a series of coloured rings around their bodies denoting their value
and accuracy. Resistors are used extensively with other passive components within
filter networks where we wish to accept or reject certain frequency signals.
When an ac voltage is applied across a resistor there is no phase shift between
the applied voltage and the current flowing through the resistor.
As with resistors these
devices come in a variety of values and voltages to suit the application. The
units used to denote the capacitance is the farad. The capacitors we may use
will be between Pico farads to approximately 1000 microfarads. The smaller
capacitors are used within filter networks and provide suppression and the
larger counterparts are used for 'smoothing' of power supplies. When an ac
voltage is applied across a capacitor the current flowing through the capacitor
leads the voltage by 90 electrical degrees making this device ideal for filter
Although not used so much
nowadays there formally called 'chokes' because they restricted ac current flow
in a circuit whilst low resistance to dc. Used mainly in filter circuits either
at audio levels or within thyristor circuitry to reduce voltage 'spikes' caused
by switching of the thyristor. When an ac voltage is applied across an inductor
the current flowing through the capacitor lags the voltage by 90 electrical
degrees making this device ideal for filter networks.
The remaining components we are likely to be
involved with within NBTV are called semiconductors. These are refered to as
active components as unlike their passive counterparts they have the ability to
amplify signals. We can break down the semiconductors further to include digital
devices such as logic chips, microprocessors, memory devices etc and analogue
components including a wide range of amplifiers. The simple transistor is a
semiconductor device although many thousand of these devices may be found within
a single Integrated circuit package. Please find several sites offering further
insight to the world of electronics.
Resistor colour code
4000 series CMOS pin