TEP FM RADIO
Code: PACK 1403
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For more information please contact:
Mindsets (UK) Limited
Unit 10
The IO Centre
Lea Road
Waltham Cross
Herts
EN9 1AS
Tel:
Fax:
Web:
01992 716052
01992 719474
www.mindsetsonline.co.uk
Copyright © 2009 Mindsets (UK) Limited
LIT0091
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TEP FM Radio
TEP FM Radio
TEP FM RADIO
OPTIONAL RADIO COMPONENTS
The following optional radio components are available from
Teaching Resources.
INTRODUCTION
The TEP radio is a high performance FM receiver based on the
industry-standard TDA 7000 chip. The radio is supplied as a
completely populated printed circuit board (PCB) that requires
only the addition of five external components: battery,
loudspeaker, tuning control, volume control and small aerial
supplied within the pack. A working radio can be assembled from
the parts provided in the TEP radio pack, but other external
components can be substituted to provide a choice of control
functions - and improved sound quality.
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Loudspeaker approx 125mm Ø
Stereo headphone socket
Small telescopic aerial
10k Linear slider variable resistor (for tuning)
10k Linear slider variable resistor (logarithmic for volume
control)
10k variable resistor for volume control with integral on/off
switch
10k multiturn variable resistor (for tuning)
10k multiturn pre-set resistor (for tuning)
2 pole multiway switch
Loudspeaker covering fabric (grey)
Loudspeaker covering fabric (black)
Matrix board (for loudspeaker grill modelling)
Stereo headphones
Loudspeaker (outline
shape indicative only)
Linear slider resistor
Multi-turn pre-set resistor
Designing and making a complete radio offers a huge range of
fascinating and potentially challenging design decisions and is a
very practical vehicle for teaching many of the principles
involved in radio electronics and acoustics.
This handbook provides basic instructions for the completion of
a working radio and also discusses key component and design
options. It also includes useful information and technical data in
the study files section. Like other TEP 'special' publications, this
book can be used in the classroom in a variety of ways. For
example, the first part may be photocopied as a basic
construction handbook; selected parts can also be provided as
back-up information or to assist pupils in making design
decisions; or the whole book can be made generally available as a
reference resource.
Headphones
Multi-turn variable resistor
Small telescopic aerial
Stereo headphone socket
VERSION 1
2
VERSION 1
7
TEP FM Radio
TEP FM Radio
Step 6
TEST and TUNE the radio by turning the volume control to the
half way position. A background 'hiss' should be heard. Turn the
tuning control slowly backwards and forwards through its full
range and at the same time adjust the inductor using the special
tool provided. When the inductor is correctly set, it should be
possible to receive the main advertised FM stations within the
frequency range 90MHz to 106MHz. It may be useful at the same
time to have a commercial radio tuned in to act as a reference for
calibration of a tuning scale etc.
Radio frequencies:
Radio 1.
Radio 2.
Radio 3.
Radio 4.
Virgin.
Classic FM.
97.6 - 99.8 MHz
88 - 90.2 MHz
90.2 - 92.4 MHz
92.4 - 94.6 MHz
105.8 MHz
100 - 102 MHz
Radios are a rich resource for
designing and making and
most pupils and students will
want to look at wider design
and styling options - including
'retro-styling'.
It is important to note that the loudspeaker needs a baffle. This is
normally provided by putting the loudspeaker into an enclosure.
The difference in sound quality and volume that this makes can
be demonstrated by listening to the sound before and after hands
are cupped around the loudspeaker.
If stereo headphones are used, they should be connected in
series. This is achieved by wiring the socket supplied from
teaching resources as shown. At maximum volume, the output
power of the radio will be excessive for most headphones. To
limit the maximum volume, resistor R4 on the PCB should be
replaced by a higher value - e.g. 220 ohm.
If the radio fails to work first time:
Rear of socket
A basic working TEP radio can be assembled using only the
components supplied in the TEP radio pack. However, a wide
variety of interesting variants and design options are discussed at
length in the various sections of this handbook.
To board
• check that batteries have been correctly inserted in the battery
box if used. Check on battery condition
• disconnect the battery and
check all external leads for
continuity - including the
battery snap. This can be
done using a continuity
checker or multimeter. For
each check, place one
probe on the PCB track
immediately adjacent to
the soldered joint and the
other at the extremity of
the component tag to
which a lead is soldered.
This will show up possible
faults in soldered joints.
ASSEMBLING THE RADIO
COMPONENTS:
Printed circuit board (PCB)
(marked 'B' on casing)
1.5 metres assorted
colour stranded wire
10k variable (logarithmic)
resistor for volume control
(marked 'A' or '-2' on casing)
NOTE: Almost all reported
problems arising from selfassembly kits are due to
faulty soldering - either
'dry' joints or bridging
across PCB tracks by
excess solder.
VERSION 1
10k variable (linear)
resistor for tuning *
Loudspeaker
2 Battery snaps
(1 snap as illustrated for PP3
battery plus larger snaps for
PP7 and PP9)
6
VERSION 1
3
*NOTE: The TEP radio is tuned by
using a variable resistor and a varicap
(whose capacitance depends on
voltage). This arrangement is cheaper
and more flexible than using a
variable capacitor.
TEP FM Radio
TEP FM Radio
Step 1
Solder on the battery snap leads - ensuring that the red lead is
connected to +ve on the PCB.
Step 5
Step 2
CHECK that all connections are correct and secure and then
connect a 9 volt battery. A PP3 type will do for test purposes at low
volumes or with headphones. Only the following are recommended
for permanent use:
Step 3
• Six AA size batteries in an appropriate holder
• PP7 type 9v battery
• PP9 type 9v battery
Solder on the loudspeaker using two lengths of stranded wire.
The loudspeaker can be connected either way round.
Solder on a length of approximately 0.5m stranded wire to act as
an aerial.
Step 4
Solder on the tuning and volume control variable resistors as
shown using three lengths of stranded wire for each. The
variable resistor marked 'A' is for volume control and the one
marked 'B' is for tuning.
Even at moderate volume levels, the voltage of a smaller 9v
battery may drop below the required 7 volt threshold and the
radio output will suddenly lock into a continuous howling
sound. This can be rectified by turning down the volume or, for
example, replacing a 'flat' battery.
For each variable resistor, the two outer leads can be connected
either way round, but this will determine the direction of tuning
and volume control when the resistor spindles are turned. It is
essential that the centre lead goes to the centre connection of
each variable resistor.
PP7
PP9
6 x AA
PP3
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VERSION 1
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Relative battery sizes
4
VERSION 1
5