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On: 07 Jan, 2021

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A. Antenna
B. Tuning (Tuner Circle)
C. Detector
D. Sound Amplifier
E. Final Brace
F. Sound Tool (Loudspeaker)
G. Source of electric current

Studying radio receivers cannot ...


A. Antenna
B. Tuning (Tuner Circle)
C. Detector
D. Sound Amplifier
E. Final Brace
F. Sound Tool (Loudspeaker)
G. Source of electric current

Studying radio receivers cannot be separated from radio transmitters, because they are related to each other. There is no meaning to a radio receiver without a radio transmitter and vice versa.

transistor three radio parts

Radio receivers are also called receivers or often known as RX, while radio transmitters are also called transmitters or known as 7X. Subsequent developments, human creative power in the field of electronic engineering resulted in a fusion or fusion of the two planes into a radio that could receive and transmit. This aircraft is called a transceiver (combination of transmitter and receiver) and is known as the TX-RX. An example of TX-RX is HT (Handy Talky).
In principle, a transmitter consists of five parts, namely as follows.
1. Audio Frequency Amplifier
2. Oscillator (oscillator), is a high frequency generator (high frequency)
3. The modulator section
4.The radio frequency amplifier section
5. Transmitting antenna

transmitter block scheme

Do you know how a radio transmitter works? The sound frequency that comes from a tape recorder or microphone is received by the sound amplifier or AF. Meanwhile the frequency and oscillator part are given to the modulator to be mixed.
The resulting mixture generates a weak radio vibration (RF) and is fed to the radio vibration amplifier (RF) section. This part of the RF amplifier generates a fairly strong radio frequency and is emitted in all directions using a transmitting antenna.
High frequency (HF) or carrier frequency, is in charge of carrying the sound frequency (AF). Radio frequency (RF) is a mixture of sound frequency (AF) and high frequency (HF) or it is also called a modulated wave. The schematic of the mixing block between high frequency (HF) and sound frequency (AF) is shown in Figure 1.2 below.

hf and rf vibration mixing block scheme

Three transistor radio consists of seven parts, namely:
1) antenna;
2) tuning;
3) detectors;
4) AF amplifier;
5) final amplifier;
6) sound tools;
7) current source.

Antenna is part of a radio receiver that functions to receive various electromagnetic waves emitted by several radio transmitters. Antennas in direct system radio receivers may use either a wire or rod type antenna. This is because the capture of electromagnetic waves on the radio receiver is very weak. This wiring must use an insulator. The antenna is stretched between the two insulators and the connecting wire (per line) which serves as a link with the radio receiver.

Tuning is also called tuner loop. This section serves to select a radio frequency offensive to the receiving antenna.
A good tuner loop only produces one radio vibration which is fed to the mixer section. The tuner loop consists of a varco (variable condensator) and a ferrite rod core antenna spool. In order for a radio to receive broadcasts from a transmitting station, the tuning must be able to resonate with the vibrations of other objects. For example a gong that is hit, the surrounding air will also vibrate so that the sound of the gong will be louder. Resonance can occur when both objects have the same frequency. The size of the vibration caused by the tuning circle depends on two factors, namely the size of the varco capacity value and the coefficient of the induction value of the antenna spool. In addition, the size of the vibration caused by the tuner can also be determined by twirling the varco shaft.

The detector serves to separate the sound frequency from the carrier frequency. Frequency separation must be carried out because the next process only requires sound frequencies, while the carrier frequency task is complete. The sound frequency (audio) is transmitted to the sound amplifier through the coupling (connecting) capacitor, while the carrier frequency is discharged to ground through the junction capacitor. The result of this part of the detector is a sound frequency that is still weak which can be amplified by the sound amplifier.
The principal components of the detector are a germanium 1 N 60, OA 80, OA 79 or similar detector diode and two ceramic capacitors for coupling and by-pass.
The detector circuit is divided into two parts, namely a rectifying circuit and a low pass filter circuit, which is a filter that is used to obtain low frequency information (news).

The sound amplifier is called an AF (Audio Frequency) amplifier, driver, or sound booster, which functions to amplify weak sound frequencies into stronger sound frequencies. The result of this sound frequency section is a sound frequency with a slightly loud amplitude (vibrating intersection). The main component of the sound amplifier is an input transformer IT 181 as a phase reverser and a racistor TR3 as an amplifier. For more details, look at the schematic of the power section in Figure 1.3.

final amplifier


Although the sound frequency produced by a sound amplifier is strong, it is not yet able to vibrate a loudspeaker. Therefore, the sound frequency of this sound amplifier must be amplified again by a final amplifier circuit. Look at Figure 1.4!

schematic of the sound amplifier part

The main components of the final amplifier are an output transformer (OT 240) and two transistors, TR1 and TR2, respectively. The output transformer (OT 240) functions as an impedance or an adjustment between the final amplifier and the loudspeaker. Transistors TR1 and TR2 are connected in balance to get a greater frequency gain. The balance connection is a connection of two transistors of a kind and similar characteristics. Similar means that the two transistors are both PNP or NPN types, while characteristic means that both transistors have the same receipt number, for example the balance connection is two NPN transistors with D 467 characteristics.Examples of balance connections can be seen in Figure 1.5 in side.

balance connection

The sound tool (loudspeaker) functions to convert the electrical vibrations of sound into audible sound vibrations. Voice instruments have unit data as follows.
1. Sound instrument diameter unit: inch (") (1 inch = 2.54 cm) Examples of sound instrument size: 2", 4 ", 8", 10 ", 12", 15 ", and 18".
2. The unit of value for sound instrument resistance: ohm (Q) Examples of resistance values ​​used: 452, 852, and 1652.
3. Maximum power unit for sound equipment: watts (W) Examples of maximum power used: 5 W, 10 W, and hundreds of Watts.

Do you know how a loudspeaker (LS) can produce sound? To find out, you need to know the parts and how LS works. The loudspeaker consists of:
1) spoke windings (container and coil),
2) membrane (paper thin),
3) paper pear,
4) permanent magnets,
5) magnetic housing / frame, and
6) LS terminal.

loudspeaker parts

Do you know how sound instruments work? Pay attention and understand how it works as follows. The two ends of the talk coil are connected to the LS terminal. Furthermore, the two terminal points are connected to the secondary coil of the OT 240 output transformer, the AC regulated coil with changing poles and containing sound electric vibrations. A coil with an arbitrary pole means that a point on the coil which has a north pole for a moment then changes to a south pole, and so on.

The way the sound instrument works uses the principle of the magnetic force. The two magnets with the same poles (north-north or south-south) will repel, while the two magnets with unnamed north-south poles will be attractive. The permanent magnet (next to the kifi) on the LS has a fixed pole, for example a north pole. Suppose coil a is north pole, then coil b is turned south. Coil a will be repelled by permanent magnets or attracted by coil b so that coil a is shifted to the left. When for a moment coil a's pole changes to a south pole, coil a will be repelled by coil b or attracted by a permanent magnet, so coil a is shifted to the right. This process will continue continuously causing the speech roll to move left and right quickly. The sleeve and the spoke coil are attached to the pear which is usually brown in color, so the pear and membrane move along as the sleeve moves back and forth, the repetitive motion of the sleeve, pear and membrane causes vibrations. Under the membrane there is a sound that vibrates to cause resonance. The movement of the sleeve, pear, and membrane corresponds to the rhythm that enters the legs a and b, so that the sound is heard like the original.

To be able to work, a series of radio receivers requires electric power drawn from the electricity, for example, and PLN. Applying an electric voltage to a circuit must pay attention to the type of current and power accordingly. The power drawn from the PLN electricity network must use an adapter.

the source of the electric current


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