Introduction of FM Transmitter:-
The FM TV transmitter uses standard 1 FM modulation for sound and PAL for video modulation.
Thus we can say that in this FM transmitter two type of modulations are being performed on two different signal, one for voice or audio signal modulation and the second for the video signal modulation. We will discuss these two modulation and how these are going to perform practiclly in the FM transmitter ciruict.
The Audio signal modulation will be discussed first which is modulated using a pre-amplifier circuit consisting of a transistor Q1 and some associated components.
While the transistor Q2 is performing two jobs:
1. production of carrier frequency and
2. modulation.
The pre-amplified audio signal from transistor Q1 is fed to the base of transistor Q2 for modulation.
The Capacitor C5 and inductor L1 forms the tank circuit which is responsible for producing the carrier frequency.
Now we will discuss the video signal modulation, the video signal is fed to the emitter of transistor Q2 via POT (variable resistor)R7 for modulation. Afte the audio and video modulation performed at transistor Q2 is ready to transmit. The modulated composite signal (audio+video) is transmitted by the antenna A1.
Construction of inductor used in the FM transmitter:-
Here we will discuss the construction of the inductor L1 used in the above transmitor circuit.
The Inductor L1 can be made by making 4 turns of 24SWG enameled copper wire on a 6mm dia: plastic former.
The Tansformer used in Transmittor:-
The tranformer T1 can be a radio frequency transformer with built in capacitor. This transformer can be obtained from any old readio.
Antenna A1 can be a 1M long copper wire. (Experiment with the length to get optimum performance). This transmitter is working in VHF band somewhat between 50 – 210MHz. This transmitter is compatible only with PAL B and PAL G systems.
List of Component used in the transmittor:
R1 = 10KOhm
R2 = 47KOhm
R3 = 15KOhm
R4 = 8.2KOhm
R5 = 47KOhm
R6 = 47KOhm
R7 = 1Kohm
R8 = 75Ohm
C1 = 10uF/25Volt
C2 = 0.001uf/10nF
C3 = 100nF
C4 = 10nf
C5 = 47pF (variable capacitor)
C6 = 10nF
C7 = 10pF
C8 = 27pF
c9 = 100nF
C10 = 470uF
c11 = 10nF
C12 = 220uF/25Volt
Q1 and Q2 = BC547 NPN transistor
T1 = T1 can be a radio frequency transformer with built in capacitor. (Can be found on old transistor radio boards).
L1 = 4 turns of 24SWG enameled copper wire on a 6mm dia: plastic former.
S: elektroarera.blogspot.com
0 comments:
Post a Comment