Frequency Modulation

-


Aim:-

To study the process of frequency modulation and to calculate the depth of modulation by varying the modulating voltage.

Apparatus:-

Trainer kit.

Circuit diagram



Theory:-

Frequency modulation is a system in which the amplitude of the modulated carrier is kept constant, while its frequency is varied by the modulating signal. The first practical system was put forward in 1936 as an alternative to AM in an effort to make radio transmission more resistance to noise. Phase modulation is a similar system in which the phase of the carrier signal is varied instead of its frequency as in FM, the amplitude of the carrier signal remains constant.

The general equation of carrier wave may be written as.

X=A Sin (ωt+θ)

Where

X=instantaneous value of voltage

A=Amplitude (max)

ω =Angular velocity, radians per second

θ = phase angle radians, radians.

 

Procedure:-

1)  Check the apparatus before making the connection.

2)  Connect the AC adaptor to the mains and another side to the experimental trainers.

3)  Observe carrier signal and modulating signal on dual trace CRO

a)   Carrier signal: Modulator output without any modulating input. Carrier frequency is 160 kHz and amplitude is

 4Vp-P

b)   Modulating signal :

4)  Connect the modulating signal to the modulator input and observe modulating signal and FM output on a dual trace CRO. And plot waveform.

       Tabular column:-


 

Amplitude of Modulation

 

Modulated Frequency

 

∆f

 

T

 

fcm=1/T

 

 

 

 

 

 

 

 

 

 

 

 




Nature  of  graph 






Result:-

Studied the process of frequency modulation and calculated the depth of modulation by varying modulation voltage.

Comments

Post a Comment

Its not necessary everyone should know everything feel free to ask or tell :)

Popular posts from this blog

Estimation of total chlorophyll by Aron's method

-
Purpose:- Estimation of total chlorophyll by Arnon's method. Requirement:- Spectrophotometer Buchner's funnel, filter paper test tube, Fresh leaves. measuring cylinder pestle & mortar 80% Acetone  Formula:- 20.2 (A645) +802 A663) / 1000 x W Principle:- Chlorophyll is extracted in 80% acetone & the absorption at 660 nm& 645 nm are read in s spectrophotometer using the absorption co-efficient, the amount of chlorophyll is calculated Procedure:- 1) Weigh 1 gm of finely cut & well mixed representative sample of a leaf or fruit tissue into a clean mortar 2) Grind the tissue to a fine pulp with the addition of 20mil of 80% acetone   3) Centrifuge (5000 rpm for 5 min) & transfer the supernatant to a 100 ml volumetric flask  4) Repeat this procedure until the residue is colorless wash the mortar and pestle  thoroughly with 80% acetone and collect the clear washing in the volumetric flask 5) Make up the volume to 100 ml with 80% acetone  6) ...
Read more

Determination of Stefan's constant

-
Image
Aim:-  To determine the value of Stefan's constant. Apparatus:-  Black body radiation unit, Ammeter, Voltmeter, connecting wires, DC source. Theory:-  Stefan's constant: A physical constant denoted by  σ , is the constant of proportionality in the Stefan's-Boltzmann law- the total intensity radiated over all wavelength increases as the temperature increases Procedure:- 1) The electrical connections are made as shown in the circuit diagram. 2) Copper black body radiator is preheated to  30 0 C   by setting maximum voltage in the power supply 3)after the temperature indicator indicates a temperature of about    30 0 C , the voltage is reduced to some value  4) increase the voltage in steps of 0.2 V and note down the current, hence calculate power l. 5) Determine the value of Stefan's constan t. Observations:-  Room temperature t o =t+273=......of 2) surface area of the black body  A=4π r 2  = .........m square Calculati...
Read more

Pre-Emphasis & De-Emphasis Networks

-
Image
Aim:-  To draw the frequency response of Pre-emphasis & De-emphasis networks. Introduction:- Educational trainer a useful kit for the demonstration of Pre-emphasis & De-emphasis at different time constants & plot the graph of the frequency response of Pre-emphasis and De-emphasis networks. The kit consists of 200 Hz-20 kHz audio oscillator 70µ sec & 50µ sec De-emphasis networks.  Pre-Emphasis Circuit Diagram:- DE-Emphasis Circuit Diagram:- Theory:- Pre-emphasis refers to boosting the relative amplitudes of the modulating voltage for higher audio frequencies from 2 to approximately 15 kHz . De-emphasis means attenuating those frequencies by the amount by which they are boosted.  However, Pre-emphasis is done at the transmitter and De-emphasis is done in the receiver. The purpose is to improve the signal-to-noise ratio for FM reception. A time constant of 75µ sec is specified in the RC or L/Z network for Pre-emphasis and De-emphasis. Tabular colu...
Read more