List out the satellite subsystems, their functions and their main characteristics.

List out the satellite subsystems, their functions and their main characteristics.

(i) Communication subsystems
(ii) Antenna subsystem
(iii) Telemetry tracking, and control subsystem
(iv) Altitude control subsystem
(v) Propulsion subsystem
(vi) Power subsystem.

What is a ROM ?

What is a ROM ?
ROM (Red only memory) is a memory device intended to store information which is fixed. That is, there is an initial operation during which information is written into the memory and thereafter the memory is read only and is not again written into. A most important attribute of the Rom is that the information it stores will not be lost if the electric power that it uses to operase should be interpupted.

“Loading an output with more than its rated fan out has several effects”. Write at least five effects.

“Loading an output with more than its rated fan out has several effects”. Write at least five effects.
(i) rise time
(ü) fall time
(iii) propagation delay time
(iv) speed of operation
(v) saturation of transistors.

Define fan out. Which factor is responsible for the limit of fan out in TTL circuits.

Define fan out. Which factor is responsible for the limit of fan out in TTL circuits.

Fan out. It specifies the number of standard loads that the output of the gate can drive without impairment of its normal operation. A standard load is defined as the current flowing in the input of a gate in the same I family.
The fan out in TTL circuits is limited by the amount of current that output transistor can sink when it is in saturation.

Define equalization. Explain with relevant mathematical equations, the principles of operation of a zero forcing transversal equalizer.

Define equalization. Explain with relevant mathematical equations, the principles of
operation of a zero forcing transversal equalizer.

Phase delay distortion can be reduced to acceptable levels by using equalization on the channel. An equalizer which can be adjusted to compensate for the delay abnormalities. The result is a channel relativily free of phase delay.

Equalizers can be obtained which are automatic in nature. These equalizers precede data transmission with a short “training period” during which test pulses are used to determine the delay characteristics of the channel. The equalizer automatically varies its delay characteristics while sampling the return signal to determine when the channel delay plus equalizer delay reach proper tolerances. At that time data transmission commences. The data is there after sampled during transmission to ensure that equalization settings are appropriate, with modifications made as required. Inverse channel filter completely eliminate, 1SI caused by the cahnnel. Since it forces the 1SI to be zero at the sampling times t =nT, this equalizer is called a zero forcing equalizer.

Define Gamma. Why is gamma correction done in the camera ? What is the value gamma for picture tube? Show that the video bandwidth is approximately 5 MHz.

Define Gamma. Why is gamma correction done in the camera ? What is the value
gamma for picture tube? Show that the video bandwidth is approximately 5 MHz.

Gamma : Video output of camera is not a linear function of the light input. Similarly the light output of the picture tube is also a non linear function of the electrical output. Thus the picture obtained at the output lacks the appearance of input in its entirety. The transfer is called the gamma of the system.

Gamma correction is done in Camera tube because there is non linear relationship between’ output current and light intensity both at the pick up tube and the output CRT in receiver. At the receiving end the light output is the square of the input video signal voltage. The effect of this is to compress the black and stretch the white. It is done with the help of black to white gray scale chart. Approximate value of gamma is 1.2.

Compare O and M-type tubes.

O-type tubes
1. These are linear beam tubes, i.e. the magnetic field is in parallel with th d.c. electric field.
2. In these tubes, electrtons receive potential energy from the d.c. beam voltage before they arrive in the microwave interaction region this energy is converted into their kinetic energy.
e.g. Klyston, Helix TWT and BWA, BWO etc.

M-type tubes
1. These are cross field devices i.e. the d.c. magnetic field and the d.c. electric field are perpendicular to each other.
2. In these tubes, the electrons emitted by the cathode are accelerated by the electric field and gain velocity but the greater their velocity, the more their path is bent by the magnetic field.
e.g. magnetron, FWCFA, Dematron. Gyrotrons etc.

Specify the characteristic features of INSAT-2E.

Specify the characteristic features of INSAT-2E.
INSAT-2E is an Indian geostationary satellite. The Satellite altitude is about 35800 km. INSAT-2E is located on 74° east over the equator. It always views the same portion of the globe.
INSAT-2E is equipped with a VISSR (VIsible and In frared Spin Scan Radiometer). The radiometer scans the earth’s surface line by line; each line consists of a series of individual image elements or pixels. For each pixel, the radiometer measures the radioactive energy of the different spectral bands. The measurement is digitally coded and transmitted to the ground station for pre-procssing before being disseminated to the user community.
VISSR is a 3 channels device Visible channel is 0.47-0.7 micro m
Infrared channel is 10.5 -12.5 micro m,
and water vapur channel is 5.7-7.1 micro m
In the visible channel, the resolution is 2km. In the infrared and water vapour channels, the resolution is 8 km.

What factors does the power carrying capacity of a 4vave guide depend upon?

What factors does the power carrying capacity of a 4vave guide depend upon?
(z) Frequency of transmission
(ii) Conductivity of wall of wave guide
(iii) Dimension of wave guide.

Why do we prefer/hollow wave guides to open wire two conductors, or coaxial” transmission lines for transmission of power?

Why do we prefer/hollow wave guides to open wire two conductors, or coaxial”
transmission lines for transmission of power?

Reasons to prefer waveguides over coaxial tra1ismission lines:
(i.) These are much less lossy at the high frequencies.
(ii) Waveguides are simpler to manufacture.
(iü) Power handling ability of waveguide is more because of absence of inner conductor and supporting dielectrics.

State clearly the Thevenin’s theorem and explain its usefulness in linear network analysis.

State clearly the Thevenin’s  theorem and explain its usefulness in
linear network analysis.

This theorem is one of the most useful network theorems and states that the current in any load impedance, connected to two terminals of a network of impedance and generators is the same as if this load impedance were connected to a constant voltage generator whose terminal voltage is the open circuited voltage at the two terminals and whose internal impedance is the impedance of the network looking back into the terminals with all the generators replaced by their interval impedance's.

This theorem is most useful when it is desired to know the effect on the response in a network or varying part of the network while keeping some other part constant.

State the advantages of state space analysis over the conventional differential equation methods of solving system behaviour.

State the advantages of state space analysis over the conventional differential equation methods of solving system behaviour.

Advantage of state space analysis
(i) State space analysis can be used for MIMO, linear/non linear, time invariant or time varying systems.
(ii) It consists of n-first order differential equations, which are easier to solve than single nth order differential equation of conventional method using digital computers.
(ii1) It is a direct time domain approach.

PNPN DIODE

PNPN DIODE

The electrical symbol representation of a four layer pnpn diode is shown in the above figure  and its VI characteristic is also  shown in the above figure


Explain why VI characteristic of the pnpn diode behaves as represented in figure
When the voltage is applied in the reverse direction, the two outer junctions of the switch are reverse biased. At an adequately large voltage, breakdown will occur at these junctions, as indicated, at;the “reverse avalanche” voltage VRA.
When a forward voltage is applied, only a small forward current will flow untill the voltage attains the re akover voltage VBO. The corresponding current is ‘BO If the voltage V, which is ipplied through a resistor is increased beyond VBO, the diode will switch from its OFF (blocked) state to its ON (saturation) state and will operate in the saturation region. The device is then said to latch, if the voltage is now reduced, the switch will remain ON untill the current has decreased to ‘H• This current and the corresponding voltage VH are called holding current and voltage, respectively. The current IN is the minimum current required to hold the switch in its ON state.

 Can the above device be used as an electronic switch? If so why?
The pnpn didoe when biased with the anode positive has two stable states. One is a very high resistance state, typically of the order of 100 M Ohms, and the other a very low resistance state, typically less tha 10 Ohms. When reverse biased, this device acts like a typical pn diode, having a very low leakage current. When external voltage is applied to make the anode positive with respect to the cathode, junctions eJ1 and J3 are forward biased and the centre junction J2 is reverse-biased. The externally impressed voltage appears principally across the reverse-biased junction, and the current which flows through the device is small. As the impressed voltage is increased, the current increases slowly untill a voltage caused the firing or breakover voltage VBQ is reached where the current increases abruptly and the voltage across the device decreases sharply. At this breakover point the pnpn diode switches from its OFF state to the ON state.