Some of the topics usually covered are1.Diode Circuits-Zener Voltage Regulator,Series Parallel diode Circuits,Rectifiers,Clippers&Clampers2.Converters-ADC,DAC3.Filters-Circuit identification,features of various filters4.Simple logic circuit simplification5.Universal gate problems-use of NAND and NOR to implement other gates6.Series parallel networks problems7.RLC Circuits-Resonant frequency,bandwidth,Q factor calculation,Time Consatant (most repeated topic)8.Amplitude Modulation-Total Power,Modulation Index,Power Saving Calculation,9.Frequency Modualtion-Deviation,Modulation Index,Sideband,Adavntages and disadvantages,Circuits for detection and modualtion,Envelope detector based time constant calculation,Pre&De emphasis circuitry10.Phase Modulation-Deviation,Comparison with FM, generation using Integrator and Differentiator11.VSWR Calculation-Using reflection coefficient,Directional Coupler,load imp& char impedance given12.Characteristic Impedance- OC and SC impedance of line given,lossless line13.Code converter circuits-Gray to Binary,Excess 3 ,etc.14.Shannon's Channel Capacity Theorem15.Standard of Laplace Transforms16.Basic Z Transforms17.OpAmps-Calculation of CMRR,Slew Rate,Application-Summer18.Relations of maxwell equations,calculation of intrinsic impedance19.Covolution with unit impulse function20.Memory Chip design-Given21.QPSK features22.Radar-Duty Cycle,Maximum Range calculation23.Counters-Modulus calculation,RING COUNTER,JOHNSON COUNTER-Calculation of counts24.Characteristic equation of Flip Flops25.Calcualtion of Noise figure in casacade blocks26.Superhetrodyne Reciever- Calculation of Image frequency,Image rejection ratio27.Microprocessor-loop based programs,some features of various registers The Above mentioned topics are important and repeated often but they themselves are not enough. Studying these will give you a scope of learning other topics.Refernce books1.Electronic Devices and Circuits-Sallivahnan2.Electronic Communication Systems-Wayne Tomsai3.Mathematics-Erwin Kreyszig4.Digital Electronics-MorrisMano5.Digital Signal processing- Sallivahnan6.Communication System-Simon HaykinSOON SOLVED PAPERS OF ISRO WILL BE UPLOADED SOON