Knowledge base :

1. Gold is the most malleable and ductile metal.
2. Radio communication happens in ionosphere .
3. Layers of atmosphere are  - Troposphere , Stratosphere , Mesosphere and Thermosphere (Ionosphere and Exosphere) .
4. Earth rotates from West to East thats why stars appear to move from East to West .
5. Radars are used to - find velocity of moving targets , detection of objects in air , surveillance of aircrafts/UAV etc .
6. Disadvantage of 2 cavity klystron is it can be used at only one operating frequency .
7. Gunn diode is a low power oscillator and IMPATT diode is a high power oscillator .
8. Schmitt trigger is used for wave shaping i.e. converting noisy waves into clean waves.
9. Two cavity klystron is an amplifier which can be converted into oscillator by providing positive feedback .
10. Reflex klystron is a low power oscillator generating 10 to 500mW power output . It is used in local oscillator of heterodyne receivers .
11.  Magnetron is a high power oscillator which is used in radar transmitters .
12. Klystron is a narrow band amplifier while TWT is a wide band amplifier .
13. TWT is preferred over magnetron in radar as it has larger duty cycle . 
14. TEM mode is the dominant mode of propagation in RF coaxial cables .
15. There are 2 types of parametric amplifiers/oscillators : those in which signal wave frequency is equal to idler wave frequency is called degenerate and other one is non-degenerate . The 3 waves are signal , idler and pump .
16. LSA [ limited space-charge accumulation] diode similar to Gunn diode except it prevents formation of charge packets (domains) .
17. Ground wave propagation is strongest at low and medium frequencies .
18. Class C amplifier is used in RF amplification not in audio amplification due to high amount of distortion but high efficiency as it is turned on for a small amount of time and the wave shape can be recovered from that part.
19. EB junction forward biased and CB junction reverse biased - high gain amplifer
20. EB junction reverse biased and CB junction forward biased - low gain amplifer
21. For Half wave rectifier : efficiency = 40.6% , ripple factor = 1.21 , TUF = 0.287 , PIV = Vm , ripple freq = 50Hz
22. For Full wave rectifier : efficiency = 81.2% , ripple factor = 0.48 , TUF = 0.693 , PIV = 2Vm - 0.7 , ripple freq = 100Hz
23. For bridge rectifier PIV =Vm and and Rf is replaced by 2Rf in expression of Im rest all parameters are same as that of full wave rectifier .
24. Secondary current is purely sinusoidal in Full wave rectifier while it is dc in case of half wave rectifier therefore there is no danger of core saturation in full wave rectifier .
25. In a filter circuit for ac to dc inductor(choke) is always connected in series and capacitor in parallel .

Important Links for AFCAT EKT exam :

        GATE study material : http://qualifygate.com/maseeasy-ec-gate-ese-hand-written-study-material/

        Google books + blogs 

1.  https://books.google.co.in/books?id=GWPfL5bxkAwC
2.  https://books.google.ca/books?id=Y-ebJYgLv4MC
3.  http://www.electronics-tutorials.ws/
4.  https://books.google.co.in/books?id=bydJMQydxFgC
5.  https://books.google.co.in/books?id=coQ6ac-fh6QC
6.  https://books.google.co.in/books?id=eM0UBBFkjWwC
7.  https://books.google.co.in/books?id=FPJeDAAAQBAJ
8.  https://books.google.co.in/books?id=ZIMkjLgLcwoC
9.  https://books.google.co.in/books/about/Analog_And_Digital_Communication.html?id=5YuNmB6Uv7AC
10.  http://www.learnabout-electronics.org/index.php
11.  http://www.satishkashyap.com/p/click-here-to-continue.html
12.  http://nptel.ac.in/courses/101108056/3
13.  http://harry-nita.blogspot.in/p/blog-page_8316.html
14.  http://avinash1260.blogspot.in/2012/12/important-psu-questionmicrowaveemtcommu_4.html
15.  http://www.gatestudy.com/wp-content/uploads/2016/12/
16.  http://www.pinoybix.org/2014/09/mcqs-in-electronics-engineering.html
17.  http://www.indiabix.com/electronics-and-communication-engineering
18.  http://people.seas.harvard.edu/~jones/es154/lectures/lecture_2/breakdown/breakdown.html
19.  http://mssabi.blogspot.in/2014/04/psu-mcqs-on-electromagnetics.html
20.  http://www.indianservers.com/jntukup/onlinebits/22/day2/ECquestions.html
21.  http://iete-elan.ac.in/SolQP/soln/DE20_sol.pdf
22.  http://www.mygatebook.com/2016/03/ece-gate-question-papers-with-solutions.html
23. http://www.iitg.ac.in/apvajpeyi/ph218/Lec-20.pdf
24. http://oldsite.mlrinstitutions.ac.in/administrator/components/com_materials/handbook/68b7141ca5ff2aa4a236612223047824-OBJ-BITS.pdf
25.  http://ecetutorials.com/
26.  http://engineeringinterviewquestions.com/communication-systems-questions-and-answers-pdf/
27. https://www.ibtindia.com/sites/default/files/GENERAL%20STUDIES%20CAPSULE%20-%20SSC%20CGL%20TIER
28. https://books.google.co.in/books?id=UTSWnDvFq7YC&printsec=frontcover&dq=k+k++tewari&hl=en&sa=X&ved=0ahUKEwis0I6Y6bTZAhXLmZQKHY54CI0Q6AEIKDAA#v=onepage&q=k%20k%20%20tewari&f=false
29. http://www.drnnce.ac.in/files/CT%20QB.pdf