Envelope Detector

Envelope detector circuit uses a diode, a capacitor and a resistor and it is just like a half wave rectifier followed by a low-pass filter. It is a linear detector which takes high frequency RF signal as input and gives an output which is the envelope of the input signal. A diode detector is a type of envelope detector and is used for the detection of AM signal.

Circuit Operation

Here the input signal is rectified by the series diode D. The combination of capacitor C and resistor R behaves like a low-pass filter. The input signal contains both the original message and the carrier wave where the capacitor helps in filtering out the RF carrier waves. The capacitor gets charged during the rising edge and discharges through the resistor R in falling edge. Thus the capacitor helps in giving an envelope of the input as output.

Advantage

• This technique is highly used in AM receivers as it is very simple and cheap. 
• The circuit acts as a linear detector as the output varies as per the voltage of input and the distortion here is very less.

Disadvantage

• The circuit does not have an amplification capability to amplify the rectified signal. Amplification should be done by separate devices.
• Before giving input to the circuit the signal must be bandpass filtered otherwise the circuit will demodulate unnecessary signals.

Compared to advantages the disadvantages are very negligible and hence these circuits are extensively used for AM detection.

Junior Research Fellowship from GATE

What is JRF-GATE ?
From 2002 onwards Council of Scientific & Industrial Research (CSIR), India has introduced a research fellowship program for the students who have qualified GATE with BTech/BE/BArch/BPharm. This fellowship is know as Junior Research Fellowship(JRF-GATE).
What the candidates will do ?
The candidates who will be selected for this will get golden opportunity of working with CSIR scientists in R&D works. The BE/BTech students after getting selected into JRF they have to either take admission directly into Ph.D program in IIT/NIT/REC etc. or they will continue doing MTech as a part of Ph.D.
Age Limit
The upper age limit to apply for JRF is 28 years. The age relaxation is 5 years in case the candidate belongs to SC, ST, OBC, women or physically handicapped.
Duration of Fellowship
Duration of this fellowship is 5 years within which the candidate has to complete the Ph.D. During this fellowship the candidate will get a stipend of Rs 16,000/- per moth in addition with HRA. The candidate will also get a contingency grant of Rs 20,000/-  per annum. After two years as JRF-GATE the fellowship may be upgraded to SRF-GATE and your stipend may increase to 18,000/- per month.

To know detail about this fellowship, eligibility criteria, selection procedure and how to apply for this please visit  http://csirhrdg.res.in/gate.htm  and  http://csirhrdg.res.in/jrfsrfra2.htm

One suggestion for all: Start preparing for GATE seriously and grab these golden opportunities of working with scientists in R&D. Good Luck.

ISRO 2011 Final Result

The interview result of ISRO in 2011 for the post of SCIENTISTS/ENGINEERS 'SC' in the discipline of ELECTRONICS, MECHANICAL and COMPUTER SCIENCE is as follows.

In Electronics total 60 candidates have been listed out, in which 54 have been short listed and 6 are in waiting list. In Mechanical total 40 students have been short listed. In Computer Science total 26 candidates have been listed out, in which 23 have been short listed and 3 are in waiting list. So in total 117 have been shortlisted to whom offer of appointment has been issued.

To get detail list of all candidates who have been short listed click here. Since very less no. of vacancies are there you have to work very hard to get this prestigious opportunity. Download previous year question papers(2006-2011) and try to solve them. This process will help you to know the question paper pattern. To get ISRO 2010 solved paper click here.

ISRO Previous year question papers for Electronics:

http://www.isro.org/pdf/EC-2006.pdf

http://www.isro.org/pdf/EC-2007.pdf

http://www.isro.org/pdf/EC-2008.pdf

http://www.isro.org/pdf/EC-2009.pdf

http://www.isro.org/pdf/EC-2010.pdf 

http://www.isro.org/pdf/Electronics-2011.pdf
 

How to contact ISRO qualified candidates: Just search their names in facebook, send them friend request and if you are lucky enough your request will be accepted. Once your request is accepted ask them all your questions regarding ISRO and take suggestions regarding preparation. To get names of the shortlisted candidates click here. Good luck.