Spread spectrum (ss) encoding: a) name four spread spectrum techniques. b) which one of them was originally devised against eavesdropping in the military environment?

Explanation:

( a )

The four types of  spread spectrum techniques are as follows -

1. Direct sequence spread spectrum .

2. frequency hopping spread spectrum .

3. chirp spread spectrum .

4. time hopping spread spectrum .

( b )

The Direct sequence spread spectrum was devised for eavesdropping in the military .

In the field of telecommunications , the Direct sequence spread spectrum , it is the technique of spread spectrum modulation which is used to reduce the overall inference of the signal .

c. heat could easily travel through the molecules in the air and escape/enter the flask. removing the air slows down the heat transfer.  

a mercury barometer is a device that uses the physical properties of mercury in a tube to measure barometric pressure. mercury barometers are used for : -

1. measurement of atmospheric pressure  

2. determining the altitude of a place

3. weather forecasting

4. calibration and checking of aneroid barometers

5. application in fluid mechanics

6. measurement of pressure in aircrafts

7. surface weather analysis

8. preparation of barographs

9. usage in physical sciences like physics, astronomy & chemistry

10. preparation of aircraft altimeters

characteristics of mercury barometer : -

1.used to define and measure atmospheric pressure.

2.on the average at sea level the column of mercury rises to a height of about 760 mm.

3.this quantity is equal to 1 atmosphere.

4.it is also known as standard atmospheric pressure.

5.a barometer in which the weight of a column of mercury in a glass tube with a sealed top is balanced against that of the atmosphere pressing on an exposed cistern of mercury at the base of the mercury column, the height of the column varying with atmospheric pressure.