LESSON 2
NETWORK LOSSES AND GAINS
SCOPE ............................. Determination of transmission losses and
gains; calculation of signal-to-noise ratios;
stating circuit impairment levels.
CREDIT HOURS ...................... 2
TEXT ASSIGNMENT ................... Attached Memorandum, para 2-1 thru 2-6
MATERIALS REQUIRED................ None
SUGGESTIONS ....................... None
LESSON OBJECTIVES
When you have completed this lesson, you should:
1.
Be able to convert dbm to milliwatts, and vice versa.
2.
Be able to determine transmission losses and gains from a transmission
level diagram.
3.
Be able to specify noise level in relative terms.
4.
Be able to calculate signal-to-noise ratio.
5.
Know that the maximum loss permitted by the Military Transmission Plan is
36 db.
ATTACHED MEMORANDUM
2-1. DECIBELS AND THEIR USE
Decibels and their derivatives are the basic tools of the circuit
conditioner.
Host of the parameters specified by the Defense Communications
Agency (DCA) are related to the decibel. The primary reason for using decibels
is to make calculations of quantities simple and quick. Instead of multiplying
or dividing large numbers, it is only necessary to add or subtract decibels to
arrive at useful answers. This simplicity results from the logarithmic nature
of the decibel formula:
db = 10 log10 P1/P2 = 20 log10 E1/E2 = 20 log10 I1/I2.
a. Ratios. A simplified table showing power, voltage, and current ratios
is shown below. Each ratio assumes equal values of impedance. This is one of
the reasons that most test sets and circuits use standardized impedances
11
Previous Page
