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