Figure 3-2. Example of analog signal with random noise interference.

TM 11-490-5

mechanism, and the relative levels of the desired and

b. Analog Signals.

interfering signals.

(1) In an analog system. a continuously

(2) Since both the desired and interfering

variable waveform is transferred. Any interference

signals are present in the system output signal, the

entering the system is added to that waveform. resulting

output signal can be monitored with an oscilloscope or

in a composite of both the desired analog signal and the

other appropriate display device to indicate the

interfering signal: this is shown in figure 3-2. As the

presence and type of interference being experienced.

level of the interfering signal increases. the amount of

'With proper equipment and experience, an operator can

degradation in system performance encountered can .be

usually identify the type of interference (noise, digital.

gradual and the overall system performance will depend

radar, jammer, etc.) and thus determine the nature of

upon the types of interfering signals. the interference

the problem.

Figure 3-2. Example of analog signal with random noise interference.

is detected and converted back to the original analog

c. Digital Signals.

form. Interference is not additive as in the analog case,

(1) Digital communications systems do not

but changes the relationship of the "ones" and "zeros"

transmit an actual analog input signal. Instead, the

for the particular sample; this is shown in figure 3-4.

initial signal is transmitted digitally. For example, the

Therefore, the interference does not appear directly in

analog signal may be sampled at some specific rate and

the output signal but causes a change in the amplitude

each sample converted to a digital signal representing

or some other characteristics of the reconstructed

the amplitude of the analog signal at the time it was

analog signal for the particular sample or samples.

sampled. Figure 3-3 shows a binary digital signal

consisting of "ones" and "zeros." This digital signal is

transmitted to the receiver where it

3-2