The process, or result of the process, of modifying andy characteristic of an information signal or carrier signal so that it varies in step with the instantaneous value of another information signal.

An example of analog-to-digital and digital-to-analog techniques.

Pulse Code Modulation (PCM) and Continuous Variable Slobe Delta (CVSD) modulation.

Amplitude Shift Keying (ASK), FSK, PSK

QAM

Amplitudes are represented using 4-bit values (rather than the 8 bits used in PCM), and the 32Kbps data-transfer rate is used (rather than 64 Kbps, as in PCM)

ADM is a variation of DM where a signal's step size may vary from sample to sample.

(1). Carrier Frequency

(2.) Carrier Plus Modulating Frequency

(3.) Carrier Minus Modulating Frequency

Upper and lower sidebands

Lower and upper sidebands.

The lower sideband.

The bandwidth requried to transmit an AM signal is twice that of the modulating signal itself.

The transmitted signal is one sideband transmitted without a carrier.

All of the power applied to the transmitter is applied to the sideband carrying intelligence. This provides a 6-to-1 power improvement.

What makes SSBSC more efficient?

The carrier, the upper sideband (carrier plus modulating frequency), and the lower sideband (carrier minus modulation frequency).

Susceptibility to noise.

The amplitude of the modulating signal.

It is directly proportional.

In PM, how is the transmitted signal modulated?

The rate of phase shift is controlled by the frequency of the modulating frequency.

(1) In PM, the spacing of the sidebands is equal to the frequency of the modulating frequency.

(2) Each sideband has an equal share of the power distribution.

(3) Because of carrier stability, the bandwidth increases proportionally as the frequency of the modulating signal is increased.

In BPSK, what amount (degrees) of phase shift of the carrier is used to represent binary 1's and 0's?

The transmitted signals are insensitive to level variations, and higher data speeds and be transmitted over smaller bandwidths.

QPSK can use the same signal bandwidth of a BPSK signal and transmit twice the amount of data, and the QPSK signal is not seriously degraded when passing through a nonlinear device.

By using pilot tones as a carrier of transmitting timing pulses in the data streams along with the pilot tones.

By changes in phase value from one sample to the next.

What are the three characteristics of a pulse train that can be varied by an information signal to produce a modulated rectangular pulse train?

(1) Peak voltage.

(2) Period

(3) Pulse width

Only the width of the pulses determines the bandwidth of a pulse train, not the frequency.

Frequency influences the number, or spacing, of the harmonics.

(1) Pulse Modulation

(2) AM or FM.

(1) PAM.

(2) PDM.

(3) PPM.

(4) PCM.

(5) DM.

A pulse carrier is amplitude modulated to convey information.

The amplitude of the modulating signal at the point of sampling.

(1) PWM.

(2) PLM.

The amplitude of the modulating signal at the point of sampling.

Noise pulses are less likely to be of the correct amplitude and time of occurence to distort the width of the PDM pulses.

Both are proportionately affected by an distortion in pulse or width or amplitude of the modulating signal.

By maintaining pulses at a constant width and amplitude.

What is a disadvantage of PPM?

The amplitude of the modulating signal at the time of sampling.

Give two reasons for converting analog signals to digital signals before transmission.

(1) Digital signals can be regenerated.

(2) Are readily encrypted.

Quantizing noise is produced when the digital signals are converted back to their analog form.

Of PAM, PDM, PPM, and PCM, which technique is least affected by noise?

First, the analog signal is passed through a band-limiting filter and the resulting pulses are amplitude sampled. Each pulse is assigned a binary code word corresponding to its amplitude. The resulting digital signals are then modulated using AM, FM, PSK, and so forth..., and trasmitted as a series of pulses and empty intervals.

Quantizing noise is the distortion produced during quantization of PAM signals where the PAM pulses are "rounded-off" to the nearest allowable assigned values differing from their true amplitude values.

Non-uniform quantizing produces less noise than uniform quantizing.

By keeping the quantized pulses at a constant duration and amplitude (encoding).

To reduce the dynamic range of a voice signal by compressing the high-amplitude portions of the signal before transmission.

To disturb PCM, noise must insert a pulse or obscure a pulse, not merely change its height or duration.

It generates a 4-bit word per PAM sample instead of an 8-bit word.

(1) A Comparator.

(2) A sampler.

(3) An integrator amplifier

The size of the steps in the approximation signal.

By varying the approximation's signal step size according to the input signal's amplitude.

In CDI, a digital "one" signal reverses the start/finish voltage relationship from the preceding bit and a digital zero keeps the start/finish voltage relationship of the preceding bit, regardless if it was a one or a zero. Since the receiving modem only uses the start/finish voltage relationships to decode the information, they are less affected by noise and therefore can be demodulated at further distances.