A square wave is made up of a sine wave plus all of its odd harmonics. A sawtooth wave is made up of sine waves of a given fundamental frequency plus all its harmonics. A sawtooth wave has a rise time significantly faster than its fall time (or vice versa). The root-mean-square value of an AC voltage is the DC voltage causing the same amount of heating in a resistor as the corresponding RMS AC voltage. The most accurate way of measuring the RMS voltage of a complex waveform is by measuring the heating effect in a known resistor. The characteristics of the modulating signal determines the PEP-to-average power ratio of a single-sideband phone signal. The waveform produced by human speech is irregular. The approximate ratio of PEP-to-average power in a typical voice-modulated single-sideband phone signal is 2.5 to 1. The period of a wave is the time required to complete one cycle. The distinguishing characteristic of a pulse waveform is narrow bursts of energy separated by periods of no signal. One use for a pulse modulated signal is digital data transmission. Sequential sampling is a methods commonly used to convert analog signals to digital signals. An advantage of using digital signals instead of analog signals to convey the same information is that digital signals can be regenerated multiple times without error. The waveform of a digital data stream signal look like a series of pulses with varying patterns on a conventional oscilloscope. All of the following answers are correct. The information can be conveyed using digital waveforms include:
The modulation index is the ratio between the frequency deviation of an RF carrier wave, and the modulating frequency of its corresponding FM-phone signal. The deviation ratio is the ratio of the maximum carrier frequency deviation to the highest audio modulating frequency.
The modulation index of a phase-modulated emission does not depend on the RF carrier frequency. It does not vary with RF carrier frequency (the modulated frequency). When using a pulse-width modulation system, a transmitter's peak power is greater than its average power because the signal duty cycle is less than 100%. The time at which each pulse occurs varies in a pulse-position modulation system. The pulses of a pulse-modulated signal are usually transmitted as a pulse of relatively short duration followed by a relatively long period of time separating each pulse. Frequency division multiplexing can be used to combine several separate analog information streams into a single analog radio frequency signal. Frequency division multiplexing is when two or more information streams are merged into a "baseband", which then modulates the transmitter. Time division multiplexing is when two or more signals are arranged to share discrete time slots of a digital data transmission. Morse code is a digital code that consists of elements having unequal length. Differences between the Baudot digital code and ASCII codes include, Baudot uses five data bits per character, ASCII uses seven; Baudot uses two characters as shift codes, ASCII has no shift code. One advantage of using the ASCII code for data communications is that it is possible to transmit both upper and lower case text. The advantage of including a parity bit with an ASCII character stream is that some types of errors can be detected. Use of sinusoidal data pulses minimizes the bandwidth requirements of a PSK-31 signal. The bandwidth required for the following modes and transmission rates are:
One advantage of using JT-65 coding is that virtually perfect decoding of signals well below the noise. Spread-spectrum communication is a wide-bandwidth communications system in which the transmitted carrier frequency varies according to some predetermined sequence. In spread-spectrum communications frequency hopping alters the center frequency of a conventional carrier many times per second in accordance with a pseudo-random list of channels. Spread-spectrum causes a digital signal to appear as wide-band noise to a conventional receiver. Spread-spectrum communications is resistant to interference because only signals using the correct spreading sequence are received. In spread-spectrum communications direct sequence uses a high speed binary bit stream to shift the phase of an RF carrier. The typical values at a common household electrical outlet are:
The easiest voltage amplitude parameter to measure when viewing a pure sine wave signal on an oscilloscope is its peak-to-peak voltage. The relationship between the peak-to-peak voltage and the peak voltage amplitude of a symmetrical waveform is 2:1. The PEP output of a transmitter that has a maximum peak of 30 volts to a 50-ohm load as observed on an oscilloscope is 9 watts. The average power dissipated by a 50-ohm resistive load during one complete RF cycle having a peak voltage of 35 volts is 12.2 watts. If an RMS reading voltmeter reads 34 volts on a sinusoidal waveform, the peak voltage is 48 volts. If an RMS-reading AC voltmeter reads 65 volts on a sinusoidal waveform, the peak-to-peak voltage is 184 volts. The input-amplitude peak voltage is valuable in evaluating the signal-handling capability of a Class A amplifier. The type of meter that should be used to monitor the output signal of a voice-modulated single-sideband transmitter to ensure you do not exceed the maximum allowable power is a peak-reading wattmeter. The advantage of using a peak-reading wattmeter to monitor the output of a SSB phone transmitter is that it gives a more accurate display of the PEP output when modulation is present. An electromagnetic wave is a wave consisting of an electric field and a magnetic field oscillating at right angles to each other. The best description of electromagnetic waves traveling in free space is changing electric and magnetic fields that propagate energy. The polarization of an electromagnetic wave with its magnetic field parallel to the surface of the Earth is vertical. The polarization of an electromagnetic wave with its magnetic field is perpendicular to the surface of the Earth is horizontal. Circularly polarized electromagnetic waves are waves with a rotating electric field. The approximately speed that electromagnetic waves travel in free space is 300 million meters per second. |