The theory of radio waves was originated by:

The time it takes a charge carrier to cross from the emitter to the collector is called:a. base timeb. transit time c. charge time d. Miller timeA real capacitor actually contains:a. capacitance and resistance onlyb. capacitance and inductance only c. capacitance, inductance, and resistance d. reactance onlyBypass capacitors are used to:a. remove RF from non-RF circuitsb. couple RF around an amplifierc. neutralize amplifiers d. reduce the Miller effectA resonant circuit is:a. a simple form of bandpass filterb. used in narrowband RF amplifiers c. both a and b d. none of the aboveLoading down a tuned-circuit amplifier will:a. raise the Q of the tuned circuitb. lower the Q of the tuned circuit c. "multiply" the Q d. have no effect on QThe "Miller Effect" can:a. cause an amplifier to oscillateb. cause an amplifier to lose gainc. reduce the bandwidth of an amplifierd. all of the aboveThe Miller Effect can be avoided by:a. using a common-emitter amplifierb. using a common-base amplifier c. increasing the Q of the tuned circuit d. it cannot be avoidedIn a BJT, the Miller Effect is due to:a. inductance of collector leadb. collector-to-emitter capacitance c. base-to-emitter capacitance d. base-to-collector capacitanceIn RF amplifiers, impedance matching is usually done with:RC coupling transformer coupling direct couplingd. lumped reactanceNeutralization cancels unwanted feedback by:a. adding feedback out of phase with the unwanted feedbackb. bypassing the feedback to the "neutral" or ground planec. decoupling itd. none of the aboveFor a "frequency multiplier" to work, it requires:a. a nonlinear circuitb. a linear amplifierc. a signal containing harmonicsd. an input signal that is an integer multiple of the desired frequencyA sinusoidal oscillation from an amplifier requires:a. loop gain equal to unityb. phase shift around loop equal to 0 degreesc. both a and b, but at just one frequencyd. none of the aboveThe conditions for sinusoidal oscillation from an amplifier are called:the loop-gain criteria the Hartley criteriac.the Bode criteriad.the Barkhausen criteriaAny amplifier can be made to oscillate if a portion of the output is fed back to the input in such a way that the following criteria, known as the Barkhausen criteria, are satisfied:The gain around the loop must be equal to one. The phase shift around the loop must total either 0 or some integer multiple of 360 at the operating frequency (and not at other frequencies)The Hartley oscillator uses:a tapped inductor a two-capacitor divider an RC time constantd. a piezoelectric crystalThe Hartley oscillator can be recognized by its use of a tapped inductor.The resonant frequency is that of the tuned circuit, including the whole inductor, that is

Inductors are typically tuned by moving a ferrite core into or out of the coil. This is known as slug tuning.The Colpitts VFO uses:a. a tapped inductorb. a two-capacitor divider c. an RC time constant d. a piezoelectric crystalColpitts Oscillator uses a capacitive voltage divider instead of a tapped inductor to provide feedback.The operating frequency is determined by the inductor and the series combination of C1 and C2.The Clapp oscillator is:a. a modified Hartley oscillatorb. a modified Colpitts oscillator c. a type of crystal-controlled oscillator d. only built with FETsThe clap oscillator is a variation of the Colpitts circuit, designed to swamp device capacitances for greater stability.The frequency of oscillation is determined by the inductor and the series combination of C1, C2, and C3A varactor is:a. a voltage-controlled capacitorb. a diode c. used in tuner circuits d. all of the aboveA varactor is a reverse-biased silicon diode whose capacitance is varied by varying the applied reverse voltage.Thus, a varactor-tuned oscillator is also called a voltage-controlled oscillator (VCO).The variation of capacitance is given approximately by:

C = capacitance at reverse voltage VCo = capacitance without reverse voltageA varactor has a maximum capacitance of 80 pF and is used in a tuned circuit with a 100 H inductor.a. Find the resonant frequency with no tuning voltage appliedb. Find the tuning voltage necessary for the circuit to resonate at double the frequency found in part a1.8 MHz, 80 kV25Crystal-Controlled oscillators are:a. used for a precise frequencyb. used for very low frequency drift (parts per million)c. made by grinding quartz to exact dimensionsd. all of the aboveFrequency stability is the ability of an oscillator to remain at a fixed frequency.Short-term stability is affected predominantly by fluctuations in dc operating voltages.Long-term stability is a function of component aging and changes in the ambient temperature and humidity.

Commercial FM broadcast stations must maintain their carrier frequencies to within +/-2 kHz of their assigned frequency which is approximately 0.002% tolerance.In commercial AM broadcasting, the maximum allowable shift in carrier frequency is only +/-20 Hz.LC oscillators are subject to frequency change from such diverse sources as voltage variations, changes in load impedance, temperature changes and mechanical vibration. The Q-factors of LC tank circuits are relatively low, allowing the resonant tank circuit to oscillate over a wide range of frequencies. (in the range of 100 to 1000 compared to crystals which is 10,000 to 100,000 and higher) Piezoelectric crystals can oscillate in either of two modes: 1. fundamental or 2. overtoneFor most crystals the upper limit is 20 MHz. The relationship between a crystals operating frequency and its thickness is expressed mathematically as

To achieve extremely thin slices of crystals, the process called chemical etching is used.With the process, crystal fundamental frequencies up to 350 MHz are possible.For ultimate stability, as required in demanding applications like test equipment and some transmitters, a crystal oven can be used.A crystal oven can improve the temperature stability of a crystal oscillator by a factor of about 100,000.The temperature dependence of the frequency of an oscillator can be given by the equation. fT = fO + kfO(T TO)A portable radio transmitter is to operate at temperatures from -5 to 35 degree Celsius. If its signal is derived from a crystal oscillator with a temperature coefficient of +1ppm/degree Celsius and it transmits at exactly 146 MHz at 20 degree Celsius, find the transmitting frequency at the two extremes of the operating temperature range.Quartz is a ____________ materialpiezoelectricThe mechanical vibrations are called ____________bulk acoustic waves (BAWs)In a balanced mixer, the output:a. contains equal (balanced) amounts of all input frequenciesb. contains the input frequenciesc. does not contain the input frequenciesd. is a linear mixture of the input signals"VFO" stands for:a. Voltage-Fed Oscillatorb. Variable-Frequency Oscillatorc. Varactor-Frequency Oscillatord. Voltage-Feedback OscillatorA "frequency synthesizer" is:a. a VCO phase-locked to a reference frequencyb. a VFO with selectable crystals to change frequencyc. a fixed-frequency RF generatord. same as a mixer