comm
TRANSCRIPT
Which of the following is not a major communications medium?
a. Fiber Optic b. Water c. Wires d. Free space
In a resonant circuit, a new inductor whose value is twice as high replaced the original inductor, what happens to the frequency in which the network will resonate?
a. it will increase by a factor of 0.707. b. it will decrease by a factor of 2 c. it will decrease by a factor of 0.707 d. it will decrease by a factor of 0.956
for a given bandwidth signal, more channel space is available in the range of
a. SHF b. UHF c. EHF d. VHF
What value of the series resistor is needed for a pi-‐pad to provide a loss of 20dB if it will be inserted in a network whose impedance is 100 ohms?
a. 150 ohms b. 495 ohms c. 400 ohms d. 122 ohms
a bridged-‐H pad is an example of
a. Asymmetrical, balanced b. Symmetrical, unbalanced c. Symmetrical, balanced d. Asymmetrical, unbalanced
What is the output voltage of a RC LPF whose R = 10kohms and C = 1 nF if a 100mVpk input signal has a frequency of 15kHz?
a. 58.59 mVpk b. 72.77 mVpk c. 68.59 mVpk d. none of the above
a series resonant circuit has the following parameters: R = 5ohms, L = 5micro Henry, C = 5nF with a 5V ac input. What is the impedance at 100kHz above resonance?
a. 4+j5 ohms b. 6+j7 ohms c. 10+j12 ohms
d. 5+j6 ohms
A passive low pass filter having a cut-‐off of 15kHz will need what capacitance value if the resistance is equal to 1 kHz?
a. 66.67 nF * b. 45.61 nF c. 10.61 nF d. 5.3 nF
The Q of a tuned circuit was improved, what happens to the bandwidth?
a. widened b. increased c. not affected d. narrowed
The visible light with the shortest wavelength is
a. Yellow b. Green c. Violet d. Red
What characteristic of the network implies that the output and input impedances are equal to the characteristic impedance
a. it is asymmetrical b. it is in the first order c. it is symmetrical d. it is a pi network
Amplifier usually found at the last stage
a. Darlington pair b. Buffer c. Driver d. Emitter follower
Three modulating signals, with index rations 3:4:5 modulate a 200kHaz carrier signal. The modulated AM has a total modulation depth of 70.7%. The individual indexes of the modulating signals are
a. 0.60, 0.80, and 1.0 b. 0.30, 0.40, and 0.50 c. 0.450, 0.60, and 0.75 d. 0.45, 0.80, and 1.0
What is the value of the image frequency of an FM broadcast-‐band receiver if the desired receive frequency is 107.5 MHz? (assume high-‐side injection)
a. 86.1MHz b. 96.8MHz c. 118.2MHz d. 128.9MHz
An AM transmitter has 50 kW unmodulated carrier, if the index is 0.75, how much of the transmitted power contains information?
a. 17.06 kW b. 7.03 kW c. 15.06 kW d. 25 kW
How much power is saved if J3E is used instead of A3E at 90% modulation?
a. 28.82% b. 85.59% c. 87.11% d. 14.41%
Which of the following is true if m is greater than 1?
a. normal operation b. carrier drops to zero c. information signal is distorted d. carrier frequency shifts
how is IFRR improved?
a. increase frequency of signal b. increase frequency of IF c. increase frequency of LO d. increase frequency of BB
in the phasing method of SSB generation, one sideband is cancelled out due to
a. phase inversion b. balanced modulator c. phase shift d. carrier suppression
what is the local oscillator frequency of a receiving tuned to DZMM?
a. 455 kHz b. 1121 kHz c. 1085 kHz d. 1075 kHz
information in an AM signal is conveyed in the
a. carrier and sidebands b. envelope c. sideband
d. carrier
which of the following is not true about AM?
a. Ec must always equal Em b. Em should be equal to or less than EC c. Em should be greater than EC d. Ec should be greater than Em
A form of AM signal which is used for TV picture transmission
a. F3F b. B8E c. C3F d. A3E
What does a balanced modulator do?
a. it produces DSBSC signal b. it produces DSBFC signal c. it produces SSBFC signal d. it produces SSBSC signal
An FB BC station operates with a peak-‐to-‐peak deviation equal to 120kHz. Calculate the percentage modulation.
a. 75% b. 80%? c. 100% d. 50%
in an FM signal,, FM is a 1.5kHz. the carrier frequency is 1000kHz, the frequencies of the third significant sidebands are
a. cannot be determined b. 1.0045MHz and 9995.5kHz c. frequency of the modulating signal d. 1.0015 MHz and 998.5kHz
A 5 V tone would result to a 20kHz deviation, what about a 7.5V tone?
a. 30kHz b. 20kHz c. 80kHz d. 40kHz
In FM, the amplitude of the modulating voltage is doubled, the maximum frequency deviation
a. Becomes four times b. Remains unaltered c. Doubles d. Becomes half
In FM, if the frequency of the modulating signal is doubled, the maximum frequency deviation
a. doubles b. becomes half c. becomes four times d. remains unaltered
In FM, if the frequency of the modulating signal is doubled, the rate of deviation of the carrier frequency
a. becomes half b. becomes four times c. remains unaltered d. doubles
in FM, the carrier frequency deviation is determined by
a. modulating voltage b. modulating frequency c. carrier frequency d. none of the above
deviation ratio allowed for sound signal in TV broadcasting
a. 1 b. 1.67 c. 3 d. 33
This is interference due to single tone or complex periodic waveform
a. insertion b. harmonic distortion c. tone interference d. inter-‐modulation distortion
The practical bandwidth of a narrowband FM signal (maximum deviation <1) is
a. FM b. Maximum deviation c. Twice the maximum deviation d. 2fm
the ideal noise figure is
a. Unity b. Infinity c. None of the choices d. 0
a kind of distortion due to sum and difference of signals entering a non linear device
a. harmonic b. amplitude distortion c. intra-‐modulation distortion d. inter-‐modulation distortion
What is a preselector
a. Tuned circuit before the mixer b. The first to select c. The receiving antenna of the system d. Tuned circuit before the demodulator
The most efficient form of AM in terms of power utilization
a. J3E b. A3E c. H3E d. R3E
What is the major advantage of a superheterodyne receiver over tuned radio frequency receiver?
a. Good sensitivity b. Good selectivity ? c. Simple circuitry d. All of the above
One of the main functions of the RF amplifier in a superheterodyne receiver is to
a. provide improved tracking b. permit better adjacent channel rejection c. increase the tuning range of the receiver d. improve the rejection of the image frequency
indicate the false statement. The superheterodyne receiver replaced the TRF receiver because the latter suffered from
a. gain variation over the frequency coverage range. b. Insufficient gain and sensitivity c. Inadequate selectivity at high frequencies d. Instability
A superheterodyne receiver is tuned to a frequency of 5MHz when the oscillator frequency of 5Mhz when the oscillator frequency is 6.65 MHz. What is the IF
a. 0.65 MHz b. 1.65 MHz c. 5 MHz d. 11.55MHz
intermediate frequency for an AM broadcasting system as per FCC rules
a. 155 kHz
b. 255 kHz c. 355 kHz d. 455 kHz
What parameter enables a receiver to detect the weakest possible signal level?
a. sensitivity b. selectivity c. fidelity d. dynamic range
A superheterodyne receiver with an IF of 450 kHz is tuned to a signal at 1200 kHz. The image frequency is
a. 750 kHz b. 900 kHz c. 1650 kHz d. 210 kHz -‐-‐-‐ 1200+2(450)
what is the local oscillator frequency needed in the previous problem to produce an IF of 450kHz
a. 1650 kHz -‐> 1200 + 450 b. 750 kHz c. 900 kHz d. 2100 kHz
Which section of a superheterodyne receiver converts the IF signal back to the original source information?
a. RF section b. Mixer c. IF section d. Detector
Most of the gain and selectivity in a superheterodyne receiver is obtained in the
a. RF Section b. IF Section ? c. Mixer d. Detector
Determine the IF bandwidth necessary to achieve a bandwidth improvement of 16dB for a radio receiver with an RF bandwidth of 320kHz
a. 8 kHz ? b. 20 kHz c. 50 Hz d. 304 kHz
it is a measure of the extent to which the carrier is varied by the intelligence
a. Bandwidth
b. Shape factor c. Bandwidth Improvement d. Modulation factor
Which is true about over modulation?
a. modulating voltage is less than carrier voltage b. modulating voltage is equal to the carrier voltage c. overmodulation procudes a distortion at the demodulated ouput d. none of the choices
A sine wave carrier is modulated by a single tone so that Emax = 18mV and Emin = 0mV. Calculate the modulation index when the unmodulated carrier is 6 mVpk-‐pk.
a. 0.667 b. 1.0 c. 2 d. None of the choices
The modulation index of an AM wave is changed from 0 to 1, the transmitted power is
a. unchanged b. halved c. doubled d. increased by 50%
The percentage of modulation for maximum amplitude of information transmission is ___ %
a. 0 b. 50 c. 75 d. 100
An AM wave has a modulation factor of 0.9, and an unmodulated carrier amplitude of 10V, what is the amplitude of the lower sideband signal?
a. 10 b. 5 c. 9 d. 4.5 V
Three tones 5V 10kHz, 7.5V 3kHz and 15V 5kHz modulate a 20V carrier. Compute for the percentage modulation
a. 83.33 b. 45.83 c. 57.50 d. 87.50
the total sideband power is what percentage of the carrier power in DSBFC AM?
a. 50 b. 33.33 c. 16.67 d. 66.67
An antenna transmits an AM signal having a total power conrtent of 15kW. Determine the power being transmitted at each of the sidebands when the percent modulation is 85%.
a. 11019W b. 1990W PLSB = PUSB -‐ PC c. 3981W d. 1019W
An AM transmitter is modulated by two sine waves at 1kHz and 2.5 kHz with modulations of 25% and 50 % respectively. What is the effective modulation index?
a. 0.58 b. 0.65 c. 0.75 d. 0.25
Determine the modulation factor if a second modulating tone having twice the amplitude of the first, but different frequency is added at the input of the modulator for simultaneous modulation.
a. 1.73 b. 1.4 c. 2 d. 2.24
A 2000 Hz audio signal having an amplitude of 15 V modulates a 100 kHz carrier which has a peak value of 25 Vwhen not modulated. Calculate the modulation factor of the modulated wave
a. 0.4 b. 0.5 c. 0.6 = 15/25 d. 0.7
In the previous problem, what frequencies would show up in a spectrum analysis of the AM wave?
a. 98kHz, 100kHz, 102kHz b. 90.8kHz, 100kHz, 102.8kHz c. 98.8kHz 100kHz, 102.8kHz d. 198kHz, 200kHz, 202kHz
what is the required bandwidth necessary to transmit the AM signal in the previous problem?
a. 2kHz
b. 4kHz c. 200kHz d. none of the choices
A bandwidth of 12 MHz becomes available for assignment. If assigned for TV broadcast service, only the two channels could be accommodated. Determine the number of AM stations that could be broadcast simultaneously if the maximum modulating frequency is limited to 5 kHz
a. 1000 b. 1200 c. 800 d. 1600
Anticipating single sideband AM, what percentage of total pwer is saved by suppressing the carrier and one set of sidebands while transmitting the other set of sidebands only for m=0.75?
a. 66.7 % b. 89 % c. 100 % d. 45 %
Which circuit produces a suppressed carrier signal?
a. Mixer b. Low pass filter c. Tuned circuit d. Balanced modulator
Which of the following is not true about single sidebands transmission?
a. SSB transmission saves power b. It occupies less bandwidth c. More expensive ? d. All of the above ?
If the carrier of a 100% modulated AM wave is suppressed, the percentage power saving will be
a. 50 b. 150 c. 100 d. 66.66
An AM wave has a total transmitted power of 4kW when modulated 85%. How much total power should an SSB wave contain in order to have the same content as the contained in the two sidebands?
a. 1061.5 W? b. 530.76 W? c. 2120 W d. 2938.5
If a transmitter power of 100 W is sufficient for reliable communication over a certain path using SSB, approximately what power level would be required using DSB?
a. 300 W b. 600 W c. 100 W d. 200 W
In the previous problem, what is the power required for full-‐carrier AM.
a. 600 W b. 100 W c. 200 W d. 800 W
CB radios was developed using full carrier DSB AM. It operates using 40 channels, each 10 kHz wide. When SSBSC is used, the same carrier frequencies are used as with conventional AM, but the transceivers are switchable to either lower or upper sideband. How many channels are available when SSB used?
a. 40 b. 60 c. 80 d. 120
A modulator circuit performs what mathematical operation on its two inputs?
a. addition b. multiplication c. division d. subtraction
one of the following cannot be used to remove the unwanted sideband in SSB. This is the
a. Filter system b. Phase shift method c. Detector d. Balanced modulator
An audio signal with 0.5kHz range and a carrier signal with 100kHz frequency are mixed together in a balanced modulator. Which of the following frequencies cannot be found at the output of the modulator?
a. 100kHz b. 105kHz c. 95kHz d. none of the choices
To provide two or more voice circuits with the same carrier, it is necessary to use
a. ISB b. Carrier reinsertion c. SSB with pilot carrier d. Lincompex
An AM receiver uses a diode detector for demodulation. This enables it satisfactorily to receive
a. SSBSC b. SSB reduced carrier c. ISB d. SSBFC