Download Multivibrators, Schmitt Triggers, and AM Receiver Basics and more Exams Electrical and Electronics Engineering in PDF only on Docsity!
ATT TEST 7 ACTUAL TEST 2025 | ALL QUESTIONS
AND CORRECT ANSWERS | GRADED A+ | VERIFIED
ANSWERS | LATEST TEST (JUST RELEASED)
If Q1 conducts first (ON 0V), how is Q2 turned OFF? (bistable) --------- CORRECT ANSWER-----------------Negative volts on Q2 base coupled through capacitor With Q1 ON, how is Q1 turned OFF? (Bistable) ---------CORRECT ANSWER-----------------Negative pulse from INPUT forward biases D1, negative signal turns Q1 OFF With Q1 OFF, how is Q2 turned ON? (Bistable) ---------CORRECT ANSWER-----------------!2V on Q1 collector coupled to Q2 base by capacitor What is troubleshooting procedure for astable multivibes? --------- CORRECT ANSWER-----------------Check output, Vcc, transistors, resistance checks What is troubleshooting procedure for monostable/bistable multivibes? ------ ---CORRECT ANSWER-----------------Check output, input trigger, Vcc, transistors, resistances What is the purpose of a schmitt trigger? ---------CORRECT ANSWER------- ----------Convert ANY shape waveform into square wave pulses of CONSTANT amplitude
Schmitt trigger is also called what other names? ---------CORRECT ANSWER-----------------Squaring amp, level detector, threshold detector What determines upper threshold in schmitt trigger? ---------CORRECT ANSWER-----------------Voltage divider What happens when upper threshold is reached? ---------CORRECT ANSWER-----------------Q1 approaches saturation (ON) and drives Q2 into cutoff (high output) What ensures very short rise/fall times in schmitt trigger? ---------CORRECT ANSWER-----------------Feedback circuit What turns Q2 on in schmitt trigger? ---------CORRECT ANSWER------------- ----Vcc How is low output formed schmitt trigger? ---------CORRECT ANSWER------ -----------Volt divider formed between R6 and R8, 0V on Q2 collector causes low voltage drops What is frequency range of AM? ---------CORRECT ANSWER----------------- 535kHz to 1605 kHz Voice, music, coded signals are all types of what? ---------CORRECT ANSWER-----------------Intelligence (Information)
What is sensitivity? ---------CORRECT ANSWER-----------------Receivers ability to correctly reproduce weak signals What is wave propagation? ---------CORRECT ANSWER----------------- Movement of electromagnetic waves through medium What are two types of waves? ---------CORRECT ANSWER----------------- Longitudinal and transverse What are two types of transverse (electromagnetic) waves? --------- CORRECT ANSWER-----------------Radio and light waves What is the most important region of stratosphere for long distance, point to point comms? ---------CORRECT ANSWER-----------------Ionosphere (31 to 250 miles above sea level) What layer of ionosphere disappears after sunset? ---------CORRECT ANSWER-----------------D-layer What layer of ionosphere has longest propagation capability? --------- CORRECT ANSWER-----------------F layer What are 4 factors that affect refraction? ---------CORRECT ANSWER-------- ---------Ionization, layer density, RF freq, penetration angle
What is critical angle? ---------CORRECT ANSWER-----------------Max angle at which radio wave can be transmitted and still be refracted back to earth? What is the purpose of multivibrators? ---------CORRECT ANSWER----------- ------Convert DC ENERGY into SQUARE WAVE ENERGY How are transistors biased in multivibrators? ---------CORRECT ANSWER-- ---------------To be in EITHER saturation or cutoff, NEVER inbetween What component determines which transistor is ON or OFF in multivibe circuit? ---------CORRECT ANSWER-----------------Feedback circuit What does it mean when a transistor is ON? How many volts on collector? ---------CORRECT ANSWER-----------------Saturation (MAX current flow), 0 V What does it mean when a transistor is OFF? How many volts on collector? ---------CORRECT ANSWER-----------------Cutoff (no current flow), 12 V If both transistors have outputs (multivibe), what is phase shift between them? ---------CORRECT ANSWER----------------- 180 Which type of multivibe circuit is free running? ---------CORRECT ANSWER-----------------Astable
With Q2 ON (0V), how is Q1 turned ON? (Astable) ---------CORRECT ANSWER-----------------C2 charging increases volts Q1 base What is another name for monostable multivibe? ---------CORRECT ANSWER-----------------One Shot How is frequency determined in monostable multivibe? ---------CORRECT ANSWER-----------------Output frequency = Input frequency How is Q1 turned on (monostable)? ---------CORRECT ANSWER-------------- ---Input pulse forward biases D1 and is applied to Q1 base What happens when Q1 turns on (monostable)? ---------CORRECT ANSWER-----------------C1 discharges and turns OFF Q2 (12V) When Q1 is ON, what causes it to turn OFF? (monostable) --------- CORRECT ANSWER-----------------C1 charges enough to turn Q2 ON which turns Q1 off How is frequency determined in bistable multivibes? ---------CORRECT ANSWER-----------------Output frequency is 1/2 Input frequency
What is skip zone? ---------CORRECT ANSWER-----------------zone of silence between the point where the ground wave becomes too weak for reception and the point where the sky wave is first returned to Earth What are two types of ground waves? ---------CORRECT ANSWER----------- ------Surface, direct Skipzone is (lengthened/shortened) at night? ---------CORRECT ANSWER-- ---------------Lengthened (bigger area of silence) Skip zone is (lengthened/shortened) during the day? ---------CORRECT ANSWER-----------------Shortened (smaller area of silence) As frequency increases, the critical angle must _____? ---------CORRECT ANSWER-----------------Decrease Which frequency has least amount of problems? ---------CORRECT ANSWER-----------------Optimum Working Frequency (owf) What is the purpose of Amplitude modulation? ---------CORRECT ANSWER-----------------Transmit over longer distances What is main purpose of AM receiver? ---------CORRECT ANSWER---------- -------Pickup electromagnetic waves/restore original low frequency intelligence (RECEIVE RADIO WAVES)
What is IF? ---------CORRECT ANSWER-----------------455kHz (LO - RF) What 4 things does mixer produce? ---------CORRECT ANSWER-------------- ---RF, LO, Sum (RF+LO), IF (LO-RF) What circuits make up detector? ---------CORRECT ANSWER----------------- Rectfier, RC circuit What does rectifier circuit do? ---------CORRECT ANSWER----------------- Eliminates pos or neg audio signal from carrier What does RC circuit do? ---------CORRECT ANSWER----------------- Removes carrier from low freq audio What circuits make up AF amp? ---------CORRECT ANSWER----------------- pre-amp, driver, PUSH-PULL amp Which part of AM receiver provides AVC? ---------CORRECT ANSWER------ -----------Detector All stages of IF amp are tuned to what? ---------CORRECT ANSWER--------- --------455kHz (IF)
What is the purpose of AVC? ---------CORRECT ANSWER----------------- Keeps volume constant What is purpose of T6 in push-pull amp (AF amp)? ---------CORRECT ANSWER-----------------Provides push-pull amp with two signals 180 degrees out of phase What frequency is C1A tuned to? ---------CORRECT ANSWER----------------- RF What signal is C1B tuned to? ---------CORRECT ANSWER-----------------LO (LF+RF) What frequency is T2 tuned to (Tuner)? ---------CORRECT ANSWER--------- --------LO What frequency is T3 tuned to (tuner)? ---------CORRECT ANSWER---------- -------IF What 3 functions do Q1 perform? ---------CORRECT ANSWER----------------- Amp, mixer, oscillator What type of signal is AVC? ---------CORRECT ANSWER----------------- Negative signal
