8-22C: Amplifiers Flashcards
Receiving Systems (4 cards)
8-22C2
The usual intermediate frequency of a shipboard RADAR unit is:
A. 455 kHz.
B. 10.7 MHz.
C. 30 or 60 MHz.
D. 120 MHz.
ANSWER C
The common intermediate frequency of shipboard RADAR untis is 30 MHz or 60 MHz between the oscillator and the transmitted frequency. The RADAR may employ automatic frequency control (AFC), or a manual tune control to keep the output of the local oscillator in a closed loop circuit. The output of the discriminator is a DC error voltage, and indicated the degree of mistuning between the transmitter and the local oscillator.
8-22C3
The I.F. Amplifier bandwidth is:
A. Wide for short ranges and narrow for long ranges.
B. Wide for long ranges and narrow for short ranges.
C. Constant for all ranges.
D. Adjustable from the control panel.
ANSWER A
Intermediate frequency amplifier bandwidth is automaticallyselected by the range control adjustmentsat the RADAR display. On short range with a faster pulse repetition rate, amplifier bandwidth is wider, and for long range echoes, IF bandwidth becomes more narrow, which assists in mitigating receiver noise.
8-22C4
A logarithmic IF amplifier is preferable to a linear IF amplifier in a RADAR receiver because it:
A. Has higher gain.
B. Is more easily aligned.
C. Has a lower noise figure.
D. Has a greater dynamic range.
ANSWER D
The characteristic of a log amplifier provides an output voltage that is proportional to the log of the input signal. This characteristic allows greater dynamic range for the receiver.
8-22C5
The high-gain lF amplifiers in a RADAR receiver may amplify a 2 microvolt input signal to an output level of 2 volts. This amount of amplification represents a gain of:
A. 60 db.
B. 100 db.
C. 120 db.
D. 1,000 db.
ANSWER C
Voltage ratio equals 2 volts / 2 microvolts : 1 x 10E6. Voltage gain in dB is : 20 log 1 ,000,000. The log-10E6 = 6. Thus db : 20 x 6 = 120 dB. Remember 2 microvolts is 2.0 x 10-6. IMPORTANT: When using VOLTAGE to calculate dB calculations (either loss or gain) it is ABSOLUTELY NECESSARY to assure that both the input and output impedances are the same, an assumption that is made in this problem. All dB calculations ultimately are POWER ratios. lf input and output impedances are either different or unknown, we cannot use the “voltage dB” formula, 20 log (Vout/Vin).
