General G8B: Mixing, bandwidth and intermod
These are the 13 official questions in group G8B of the 2023–2027 General question pool, with the correct answer marked and a plain-English explanation of why it's right. The real exam asks one question from this group.
- G8B01Question 1
Which mixer input is varied or tuned to convert signals of different frequencies to an intermediate frequency (IF)?
- AImage frequency
- BLocal oscillator Correct
- CRF input
- DBeat frequency oscillator
Why: The local oscillator is tuned to convert different signals to the IF.
- G8B02Question 2
What is the term for interference from a signal at twice the IF frequency from the desired signal?
- AQuadrature response
- BImage response Correct
- CMixer interference
- DIntermediate interference
Why: A signal twice the IF away from the desired one causes image response.
- G8B03Question 3
What is another term for the mixing of two RF signals?
- AHeterodyning Correct
- BSynthesizing
- CFrequency inversion
- DPhase inversion
Why: Mixing two RF signals is called heterodyning.
- G8B04Question 4
What is the stage in a VHF FM transmitter that generates a harmonic of a lower frequency signal to reach the desired operating frequency?
- AMixer
- BReactance modulator
- CBalanced converter
- DMultiplier Correct
Why: A multiplier generates a harmonic to reach the operating frequency.
- G8B05Question 5
Which intermodulation products are closest to the original signal frequencies?
- ASecond harmonics
- BEven-order
- COdd-order Correct
- DIntercept point
Why: Odd-order intermodulation products land closest to the original frequencies.
- G8B06Question 6
What is the total bandwidth of an FM phone transmission having 5 kHz deviation and 3 kHz modulating frequency?
- A3 kHz
- B5 kHz
- C8 kHz
- D16 kHz Correct
Why: 2 × (5 kHz + 3 kHz) = 16 kHz.
- G8B07Question 7
What is the frequency deviation for a 12.21 MHz reactance modulated oscillator in a 5 kHz deviation, 146.52 MHz FM phone transmitter?
- A101.75 Hz
- B416.7 Hz Correct
- C5 kHz
- D60 kHz
Why: 146.52 ÷ 12.21 = 12 times multiplication, so 5 kHz ÷ 12 ≈ 416.7 Hz.
- G8B08Question 8
Why is it important to know the duty cycle of the mode you are using when transmitting?
- ATo aid in tuning your transmitter
- BSome modes have high duty cycles that could exceed the transmitter’s average power rating Correct
- CTo allow time for the other station to break in during a transmission
- DTo prevent overmodulation
Why: High-duty-cycle modes can exceed the transmitter's average power rating.
- G8B09Question 9
Why is it good to match receiver bandwidth to the bandwidth of the operating mode?
- AIt is required by FCC rules
- BIt minimizes power consumption in the receiver
- CIt improves impedance matching of the antenna
- DIt results in the best signal-to-noise ratio Correct
Why: Matching receiver bandwidth to the mode gives the best signal-to-noise ratio.
- G8B10Question 10
What is the relationship between transmitted symbol rate and bandwidth?
- ASymbol rate and bandwidth are not related
- BHigher symbol rates require wider bandwidth Correct
- CLower symbol rates require wider bandwidth
- DBandwidth is half the symbol rate
Why: Higher symbol rates need wider bandwidth.
- G8B11Question 11
What combination of a mixer’s Local Oscillator (LO) and RF input frequencies is found in the output?
- AThe ratio
- BThe average
- CThe sum and difference Correct
- DThe arithmetic product
Why: A mixer's output contains the sum and difference of the LO and RF frequencies.
- G8B12Question 12
What process combines two signals in a non-linear circuit to produce unwanted spurious outputs?
- AIntermodulation Correct
- BHeterodyning
- CDetection
- DRolloff
Why: Intermodulation combines signals in a non-linear circuit to make spurious outputs.
- G8B13Question 13
Which of the following is an odd-order intermodulation product of frequencies F1 and F2?
- A5F1-3F2
- B3F1-F2
- C2F1-F2 Correct
- DAll these choices are correct
Why: 2F1 − F2 is a third-order (odd) intermodulation product.