Amateur Extra E7F: Digital signal processing and SDRs
These are the 14 official questions in group E7F of the 2024–2028 Amateur Extra 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.
Learn E7F step by stepThe Amateur Extra course teaches this group in a short guided lesson, then drills you on the questions you miss. Start with the free lessons to see how it works.
- E7F01Question 1
What is meant by “direct sampling” in software defined radios?
- ASoftware is converted from source code to object code during operation of the receiver
- BI and Q signals are generated by digital processing without the use of RF amplification
- CIncoming RF is digitized by an analog-to-digital converter without being mixed with a local oscillator signal Correct
- DA switching mixer is used to generate I and Q signals directly from the RF input
Why: Direct sampling digitizes the RF without mixing it with an LO first.
- E7F02Question 2
What kind of digital signal processing audio filter is used to remove unwanted noise from a received SSB signal?
- AAn adaptive filter Correct
- BA crystal-lattice filter
- CA Hilbert-transform filter
- DA phase-inverting filter
Why: An adaptive filter removes noise from received SSB.
- E7F03Question 3
What type of digital signal processing filter is used to generate an SSB signal?
- AAn adaptive filter
- BA notch filter
- CA Hilbert-transform filter Correct
- DAn elliptical filter
Why: A Hilbert-transform filter is used to generate SSB.
- E7F04Question 4
Which method generates an SSB signal using digital signal processing?
- AMixing products are converted to voltages and subtracted by adder circuits
- BA frequency synthesizer removes unwanted sidebands
- CVarying quartz crystal characteristics are emulated in digital form
- DSignals are combined in quadrature phase relationship Correct
Why: DSP makes SSB by combining signals in quadrature.
- E7F05Question 5
How frequently must an analog signal be sampled to be accurately reproduced?
- AAt least half the rate of the highest frequency component of the signal
- BAt least twice the rate of the highest frequency component of the signal Correct
- CAt the same rate as the highest frequency component of the signal
- DAt four times the rate of the highest frequency component of the signal
Why: Sample at least twice the highest frequency (the Nyquist rate).
- E7F06Question 6
What is the minimum number of bits required to sample a signal with a range of 1 volt at a resolution of 1 millivolt?
- A4 bits
- B6 bits
- C8 bits
- D10 bits Correct
Why: 1 V ÷ 1 mV = 1,000 levels; 2¹⁰ = 1,024, so 10 bits.
- E7F07Question 7
What function is performed by a Fast Fourier Transform?
- AConverting analog signals to digital form
- BConverting digital signals to analog form
- CConverting signals from the time domain to the frequency domain Correct
- DConverting signals from the frequency domain to the time domain
Why: An FFT converts the time domain to the frequency domain.
- E7F08Question 8
What is the function of decimation?
- AConverting data to binary-coded decimal form
- BReducing the effective sample rate by removing samples Correct
- CAttenuating the signal
- DRemoving unnecessary significant digits
Why: Decimation reduces the sample rate by removing samples.
- E7F09Question 9
Why is an anti-aliasing filter required in a decimator?
- AIt removes high-frequency signal components that would otherwise be reproduced as lower frequency components Correct
- BIt peaks the response of the decimator, improving bandwidth
- CIt removes low-frequency signal components to eliminate the need for DC restoration
- DIt notches out the sampling frequency to avoid sampling errors
Why: The filter removes high frequencies that would alias into false low frequencies.
- E7F10Question 10
What aspect of receiver analog-to-digital conversion determines the maximum receive bandwidth of a direct-sampling software defined radio (SDR)?
- ASample rate Correct
- BSample width in bits
- CIntegral non-linearity
- DDifferential non-linearity
Why: The sample rate sets a direct-sampling SDR's maximum bandwidth.
- E7F11Question 11
What sets the minimum detectable signal level for a direct-sampling software defined receiver in the absence of atmospheric or thermal noise?
- ASample clock phase noise
- BReference voltage level and sample width in bits Correct
- CData storage transfer rate
- DMissing codes and jitter
Why: The ADC's reference voltage and bit width set the smallest detectable signal.
- E7F12Question 12
Which of the following is generally true of Finite Impulse Response (FIR) filters?
- AFIR filters can delay all frequency components of the signal by the same amount Correct
- BFIR filters are easier to implement for a given set of passband rolloff requirements
- CFIR filters can respond faster to impulses
- DAll these choices are correct
Why: FIR filters can delay all frequencies by the same amount.
- E7F13Question 13
What is the function of taps in a digital signal processing filter?
- ATo reduce excess signal pressure levels
- BProvide access for debugging software
- CSelect the point at which baseband signals are generated
- DProvide incremental signal delays for filter algorithms Correct
Why: Taps provide incremental signal delays for the filter.
- E7F14Question 14
Which of the following would allow a digital signal processing filter to create a sharper filter response?
- AHigher data rate
- BMore taps Correct
- CLower Q
- DDouble-precision math routines
Why: More taps make a sharper DSP filter.
Learn E7F step by stepThe Amateur Extra course teaches this group in a short guided lesson, then drills you on the questions you miss. Start with the free lessons to see how it works.