General exam: signals and emissions
Modulation, mixing, bandwidth, digital modes and signal quality. 42 questions, 10 at a time, starting with ones you haven't seen.
Rules to remember10 key signals and emissions rulesShow the rules
- Varying the phase angle of an RF signal to carry information is called phase modulation. (p. 66)
- Amplitude modulation varies the strength, and so the instantaneous power, of the RF signal to carry information. (p. 66)
- Combining two RF signals in a mixer to produce sum and difference frequencies is called heterodyning. (p. 68)
- Sending symbols faster requires more bandwidth, so higher symbol rates need wider bandwidth. (p. 70)
- A mixer's output contains the sum and the difference of the local oscillator and RF input frequencies. (p. 70)
- When two signals pass through a non-linear circuit, they combine to create unwanted new frequencies; this is intermodulation. (p. 70)
- Baudot is the 5-bit code used for RTTY, with start and stop bits added around each character. (p. 71)
- In a mesh network, packets can route through any working node, so if one node fails traffic can still reach its destination by another path. (p. 72)
- The two frequencies of an FSK signal are called mark and space, a naming carried over from early telegraph and teletype systems. (p. 72)
- PSK31 sends characters using Varicode, a variable-length code where common characters have shorter bit patterns. (p. 72)
Taken from the explanations to checked practice questions; page numbers link to the official handbook.
Sample signals and emissions questions
1.What does an FT8 signal report of +3 mean?
- AThe signal is 3 times the noise level of an equivalent SSB signal
- BThe signal is S3 (weak signals)
- CThe signal-to-noise ratio is equivalent to +3dB in a 2.5 kHz bandwidth
- DThe signal is 3 dB over S9
Show the answer
✓ C. The signal-to-noise ratio is equivalent to +3dB in a 2.5 kHz bandwidth
FT8 reports are signal-to-noise ratios referenced to a 2.5 kHz bandwidth, so +3 means the signal is 3 dB above the noise in that bandwidth.
2.What is the name of the process that changes the instantaneous frequency of an RF wave to convey information?
- AFrequency conversion
- BFrequency modulation
- CFrequency transformation
- DFrequency convolution
Show the answer
✓ B. Frequency modulation
Varying the instantaneous frequency of an RF wave to carry information is called frequency modulation (FM).
3.Which of the following statements is true about PSK31?
- AHigher power is needed as compared to RTTY for similar error rates
- BError correction is used to ensure accurate message reception
- CUpper case letters use longer Varicode bit sequences and thus slow down transmission
- DUpper case letters are sent with more power
Show the answer
✓ C. Upper case letters use longer Varicode bit sequences and thus slow down transmission
PSK31 uses Varicode, where common lowercase letters get short codes and uppercase letters get longer ones, so sending capitals slows transmission.
4.What is QPSK modulation?
- AModulation using quasi-parallel to serial conversion to reduce bandwidth
- BModulation in which digital data is transmitted using 0-, 90-, 180- and 270-degrees phase shift to represent pairs of bits
- CModulation using quadra-pole sideband keying to generate spread spectrum signals
- DModulation using Fast Fourier Transforms to generate frequencies at the first, second, third, and fourth harmonics of the carrier frequency to improve noise immunity
Show the answer
✓ B. Modulation in which digital data is transmitted using 0-, 90-, 180- and 270-degrees phase shift to represent pairs of bits
Quadrature phase shift keying uses four phase states, 0, 90, 180 and 270 degrees, so each symbol carries two bits of data.