Hint: FSK (Frequency Shift Keying) = digital control

FSK is a method of rapidly changing the carrier frequency of a transmitter between two different frequencies. These two carrier frequencies are often referred to as the Mark frequency and the Space frequency, or simply Mark and Space. FSK is commonly used for RTTY (radioteletype) as well as ASCII-based transmissions like packet. Since there are only two frequencies to generate, a digital control signal is used. The terms digital, binary, ON-OFF, and two-state are all basically equivalent. This two-state control signal can be used to shift the frequency of an oscillator back and forth between a Mark frequency and a Space frequency. After appropriate amplification, the carrier signal generated by the oscillator can leave the transmitter to energize an antenna.

Quick and dirty mnemonic: "F"requency "S"ignal "K"ontrol.

Silly hint; the correct answer is the only one that has the word "direct" in the answer.

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(B). Phase modulation is the name of the process that changes the phase angle of an RF wave to convey information. Phase modulation changes the signal by modifying the instantaneous phase angle of the carrier. PM is often used for data transmission methods such as PSK (phase-shift keying).

For more info see Wikipedia: Phase modulation

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Hint: modulate CONVEYs & controls

Frequency modulation (FM) is the process which changes the frequency of an RF wave to convey information. The instantaneous frequency of the carrier is altered to convey the information, while the amplitude remains constant. FM is used for frequency-shift keying, radar in addition to radio voice transmissions.

For more info see Wikipedia: Frequency modulation

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Hint: PHASE MODULATION is produced by REACTANCE

Phase modulation is the emission produced by a reactance modulator connected to an RF power amplifier. The reactance modulator changes the instantaneous phase angle of the carrier, generating phase modulated signals.

Silly hint: The child REACTED because they were going through a PHASE.

For more info see Wikipedia: Phase modulation

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Hint: “Amplitude” is the power level of RF.

(D). Amplitude modulation (AM) is the type of modulation that varies the instantaneous power level of the RF signal. The power or signal strength of the wave is measured as the wave amplitude (may also be called the envelope).

For more info see Wikipedia: Amplitude modulation (AM)

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Hint: Quick Provide Sideband = ALL

QPSK31 stands for Quadrature Phase Shift Keying, 31-baud

From http://www.podxs070.com/frequently-asked-questions/introduction-to-psk, here's an explanation of QPSK31: So what's different about QPSK31?

The QPSK31 format transmits two bits per phase state, and transmits one of four phase states each time. (If you think about it, there are four possible combinations of two bits, and each of these combinations is assigned a unique phase.) This allows twice as many bits to be sent in the same period of time (and bandwidth) as with BPSK. Martinez coupled this with a rate-1/2, constraint length 5 convolutional code to improve the power efficiency of the modulation (defined as the signal-to-noise ratio required to deliver a specified bit-error-rate, or BER).

This adds a step in the transmission process - generation of the coded bitstream - after the insertion of fill bits. It also adds a corresponding step in the receive process. After the bits are recovered from the phase transition, a Viterbi decoder removes the redundancy inserted by the code, corrects bit errors (up to a point) and recovers the original bit stream for translation of the Varicode.

One interesting note is that while the BPSK31 signal is phase-symmetric, QPSK31 is not. This means that if you are using BPSK, it doesn't matter if you are using USB or LSB - the signal is the same. If you are using QPSK, both stations must be using the same sideband, or one must use the "invert" function in their software.

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(A). Single sideband is the phone emission which uses the narrowest frequency bandwidth. For each part of the signal that is suppressed, the bandwidth will be reduced. By supressing the carrier and filtering the unwanted sideband, the typical bandwidth of a single-sideband signal is reduced to only about 3 kHz.

For more info see Wikipedia: single-sideband (SSB)

Hint: Single is less than double.

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Hint: Over-modulation = EXCESSIVE BANDWIDTH

Excessive bandwidth is an effect of over-modulation. Overmodulating the signal causes increased distortion or deviation of the waveform. This increases the formation of spurious emissions with distortion outside the normal bandwidth.

For more info see Wikipedia: Overmodulation

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Hint: FT8 means Frequency Tone 8. Bingo!

FT8 uses 8 tone FSK (frequency shift keying) to encode time-sequenced digital data transmissions.

From http://physics.princeton.edu/pulsar/K1JT/Release_Notes_1.8.0.txt

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Brief Description of the FT8 Protocol:

WSJT-X Version 1.8.0 includes a new mode called FT8, developed by K9AN and K1JT. The mode name "FT8" stands for "Franke and Taylor, 8-FSK modulation". FT8 uses 15-second T/R sequences and provides 50% or better decoding probability down to -20 dB on an AWGN channel. An auto-sequencing facility includes an option to respond automatically to the first decoded reply to your CQ. FT8 QSOs are 4 times faster than those made with JT65 or JT9. FT8 is an excellent mode for HF DXing and for situations like multi-hop E_s on 6 meters, where deep QSB may make fast and reliable completion of QSOs desirable.

Some important characteristics of FT8:

• T/R sequence length: 15 s
• Message length: 75 bits + 12-bit CRC
• FEC code: LDPC(174,87)
• Modulation: 8-FSK, tone spacing 6.25 Hz
• Constant-envelope waveform
• Occupied bandwidth: 50 Hz
• Synchronization: 7x7 Costas arrays at start, middle, and end
• Transmission duration: 79*1920/12000 = 12.64 s
• Decoding threshold: -20 dB; several dB lower with AP decoding
• Multi-decoder finds and decodes all FT8 signals in passband
• Optional auto-sequencing and auto-reply to a CQ response
• Operational behavior similar to JT9, JT65

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Flat-topping (or clipping) is where overmodulation causes a distortion of the waveform in which the amplitude appears flattened on the oscilloscope, because the maximum levels of output voltage or current are exceeded.

For more info see Wikipedia: Flat-topping or Clipping

(Hint: You will DRIVE faster when on FLAT ground.) {OR} You drive on a flattop slang for a road)

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Hint: Think of an envelope's four corners, these would be the peak values.

In AM, the frequency is stable and only the amplitude modulates (Amplitude Modulation). When this happens, the carrier signal's peak value will change during modulation. In FM, the signal's peak value remains constant.

Amplitude Modulation

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QPSK (Quadrature Phase Shift Keying) modulation is a digital modulation technique used in communication systems to transmit data over radio waves or other transmission media.

In QPSK modulation, the information is encoded into four different phase states of the carrier signal. These phase states are 0 degrees, 90 degrees, 180 degrees, and 270 degrees. Each phase state represents a specific combination of two bits of data.

To transmit the data, the carrier signal's phase is shifted to match the corresponding phase state of the data. By changing the phase of the carrier signal, the receiver can detect and decode the transmitted information.

QPSK modulation is widely used in various communication systems, including satellite communications, wireless networks, and digital television broadcasting. It is known for its efficiency in transmitting data and its ability to provide higher data rates compared to simpler modulation schemes.

Memory visualization: Think of a QPSK signal like an analog clock; 0, 90, 180, and 270 degrees would be 12, 3, 6, and 9 respectively. There are 4 characters in "QPSK" and 4 phases that the modulation is encoded into, matching the 4 "quarter hour" positions on a clock.

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A "link" budget can be seen as a series (like "links" of a chain) of events that take place from a transmitter output to the receiver effecting power of signal. Therefore, to calculate the power at receiver we need to know what the power output is from transmitter, plus any gain from antenna such as Dipole 2.15dB, yagi etc, and then deduct any losses, such as distance signal travels, feed line at receiver, mismatched impedance etc, to come up with the final actual power of signal at receiver.

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A receiver requires a minimum signal strength to operate effectively to enable signals to be heard (depending on manufacturers specifications). The difference in the minimum value needed by receiver, and the actual power level received is known as the "link" margin.

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