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E2E

OPERATING PROCEDURES

Operating methods: digital modes and procedures for HF

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E2E011 of 13

Which of the following types of modulation is used for data emissions below 30 MHz?

Why On HF, data signals are almost universally sent by shifting the carrier between discrete frequencies, that is frequency shift keying. Classic RTTY uses direct FSK with a mark and space tone pair, and AFSK feeding an SSB transmitter produces the same on-air J2B/F1B type signal. FSK is favored below 30 MHz because constant amplitude tones survive fading and can be copied through noise better than amplitude-based schemes.
Watch out Spread spectrum is tempting because it is a modern data technique, but Part 97.305 only authorizes SS emissions on bands at 222 MHz and above; likewise pulse emissions are restricted to the microwave bands, and DTMF tones over FM are control/signaling tones, not a data emission.
HF data = shifting tones. Spread spectrum and pulse live up high (222 MHz and above), never below 30 MHz.
HamSandwich explanation, first draft. The question and answers are the NCVEC text.
E2E022 of 13

Which of the following synchronizes WSJT-X digital mode transmit/receive timing?

Why WSJT-X modes such as FT8, FT4, JT65 and WSPR use fixed transmit/receive sequences keyed to UTC, for example FT8's 15-second slots that begin at 0, 15, 30 and 45 seconds past the minute. The decoder expects the signal to start at a known instant, so each station's computer clock must be set accurately, typically within about a second, using an internet time service (NTP) or GPS. If your clock drifts, your transmissions land outside the slot and other stations cannot decode you.
Watch out Sync fields or sync pulses embedded in the transmission are how many other digital protocols, like packet or PACTOR, establish timing, but WSJT-X relies on external clock accuracy instead of an in-signal sync marker.
FT8 lives on the clock: keep your PC within a second of UTC or nobody decodes you.
HamSandwich explanation, first draft. The question and answers are the NCVEC text.
E2E033 of 13

To what does the "4" in FT4 refer?

Why In the FT-family modes designed by Joe Taylor K1JT and colleagues, the number names the number of tones used by the modulation. FT4 sends four-tone continuous-phase (Gaussian-shaped) frequency shift keying, just as FT8 uses eight tones. The tone count sets the occupied bandwidth and the number of bits carried per symbol.
Watch out The timing answer is the trap: FT4 uses 7.5-second transmit/receive sequences, which is eight cycles per minute, while it is FT8 with its 15-second sequences that gives four cycles per minute.
The digit counts tones, not seconds: FT4 = 4 tones, FT8 = 8 tones.
HamSandwich explanation, first draft. The question and answers are the NCVEC text.
E2E044 of 13

Which of the following is characteristic of the FST4 mode?

Why FST4 (and its beacon-like cousin FST4W) was designed by the WSJT-X developers for the LF and MF bands, 2200 and 630 meters, where extremely narrow signals and long integration times pay off. It uses 4-tone Gaussian FSK, which shapes the tone transitions to keep the spectrum tight. It offers a menu of transmit/receive sequence lengths (15, 30, 60, 120, 300, 900 and 1800 seconds), and because tone spacing scales with the symbol rate, each of those seven period choices has its own tone spacing. Since all three statements describe the mode, the combined choice is correct.
Watch out Each individual statement is true on its own, so picking just the four-tone GFSK description or just the variable T/R periods leaves out equally valid characteristics.
FST4 = Four tones, and seven T/R periods each with its own spacing. Everything listed is true, so pick 'all'.
HamSandwich explanation, first draft. The question and answers are the NCVEC text.
E2E055 of 13

Which of these digital modes does not support keyboard-to-keyboard operation?

Why WSPR (Weak Signal Propagation Reporter) is a beacon mode, not a conversational one. Each transmission is a rigid, highly compressed message containing only callsign, 4-character grid square, and power level, sent over about 110 seconds in a 2-minute window, so there is no way to type free text. Its purpose is to test propagation paths at very low power and report spots to a database. RTTY, PSK31, and MFSK16 all send arbitrary characters as you type them, so they support real-time keyboard-to-keyboard QSOs.
Watch out PSK31 is the classic keyboard chat mode of the group, designed specifically for relaxed typed conversation at about typing speed, so it is the opposite of the right answer.
WSPR only whispers three things: call, grid, power. No typing, no QSO.
HamSandwich explanation, first draft. The question and answers are the NCVEC text.
E2E066 of 13

What is the length of an FT8 transmission cycle?

Why FT8 uses fixed, clock-synchronized transmit/receive slots of 15 seconds, starting at 0, 15, 30 and 45 seconds past each minute. The actual signal lasts about 12.6 seconds within that window, leaving time for decoding and for the operator to pick the next message. Because the slots are fixed, your computer clock must be accurate to within about a second or you will not be decoded.
Watch out The choice saying it varies with the amount of data describes packet or other asynchronous modes; FT8 always sends the same 77-bit payload in the same fixed-length frame. The 30 second and 8 second options confuse it with other WSJT-X modes: JT65 and JT9 use 60 second cycles and FT4 uses 7.5 seconds.
FT8: the 8 is the 8-FSK tones, not the timing. Four slots per minute means 15 seconds each.
HamSandwich explanation, first draft. The question and answers are the NCVEC text.
E2E077 of 13

How does Q65 differ from JT65?

Why Q65 is the newest of the WSJT-X weak-signal modes, built on JT65's 65-tone FSK framework but with a stronger Q-ary repeat-accumulate error-correcting code. Its key operational advantage is message averaging: the software can accumulate and combine several successive receive sequences of the same message, pulling a signal out of the noise that no single 60-second cycle could decode. That makes it the choice for extremely weak paths such as EME, ionospheric scatter, and troposcatter on VHF/UHF, as well as very weak HF work.
Watch out The quadrature modulation answer misreads the name: the Q refers to the Q-ary (65-symbol) code, not QPSK, since the mode is still multi-tone FSK. Keyboard-to-keyboard chat is not supported either, because Q65 uses structured, fixed-format messages like the other WSJT-X modes.
Q65: Q is for Q-ary code, and its trick is stacking multiple receive cycles (averaging) to decode.
HamSandwich explanation, first draft. The question and answers are the NCVEC text.
E2E088 of 13

Which of the following HF digital modes can be used to transfer binary files?

Why Transferring binary files requires a mode that handles full 8-bit data and guarantees error-free delivery. PACTOR does exactly that: it uses ARQ (automatic repeat request) with acknowledgements and data compression, so any block received with errors is resent until it is correct, making it suitable for file and email transfer over HF. The other listed modes are keyboard-to-keyboard chat modes built around limited character sets.
Watch out AMTOR is the closest relative and also uses ARQ, but it is based on 5-bit Baudot-style code and can only pass a restricted character set, not arbitrary binary data; PSK31 uses varicode text and RTTY uses 5-bit Baudot, both without error correction.
PACTOR = packet + AMTOR: it inherited packet's 8-bit binary data handling, so it is the file-transfer mode.
HamSandwich explanation, first draft. The question and answers are the NCVEC text.
E2E099 of 13

Which of the following HF digital modes uses variable-length character coding?

Why PSK31 encodes text with Varicode, a variable-length alphabet in which the most frequently used characters (space, e, t) get the shortest bit patterns and rare characters get longer ones. That keeps the average throughput near 31.25 baud typing speed while holding the signal in about 31 Hz of bandwidth. The idea is the same efficiency trick Morse code uses: common letters, short symbols.
Watch out RTTY is the usual trap, but it uses Baudot, a fixed 5-bit code for every character, so all characters take the same time to send.
PSK31 = Varicode = VARiable. Baudot (RTTY) is always 5 bits, no more, no less.
HamSandwich explanation, first draft. The question and answers are the NCVEC text.
E2E1010 of 13

Which of these digital modes has the narrowest bandwidth?

Why Bandwidth of a digital signal depends on its symbol rate and, for FSK modes, the tone spacing. FT8 uses 8-tone FSK with a symbol rate of about 6.25 baud and tones spaced 6.25 Hz apart, so the whole signal fits in roughly 50 Hz. That is far narrower than the other modes listed, which is why FT8 works at signal-to-noise ratios well below what the ear can hear.
Watch out The 170 Hz shift, 45-baud RTTY signal is the usual runner-up, but the shift alone is 170 Hz and the occupied bandwidth is around 250 Hz. MFSK16 runs about 316 Hz, and PACTOR IV spreads across roughly 2.4 kHz to get its high data rate.
FT8 = slow tones, tiny footprint: about 50 Hz. More speed or more shift means more bandwidth.
HamSandwich explanation, first draft. The question and answers are the NCVEC text.
E2E1111 of 13

What is the difference between direct FSK and audio FSK?

Why In direct FSK the keying signal shifts the transmitter's oscillator (VFO) itself, so the radiated carrier jumps between the mark and space frequencies with no audio stage involved. Audio FSK instead feeds two audio tones into an SSB transmitter's microphone or line input, and the SSB mixer translates those tones up to RF. The final on-air signal has the same shift, the same bandwidth and the same baud rate either way; the difference is only where in the chain the frequency shift is generated. Direct FSK avoids audio-stage distortion and overdrive that can create AFSK sidebands, but it is not inherently narrower or faster.
Watch out The bandwidth and baud rate choices are tempting because AFSK can sound dirty when overdriven, but occupied bandwidth depends on the shift and keying speed, not on how the shift is produced, so those claims are false and the all-of-these choice fails with them.
Direct FSK shifts the VFO; AFSK shifts audio tones into an SSB rig. Same bandwidth, same speed, different injection point.
HamSandwich explanation, first draft. The question and answers are the NCVEC text.
E2E1212 of 13

How do ALE stations establish contact?

Why Automatic Link Establishment (ALE) radios continuously scan a preset list of channels, listening for short digital bursts that carry station addresses (call signs). When a radio hears its own address on one of the scanned channels, it stops scanning, handshakes with the caller, and the link is established on whichever channel is currently propagating best. Stations also transmit periodic "soundings" so others can build a table of which channels reach them.
Watch out The internet-monitoring choice describes internet-linked systems like Winlink gateways or DMR networks, not ALE, which is designed to work entirely over HF radio with no outside infrastructure.
ALE = Automatic Link Establishment: scan the channel list, wake up when you hear your own call sign.
HamSandwich explanation, first draft. The question and answers are the NCVEC text.
E2E1313 of 13

Which of these digital modes has the highest data throughput under clear communication conditions?

Why PACTOR IV is an adaptive ARQ mode that steps up to high-order modulation with data compression, reaching several thousand bits per second on a clear channel, far more than any of the other modes listed. The PACTOR family was designed specifically for message and file transfer, so each generation (I through IV) raised the top speed. The other choices are keyboard-to-keyboard or weak-signal modes whose speeds are fixed and very low by comparison.
Watch out FT8 tempts people because it is modern and popular, but it is a weak-signal mode that sends only about 75 bits in a 15-second transmission, making it one of the slowest modes in use; 45 baud RTTY and MFSK16 are both roughly 60 words per minute.
PACTOR I to IV: the number is the speed rank. IV is the throughput champ; FT8 trades speed for sensitivity.
HamSandwich explanation, first draft. The question and answers are the NCVEC text.
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