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E2D

OPERATING PROCEDURES

Operating methods: digital modes and procedures for VHF and UHF; APRS; EME procedures; meteor scatter procedures

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E2D011 of 11

Which of the following digital modes is designed for meteor scatter communications?

Why Meteor scatter bounces signals off the ionized trails left by meteors, which last only fractions of a second, so the mode must pack a whole message into a very short burst and repeat it rapidly. MSK144, part of the WSJT-X suite, does exactly that: it sends messages in 72 ms frames repeated continuously within 15-second sequences, so any brief ping can carry a complete decodable transmission. The "144" in the name is a reminder that it is used mainly on 6 meters and 2 meters where meteor scatter works best.
Watch out WSPR is the other WSJT-family mode in the list, but it is a very slow, very weak-signal beacon mode for probing propagation paths, the opposite of a fast burst mode. Hellschreiber is an old facsimile-style text mode, and APRS is a packet-based position and data reporting system.
MSK144: Meteor Scatter Kilobits in 144 ms-ish bursts, used on 144 MHz. WSPR whispers slowly, meteors need speed.
HamSandwich explanation, first draft. The question and answers are the NCVEC text.
E2D022 of 11

What information replaces signal-to-noise ratio when using the FT8 or FT4 modes in a VHF contest?

Why Standard FT8/FT4 QSOs send a signal report expressed as signal-to-noise ratio in dB (for example -15). In VHF/UHF contests the required exchange is the four-character Maidenhead grid locator, so WSJT-X's contest mode substitutes the grid square in the message slot where the SNR normally goes. This works because FT8 messages are only 77 bits, so one fixed field carries whichever piece of information the contest needs.
Watch out An RST report is a human-judged readability/strength/tone value used on CW and SSB; FT8 decodes are machine-measured, so RST is never sent. Serial numbers appear in FT4/FT8 RTTY Roundup contest mode, not VHF contests.
VHF contests score on grids, so FT8 sends the grid where the dB report would go.
HamSandwich explanation, first draft. The question and answers are the NCVEC text.
E2D033 of 11

Which of the following digital modes is designed for EME communications?

Why Q65 is part of the WSJT-X suite and uses 65-tone frequency-shift keying with long transmit sequences (15 to 300 seconds) and strong forward error correction, which suits the very weak, Doppler-spread, fading signals returned from the Moon. Its submodes let you trade sequence length against speed, so EME operators on VHF, UHF and microwave can decode signals well below the noise floor. It descends from the older JT65 mode that made digital EME popular.
Watch out MSK144 is the tempting one, but its very short 72 ms transmissions are built for meteor scatter pings, not the long path delay and fading of moonbounce; WSPR is a low power propagation beacon mode and PACTOR III is an HF ARQ data mode.
Q65 = Quiet moon (EME); MSK144 = Meteor Streaks; WSPR = whisper beacons.
HamSandwich explanation, first draft. The question and answers are the NCVEC text.
E2D044 of 11

What technology is used for real-time tracking of balloons carrying amateur radio transmitters?

Why APRS, the Automatic Packet Reporting System, was designed exactly for this: a GPS receiver feeds position, altitude and telemetry into a packet TNC, which beacons short AX.25 bursts (1200 baud on 144.390 MHz in the US). Digipeaters and internet gateways relay those beacons so anyone can watch the balloon's track on a map in near real time. The same system tracks vehicles, weather stations and public service events.
Watch out FT8 is a weak-signal mode for very short exchanges (call signs, grid square, signal report) and carries no live telemetry, while PACTOR III is an HF ARQ mode used for message and email forwarding, not position beacons.
APRS = Automatic Packet Reporting System. Position beacons on 144.390 MHz: balloons, cars, weather stations.
HamSandwich explanation, first draft. The question and answers are the NCVEC text.
E2D055 of 11

What is the characteristic of the JT65 mode?

Why JT65 is one of the WSJT family of weak-signal modes Joe Taylor developed for EME and other marginal paths. It sends a very slow 65-tone MFSK signal (about 2.7 symbols per second) in fixed one-minute transmissions with heavy Reed-Solomon forward error correction and rigid, compressed message formats. That combination lets the software pull a callsign, grid and report out of a signal roughly 25 dB below the noise in a 2500 Hz bandwidth, far weaker than the ear can hear.
Watch out The tempting picks read the 65 as a bandwidth or baud figure, but it is the number of tones; JT65 occupies only about 178 Hz and its symbol rate is under 3 baud.
The 65 in JT65 counts tones, not hertz or baud. What it buys you is decoding way down in the noise.
HamSandwich explanation, first draft. The question and answers are the NCVEC text.
E2D066 of 11

Which of the following is a method for establishing EME contacts?

Why Earth-Moon-Earth signals are extremely weak, so operators use strict timed sequences: one station transmits during a defined period (commonly one minute or 30 seconds keyed to UTC), then listens while the other transmits. Everyone's clock is synchronized to UTC, which is also what digital EME modes like JT65 and Q65 require in order to decode. That discipline lets weak-signal software integrate an entire transmission period and dig signals out of the noise well below what the ear can hear.
Watch out There are no beacons bouncing off the moon to monitor; EME path timing is predicted from moon rise/set, declination and path loss software, not from lunar beacons. Store-and-forward describes packet or satellite mailbox operation, not EME.
EME = take turns by the clock. Sync to UTC, transmit on your period, listen on theirs.
HamSandwich explanation, first draft. The question and answers are the NCVEC text.
E2D077 of 11

What digital protocol is used by APRS?

Why APRS rides on the AX.25 packet radio link layer, the same protocol used for conventional packet. APRS sends position and telemetry data in unconnected (UI, unnumbered information) AX.25 frames, so any station in range can hear the beacon without establishing a connection. On 2 meters this is typically 1200 baud AFSK on 144.390 MHz in the US.
Watch out PACTOR and AMTOR are HF ARQ modes built for point-to-point message handling, not one-to-many beaconing, and QAM is a modulation scheme rather than a protocol.
APRS = AX.25 broadcast beacons. Both start with A and the packet lineage is the link.
HamSandwich explanation, first draft. The question and answers are the NCVEC text.
E2D088 of 11

What type of packet frame is used to transmit APRS beacon data?

Why APRS runs on AX.25 but in connectionless mode: beacons are broadcast to everyone with no session set up and no acknowledgment expected. The frame type that carries data without a connection or sequence number is the Unnumbered Information (UI) frame, which is why APRS packets are often called "UI frames" and are addressed to a generic destination like APRS or BEACON.
Watch out Connect and Acknowledgement frames belong to normal connected-mode AX.25, where two stations establish a link and confirm each numbered packet; APRS deliberately skips that overhead so any station in range can copy the beacon.
APRS = Unconnected broadcast = UI frame. No connection, no ack, no sequence numbers.
HamSandwich explanation, first draft. The question and answers are the NCVEC text.
E2D099 of 11

What type of modulation is used by JT65?

Why JT65 is a multi-frequency-shift-keying mode: each symbol is one of 65 audio tones (a sync tone plus 64 data tones) keyed one at a time into an SSB transmitter, so the RF output is a series of shifted single tones. Because the tone shifting is done at audio and fed through SSB, it is described as multitone AFSK. The constant-envelope, narrow, slow (about 0.37 second per symbol) signal is what lets JT65 decode EME and other signals well below the noise floor.
Watch out PSK is the usual trap because of PSK31 and because both are weak-signal keyboard modes, but PSK varies the carrier phase while JT65 varies frequency; RTTY is only two-tone FSK with Baudot code, and QAM mixes amplitude and phase and is used in commercial high-rate data links, not in weak-signal amateur work.
JT65: the 65 is the tone count. 65 tones means many tones, so multitone AFSK, not phase shifting.
HamSandwich explanation, first draft. The question and answers are the NCVEC text.
E2D1010 of 11

What does the packet path WIDE3-1 designate?

Why In APRS the WIDEn-N path is a two-number counter: the first digit (n) is the total number of digipeater hops originally requested, and the second digit (N) is how many hops are still left. Each digipeater that repeats the packet decrements the second number, and when it reaches zero the packet is no longer repeated. So WIDE3-1 started life as WIDE3-3, has already been digipeated twice, and has one hop remaining.
Watch out The choices about subcarriers, simultaneous stations on frequency, or internet gateways describe nothing in the WIDEn-N scheme; digipeater counting has nothing to do with how many stations may transmit or how many IGates hear the packet.
WIDEn-N: first number = hops asked for, second number = hops left. WIDE3-1 means 2 already used.
HamSandwich explanation, first draft. The question and answers are the NCVEC text.
E2D1111 of 11

How do APRS stations relay data?

Why APRS is an AX.25 packet network, usually on 1200 baud AFSK at 144.390 MHz in the US. Coverage is extended by digipeaters, stations that receive a packet and immediately retransmit it on the same frequency, with the path set by aliases such as WIDE1-1 and WIDE2-1 that limit how many hops a packet takes. This unconnected (UI frame) broadcast approach lets one beacon reach many listeners and Internet gateways without any point to point link setup.
Watch out The choice about ACK/NAK relay describes connected-mode packet, where each frame is acknowledged; APRS deliberately uses unconnected beacons with no acknowledgment. C4FM and DMR are digital voice modes on their own repeater systems and do not carry standard APRS packets.
APRS = packet, and packet repeaters are digipeaters. Think WIDE1-1, WIDE2-1 hops on 144.390.
HamSandwich explanation, first draft. The question and answers are the NCVEC text.
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