WEBVTT NOTE Digital Modes 1 00:00:00.000 --> 00:00:02.262 The oldest digital mode. 2 00:00:02.262 --> 00:00:05.840 Question. What is CW? 3 00:00:06.740 --> 00:00:11.580 Answer. Another name for a Morse code transmission. 4 00:00:12.180 --> 00:00:18.849 Morse is a digital mode, a carrier switched on and off in a coded pattern. 5 00:00:18.849 --> 00:00:34.349 It predates everything else here by a century, occupies about 150 Hz, and remains one of the most effective ways to get a message through a poor path with simple equipment. 6 00:00:34.349 --> 00:00:51.020 No US amateur licence has required Morse proficiency since 2007. It is worth learning anyway, for the same reason it survives: it works when nothing else does. Weak-signal digital: FT8. 7 00:00:51.020 --> 00:00:54.907 Question. What is FT8? 8 00:00:55.807 --> 00:01:01.807 Answer. A digital mode capable of low signal-to-noise operation. 9 00:01:02.407 --> 00:01:14.540 FT8 sends a fixed, tiny message, call signs, grid square, signal report, in a precisely timed 15-second slot, occupying about 50 Hz. 10 00:01:14.540 --> 00:01:31.084 Its decoder works well below the noise floor, roughly 20 dB under what a human ear can pull out of static. The consequence is that contacts happen on paths that carry nothing else. 11 00:01:31.084 --> 00:01:44.687 The trade is that the message is fixed-format: you exchange call signs and a report, and that is the entire conversation. Keyboard-to-keyboard: PSK. 12 00:01:44.687 --> 00:01:50.567 Question. What does the abbreviation "PSK" mean? 13 00:01:51.467 --> 00:01:54.947 Answer. Phase Shift Keying. 14 00:01:55.547 --> 00:02:02.189 The carrier's phase is shifted to encode data, rather than its amplitude or frequency. 15 00:02:02.189 --> 00:02:18.561 PSK31, the popular variant, occupies about 31 Hz, roughly the bandwidth of a typed conversation at human speed, and it is a real keyboard-to-keyboard chat mode rather than a fixed exchange. Packet radio and APRS. 16 00:02:18.561 --> 00:02:34.856 Packet radio breaks data into addressed packets. The pool asks what is included in a packet transmission and answers "all these choices are correct", a check sum, the sending station's call sign, and an address. 17 00:02:34.856 --> 00:02:49.375 That combination is what makes packet a network rather than a link: packets can be routed and errors detected. APRS, the Automatic Packet Reporting System, is packet put to a specific use. 18 00:02:49.375 --> 00:03:07.975 Question. What kind of data can be transmitted by APRS? A. GPS position data. B. Text messages. C. Weather data. D. All these choices are correct. 19 00:03:08.875 --> 00:03:12.395 Answer. All these choices are correct. 20 00:03:12.995 --> 00:03:18.915 Question. Which of the following is an application of APRS? 21 00:03:19.815 --> 00:03:29.215 Answer. Providing real-time tactical digital communications in conjunction with a map showing the locations of stations. 22 00:03:29.815 --> 00:03:41.796 That is exactly what it does in public-service work: every station's position on a shared map, updating live, with short messages alongside. 23 00:03:41.796 --> 00:03:55.575 For anyone who has flown a drone under Part 107, the mental model is familiar, situational awareness as a shared map rather than a radio net. Digital voice: DMR. 24 00:03:55.575 --> 00:04:00.655 Question. Which of the following describes DMR? 25 00:04:01.555 --> 00:04:11.047 Answer. A technique for time-multiplexing two digital voice signals on a single 12.5 kHz repeater channel. 26 00:04:11.647 --> 00:04:24.838 The key word is time-multiplexing. DMR splits a channel into two alternating time slots, so one repeater channel carries two independent conversations. 27 00:04:24.838 --> 00:04:37.767 That is why DMR repeaters seem to do more with the same spectrum, and why talkgroups and time slots both appear in DMR programming. Mesh networking. 28 00:04:37.767 --> 00:04:44.567 Question. Which of the following best describes an amateur radio mesh network? 29 00:04:45.467 --> 00:04:54.271 Answer. An amateur-radio data network using commercial Wi-Fi equipment with modified firmware. 30 00:04:54.871 --> 00:05:10.989 Consumer Wi-Fi hardware operates in bands that overlap amateur allocations, and with amateur firmware it can run at amateur power levels and with directional antennas, under an amateur licence. 31 00:05:10.989 --> 00:05:21.511 The result is a self-organising IP network, video, file transfer, chat, over paths no consumer Wi-Fi would manage. Television. 32 00:05:21.511 --> 00:05:26.631 Question. What is meant by the term "NTSC?" 33 00:05:27.531 --> 00:05:33.011 Answer. An analog fast-scan color TV signal. 34 00:05:33.611 --> 00:05:48.866 The legacy US broadcast television standard, about 6 MHz wide, still used by amateurs on the higher bands where there is room for it. ARQ: getting it right. 35 00:05:48.866 --> 00:05:54.706 Question. What is the role of ARQ in a transmission system? 36 00:05:55.606 --> 00:06:05.206 Answer. An error correction method in which the receiving station detects errors and sends a request for retransmission. 37 00:06:05.806 --> 00:06:18.314 Automatic Repeat reQuest. Rather than adding enough redundancy to correct every possible error in advance, ARQ detects that something is wrong and asks again. 38 00:06:18.314 --> 00:06:27.260 It is the right choice when the link is two-way and the data must be exact, a file, a form, an emergency message. 39 00:06:27.260 --> 00:06:39.056 It is the wrong choice when there is no return path or when latency matters, which is why broadcast-style modes use forward error correction instead. 40 00:06:39.056 --> 00:06:51.406 Winlink, the amateur email system, is built on ARQ protocols for exactly this reason: an email that arrives with a corrupted address is worse than no email. 41 00:06:51.406 --> 00:07:10.428 The mode-to-purpose map. Need, A contact on a nearly dead path; Mode, FT8. Need, A typed conversation; Mode, PSK31. Need, Position reporting and tactical mapping; Mode, APRS. 42 00:07:10.428 --> 00:07:30.216 Need, Exact text or files, error-free; Mode, Winlink over ARQ. Need, Two voice conversations on one channel; Mode, DMR. Need, Broadband data over a link; Mode, mesh. Check yourself. 43 00:07:30.216 --> 00:07:51.315 Which mode would you reach for to make a contact on a path where you can hear nothing at all? What does DMR time-multiplexing buy? Why does Winlink use ARQ rather than forward error correction? 44 00:07:57.315 --> 00:08:15.715 FT8, capable of low signal-to-noise operation, roughly 20 dB below what the ear can decode. Two independent voice conversations on one 12.5 kHz repeater channel, via alternating time slots. 45 00:08:15.715 --> 00:08:31.875 The message must be exact, and there is a return path to ask again with. ARQ retransmits on detected error rather than padding every message with correction overhead.