Digital JT and FT modes: where to begin and how to use them. Alexander O. Korotkevich W5KAO and RV3DFL. w5kao@yahoo.com 9th of March, 2018 Alexander O. Korotkevich (W5KAO) Digital JT and FT modes... Caravan Club 1 / 17
Introduction Why digital? Why one need digital modes? Digital communication gives robust signal detection (if possible): Signal represented as 1 s (signal present) and 0 s (signal absent) First digital mode: Morse code ( dit =10, dah =1110) Modern computers allow for sophisticated signal processing Now even the cheapest computer can do this crazy fast You don t need to update your hardware for new modes, everything is software You have an access to ALL modes through FREE software Sophisticated Error Correction Codes can be used (later). Alexander O. Korotkevich (W5KAO) Digital JT and FT modes... Caravan Club 2 / 17
Introduction What hardware you need? Things necessary for beginning. Practically everything is already in your shack: Standard SSB-capable transceiver (most modes use USB) Any relatively modern personal computer (Linux, Windows, MAC) Audio interface (can be just wires (NOT RECOMMENDED!)) PTT switch interface (Preferably) CAT interface (Preferably) It is a good idea to electrically decouple TRX and computer. Alexander O. Korotkevich (W5KAO) Digital JT and FT modes... Caravan Club 3 / 17
Introduction Simple interface Simple interface for Audio and PTT. Alexander O. Korotkevich (W5KAO) Digital JT and FT modes... Caravan Club 4 / 17
Introduction Software A lot of FREE (as in Freedom!) software. Free and open source software is available for all modes: FLDIGI (RTTY, PSK31, etc.) SSTV - just google "best sstv software" (e.g. MSSTV) WSJT-X (JT65, JT9, FT8, WSPR, MSK144 etc.) Most of these software is available as a source code as well There is an active community, it will continue to be developed no matter what It is a good feeling to know that your favorite software will not be abandoned or sold to a big corporation Alexander O. Korotkevich (W5KAO) Digital JT and FT modes... Caravan Club 5 / 17
A little bit of history Joseph Hooton Taylor Jr. (K1JT) Was born March 29, 1941 in Philadelphia. Taylor s Ph.D. thesis work at Harvard was on lunar occultation measurements. About the time he completed his Ph.D., Jocelyn Bell (who is also a Quaker) discovered the first radio pulsars with a telescope near Cambridge, England. Alexander O. Korotkevich (W5KAO) Digital JT and FT modes... Caravan Club 6 / 17
A little bit of history In 1974, Hulse and Taylor discovered the first pulsar in a binary system, named PSR B1913+16 after its position in the sky, during a survey for pulsars at the Arecibo Observatory in Puerto Rico. The orbit of this binary system is slowly shrinking as it loses energy because of emission of gravitational radiation, causing its orbital period to speed up slightly. The rate of shrinkage can be precisely predicted from Einstein s General Theory of Relativity, and over a thirty-year period Taylor and his colleagues have made measurements that match this prediction to much better than one percent accuracy. This was the first confirmation of the existence of gravitational radiation. In 1993 both were awarded a Nobel Prize in Physics for this. Joe Taylor first obtained his amateur radio license as a teenager, which led him to the field of radio astronomy. Taylor is well known in the field of amateur radio weak signal communication and has been assigned the call sign K1JT by the FCC. He had previously held the callsigns K2ITP, WA1LXQ, W1HFV, and VK2BJX (the latter in Australia). Alexander O. Korotkevich (W5KAO) Digital JT and FT modes... Caravan Club 7 / 17
A little bit of history History of different JT-modes. Most of the popular JT modes were not designed to the way they used today: The very first mode JT65 -designed for EME. Current usage - HF weak signal around the globe communication The most popular now and the most recent FT8 - designed for sporadic-e on 60m Current usage - LF, MF, and HF DXing. Some of the modes never were very popular, although suited the goal WAY better than the popular ones (like JT9). What is good, current high interest in FT8 mode made WSJT-X very popular and it will make all these modes easily accessible to everybody. Alexander O. Korotkevich (W5KAO) Digital JT and FT modes... Caravan Club 8 / 17
A little bit of history What to read? Main sources of information about JT-modes: "Work the World With JT65 and JT9" by Steve Ford (WB8IMY). Articles by Joe Taylor, Steve Franke, and Bill Somerville "Working the World With WSJT-X: Parts 1 and 2" QST October and November 2017. Joe Taylor web-site: https://physics.princeton.edu/pulsar/k1jt/wsjtx.html (just google "WSJT-X download") Alexander O. Korotkevich (W5KAO) Digital JT and FT modes... Caravan Club 9 / 17
In practice Almost all JT-modes are very similar inside, on the level of information to be transmitted: Message is 72 bits (12 simbols 6 bits each). 72 bits normally are 1 two fields 28 bits each for callsigns 2 15 bits for grid locator/report/acknowlegment/73 One extra bit is used to flag messages which contain random text (up to 13 characters) FT8 adding three extra bits to define 14 additional message types Then message is encoded using Forward Error Correction Codes (different for different modes) Alexander O. Korotkevich (W5KAO) Digital JT and FT modes... Caravan Club 10 / 17
In practice How all these signals look like? Shapes of signals for different JT-modes: Alexander O. Korotkevich (W5KAO) Digital JT and FT modes... Caravan Club 10 / 17
In practice Different modes have different parameters. Bandwidth ranges from 177.6 Hz (JT65) to 5.9 Hz (WSPR). Practically all modes use 1 minute time sequence, but FT8 uses 15 seconds and WSPR uses 2 minutes. IMPORTANT: Your computer has to synchronize time with atomic clock! Alexander O. Korotkevich (W5KAO) Digital JT and FT modes... Caravan Club 11 / 17
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