WSJT: A software package for VHF DXers

1. WSJT:A software package for VHF DXers

2. WSJT: What is it? • WSJT = Weak Signal by K1JT • Developed by Joe Taylor, K1JT • Supports two digital modes: FSK441 for meteor-scatter JT44 for extremely weak signals • Uses computer soundcard • Requires no fancy equipment

3. FSK441: Meteor scatter anytime and anywhere!

4. Meteor-scatter basics

5. Science fiction? • Pieces of space dust enter the earth’s atmosphere at relatively high speeds • Mostly “dustballs” –light, porous particles composed of light metals. • About the size of dust-specks to grains of sand. • Friction rips electrons away from their parent atoms ( = ionization)

6. Time is of the essence! • Very short communication windows • SSB and fast CW (>30 WPM) are the traditional mediums • (Good) operators employ special operating practices to be most efficient • SSB/CW QSO’s on 144 MHz or higher only possible during major showers

7. “Underdense” vs. “Overdense” • Overdense bursts are caused by bigger and faster meteors. They ionize a thick column of air that cannot neutralize quickly. • Bursts can last many seconds, often long enough for a complete QSO. • Useful for SSB and CW • Associated with major showers, and very uncommon at other times.

9. Typical overdense burst (70WPM CW) Here’s a weird one…..

10. “Underdense” vs. “Overdense” • Underdense trails are caused by smaller and slower meteors. These meteors create just enough ionization to scatter a radio wave. • These meteors case very short bursts of signal, usually < ½ second at the longest. • Not very useful for conventional SSB or CW—often referred to as “pings” • Very common, even outside showers

12. Underdense “ping”

13. Using underdense trails—HSCW • Send short messages in a loop • Operators use several short bursts of signal to piece together a QSO over time, rather than “all-at-once.” • Tape recorders slow down the 100 WPM or faster CW. (Computer software has increased speed to ~2000 WPM.) • Popular in Europe since the 1960’s

14. Problems with HSCW • Lots of energy wasted in keying sidebands. • S/N gets worse as speed increases. • Key-clicks can be a problem for other users, especially if transmitter is overdriven. • Requires a full-duplex soundcard, or two computers

16. A digital solution: FSK441 • Like HSCW, one uses a high-speed loop to complete a QSO over several short bursts of signal • 100% duty cycle, so no extra energy wasted by OOK. • More user-friendly interface--like RTTY or PSK31 modes. • Much better S/N than HSCW at same speed

17. FSK441: What’s in a name? • “FSK…” –it uses frequency shift keying. You can think of it as fancy RTTY, however, FSK441 switches among four tones rather than alternating between two. • Tones: 882Hz, 1323Hz, 1764Hz, 2205Hz. • “…441” –Each character takes about 2.3ms to send. Each character is composed of three tones. That’s 441 baud.

18. Spectral display: FSK441 “ping”

19. Spectral display in WSJT

20. How it works…. • Operators take turns transmitting in 30-sec intervals. • This ensures that only one station is sending and only one station is listening at a given moment. • After each receive period, the program decodes any signals that it detected and displays the text on the screen.

21. How it works…. • The program calculates the average amplitude for the recorded audio. • The program looks for “spikes” in the amplitude—these could be meteor pings above the noise floor…could be QRN! • If the detected spike satisfies certain other parameters, the program will decode it as text and display it on the screen.

22. WSJT in FSK441 mode

23. The FSK441 code • Code only supports characters we are interested in sending: callsigns, signal reports, and very short messages. • Uses the PUA43 alphabet: A-Z, 0-9, space, period, comma, ?, /, #, and $. No formatting characters, such as <CR> or <LF>. • No stop bits: synchronization achieved with no overhead!

24. RTTY (5-bit) A 00011 B 11001 C 01110 Z 10001 6 10101 <SP> 00100 FSK441 (3-bit) A 101 B 102 C 103 Z 231 6 012 <SP> 033 * RTTY and FSK441

25. FSK411 synchronization • Space is encoded as “033”. • No character starts with a “3”. • All messages contain at least one space. If the user does not enter one, the program will add one to the end of the message. • When WSJT finds a signal, it “looks” for the sequence “033”. This is the point of synchronization.

26. FSK411 synchronization • A burst of signal contains the following: ….123001122210033123223203131….. • WSJT finds the “space” character: ….123001122210033123223203131….. • WSJT can now find the message: ….123 001 122 210 033 123 223 203 131… K 1 J T K 0 S M

27. Single-tone messages • Each character in the FSK441 code contains at least two different frequencies—no “000” “111” “222” or “333”. • These characters are reserved for “shorthand” messages: “R26” “R27” “RRR” “73”. • If one sends one of these messages in a loop, the result is a pure single-frequency carrier. (Hence the name!)

28. Single-tone messages • These messages are shorthand for the most common messages in an FSK441 sked. • WSJT can use a separate algorithm to look for single-tone messages, which means better S/N than with the multi-tone encoding. • It can occasionally result in false signals. • You have to use your ham skills: Listen!

29. FSK441 operating procedures • Very similar to SSB meteor-scatter operation • Operators send information based upon what they have copied from the other station. • QSO is complete when both stations have received complete callsigns, a piece of information (usually report), and a confirmation that it was received (“roger”).

30. FSK441 operating procedures • 30-second sequences are standard. • Western-most station transmits first. This is in the Western hemisphere. • DXpeditions usually run all schedules and CQ’s on the same frequency and period, regardless of direction. • “Regular” CQ’s can be either first or second period. This eases QRM (contests/showers)

31. First number (1-5) “Length” 1: no info (not sent) 2: up to 5 seconds 3: 5 to 15 seconds 4: 15 to 60 seconds (!) 5: more than 60 s (!!!) Second number (6-9) “Strength” 6: up to S3 7: up to S5 8: up to S7 9: S7 or stronger FSK441 reporting system

32. If you have copied…. Nothing…………….. Partial callsigns…….. Both callsigns………. Both calls and report... “R” + report………… “RRR”………………. then send…. Callsigns only Callsigns only Calls + report (or grid) “R” + report “RRR” QSO is complete, send “73” or (or QRZ, CQ) Making a QSO

33. ….other meaningful messages… Sometimes you need specific information: • MMM………. “I need my callsign” • YYY………… “I need your callsign” • SSS………….. “I need your report” • UUU………... “Your keying is unreadable” These messages could be very useful when pings are very short—222 and 432 MHz.

34. What equipment do I need? • Most popular bands are 144 and 50MHz. There is growing activity on 222MHz, and a few 432 MHz QSO’s have been made. • More is better, but “brick and yagi” are sufficient on 144 and 222 any time of year. • Brick and yagi has worked on 432, but more operation is needed to draw conclusions. • Preamp—you don’t know what you’re missing!

35. What equipment do I need? • A computer and a soundcard-- 60Mhz Pentium with 24Mb of RAM will work, but you’ll be happier with more! • The (free!) software • A way to interface the soundcard with the radio. You can use a commercial “PSK31” interface (Rigblaster, MFJ, etc) or make your own.

36. WSJT Station

37. What can I expect to work? • On 144MHz, the average “brick and yagi” station should be able to work a similar station in the 600-1000mi range fairly consistently, any time of year. • Geometric limit of ~1400mi (based on the height at which meteors ionize sufficiently) • Limits, schlimits! Records are meant to be broken!

38. 144 MHz QSO’s from EN10rt

39. When should I operate? • The daily “random” meteor rate peaks around sunrise local time, but QSO’s are possible anytime of day or night—it just might take longer to complete it. • Minor showers can “enhance” the background meteor rate (June-December) • Before and after major shower peaks

40. How about portable operation? • No need to haul large antennas and big amplifiers to the top of a mountain for success. • One doesn’t need to plan DXpedtion around major showers

41. The road to DN90wp

42. K0SM/P DN90wp

43. CY9DH—FN97we July 1-7144 MHz FSK441 (37 QSOs)

44. FSK441 in contests • Rovers can stray to distant grids and still make contacts—that means new grids and more multipliers. • “Big guns” should be able to work anyone within 1200mi on 144Mhz. • Fills the “dead time” in the small hours of the morning with valuable mulipliers.

45. JT44: A really weak signal mode

46. JT44 • Uses long term signal averaging to recover a signal that is below the noise floor. • Humans have “short ears” limited by their sensory memory—they can only analyze a signal in a small timeframe. • Computers can analyze a signal in relatively large timeframes.

47. Time for a demonstration! “Long Ears” and “Short Ears”

48. The JT44 code • Inspired by the PUA43 mode • Uses 44 tones, one for each character in the PUA43 alphabet (same as FSK441), plus a synchronization tone. Each character is assigned a unique frequency. • Slow transmission speed: 5.38 baud. • Highly redundant (FEC)

49. Z 1755.0 Hz : : A 1485.8 Hz $ 1475.0 Hz : : . 9 1399.7 Hz : : 0 1302.8 Hz Sync1270.5 Hz Bandwidth of 485Hz Tones spaced at 10.8Hz Sync tone 32.3Hz below data. Allows for frequency error and EME Doppler shift with and 2.7 KHz passband. JT44 Tones

50. The JT44 code • Transmission lasts about 25 s, with a gap at the beginning and end to allow for timing error and EME delay. (Like FSK441, operators use alternating 30-second periods) • 135 intervals (bits) • 69 are devoted to sending the sync tone • Other 66 intervals are used to send the 22-char message three times.