WSJT: A software package for VHF DXers

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

FSK441: Meteor scatter anytime and anywhere!

Meteor-scatter basics

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)

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

“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.

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

“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

Underdense “ping”

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

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

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

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.

Spectral display: FSK441 “ping”

Spectral display in WSJT

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.

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.

WSJT in FSK441 mode

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 or. No stop bits: synchronization achieved with no overhead!

RTTY and FSK441 RTTY (5-bit) A B C Z FSK441 (3-bit) A 101 B 102 C 103 Z *

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.

FSK411 synchronization A burst of signal contains the following: … ….. WSJT finds the “space” character: … ….. WSJT can now find the message: … … K 1 J T K 0 S M

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!)

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!

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”).

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)

FSK441 reporting system 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

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

….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.

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!

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.

WSJT Station

What can I expect to work? On 144MHz, the average “brick and yagi” station should be able to work a similar station in the mi 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!

144 MHz QSO’s from EN10rt

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

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

The road to DN90wp

K0SM/P DN90wp

CY9DH—FN97we July MHz FSK441 (37 QSOs)

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.

JT44: A really weak signal mode

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.

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

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)

JT44 Tones Z Hz : A Hz $ Hz : Hz : Hz Sync 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.

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.

Why have a sync tone? Tones spaced at 10.3-Hz intervals. Most VHF radios are not that accurate—the digital readout is lying to you! Most radios drift a little over long periods of time. Sync tone provides a frequency reference for the data.

How WSJT decodes JT44: Finding the frequency WSJT does a frequency-analysis the whole 30-sec. Because the sync tone is sent over half of the time, it should outweigh any other frequencies (characters). This gives WSJT a frequency reference to find the data. The frequency discrepancy is displayed in the “DF” column on the screen.

Spectral analysis of a strong (audible) JT44 signal

The pseudo-random pattern of the sync tone 1-20: : : : : : :

How WSJT decodes JT44: Timing WSJT looks for the “best match” to this known pattern. Quality of sync from 0-9 is displayed in the “sync” column. The time discrepancy is displayed in the DT column on the screen Clocks must be synchronized within ~1 sec of each other.*

Decoded JT44 signal

JT44 Message Averaging Single letters will appear 6.8dB below the sync tone because less time is spent sending these frequencies. (Sync tone sent 69/135 of the time, individual character sent 3/135 of the time) Every doubling of the number of receive periods adds 1.5dB of in S/N. Four periods get you 3dB improvement, 16 periods get you 6dB, etc. This assumes JT44 can synchronize each time (i.e., signal is stronger than ~-29dB).

Message “folding” Some messages have symmetrical content: 22 characters is often enough room to send two pairs of callsigns: “K1XXX W2ZZZK1XXX W2ZZZ” Message can be “broken in half” and averaged to achieve a better copy: K1XXX W2ZZZ

Line averages Some messages are even more redundant: “RORORORORORORORORORORO” “ ” And finally: “RRRRRRRRRRRRRRRRRRRRRR” Averages of even, odd, and last four characters given after each reception.

Line averages

JT44 and CW comparison S/N S/N Type of signal (50Hz BW) (2500Hz BW)* Minimum intelligible CW +6.0dB -11.0dB JT44 random message -6.1dB -23.1dB JT44 message after 4 min -9.1dB -26.1dB JT44 “RORORORORO” -11.3dB -28.3dB JT44 “RRRRRRRRRR” -12.8dB -29.8dB JT44 limit of synchronization -12.9dB -29.9dB *WSJT reports S/N in a 2500Hz bandwidth (dB column)

A demonstration… Copy this CW signal: Here’s a JT44 signal at an even lower S/N:

CW JT44

JT44 signal decoded in WSJT

JT44 operating procedures 30-second sequencing Same as MS for terrestrial operation EME operation almost always by schedules Some “big guns” call CQ, but will often announce beforehand ( , web, packet).

JT44 operating procedures Terrestrial operation is similar to FSK441, though grid squares are usually sent instead of a report. Westernmost goes first (Region 2) EME operation usually uses the “TMOR” system—same as CW. Always check with your sked partner!

Operator responsibilities Lock onto the other station’s signal and adjust for frequency drift Identify and reject “bad syncs” so they are not counted in the average message Adjust controls for QRN and birdies

JT44—terrestrial operation JT44 works well on troposcatter paths that are too short for MS enhancement. Several operators have used it on 6m for borderline TE, and marginal Es openings. Microwave non-line-of-sight paths

Other terrestrial applications Perhaps useful on extremely long IOS paths between big stations. Could be a good way of overcoming atmospheric absorption above 10GHz.

JT44: EME applications JT44’s ability to recover extremely weak signals makes it ideal for EME Most activity by arranged schedule. 144MHz is the most popular band. Also operation on 50 MHz, 432MHz, and 1296 MHz so far….

What do I need to make EME QSOs? A pair of single-yagi stations should be able to work each other, with QRO power. “Brick and yagi” stations can work larger stations at moonrise/moonset. Single-yagi and a few hundred watts on 6m to work big guns (W7GJ, ON4ANT) W5UN has been copied with a “Ringo- Ranger” vertical on 2m!

EME possibilities EME is possible with medium-power, solid- state amplifiers (bricks) Portable EME operation can be a reality. DXpedtions can afford to bring gear

CY9DH—FN97we JT44 Worked JT44 on 50MHz “marginal Es” VE1ALQ and VE9AA (FN65) 2m JT44 troposcatter W7GJ on 144Mhz and 50MHz EME Partial with W7MEM 144MHz EME EME limited by terrain—no elevation control, hill to east.

Clock synchronization Dimesion 4 Clock utility: Keeps computer clock synchronized with WWV by internet You can also use GPS synchronization. Setting by hand is difficult.

Where to get WSJT: WSJT homepage: 5.6Mb download Self-extracting.EXE file— “click-click!” You get a color, 38-page manual in.PDF format, complete with pictures and index of buttons and other controls!