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 <CR> or <LF>.

• No stop bits: synchronization achieved with no overhead!

RTTY and FSK441

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 *

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: ….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

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

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 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!

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 1-7144 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 1755.0 Hz:: A 1485.8 Hz $ 1475.0 Hz:: . 9 1399.7 Hz:: 0 1302.8 HzSync 1270.5 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.

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: 1110100001110011000021-40: 1001000101011101011141-60: 1001001011100111000061-80: 0011101110100111101081-100: 10010100000010101010101-120: 11111010110100000110121-135: 111011011010110

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”

“7373737373737373737373”

• And finally:

“RRRRRRRRRRRRRRRRRRRRRR”

• Averages of even, odd, and last four characters given after each reception.

Line averages

JT44 and CW comparison

S/N S/NType of signal (50Hz BW) (2500Hz BW)*Minimum intelligible CW +6.0dB -11.0dBJT44 random message -6.1dB -23.1dBJT44 message after 4 min -9.1dB -26.1dBJT44 “RORORORORO” -11.3dB -28.3dBJT44 “RRRRRRRRRR” -12.8dB -29.8dBJT44 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 (e-mail, 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: http://www.thinkman.com/dimension4/

• 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: http://pulsar.princeton.edu/~joe/K1JT/

• 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!