By Joe Taylor, K1JTWSJT: New Software for
VHF Meteor-Scatter
Communication
Interplanetary dust particles are plunging into Earth’s atmosphere
continuously. With this revolutionary software you can communicate
over distances up to 1400 miles by bouncing signals off theionized trails of these tiny meteors.

In

February 2000 I started playing
with meteor scatter on the 2- and6-meter bands, using the relatively new computer-assisted high speed
CW technique (HSCW). I had done somemeteor and ionospheric scatter work in an
earlier hamming life, more than 40 years
ago.1 My long-dormant interest in Amateur Radio having been warmly rekindled,
I was anxious to see what advantages modern equipment and techniques might bringto this fascinating and always-available
communication mode for VHF DX.
I quickly learned that the high-speed
CW mode of carrying out meteor-scatter
QSOs can be very effective. The mode
was entertainingly described by Shelby
Ennis, W8WN, in a recent QST article.2
HSCW makes it possible to use the very
brief “pings” of signals reflected from theionized trails of meteors entering the
Earth’s atmosphere some 100 km above
the surface. On the 50 and 144 MHz
bands these pings can be received at almost any time from a moderately wellequipped station at a distance of 500 to1100 miles (800 to 1800 km). The pings
typically last no more than a few tenthsof a second at 144 MHz, so they are useless for voice communication or normalspeed CW. Indeed, single-sideband
operators who get on during the peaks ofmajor meteor showers call them “theabominable pings,” and in order to make
QSOs they wait patiently for the muchless frequent “blue whizzers” whose
stronger ionization can support two-meter1

Notes appear on page 41.

36

December 2001

SSB exchanges for a few seconds orlonger. Outside the major showers, blue
whizzers are so rare that they, too, areessentially useless for communication
unless you are extremely lucky or willing to run in unattended “beacon” mode.
As a result, SSB meteor-scatter contacts
are virtually nonexistent on 2 meters except near the peaks of major showers.
On the other hand, pings from meteor
trails with “underdense” ionization are
nearly always available in usable numbers. Even 100-W, single-Yagi stations at
suitable distances can usually hear several pings from each other in a 10 to 20
minute period. At typical HSCW speeds
around 8000 letters per minute, a pinglasting 0.1 second contains about 13 characters—just about enough for your call,the other station’s call, and perhaps a signal report. With coordinated timing, goodfrequency calibration, and some diligence,
operators who take the time to learn thetechnique can easily complete QSOs thisway. It’s a fascinating way to work abunch of new states, VUCC grid locators,or (if you live in Europe) DXCC entities.
It can also work wonders for fattening
your multiplier total in a VHF contest. You
do not need an EME-class station, and bestof all, you don’t need to wait for a meteor
shower or for one of those all-too-elusive
band openings that usually happen when
you had to be out of town.
Alas, all too few stations in North
America have cared to put the effort into
learning the HSCW technique for working meteor scatter. Our European friends
have put us to shame in this respect; many

hundreds of amateurs over there use thetechnique regularly. In our own hemisphere, HSCW meteor scatter has attracted
surprisingly few converts. A North American High Speed Meteor Scatter Contest has
been run for each of the past four years,
and I’ve had great fun taking part in the2000 and 2001 events. The total numberof participants, however, has been under
two dozen in any given year—and it seems
that these include nearly all of the North
American hams who have been active and
HSCW-capable in those years.
Having learned International Morse as
a youngster and never having lost my proficiency, I love CW as a mode of communication. But I also appreciate theprogress that modern digital methods
have brought to our hobby. Motivated inpart by a desire to make VHF meteorscatter communication accessible and attractive to a much larger number of fellow
hams, and in part by a simple desire toshow that it could be done, in April 2001
I set out to design a digital encoding
scheme and software package to enable
amateur QSOs using the brief pings fromunderdense meteor trails. The result has
led to a computer program called WSJT
(for “Weak Signal Communication, by
K1JT”) that implements a signal protocol called FSK441. The mode works sowell that it has been rapidly embraced by
the VHF fraternities in Europe and North
America, and is now making inroads inAfrica and the South Pacific, as well.
If your station is capable of weak signal SSB work on the 6 meter or 2 meterbands—say, if you have 100 W or more

Figure 1—Audio waveform corresponding to the letter C in an
FSK441 transmission. Each tone lasts for exactly 25 samples(filled circles) at the 11025 Hz sampling rate, or about 2.3 ms.
Each character requires three tone intervals. The code for theletter C is 103, which means that the transmitted tones are at
the frequencies 1323, 882 and 2205 Hz.

to a modest Yagi up at least 40 feet—thenwith the help of WSJT you should be able
to work similarly equipped stations in the
500-1100 mile range at nearly any timeof the day or year. (On the minimum endof the scale, WSJT QSOs have been madewith as little as 10 W, and I have worked
N4KZ rather easily at 610 miles when he
was using an 80-meter loop antenna on
6 meters.) With a higher antenna andmore power, QSOs out to 1300 or 1400
miles become possible. A few QSOs
have already been made with WSJT on
222 MHz, as well, and contacts on 432
MHz might be possible near the peak of
a major meteor shower.

What Do I Need?
Like a number of other digital andquasi-digital communication modes thathave recently become popular on theamateur bands, such as PSK31, MFSK16
and Hellschreiber, WSJT requires an SSB
transceiver, a computer running the Windows operating system, and a soundcard
interfaced to the radio’s “microphonein” and “speaker out” ports. A 75 MHz
Pentium-class computer is a minimum,and you will be happier with a faster
CPU, especially if you want to use otherprograms (such as a Web browser) whenrunning WSJT. Your computer shouldhave at least 24 MB of RAM, 40 MB offree disk space, and a monitor with 800
× 600 or higher resolution. Microsoft
Windows 95, 98, NT, 2000 and XP haveall been used successfully. You will, ofcourse, need a station capable of weaksignal work on one or more VHF bands.
The WSJT program is available fordownload free of charge at the Web sitepulsar.princeton.edu/~joe/K1JT and at

Figure 2—Computed spectrum of the FSK441 message“W8WN 27 K1JT 2727.” The frequencies of the four basic
tones are indicated by the tick marks above the spectrum.
Note that nearly all of the transmitted power falls in the range
660–2425 Hz.

the European mirror site www.vhfdx.de/
WSJT. Download the file WSJT100.ZIP
for Version 1.00, or a similar file namewith a higher version number, if one exists. Unzip the distribution file into a convenient directory such as C:\TEMP andthen run SETUP.EXE in that directory
to install WSJT to a permanent locationof your choice. The default installation
directory on most computers will be
C:\Program Files\WSJT.
You will need a simple computerto-radio interface like those required forsuch modes as PSK31, MFSK16, andHellschreiber. The DTR or RTS line of oneof the computer’s serial communication(COM) ports is used to key yourtransmitter’s push-to-talk (PTT) line. Connections are also required between thetransceiver audio output and computer
sound card input, and vice versa. Station
accessories that accomplish these things
are easy to build 3 and are available commercially from a number of sources advertising in QST. You will need a methodof synchronizing your computer clockwith UTC to an accuracy around one second or better. I heartily recommend a free
software utility 4 called Dimension 4,
which synchronizes your computer clockwith atomic time standards at national
timekeeping laboratories whenever you
are connected to the Internet.
Sometime during the beta-test phase ofdeveloping WSJT, when I was getting
swamped with requests for enhancements,
Andy Flowers, K0SM, took pity on me andvolunteered to help flesh out the online
instructions I had written. With that collaborative effort as a start, further work at
my end led to the presently available 13page User’s Guide and Reference Manual.

If you plan to give WSJT and VHF meteor
scatter a try, I urge you to download theUser’s Guide, print it out, and read it carefully. Although many have shown that it
is possible to install WSJT and learn to use
it by trial and error, the manual should
definitely be read by anyone serious about
getting the most from WSJT.

How Does It Work?
The encoding scheme used in WSJT
was designed to make the best use of signals just a few decibels above the receivernoise, exhibiting rapid fading and Doppler shifts up to 100 Hz, and typicallylasting from 20 to a few hundred milliseconds. The Doppler shifts and effective
path-length variations make any sort ofphase-shift keying (for example, a system analogous to PSK31) a poor candidate for this kind of signal. Large andrapid signal strength variations make onoff keying difficult to decode reliably. In
addition, such modulation is inefficientin spectral usage at high speeds, and isvery prone to errors caused by atmospheric noise. After considering many
possible encoding schemes and testing
several of them under real meteor-scatter conditions (thanks to the patient andtireless early morning efforts of Shelby,
W8WN, who has seldom refused my request for a schedule!) in early June I decided on a scheme that uses four-tone
frequency shift keying at a rate of 441
baud. The adopted scheme has been given
the technical name FSK441, althoughmost people seem to be calling it simply“the WSJT mode.”
In a normal FSK441 message, eachcharacter is encoded as three audio-frequency tones sent sequentially. Each tone
December 200137

can have one of four possible frequencies, so the maximum number of
encodable characters is 4 × 4 × 4 = 64.
For reasons described below, the four
sequences that have the same tone sent
three times in succession are reserved fora special purpose; in addition, the 15 remaining sequences that begin with thehighest frequency tone are not used. This
leaves 45 character codes available forgeneral use. For the sake of consistency,
and because I intended for WSJT also to
implement the weak signal mode called
PUA43, designed by Bob Larkin,
W7PUA, I chose to use the same
43-character “alphabet” that is incorporated in that mode. This character set includes 26 letters, 10 digits, the spacecharacter, and the six special characters:. , ? / # $. Two available character codes
remain undefined in FSK441.
Digital computers use binary arithmetic, and the basic unit of information
is given the contracted name “bit” for“binary digit.” When expressed in numerical terms, a bit can have the value 0
or 1. Since the FSK441 scheme uses fourbasic tones, base-four notation is the mostconvenient way of describing its code.
For want of a better term, I call the digitsof the base-four code “dits,” rather
than “bits.” Each character in the FSK441
alphabet is described by a sequence of
three dits, whose numerical values fall in
the range 0 to 3. The full coding schemeof FSK441 is presented using this notation in Table 1. Three-digit numbers represent the three-tone sequences corresponding to each character. Tones 0
through 3 correspond to the audio frequencies 882, 1323, 1764 and 2205 Hz.
Since the modulation rate is specified as
441 baud, or 441 dits per second, thecharacter transmission rate is 441/3 = 147
characters per second. At this speed aping lasting 0.1 seconds can convey avery respectable 15 characters of text.
The timing of FSK441 is such thateach dit of each character consists of exactly two full cycles of the audio tone at
882 Hz, three cycles at 1323 Hz, four at
1764 Hz, or five at 2205 Hz. WSJT runs
the computer sound card at a sampling
rate of 11025 Hz and therefore each dit,
1/441 of a second long, requires exactly
25 samples for its representation in thedigitized waveform. Each generated tone
blends into the next one in a phase- andamplitude-continuous manner. An example of the generated signal is presented
in Figure 1, which shows the audio waveform corresponding to the letter “C”(code 103; see Table 1). An FSK441
transmission contains no dead spaces between tones or between characters; thetypical short messages exchanged in meteor scatter QSOs are sent repeatedly and38

December 2001

Table 1
FSK441 Character Codes
Character Tones Character Tones
1
2
3
41
5
6
7
8
9
.
,
?
/
#
space
$
A
B
C
D
F
G

001
002
003
010
011
012
013
020
021
022
023
030
031
032
033
100
101
102
103
110
112
113

H
I
J
K
L
M
N
O
P
Q
R
S
T
U
V
W
X
Y
0
E
Z

120
121
122
123
130
131
132
133
200
201
202
203
210
211
212
213
220
221
223
230
231

continuously, usually for 30 seconds at atime. Different tones do not overlap intime, so there is little opportunity for evena poorly adjusted transmitter to produce
intermodulation products. For all of thesereasons, the audio signal used to generate FSK441 signals is spectrally clean
and largely confined to the range 6602425 Hz, thereby making very effective
use of the audio bandwidth of a modern
SSB transceiver. In a well-designed andwell-adjusted transmitter, the resulting
RF spectrum will be similarly clean, andit will remain so even if Class C power
amplifiers (or poorly designed solid state
amplifiers driven into their limiting regions) are used. An example audio frequency spectrum is shown in Figure 2,
computed for the message “W8WN 27
K1JT 2727.” The four individual tones
can be seen in the spectrum, as well as
the sidebands produced by their keying
pattern in this particular message. Tones
0 and 3 happen to be used more frequently than tones 1 and 2 in this message, so their spectral peaks areproportionally higher in the average spectrum.
WSJT has another highly effective
ploy in its bag of tricks, based on the useof the reserved character codes 000, 111,
222 and 333. Originally I identified thesefour codes with the ASCII characters +,*, % and @, but I recognized that if amessage were composed of any one ofthese characters sent repeatedly, with nointervening spaces, the transmitter would
send a pure tone: an unmodulated carrierat the frequency of the suppressed SSB
carrier plus that of the appropriate audio
tone. I decided to define such transmissions as having the meaning of the mostfrequently used short messages in high-speed meteor scatter QSOs, namely R26,
R27, RRR and 73. Because these shorthand messages are transmitted as single
tones, they have very narrow bandwidths
upon reception, even after allowing forthe vagaries of propagation. They are
therefore easy to recognize, both by ear
and by the software. The narrow bandwidth means that a suitable DSP algorithm can dig the signals out of the noisevery effectively, even if they are significantly weaker than the weakest decodable
multi-tone messages. Single-tone messages have proven to be very effective
and reliable, except where co-channel
QRM is a severe problem. When pings
are few and weak, they can speed up the
average time to complete a QSO by a factor of two or more.

Decoding the Pings
The computer algorithm for decodinga received FSK441 message must be able
to detect pings, carry out two stages ofsynchronization on the signals within thepings, and finally translate a sequence ofmeasured frequencies back into a text
message. The code that finds pings anddetermines their length starts by measuring the received power in the full receiverpassband, smoothed and sampled at 20
ms intervals. When the signal exceeds the
background level by more than a specified threshold, a ping is said to havestarted. When the power has dropped toat least 1 dB below the threshold, the pingis said to have ended. Pings with deep
fading may be interpreted as several
closely spaced pings.
The synchronization required for message decoding occurs in two stages. The
program first identifies the starting pointsof the sequences of 25 consecutive waveform samples that convey each transmitted tone. This task is tractable because
within properly phased 25-sample intervals, FSK441 signals always consist of asingle tone. The decoding software therefore needs to align things so that a mixture of tones is not found in any such
25-sample sequence. The result of thisprocess is a series of measurements of thereceived audio tone frequencies that reproduce the sequence generated at thetransmitter. In practice, the software also
needs to account for some frequency offset between transmitter and receiver, perhaps up to 200 Hz or so. Having made its
best estimate of the frequency error, theprogram identifies each received tone
with one of the four nominal FSK441 frequencies and labels it with a dit value inthe range 0–3, as defined earlier.
The second necessary synchronizing
step is to establish which dits in an arbitrary sequence are the leading membersof the three-dit sequences defining charac-

Figure 3—This screen-capture photo shows the main WSJT screen during a meteor
scatter QSO with W8WN. Thunderstorms were present to the west of K1JT at the time,
explaining the two static crashes near the beginning of the displayed 30-second
recording as well as the noisier-than usual baseline of receiver background noise (thegreen line). The signal about 18 seconds into the record is a ping from an underdense
meteor trail, and the message it conveyed is displayed in the central text box.

ters in the message. For reasons oftransmission efficiency, no special synchronizing information is embedded in an
FSK441 message. Instead, the proper synchronization is established from the message content itself, making use of the facts
that (a) three-dit sequences starting with “3”are never used, and (b) the “space” character is coded as 033, as shown in Table 1.
Messages sent by WSJT always contain atleast one trailing space—the software inserts one, if you do not include it explicitly—and most messages will include
additional spaces to improve readability.
Other characters may have dits with value
3 in the second or third positions, but neverin the first. Therefore, to properly synchronize a received signal the decoding algorithm examines the sequence of measured
dit values, skipping through the time series in steps of three, and selects as the properly synchronized starting point a dit
numbered N in the sequence such that noneof the dits N, N+3, N+6, N+9, ... has thevalue 3. Under the conditions specified
above, such a dit will necessarily be theleading one of an FSK441 character code.
After synchronization has been accomplished, message decoding is a snap.
The sequences of dit values are converted
from base-four notation into thecomputer’s native binary arithmetic, andthe numerical codes are converted tocharacters by means of a lookup table.

Two other subtleties of the decoding
software are worth mentioning here. As you
will quickly learn from listening to an
FSK441 transmission, the audio waveform
has a distinctive and easily recognizable“burbling” sound that is largely independent of the exact message content. This
character can be described in terms ofmodulation of the signal power in each of
the four tone frequencies, at the 441 Hz
keying rate and its harmonics. The software
readily detects this modulation; its absence
implies that the signal being examined is
not an FSK441 signal and that it may besafely rejected as interference or noise.
Single-tone messages are transmitted
as pure carriers, and their effective bandwidths upon reception are essentiallyequal to the inverse of the duration of theping. Even an extremely short ping of 20
ms duration will exhibit a bandwidth of
only 50 Hz, far less than the modulated
widths of the individual tones in a multitone message. Consequently, a different
and much more sensitive detection
method is appropriate. The spectrum ofa ping suspected of carrying a single-tonemessage is examined with a spectral resolution of about 40 Hz, leading to very
high sensitivity and an excellent ability
to avoid spurious decodings.

Normal Operation
Figure 3 shows a screen-capture imageof WSJT in operation at my station. At the
top of the form are two graphical areas.
The larger one displays a “waterfall” spectrogram in which time runs left to right andaudio frequency increases upward. The
signal displayed here is a 30 second recording from a QSO with W8WN; it includes two strong static crashes near the
beginning, followed by a moderately
strong ping about 18.5 seconds into therecord. The green line at the bottom of thisplot area represents the power in the fullreceiver passband, sampled every 0.1 second. The vertical displacement of eachpoint on the green curve is proportional to
the total power in all of the waterfall pixels directly above it, on a dB scale.
The smaller graphical window at theright displays two spectral plots, also on
a dB scale. The purple line graphs the
spectrum of audio-frequency noise, averaged over the full 30 seconds; in the absence of any strong signal, it effectively
illustrates the receiver’s passband shape.
The red line displays the spectrum of thestrongest detected ping. Yellow tickmarks at the top of this plot area (and also
at the left, center, and right of the largerarea) indicate the nominal frequencies ofthe four FSK441 tones. The 441-baudmodulation broadens out the pure tones
so that their widths begin to approach
their spacing, thereby creating an approximately flat transmitted spectrum for mostmessages. (Note, however, that local
peaks may still exist in the spectrum, as
illustrated in Figure 2.) In the red curveof Figure 3 you can just about recognize
the peaks corresponding to the four basic
tones. Each tone has been shifted slightly
to the left, relative to the yellow tickmarks, because of a small frequency offset between transmitter and receiver.
The large text box in the middle of the
WSJT screen displays decoded text fromany pings detected in the receiving interval. One line of text appears for each validated ping. Information in the text line
in Figure 3 shows that the recording interval began at 11:04:00 UTC and that aping was detected 18.5 seconds into theinterval. The ping was 740 ms long, andpeaked 10 dB above the noise. According to the somewhat arbitrary criteria
coded into WSJT (which are made to beroughly equivalent to the operator-judged
signal reports sent in high-speed CW
meteor scatter work), such a signal rates
a “26” signal report. The next number
shows that the program estimates W8WN
to have been transmitting at a frequency
offset by –150 Hz relative to myreceiver’s frequency. Finally the decoded
message is shown, with Shelby thanking
me for another fine 2-meter meteor-scatter ragchew over our 640-mile path.
You may have noticed that the two
December 200139

ping-like signals near the start of the 30second receiving interval did not produce
any decoded text. In the green-line plot andeven in the waterfall spectrogram, thesesignals look very similar to the real pinglater in the recording. However, theywould not have sounded the same. As described earlier, the WSJT program has beentaught how to recognize the “burbling”
characteristic sound of an FSK441 signal.
In the present instance the program would
have examined the two early pulses, decided that they did not “smell quite right,”
and properly rejected them as noise.
A few additional comments on the decoded text in Figure 3 may be helpful. At
147 characters per second, a 740 ms pingshould contain more than 100 characters.
All displayed messages are truncated to 40
characters, however. Since the actual messages transmitted by WSJT are limited to a
maximum of 28 characters, even the longest ones can be displayed to their full extent, perhaps with some repetition. Under
some circumstances, WSJT gains additional
sensitivity by detecting the repetition pattern of a message and averaging over all
the cycles contained in the length of a received ping. This process is most useful for
weak pings whose duration is 0.2 seconds
or longer, and it can be especially effective
on 6 meters where ping lengths are greater.
When the program has taken advantage
of message averaging, an asterisk is appended to the line of decoded text.
You can control the behavior of WSJT
by selecting items from the four menus at
the top of the screen and using the controls and text boxes in the lower part of
the form. As one example, the “Options”
item on the “Setup” menu causes thescreen shown in Figure 4 to be displayed.
This form permits the entry of various station parameters that typically do notchange very often. I will not describe thefunctions of the on-screen controls any
further here; you can readily guess the
purpose of many of them from the labels
visible in Figures 3 and 4, and they aredescribed in full detail in the downloadable
User’s Guide and Reference Manual.

Standard Procedures
Meteor scatter is not a communication
mode well suited to ragchewing! QSOs canbe completed much more easily if you adhere to a set of standard procedures thathave evolved from HSCW and other earlier techniques. A standard message format
and message sequence helps the process
considerably. WSJT generates standard
messages automatically, as illustrated in
the text boxes at the lower right of Figure
3. The formats of the messages are designed
for efficient transfer of the most essential
information: the exchange of both callsigns, a signal report or other information,
and acknowledgments of same. Timed mes40
December 2001

Figure 4—The “Options” screen of WSJT,
called up from an item on the “Setup”
menu. Use this screen to set a number ofstation parameters, typically ones that do
not change frequently. Amplitudes of thefour FSK441 tones can be set individually, if desired, to correct for certain transmitter idiosyncrasies. Programmable templates are available for establishing theformat of standard messages, and default
standards are provided for both North
American and European conventions.

sage sequences are a must, and WSJT defaults to 30 second transmitting and receiving periods. Although other intervals canbe selected, it helps to minimize QRM fromnearby stations if everyone adheres to one
standard. According to the procedures usedby common consent in North America, thewesternmost station transmits first in eachminute.
At the start of a QSO you should send
the other station’s call and your own callalternately. Then, as the QSO proceeds…
1. If you have received less than bothcalls from the other station, send bothcalls.
2. If you have received both calls, send
both calls and a signal report.
3. If you have received both calls anda report, send R plus signal report.

4. If you have received R plus signal
report, send RRR.
5. If you have received RRR—that is,a definite acknowledgment of all of yourinformation—your QSO is officiallycomplete. However, the other station may
not know this, so it is conventional tosend 73 (or some other conversational
information) to signify that you are done.
Signal reports are conventionally sent
as two-digit numbers chosen from nonoverlapping ranges. The first digit characterizes the lengths of pings being
received, on a 1-5 scale, and the second
estimates their strength on a 6-9 scale. The
most common signal reports are “26” forweak pings and “27” for stronger ones, but
under good conditions reports such as “38”and higher are sometimes used. Whateversignal report you decide to send to yourQSO partner, it is important that you do
not change it, even if stronger pings shouldcome along later in the contact. You neverknow when pings will successfully convey fragments of your message to the otherend of your path, and you want your received information to be consistent.
Slightly different standard procedures
have been adopted for high-speed meteorscatter in Europe. You will undoubtedly
find it useful to seek out and read additional information on current practices
available on the Internet. Some goodstarting places are listed in the sidebar
entitled “Meteor Scatter Resources.”
The 6- and 2-meter calling frequencies in common use for WSJT in North
America are 50.270 and 144.140 MHz.
Typical practice for calling CQ is to send
something like CQ U5 K1JT or CQ D9
K1JT, indicating that you will listen for
replies up 5 kHz or down 9 kHz from yourtransmitting frequency, and will respondon that frequency. However, the easiest
way to initiate a QSO is to post a oneline invitation on a Web page known as“Ping Jockey Central” (see sidebar).
Someone at a suitable range from you will

Meteor Scatter Resources
For additional reading on the history and astrophysics of amateur meteor-scatter communications, as well as operating hints and details concerning practices incurrent use, the following references and Internet addresses are recommended.
1. The classic papers on amateur meteor-scatter communications are the two
by Walter F. Bain, W4LTU: “VHF Meteor Scatter Propagation,” Apr 1957 QST ,p 20, and “VHF Propagation by Meteor-Trail Ionization,” May 1974 QST, p 41.
The second one is reprinted in the ARRL publication Beyond Line of Sight.
2. Many additional papers, unpublished hints, and extremely useful bits of information can be found on the Web pages www.qsl.net/w8wn/hscw/hscw.html andwww.meteorscatter.net/hsms.htm, and links contained therein.
3. A number of highly useful explanatory files are bundled with a freely available program called MS-Soft , by OH5IY, available at www.sci.fi/~oh5iy.
4. At least two subscriber reflectors are devoted to meteor scatter communications. Their addresses are hsms@qth.net (primarily used in North America) andmeteor-scatter@qth.net (primarily in Europe).
5. Meteor scatter schedules can be made in near real time by posting a message on the Web page known as Ping Jockey Central at www.pingjockey.net/
cgi-bin/pingtalk.

likely reply to such a posting, suggestinga specific frequency, and your QSO canbegin. The ranges of frequencies now being used for WSJT in North America are
50.270-50.300 and 144.100-144.150.

Increasing Levels of Activity
Version 0.82 of WSJT was first madeavailable to a group of about 20 volunteer beta-testers, nearly all of them
HSCW veterans, on June 20, 2001. A
majority of this group started making
QSOs immediately, and they helped me
to polish some of the program’s roughedges and root out some bugs. An open
beta release of Version 0.92 was announced on July 7, and within two more
weeks the program was being widelyused and discussed on VHF- and meteorscatter Internet reflectors and DX clusters in both America and Europe. Releaseof a stable and more polished Version 1.0
of WSJT was announced on August 26.
Since that time the installation package
has been downloaded more than 1700
times from my own Web site, and morethan 3000 times from the European mirror site.
I have made more than 150 contacts
with WSJT myself, including 45 “initials”(first contacts with a new call sign). These
QSOs include 19 states and 38 Maidenhead grid locators on 2 meters, and they
do not include stations within 500 milesof me. Most of my contacts were madewith a 160 W brick and an 11 element
Yagi at 45 feet. Many other stations havebeen far more successful; for example,
K0PW told me recently that in threemonths he had worked 73 initials and 30
states on 2 meters, using WSJT. I havecounted more than 120 North American
hams that are actively using the mode
now, and additional calls are showing up
every week. In Europe the activity levels
appear to be substantially higher: I haveheard estimates suggesting that at least
500 amateurs there are using WSJT, representing more than 50 DXCC entities.
These numbers include extra activity centered around the Perseids meteor shower,
which peaked on August 12, and it islikely that similar increases will occur
near the peaks of the remaining membersof the “big four” of the annual meteor
showers: the Leonids around November
18, Geminids around December 13, andQuadrantids around January 3.
Another indicator of the growing interest in WSJT is its significant presencein the September 2001 VHF QSO Party,
the first major North American VHF contest since the release of the program. I
have no idea how many QSOs and multipliers were made using the mode during
the contest, but I suspect the answer mustbe at least in the hundreds. I saw plentyof efforts to make WSJT schedules in ad-vance of the contest period, and in theEast, at least, the larger mountaintop“super stations” were involved. Without
really trying very hard, I made 18 meteor scatter contacts during the contest,
17 of them being multipliers I would nototherwise have worked. These were not
the quickest QSOs made during the contest, but they were not unreasonably long
either. The median time to complete a
QSO was 5 minutes on 6 meters and 13
minutes on 2 meters.

Looking Ahead
On a time-available basis, I hope tomake further improvements in WSJT’s
decoding algorithms and its convenienceof use. Even more interesting, from atechnical point of view, will be the incorporation of the extreme weak-signal
mode known as PUA43. Unlike FSK441,
PUA43 is designed for signals that are
more or less constant in amplitude butburied deep below the level of the receiver noise. Even though quite inaudible,
such signals can convey a slow but steadystream of information that is decodable
by using DSP integration techniques.
W7PUA and his collaborators have demonstrated the impressive capabilities of
the PUA43 mode by making EME (moonbounce) contacts with 150 W and single
Yagis on 2 meters, and with 5 W and 10
foot dishes on 1296 MHz. To my knowledge, the PUA43 mode is presently available only in software written for theelegant home-brewed DSP-10 2-metertransceiver, 6 also designed by W7PUA. I
hope to incorporate the mode into WSJT,
as well, thereby making its capabilities
available to amateurs using a much wider
range of equipment.
As a sort of enticement for things tocome, let me quote some numbers comparing the theoretical sensitivities andtransmission rates of modes being discussed here, as well as the more familiar
CW and SSB. In a typical transceiver’s
2.5 kHz bandwidth, an SSB signal needs
to be 4-6 dB above the noise to becopyable. Normal speech rates are twoor three words per second; when one issending call signs by voice as part of aminimal QSO, this means about three orfour letters per second. In the same receiver bandpass, FSK441 signals can becopied at about 2 dB above the noise, andthe special single-tone messages used in
WSJT are copied down to 4 or 5 dB below the noise. The FSK441 transmission
rate is a hefty 147 characters per second,
but of course the useful throughput depends on the availability of meteors.
Morse code at 20 WPM can be copied if
it is about 6 dB below the noise in a
2.5 kHz bandwidth. (Note that such asignal would be about 1 dB above thenoise in a 500 kHz bandwidth.) At 20

WPM, the throughput of CW is about 1.7
characters per second.
Amateurs customarily think of CW as
being the most effective mode for weaksignal communication, and the numbers
just quoted seem to bear this out. However, please take note that a one-minute
PUA43 transmission, containing 28 characters sent at 0.5 characters per second,can be copied all the way down to some
27 dB below the receiver noise. Post-detection averaging can yield nearly another
6 dB improvement in half an hour of alternating one-minute intervals of transmission and reception. The slower
transmission rate, and even more importantly the coherent detection of the narrow band signal over 2-second intervals,
accounts for the very substantial increasein signal to noise ratio.
PUA43 is a highly effective mode for
VHF/UHF tropospheric propagation, in
addition to EME. Because it works wellwith weak but steady signals, it nicelycomplements the short-ping capabilities
of FSK441. With both PUA43 andFSK441 in its bag of tricks, the modest
VHF station described earlier should be
able to work out to 500 miles or so at any
time with tropospheric propagation and
the PUA43 mode, and from there out to1100 miles and beyond by using FSK441
and meteor scatter. If you are within thosedistances of central New Jersey, I lookforward to working you with one of thesemodes soon!
Joe Taylor was first licensed as KN2ITP in
1954, and has since held the Amateur Radiocall signs K2ITP, WA1LXQ, W1HFV, VK2BJX
and K1JT. Trained in the academic fields ofphysics and astronomy, he was Professor of
Astronomy at the University of Massachusetts
from 1969 to 1981 and since then has been
Professor of Physics at Princeton University.
His research specialty is radio astronomy, andhe was awarded the Nobel Prize in Physics
in 1993 for discovery of the first orbiting pulsar. He currently serves as Dean of the Faculty at Princeton and chases DX from 160
meters through the microwave bands. You cancontact Joe at 272 Hartley Ave, Princeton,
NJ 08540-5656; k1jt@arrl.net.
Notes
1
Joe Taylor, K2ITP, “Working Ionospheric
Scatter on 50 MHz,” Dec 1958 QST, p 28.
2
Shelby Ennis, W8WN, “Utilizing the ConstantBombardment of Cosmic Debris for Routine
Communication,” Nov 2000 QST , p 28.
3
Steve Ford, WB8IMY, “PSK31 2000,” May
2000 QST , p 42.
4
Download the computer clock utility
Dimension 4 from www.thinkman.com/
dimension4.
5
The WSJT home page is at pulsar.
princeton.edu/~joe/K1JT.
6
Bob Larkin, W7PUA, “The DSP-10: An AllMode 2-Meter Transceiver Using a DSP IF
and PC-Controlled Front Panel,” Sept 1999
QST, p 33, Oct 1999 QST, p 34, and Nov
1999 QST, p 42.

December 2001

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