Quest for Optimum Coding and Modulation Schemes for EME
Joe Taylor, K1JT
13th International EME Conference: Florence, August 8–10, 2008
Ten years of fascination with amateur radio in the 1950s and early 1960s led me to a professional
life in basic research and university teaching. Over the next forty years, my research in radio
astronomy taught me a great deal about extracting extremely weak signals from noise, andanalyzing their content. In 2001, back on the air as an active radio amateur, I began thinking aboutways to apply techniques learned and developed in the research world to the problems of weaksignal communication on our VHF and UHF bands.
My presentation in Florence will review some basics of communication theory, a complex field inwhich I have much interest but no professional expertise. I will then describe the motivation,
rationale, and performance trade-offs leading to the digital communication modes implemented in
my software programs WSJT, MAP65, and WSPR, with particular emphasis on the most recent
developments and the modes suitable for EME. My quest for the optimum ways to exchange
messages with high reliability, despite having very weak signals, has been a fascinating learning
experience involving much study and many experiments. By no means have all of my ideas beensuccessful! — but all have been fun, as well as instructive.
Most attendees at this conference are already familiar with the JT65 protocol, which was designed
especially for VHF EME. In this summary paper I assume such familiarity and describe two
relatively new projects: the MAP65 software and a new experimental mode called WSPR.
MAP65
MAP65 is a computer program designed as the back end of a wideband polarization-matchingreceiver for JT65 signals. It works together with the Linrad 1 software written by SM5BSZ, andtakes advantage of RF and IF hardware providing signal channels for two orthogonal polarizations.
As an example, my current 144 MHz station uses dual-polarization yagis and matched baseband
converters. I configure Linrad to use a four-channel, 24-bit soundcard to sample I and Q baseband
signals for each polarization at a 96 kHz rate. After Linrad’s superb wideband noise blanking has
been applied, the digitized signals are passed to MAP65 in the form of UDP packets. MAP65automatically finds all detectable JT65 signals in a 90 kHz passband, matches the linear
polarization angle of each one, decodes their messages, and provides the operator with a “bandmap” displaying callsigns, operating frequencies, polarization angles, and messages received overthe past 20 minutes or so. The program provides a companion transmitting facility, and it runs
under either Windows or Linux. With my available hardware I choose to run Linrad under Linuxand MAP65 under Windows, but any combination is possible — including running both programsin a single computer.

1Linrad Home Page: www.nitehawk.com/sm5bsz/linuxdsp/linrad.htm

MAP65 uses the JT65 protocol 2 popularized in the program WSJT 3 . JT65 was designed to enable
EME contacts between moderate-sized amateur VHF/UHF stations. Its high efficiency is a resultof using time-synchronized transmissions, compact structured messages, strong forward error
correction, and 65-tone frequency shift keying. The most important difference between MAP65 andWSJT (when the latter is running in JT65B mode) is that WSJT receives a single 2 – 4 kHz
bandwidth and decodes one signal at a time. In contrast, MAP65 works with dual-polarization
antennas and accepts a full 90 kHz bandwidth. MAP65 scans the entire received passband,
automatically determining the frequency, drift rate, time offset, and polarization state of every
detectable JT65 signal, and decoding each one.
I have been testing various versions of MAP65 on the air since May 2007, and have used it to makemore than 600 EME QSOs on 144 MHz. I find it a pleasure to use. It’s very exciting to have thewhole 144 MHz digital EME sub-band (say, 144.070 – 144.160) available on one’s computer
screen simultaneously, including panoramic spectral displays and the text of all messages being
sent and received. If the moon is up, and especially if it has not yet set in Europe, I generally see
ten to twenty EME signals on my screen at any given time. The signals may originate anywhere in
the world where the moon is above the horizon, and the program decodes them all. When a newstation shows up and calls CQ, I see his signal and callsign immediately and can respond after hisfirst transmission. No advance knowledge, schedules or internet liaison is required.
A screen shot of MAP65 is shown in Figure 1. This snapshot was taken after MAP65 hadprocessed data recorded between 0745 and 0800 UTC on November 11, 2006, during the second
weekend of the 2006 ARRL EME contest. (Odd-numbered minutes from 0747 to 0753 UTC areabsent from the recording because I was transmitting then, working WA8CLT on 144.131.) If you
were “on the moon” at this time using JT65B on 2 meters, your signal is probably among thosefound and decoded by MAP65. My EME antenna in 2006 was very modest: a pair of 3λ crosspolarized yagis stacked side by side, a few feet above the roof of my house.
Figure 1 shows four active MAP65 windows:
1. The main window, similar to that of WSJT, used for conducting QSOs.
2. A “Waterfall” window with separate panels presenting a wideband spectral view and azoomed-in region around the selected QSO frequency.
3. A scrolling “Messages” window listing the results of all transmissions decoded over a
specified time interval, typically 10–20 minutes.
4. A “Band Map” window presenting a summary listing by frequency of all stations decodedin the specified time interval.
Many additional details of the MAP65 program and its capabilities are contained in a paper
presented at Microwave Update 2007 and published in the proceedings 4 of that conference.
MAP65 was used by several stations, including my own, during the 2007 ARRL EME contest, andwas found to be highly effective for contest use.

2J. Taylor, K1JT, “The JT65 Communications Protocol”, QEX, September-October 2005, pp. 3–12.
This paper assumes some basic familiarity with WSJT. If you need more background, the WSJT Home Page can befound at physics.princeton.edu/pulsar/K1JT/.
4J. Taylor, K1JT, “MAP65: A Panoramic, Polarization-Matching Receiver for JT65,”
http://physics.princeton.edu/pulsar/K1JT/MAP65.pdf
3Figure 1. MAP65 screen shot after receiving 11 minutes of wideband data recorded
during the 2006 ARRL EME contest at 144 MHz.

WSPR
WSPR mode was created in March 2008. The name is pronounced “whisper,” which seems
appropriate for a mode designed for extremely weak signals; it is an acronym for “Weak Signal
Propagation Reporter,” and has come to be used for both the protocol and a computer program thatimplements it. The protocol was developed for beacon-like signals originating from QRP
transmitters on the LF, MF, and HF bands, but also with advance thinking toward its possible use
for VHF EME QSOs. WSPR uses structured messages with a high degree of compression, strong
forward error correction, an embedded sync vector for establishing accurate time and frequency
offsets between transmitter and receiver, and 4-tone frequency shift keying at 1.46 baud.
Transmissions last for slightly less than 2 minutes. Total signal bandwidth is about 6 Hz, so WSPR
signals are about 1/60 the bandwidth of JT65B signals and 1/4 the bandwidth of 20 wpm CW.
Many WSPR signals can fit into a few hundred Hz of spectrum, with few collisions. Figure 2
presents a screen shot of WSPR in use on the 30 m band.

Figure 2. Screen shot showing many WSPR-mode signals received on 30 m, in abandwidth of 200 Hz.

Over the past two months WSPR had been actively used by some four hundred operators aroundthe world, mostly using QRP and QRPP power levels on the HF bands. Successful tests have also
been made at 508 kHz and on the VHF bands. In its original mode of operation (which was notintended for making 2-way QSOs) the program transmits during a specified fraction of available 2minute slots, and receives in the rest. A typical “transmitting percentage” is 25%. Messages
consist of callsign, grid locator, and transmitter power in dBm; on the HF bands, most operators
have been using power levels of 100 mW to 1 W. As you can see in Figure 2, WSPR signals canbe decoded with signal-to-noise ratios as low as –29 dB in the standard reference bandwidth of2500 Hz. As in JT65, strong forward error correction guarantees that messages are almost always
received exactly as transmitted, or not at all.
Figure 3 is a screen shot showing signals from the first test of WSPR on an EME path. The signal
was provided by VK7MO and received at K1JT. Rex has a modest 4 x 10 element array, and forthis test he ran just 150 Watts.

Figure 3. Screen shot showing the WSPR signal of VK7MO being received at K1JT
via 144 MHz EME.

In addition to its beacon-like messages, the WSPR protocol offers a rich variety of message types
useful for 2-way contacts. Their formats are illustrated by the templates and examples presented inTable 1. This list is still being developed as I write; more complete information will be available atthe time of the conference in Florence.
Upper-case letters and numerals are conveyed in the WSPR protocol exactly as shown in thetemplates. Lower-case items are replaced by appropriate variable information, for example
call=K1JT, grid=FN20, rpt=S1 to S9, name=VICTORIA, wx=SNOW, freetext=CUL JACK,and so on, as shown in the examples.

Table 1. Templates and examples of WSPR messages.
Template

Example of usage

CQ call grid
CQ p/callCQ K1JT FN20CQ PJ4/K1JT<call1> call2
DE call gridDE p/call<K1JT> W6CQZ
DE W6CQZ CM87
DE PJ4/K1JT

call1 <call2> rpt
QRZ callp/call rpt

W6CQZ <K1JT> S4
QRZ K1JT
PJ4/W6CQZ S4

call1 <call2> R rptp/call R rpt

K1JT <W6CQZ> R S3
PJ4/K1JT R S3<call1> call2 RRR
call1 <call2> RRR
DE p/call RRR<W6CQZ> K1JT RRR
W6CQZ <K1JT> RRR
DE PJ4/K1JT RRR

73 DE call grid
73 DE p/call
TNX name 73 GL
OP name 73 GL
pwr W DIPOLE
pwr W VERTICAL
pwr W gain DBD
pwr W gain DBD 73 GL
PSE QSY freq KHZ
WX wx temp F/C wind
freetext

73 DE W6CQZ CM87
73 DE PJ4/K1JT
TNX VICTORIA 73 GL
OP HARRY 73 GL
5 W DIPOLE
10 W VERTICAL1 W 0 DBD
1500 W 21 DBD 73 GL
PSE QSY 1811 KHZWX SNOW -5 C CALM
CUL JACKWSPR messages may contain one full callsign and one “hash-coded” callsign. The transmission ofhash codes is indicated by angle brackets surrounding the call, as in <K1JT>; the brackets appear indisplays of both transmitted and received messages. Since hashing is a many-to-one mapping, theprocess is not reversible. However, if a full callsign has been decoded in a previous transmission,
the decoder may assume that matching hash codes usually imply matching callsigns. With a 15-bit
hash code, the chances of misidentification are small, especially within the confines of a particular
QSO.
A minimal QSO using WSPR mode might look like the following sequence of messages:
1.
2.
3.
4.
5.
6.

CQ K1JT FN20
<K1JT> W6CQZ
W6CQZ <K1JT> S4
K1JT <W6CQZ> R S3
<W6CQZ> K1JT RRR
TNX JOE 73 GL

A third-party operator listening to this QSO from the beginning would copy everything just as theparticipating stations do. Even if only one of the QSO partners can be copied at the third station,
both callsigns will be received in full. If the third-party operator tunes into the middle of a QSO, sothat his decoder cannot yet identify one of the hashed callsigns, it will produce something likeW6CQZ <...> S4

instead of the full message. He must then stay tuned to determine the identity of the missing
callsign. There will be no ambiguities at all for the QSO partners themselves. Full callsigns arealways decoded (or already available, in the case of one’s own call) before their hash codes areneeded.
Signal report S1 corresponds to –30 dB on the WSJT scale, S2 = –27 dB, S3 = –24 dB, etc., up toS9 = –6 dB. On this scale, the threshold for signal audibility is around S5 to S6. The placeholder"p/" stands for an add-on prefix or suffix in compound callsigns like ZB2/DF2ZC or DH7FB/P.
Information conveying the prefix or suffix replaces the information that would otherwise carry agrid locator or hashed callsign. Some extended-length callsigns like VK3ABCD are accommodated
in a similar way.
Items in Table 1 like "pwr", "gain", "temp", and "freq" stand for numbers. A 2m EME
station might send the message
1500 W 21 DBD

to inform his QSO partner about his equipment. Similarly, a QRP HF station might send
1 W 0 DBD

or
5 W DIPOLE

If an operator finishes a QSO on 80 m and wants to try 160 m next, he might send
PSE QSY 1811 KHZ

Weather reports can be conveyed by setting "wx" to SUNNY, CLOUDY, RAIN, or SNOW;"temp" can be transmitted in degrees C or F, with appropriate conversions made automatically at
the receiving end; "wind" can be set to CALM, BREEZES, or WINDY. Names may contain up tonine letters, and "freetext" may contain any combination of eight or fewer letters, numerals,spaces, and the punctuation marks + . / ? . Space has been reserved in the WSPR protocol formany more “canned” or “partly canned” messages like those in the final group of templates. I
hereby solicit suggestions for additional messages to be included in this group. Note that thevariable information to be inserted in a partly-canned message should be no more than one, two, or
possibly three numbers or words.
Regular users of JT65 will be interested in a more detailed comparison of the JT65 and WSPRprotocols. Table 2 presents such a comparison; in this table the specified JT65 bandwidth is thatfor sub-mode JT65B.

Table 2. Basic specifications for the JT65 and WSPR protocols.

Message length (bits)
Forward error correction
Channel symbols
Sync vector (bits)
Modulation
Keying rate (baud)
Transmission length (s)Occupied bandwidth (Hz)JT65
72
RS (63,12)
126
126
65-FSK
2.69
46.8
355WSPR50Convolutional, K=32, r=1/2
162
162
4-FSK
1.46
110.6
5.9

The first WSPR-mode QSO was made just one week ago as I write, using a special version of theWSPR program. However, future software evolution will most likely follow a different path. It
seems best to keep the WSPR program relatively simple and intended for the purpose of automatic,
beacon-like transmission and reception of propagation test signals. The next released version ofWSPR will, however, be able to decode the QSO-mode messages as well as the beacon-likesignals. For QSO purposes the WSPR protocol will be absorbed into a future version of WSJT.
This seems desirable and efficient because WSJT already has the necessary tools for setting up
messages, controlling transmit/receive sequences, and the like.
How does WSPR compare in sensitivity with other weak signal communication modes? Under theassumption of additive white Gaussian noise, no QSB, and Doppler spreading less than 1 Hz, thenumbers given in Table 3 will apply. (It should be noted that JT65 uses 1-minute T/R sequences
while WSPR uses 2-minute sequences, and that averaging of multiple WSPR transmissions has notyet been tested.) In general, I believe that WSPR will be effective over any propagation path thatprovides S/N exceeding –29 dB in reference bandwidth 2500 Hz, with Doppler spreading less thanabout 1 Hz. Such paths should include most LF, MF, and HF paths of interest to amateurs, as wellas the EME path at VHF. At the time of writing, EME tests of WSPR have been made only on
144 MHz, where it works well. I do not expect WSPR to be effective (in its present form) at 432
MHz and higher, because of too much Doppler broadening.
Table 3. Approximate sensitivity comparisons for CW, JT65B, and WSPR.

CW (best human operators)
JT65B (KV decoder)
JT65B (Average of 3transmissions, KV decoder)
JT65B (Deep search)
WSPR
WSPR (Average of 3transmissions)Threshold S/N (dB)
–18
–24
–27
–28
–29
–32

For those with technical interest in the WSPR protocol, here are a few additional details. TheWSPR message payload is 50 bits of information in every transmission. Most message formats use
28 bits for a standard callsign and 15 bits for a hash-coded callsign or grid locator. The remaining
7 bits convey signal reports, acknowledgments, power levels, and special message types. Special
messages can use the first 43 bits for any dedicated purpose. The WSPR protocol uses continuousphase 4-tone FSK with tone spacing and keying rate equal to 12000/8192 = 1.46 Hz. Eachtransmission contains (50+K-1) × 2 = 162 channel symbols, and each symbol conveys both a databit (MSB) and a synchronizing bit (LSB). Transmissions last for 162*8192/12000 = 110.6 s.
The WSJT, MAP65, and WSPR programs are available for free download on the WSJT Home
Page, physics.princeton.edu/pulsar/K1JT/. These programs are all open-source,
licensed under the Gnu General Public License. Contributions to the programs by other interested
amateurs are encouraged. Source code for the programs is maintained in an open repository atdeveloper.berlios.de/projects/wsjt/.