WSJT: A software package for VHF DXers

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WSJTA software package for VHF DXers
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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

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FSK441

• Meteor scatter anytime and anywhere!

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Meteor-scatter basics
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Science fiction?

• Pieces of space dust enter the earths 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)

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Time is of the essence!

• Very short communication windows
• SSB and fast CW (30 WPM) are the usual
  communication mediums in NA
• (Good) operators employ special operating
  practices to be most efficient
• (K5VH EM00, 144MHz, Aug 1997)
• SSB/CW QSOs on 144 MHz or higher only possible
  during major showers for normal stations

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Overdense vs. Underdense

• 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 quick exchange on SSB or CW.
• (WA3UUM EL29, 0839z 12 Aug 1997 )
• Associated with major showers, and very uncommon
  at other times.

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Typical overdense burst (70WPM CW)

• Heres a fun one..(K9MRI)

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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
• Not very useful for conventional SSB or CWoften
  referred to as pings
• Tend to preserve polarization
• Very common, even outside showers

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Underdense CW ping on 144.200
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Using underdense trailsHSCW

• 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 1960s

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Problems with HSCW

• Lots of energy wasted in keying sidebands.
• S/N gets worse as speed increases.
• Audio tone gets too low above 2000 LPM
• Special DSP algorithms necessary at high speeds
  to keep tone high enough to copy by earresults
  in further S/N loss.
• Key-clicks can be a problem for other users on
  band, especially if transmitter is overdriven.

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Waveform of SM sent at 4000 LPM (800 WPM)
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Spectral display of HSCW showing keying sidebands
due to OOK (W8WN, 100 WPM) normal
slowed
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The solution FSK441

• Like HSCW, it 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
  sidebands
• Much better S/N than HSCW at same speed
• More user-friendly interface--like RTTY or PSK31
  modes.

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FSK441 Whats 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 (notice
  relationship to harmonic series. This keeps
  computer calculation to a minimum.
• 441 Each character takes about 2.3ms to send.
  Each character is composed of three tones.
  Thats 441 baud.
• Actual sending speed is about 1800 WPM

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Waveform of the letter C in FSK441
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Spectral display FSK441 ping
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Spectral display in WSJT
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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 attempts
  to decode any signals that it detects and
  displays the text on the screen.

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How it works.

• The program calculates the average amplitude for
  the recorded audio.
• The program looks for spikes in the
  amplitudethese could be meteor pings above the
  noise floorcould be QRN!
• If the detected spike satisfies certain other
  parameters, the program will decode it as text
  and display it on the screen.
• Operator intervention often needed for manual
  decoding.

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WSJT in FSK441 mode
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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!

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RTTY and FSK441

• RTTY (5-bit)
• A 00011
• B 11001
• C 01110
• Z 10001
• 6 10101
• 00100

• FSK441 (3-bit)
• A 101
• B 102
• C 103
• Z 231
• 6 012
• 033 --the secret!

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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 searches for the
  sequence 033. This is the point of
  synchronization.

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FSK411 synchronization

• A burst of signal contains the following sequence
  of tones .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

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Single-tone messages

• Each character in the FSK441 code contains at
  least two different frequenciesno 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!

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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!

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FSK441 operating procedures

• Philosophy is 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).

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FSK441 operating procedures

• 30-second sequences are standard.
• Western-most station transmits first. This is in
  the Western hemisphere.
• Regular CQs can be either first or second
  period.
• CQs use the QSY method.
• DXpeditions usually run all schedules and CQs on
  the same frequency and period, regardless of
  direction.
• Calling frequencies 50.270 and 144.140 MHz

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The QSY method

• The CQing station calls CQ on the FSK441 calling
  frequency, and announces that he/she is listening
  elsewhere.
• After getting a response, the rest of the QSO
  takes place on the NEW frequency.
• This is NOT the same thing as split operation!

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The QSY method U/D system

• CQer announces that he/she is listening up or
  down a certain number of KHz.
• CQ D27 K0SM means that K0SM is listening for a
  response 27KHz below this frequency.
• CQ U7 K1JT FN20 means that K1JT is listening 7
  KHz above this frequency. (Notice that he also
  added his grid so that a potential answerer knows
  where to point the antennasomething commonly
  done in CQs.)

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How to answer a CQ

• You hear CQ U25 K0SM EN10 CQ.. on 144.140 MHz,
  the 2m FSK441 calling frequency. The burst
  occurred durning the second 30sec of the
  minutedouble-check the time!
• You tune your radio to 144.140 23 Khz 144.153
  MHz. And start calling with callsigns only on
  the first half of the minute. You are now TX
  and RX on .153 and no longer listening to the
  calling frequency.
• When K0SM hears you, he will move his transmitter
  to 144.153 and you will complete the QSO simplex
  on the new frequency.

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Why use the QSY method?

• Makes it possible for several people to call CQ
  at once without QRMing each other. You can call
  CQ at the same time on the same frequency as your
  neighbor down the street!
• Its just like 144.200 during a showerit is
  impossible to tell who is sending RRR or 73
  if there are six QSOs on the same frequency!
  This method greatly reduces the chance of a
  busted QSO because of QRM.

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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

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QSO procedure

• If you have copied.
• Nothing....?
• Partial callsigns....?
• Both callsigns...?
• Both calls and report?
• R and report..?
• RRR..?

• then send.
• Callsigns only
• Callsigns only
• Calls report (or grid)
• R report
• RRR
• QSO is complete, send 73 or (or QRZ, CQ)

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.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 short222 and 432 MHz.

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What equipment do I need?

• Most popular bands are 144 and 50MHz. There is
  growing activity on 222MHz, and a few 432 MHz
  QSOs have been made.
• More is better, but brick and yagi are
  sufficient on 144 and even 222 MHz any time of
  year.
• Brick and yagi has worked on 432 MHz, but more
  operation is needed to draw any conclusions.
• Preampyou dont know what youre missing!

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What equipment do I need?

• A computer and a soundcard-- 60Mhz Pentium PC
  with 24Mb of RAM will work, but youll be happier
  with more!
• A way to interface the soundcard with the radio.
  You can use a commercial PSK31 interface
  (Rigblaster, MFJ, etc) or make your own.
• The (free!) software

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Sound Card ? ? Radio
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What about other platforms?

• G4KLX/HB9DRD has compiled a beta version of JT44
  that runs under Linux (as of October 2002)
• FSK441 is in progress--the TX part of the program
  is working. FSK441 RX is not good.
• Available as C open source code under GPL, may
  require some extra libraries.
• http//www.qsl.net/g4klx/

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When should I operate?

• The daily random meteor rate peaks around
  sunrise local time, but QSOs are possible anytime
  of day or nightit just might take longer to
  complete it.
• Minor showers can enhance the background meteor
  rate (June-December)
• Before and after major shower peaks

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When should I NOT operate?

• During shower peaks, unless of course, you are
  after that one super-QSO
• SSB random operation is faster during peaks, when
  you can work several stations on one big rock.

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What can I expect to work?

• On 144MHz, the average brick and yagi station
  should be able to work a similar station in the
  600-1100mi 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!

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How about portable operation?

• No need to haul large antennas and big amplifiers
  to the top of a mountain for success.
• One doesnt need to plan DXpedtion around major
  showers
• Casual, weekend or vacation operation is
  possible. Good excuse to visit a friend who
  lives in the middle of nowhere ( rare grid).

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The road to DN90wp
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K0SM/P DN90 Equipment list

• FT-290R II 2m radio (25w)
• Mirage 160w amplifier with built-in GaAsFET
  preamp
• The array two 3-el Arrow yagis with 435-MHz
  elements removed. RG-59 used for phasing line.
• 12ft of scrap PVC pipe and joint for mast. I
  mean scrap.
• Nylon rope and cinder blocks for anchoring
  antenna.
• U-bolts for securing antennas
• (duct tape for securing the mast)

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K0SM/P DN90wp
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K0SM/P DN90 2m QSOs Evening and morning 27-28
December 2001
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CY9DHFN97we July 1-7 2002144 MHz FSK441 (37
QSOs)
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FSK441 in contests

• Rovers can stray to distant grids and still make
  contactsthat 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 multipliers.

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Sked Sheet
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2002 September VHF QSO Party W2FU
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Things learned from the contest

• 5 hours of 100 duty cycle on three bands at once
  is a good stress test of.....well
• everything.
• Molten N-connectors smell funny.
• That whirring sound we heard outside at 3am was
  probably the electricity meter on Jeffs house
  coming loose from it bearing.
• Need to improve water cooling system for 6m
  brick amplifier..or buy more fans.

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FSK441 recap..

• Uses underdense meteor pings
• Makes meteor-scatter possible anytime of the year
  on 50, 144, 222 MHz.
• 432 MS possible between smaller stations
• Makes portable VHF DXpeditions successfulyoull
  always have some propagation
• Requires no special equipment

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JT44

• A really weak signal mode

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JT44

• Uses long term signal averaging to recover a
  signal that is below the noise floor.
• Humans have short ears limited by their sensory
  memorythey can only analyze a signal in a small
  timeframe.
• Computers can analyze a signal in relatively
  large timeframesminutes, hours, even days!

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The JT44 code

• Inspired by the PUA43 mode
• Uses 44 tones, one for each character in the
  PUA43 alphabet, plus a synchronization tone.
  Each character is assigned a unique frequency.
• Slow transmission speed is 5.38 baud.
• Highly redundant

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JT44 Tones

• Z 1755.0 Hz
• A 1485.8 Hz
• 1475.0 Hz
• .
• 9 1399.7 Hz
• 0 1302.8 Hz
• Sync 1270.5 Hz

• Bandwidth of 485Hz
• Tones spaced at 10.8Hz
• Sync tone 32.3Hz below first data tone.
• Allows for frequency error and EME Doppler shift
  with 2.7 KHz passband.

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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 in 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.

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Why have a sync tone?

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

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How WSJT decodes JT44Finding the frequency

• WSJT does a frequency-analysis (FFT) of the
  entire 30-sec period. Because the sync tone is
  sent more than half of the time, it should
  outweigh any other data tones
• This gives WSJT a frequency reference to find the
  data.
• The frequency discrepancy is displayed in the
  DF column on the screen.

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FFT of a strong (audible) JT44 signal
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The pseudo-random pattern of the sync tone

• 1-20 11101000011100110000
• 21-40 10010001010111010111
• 41-60 10010010111001110000
• 61-80 00111011101001111010
• 81-100 10010100000010101010
• 101-120 11111010110100000110
• 121-135 111011011010110

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How WSJT decodes JT44Timing

• 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.

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Decoded JT44 signal
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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 S/N improvement.
• 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 sync
  limit).

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144 MHz EME QSO between K1JT AND GM4JJJ
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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

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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.

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Line averages
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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)

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A demonstration

• Copy this CW signal
• Heres a JT44 signal at an even lower S/N

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CW

• JT44

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JT44 signal decoded in WSJT
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JT44 operating procedures

• 30-second sequencing
• EME operation almost always by schedules or
  announced operation
• Some big guns call CQ, but will often announce
  beforehand (e-mail, web, packet).

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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 systemsame
  as CW.
• Always check with your sked partner!

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Operator responsibilities

• Lock onto the other stations 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

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JT44terrestrial operation

• JT44 works well on troposcatter paths that are
  too short for or too high in frequency for MS
  enhancement.
• Several operators have used it on 6m for
  borderline TE, and marginal Es openings.
• What about that weak 48-MHz video? Skew path to
  southern Europe on 50 MHz???
• Microwave non-line-of-sight paths? --need
  frequency stability

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Other terrestrial applications

• Perhaps useful on extremely long IOS paths
  between big stations.
• Could be a good way of overcoming atmospheric
  absorption above 10GHz. (frequency stability will
  be an issue here)
• Contests! What are the 222 and 432 MHz stations
  doing in the middle of the night?

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JT44 EME applications

• JT44s 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. (doppler shift/drift could become an
  issue on higher bands)
• 50 MHz EME for mortals!

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What do I need to make EME QSOs?

• A pair of single-yagi stations should be able to
  work each other, with QRO power and good receive
  system (good preamps!)
• Brick-and-yagi stations can work larger
  stations at moonrise/moonset.
• Single-yagi and a few hundred watts on 6m to work
  big guns on 6m (W7GJ, ON4ANT)
• W5UN has been copied in VK with a Ringo-Ranger
  vertical on 2m!

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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,
  C6AIE)

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CY9DHFN97we JT44

• Worked JT44 on 50MHz marginal Es
• VE1ALQ and VE9AA (FN65) 2m JT44 troposcatter
• W7GJ on 144Mhz and 50MHz EME
• EME limited by terrainno elevation control, hill
  to east.

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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, and not very
  accurate.

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Where to get WSJT

• WSJT homepagedownload and updates
  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!
• http//www.pingjockey.net set up skeds