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WSJT Meteors, Moonbounce, and More …. JT65. JT6M. FSK441. Joe Taylor, K1JT. Mid-Atlantic States VHF Conference September 24, 2005. How to push the DX Limits on VHF/UHF bands . Wait for a band opening Get a bigger amplifier Bigger antenna, better feedline, low-noise preamp, …. – or –.

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WSJT Meteors, Moonbounce, and More …

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Wsjt meteors moonbounce and more l.jpg

WSJTMeteors, Moonbounce, and More …

JT65

JT6M

FSK441

Joe Taylor, K1JT

Mid-Atlantic States VHF Conference

September 24, 2005


How to push the dx limits on vhf uhf bands l.jpg

How to push the DX Limitson VHF/UHF bands

  • Wait for a band opening

  • Get a bigger amplifier

  • Bigger antenna, better feedline, low-noise preamp, …

– or –

  • Use efficient coding and modulation


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WSJT: What is it?

  • A computer program

  • Provides modulation and encoding/decoding, as in PSK31

  • Offers several modes

    • FSK441 for meteor scatter

    • JT6M for ionoscatter on 6m

    • JT65 for EME

    • CW for EME


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Requirements for optimizing minimal QSOs

  • Meteor scatter

    • Speed > 100 cps

    • Good copy at 0 dB S/N in SSB BW

  • EME

    • Speed ≈ 0.3 cps

    • Good copy at –20 to –30 dB S/N


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Design of FSK441

  • Four-tone FSK: 882, 1323, 1764, 2205 Hz

  • Three tones or “symbols” per character

  • Keying rate 441 baud

  • Transmission rate 147 cps

  • Detection bandwidth 4 × 441 Hz

  • Short messages sent repeatedly

  • 30s T/R sequences


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Design of JT6M

  • 44-tone FSK

  • Sync tone every 3rd symbol

  • Keying rate 21.5 baud

  • Detection bandwidth 44 × 21.5 Hz

  • Short messages sent repeatedly

  • Message averaging

  • 30 s T/R sequences


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Design of JT65

  • Structured messages

  • Sync tone plus 64 data tones

  • Keying rate 2.7 baud

  • Detection BW 66 × 2.7/5.4/10.8 Hz

  • Powerful Error-Correcting Code

  • Short messages: RO, RRR, 73

  • T/R sequences 60 s


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FEC in JT65

  • Seems like magic ?

  • Mathematically rigorous …

  • RS(63,12) code, 6-bit symbols

  • Corrects 25 (or even more) symbol errors

  • “Deep search” does 4 dB better

  • Soft-decision decoder by Koetter and Vardy (US patent #6,634,007)


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Compressed and Encoded JT65 Messages

Message Compressed to 72 bits (12 six-bit symbols)

----------------------------------------------------------------------

1. G3LTF DL9KR JO40 61 37 30 28 9 27 61 58 26 3 49 16

2. G3LTE DL9KR JO40 61 37 30 28 5 27 61 58 26 3 49 16

3. G3LTF DL9KR JO41 61 37 30 28 9 27 61 58 26 3 49 17

First 21 (of 63) encoded channel symbols, including FEC:

----------------------------------------------------------------------

1. 14 16 9 18 4 60 41 18 22 63 43 5 30 13 15 9 25 35 50 21 0 ...

2. 20 34 19 5 36 6 30 15 22 20 3 62 57 59 19 56 17 35 2 9 41 ...

3. 47 27 46 50 58 26 38 24 22 3 14 54 10 58 36 23 63 35 41 56 53 ...


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Does it work ?

  • Several thousand users, worldwide

  • You can work “anyone” at 500 to 1300 miles on 6 or 2m, any time

  • K1JT on 2m (4 x 9 el, 700 W):

    • WAC ─ EME initials 109

    • DXCC 39 ─ Grids 268

    • WAS 42


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Measured sensitivity

Measured sensitivity of JT65


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Measured “sync and shorthand” sensitivity


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What equipment do I need?

  • Windows computer with sound card

  • Minimum: 400 MHz Pentium II, 64 MB RAM (you’ll be happier with more)

  • WSJT software: free download

  • Simple interface, serial port to PTT

  • Audio connections, sound card to radio


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Installing WSJT

  • Free download from WSJT home page:

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

  • Self-extracting EXE file — “click-click!”

  • Includes a detailed manual in PDF format

    • full description of each mode

    • screen pictures

    • operational hints

    • index of controls

    • technical appendices


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VK7MO EME DXpedition

  • Destinations: Cocos-Keeling Island (VK9C) and Christmas Island (VK9X)

  • Bands: 144, 432 MHz

  • Antennas: single yagi on each band

  • Power: 300 W on 2m, 65 W on 70 cm

  • Mode: JT65B


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VK7MO DXpedition Scorecard

  • EME QSOs on 2m: 156

  • EME QSOs on 70 cm: 6+

  • Nearly all QSOs random: no internet


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… to the demos …


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WSJT in FSK441 mode


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Does it work? -- 231 grids on 2m


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ZS5LEE works K1JT on 2m


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ZS5LEE works K1JT on 2m


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K1JT works RN6BN on 2m


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