Introduction to Meteor Scatter Operation

1
Introduction to Meteor Scatter Operation

• by Marc C. Tarplee, Ph.D.
• N4UFP

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Meteor Scatter Theory
3
Introduction

• The earth is bombarded 24/7 by small meteors
• They generally arrive from a variety of
  directions
• They arrive with random velocities reaching up to
  70 km/sec (45 mi/sec)

Leonid Meteor Shower from Space
4
Introduction

• The rate at which meteors the Earths atmosphere
  peaks at around 600 AM local time
• Between midnight and 600 AM the Earth is turning
  into the path of oncoming meteors
• Meteors strike with higher velocity during this
  time.

5
Introduction

• The meteor strike rate also varies annually.
• Approximately twice as many meteors strike the
  Earths atmosphere per hour during the summer as
  during the winter.

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Meteor Scatter Geometry
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Meteor Scatter Path GeometryHot Spots

• Because the Earth rotates and moves around the
  Sun, random meteors appear to cluster around one
  of two hot spots approximately /- 10 degrees
  off the great circle bearing between transmitter
  and receiver
• Which hot spot has the greatest meteor
  concentration depends on the time of day

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Meteor Trails

• As meteors are vaporized in the upper atmosphere,
  they leave behind ionized trails at heights of 60
  70 miles that are sufficiently dense to reflect
  radio waves in the HF and VHF range.
• A long trail lasts only 15 seconds most trails
  are less than 1 second long
• Meteor trails are classified according to
  electron line density
• Underdense (n lt 21014 m-1)
• Overdense (n gt 21014 m-1)
• Most meteor trails are underdense

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Signal Strength Equation

• P0 RF power scattered by meteor
• PT transmitter power
• GT, GR transmit and receive antenna gains
• L RF wavelength
• re classical electron radius

• q line electron density
• g angle between E-field vector an the
  direction to the receiver
• f scatter half-angle
• b angle between meteor trail and propagation
  plane
• RR, RT distance from transmitter and receiver
  to scatter point

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Meteor Trails and RF

• The electron density within an ionized meteor
  trail is often high enough to reflect RF
• The amount of scattering decreases with
  increasing frequency.

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Meteor Trails and RF

• After the trail has been created, electrons and
  ions slowly recombine, reducing the ionization
  and scattering ability of the trail
• The length of time over which a trail can
  scatter RF decreases rapidly with increasing
  frequency.

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Meteor Showers

• In additon to the random meteors that
  continuously strike the Earth, there meteor
  showers that occur throughout the year, during
  which the meteor rate climbs above 100 meteors
  per hour.
• Meteor showers occur when the Earth passes
  through a region of space rich in debris, perhaps
  the leftovers of a destroyed comet.
• Meteor showers are generally named after the
  constellation from which the meteors apparently
  come.
• The most famous meteor shower is the Perseid
  meteor shower which occurs around 12 August.

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Meteor Scatter Communications

• Under normal circumstances, at least 5 10
  large meteors per hour enter the Earths
  atmosphere and leave behind ionized trails, so it
  is possible to communicate by scattering RF off
  of meteor trails
• Since individual trails last for only a short
  time, information must be sent in small packets
• The exact time a trail will occur is unknown, so
  the information must be sent repeatedly.
• To keep the SNR high, the signal bandwidth should
  be as narrow as possible.

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Meteor Scatter Modes

• The earliest experiments with MS communications
  used CW and AM phone.
• Today, the following modes are used
• HSCW
• SSB
• FSK-441

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HSCW

• CW sent at high speeds (200 wpm or more)
• Used primarily for meteor scatter
• Is being phased out in favor of new digital modes
• Most QSOs are made via sked using defined
  protocols
• HSCW activity occurs primarily in the following
  band segments
• 50.250 50.300 MHz
• 144.100 144.150 MHz
• 222.000 222.200 MHz

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HSCW Protocols

• Messages sent in 30 sec intervals westernmost
  station transmits during first 30 seconds of each
  minute.
• CQs are sent in 60 second intervals.
• In North America a speed of 6000 lpm (1200 wpm)
  is the standard
• A complete HSCW QSO consists of exhange of call
  signs, signal reports and rogers by both stations
• Message sequence
• 1. both call signs (ex N0ABC N4UFP)
• 2. call signs plus signal report (ex N0ABC 26
  N4UFP 2626)
• 3. roger report (ex R27 R27)
• 4. final roger (RRR RRR)
• Both stations begin by sending both call signs.
• First station to copy both call signs sends calls
  plus signal report.
• When other station receives calls signal
  report, he sends roger his report
• When first station receives roger report, he
  sends his roger.
• Final exchange of 73 is optional

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SSB

• Used primarily on 6 m
• Can be used with random meteors, but generally
  works better during a meteor shower
• SSB activity occurs primarily in the following
  band segments
• 50.125 50.250 MHz
• 144.200 144.250 MHz

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SSB Protocols

• Messages sent in 15 sec intervals westernmost
  station transmits during first and third 15
  second periods of each minute.
• Exact sequencing is not followed break in
  operation is used
• A complete HSCW QSO consists of exhange of call
  signs, signal reports and or grid squares and
  rogers by both stations
• Signal reporting on SSB is generally the burst
  length
• S1 - ping with no information
• S2 - ping up to 5 seconds long
• S3 - ping 5 15 seconds long
• S4 - burst 16 60 seconds long
• S5 - burst over 60 seconds
• Four character grid squares are used for reports
  (ex EM94)

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FSK-441

• FSK441
• Uses triplets of 4 tones to transmit data
• 882, 1323, 1764, 2205 Hz
• Each character is sent as a 3 tone sequence
• 43 Character alphabet (letters, numbers . , / ?
  ltspgt)
• Single tone characters used for shorthand
  messages
• 882 Hz - R26 1764 Hz - RRR
• 1323 Hz R27 2205 Hz - 73
• Data rate 147 characters per second (3
  tones/char)
• Used for meteor scatter communications
• Most activity takes place near 50.270 MHz

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FSK-441 Protocols

• Messages sent in 30 sec intervals westernmost
  station transmits during first 30 seconds of each
  minute.
• A complete FSK441 QSO consists of exhange of call
  signs, signal reports and rogers by both stations
• Message sequence
• 1. both call signs (ex N0ABC N4UFP)
• 2. call signs plus signal report (ex N0ABC 26
  N4UFP 2626)
• 3. roger report (ex R27 R27)
• 4. final roger (RRR RRR)
• Both stations begin by sending both call signs.
• First station to copy both call signs sends calls
  plus signal report.
• When other station receives calls signal
  report, he sends roger his report
• When first station receives roger report, he
  sends his roger.
• Final exchange of 73 is optional
• Time to complete a QSO ranges from 2 minutes to
  over an hour.

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Getting on the AirStation Requirements
andOperating Notes
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VHF Station Requirements

• RF output at least 100 W
• Good VHF transceiver or transverter with MDS of
  -125 dBm (3 KHz BW)
• Mast-mounted pre-amp, gain gt 10 dB
• Horizontally polarized beam antenna, gain gt 10 dB

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Antennas for MS

• Antennas do not need to have high gain
• Lower-gain antennas illuminate more trails
• Higher-gain antennas illuminate weaker trails
• MS contacts on 6m can be made with a 2 element
  yagi or quad
• Higher gain antennas often result in quicker
  QSOs

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Operating Notes

• Time synchronization is important be sure to
  set your PCs clock to WWV before beginning a MS
  contact.
• MS contacts may be made at any time, but the best
  time is in the early morning hours (around 600
  AM)
• Links to MS QSO scheduling sites
• http//www.pingjockey.net/
• http//www.dxworld.com/hsms.html

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Useful Tools

• General Meteor Scatter Info
• http//www.qsl.net/w8wn/hscw/hscw.html
• Aurora Info
• http//aurora.n1bug.net/
• Tropospheric propagation prediction tools
• VHF Propagation from APRS data
• William Hepburns Tropo Forecasts