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AN INTRODUCTION
TO VHF METEOR
SCATTER
Dr. Kevin Johnston VK4UH
Brisbane VHF Group
Redcliffe and Districts radio Club
Presented by
Matt Bowman VK1MT
With contributions from
VHF-2m DX Modes of Propagation
Tropospehric Ducting Sporadic E (Es)
Satellite EME (Moonbounce)
Auroral Field Aligned
Anomlies
Tropo-scatter Trans Equatorial (TEP)
Aircraft Enhancement Meteor Scatter
18,949km
1,300km
500km
2,000km
Meteor
or
Meteorite
Meteor =
“Shooting Star” “Falling Star”
“Wishing Star”
Meteorite
“Extra terrestrial
matter that
reached the
surface of the
earth without
burning up”
Meteor scatter propagation
Reflection from the ionised trail from a meteor
Approx 100 Km above the earth – within the E-layer
Distance limited to around 2250 km due to height of E Layer
Meteor scatter propagation
Ping or Burn What’s the Difference
“PING” supports propagation of signals for fraction of a second
(0.1 – 0.5 seconds on 2m)
“BURN” supports propagation for 20 - 30 seconds or more
Meteors When do they come?
Random Meteors
Meteor Showers
Meteors When do they come?
Random meteors - 24/7All day – Every Day of the year
Peak just before dawn
Optimum mass/size 0.1g – 1g “grains of sand – pea sized rocks”
Optimum velocity” 10 – 100 km/s
Meteor Showers Leonids 1833 Volmey
Meteor
Showers
Large number of Large
meteors
Predictable
Named after the
constellation from where
they appear to originate
Earth passing through the
tail of a comet
11 major showers per year
Tens to hundreds of
meteors per hour
Support up to 70 cms
Meteor Showers
Name Date of Shower peak
Lyrids 22rd April
Eta Aquarids 5/6th May
Southern Delta Aquarids 28/29th July
Orionids 21st October
Leonids 17/18 November
Geminids 13/14th December
Meteor Scatter
How much material enters the
earth’s atmosphere?
Meteor Scatter
How much material enters the
earth’s atmosphere?
100,000 tonnes per
year
“OK so you get a signal for a
fraction of a second from 2000 km
away on 2 m”
“Well Whoopty Doo!”
How are you going to get a QSO
out of that?
High Speed CW
High Speed CW - 1960
High Power, sensitive receivers, big beams
Pre-arranged skeds by phone or snail-mail
Electronic keyers played at high speed (120wpm)
Received on multi-speed reel-to reel tape recorders
Timing of transmission 5-10 mins periods
telephone speaking clock
Abbreviated reporting system
High Speed CW
1960s to 1970s
Pre home computers
Pre Internet
Pre E-mail
M/S realm of the super-geek
K1JT
Prof. Joe
Taylor
Inventor of
WSJT
WSJT
Weak Signal – Joe
Taylor
2001
WSJTWeak Signal – Joe Taylor
FSK441 Meteor Scatter JT65 (a,b,c)
EME
Troposcatter
HF-QRP
I-SCAT Microwave AE
WSJT - FSK441Frequency Shift Keying 4 tones (882, 1323, 1764, 2205 Hz) 41
Baud
43 Character alphabet
3 tone intervals per character
3/441 seconds per character 2.3 ms
WSJT - FSK441MASSIVE REPETITION
Short message (max 23 characters)
Transmit 30 seconds Receive 30 seconds
50% duty
FIRST period 0-30 SECOND period 30-60
No FEC
2018
FSK441
MSK144 MSKMSWSJTx MSHV
Forward Error Correcting (FEC)
15 second periods
100% decodes <100ms pings
2019
v2
V2 – not compatible with
previous versions.
Deeper dive into MSK144But not too deep
The MSK144 Protocol for Meteor-Scatter Communication
http://www.arrl.org/files/file/QEX_Next_Issue/SeptOct2017/FrankeT
aylor.pdf
WSJT-X User Guide
http://physics.princeton.edu/pulsar/k1jt/wsjtx-doc/wsjtx-main-
1.7.0.html#_msk144
A full frame can be decoded with as little as 72ms and 0dB SNR
Shorthand (Sh.) Mode can be selected, which limits the reporting
choices but will further reduce time required for a frame decode
down to 20ms. This helps tremendously during poor conditions
outside of official documented showers.
MSK144 is a highly efficient protocol for conducting minimal QSOs
via meteor scatter. The protocol’s effective character transmission
rate, occupied bandwidth, and sensitivity are close to optimum for
the stated purpose, while remaining consistent with the capabilities
of standard amateur SSB transceivers.
What
Makes a
QSO?
What
Makes a
QSO?Exchange of callsigns
Exchange of Signal reports
Confirmation of receipt of information
Typical Meteor Scatter
QSO
CQ VK1MT QF44
VK1MT VK4UH +02
VK4UH VK1MT R+06
VK1MT VK4UH RRR or
VK1MT VK4UH RR73
VK4UH VK1MT 73
Signal
Reporting on
M/S
2 digitsFirst Digit (duration) Second digit (amplitude)
0 < 40 ms 6 0-10 dB
1 40-80 ms 7 11-16 dB
2 100-980 ms 8 17-22 dB
3 >1000 ms 9 >22 db
26 report = 59
VKLOGGERUsed for arranging QSO’s and Confirming them – Still used for 2, 70 and
23cm
End of life: VK Logger will cease operation
on 24-April due to being obsolete.
144/432 MHz IARU R 3
http://www.on4kst.info/chat/index.php
PSK REPORTER
So How Far can You
work
On Meteor Scatter?
You can work out to ~2000km
BUT
You need someone to respond to your calls…..
Reliable MS communications can achieved as close as 700km
out to 2000km
Antennas and Path GeometriesLets play pool blindfolded
Big Gain Arrays are not an advantage. They will yield less MS contacts
in the 700 – 1500km zone. But will shine out to 1500 - 2500km.
It is all about putting enough power in the “probable path” to gain a
random reflection. Remember – you don’t know where these meteors
are coming from.
Depending upon the distance – normally 1000-1300km you want to
cover ~15 degrees either side of the direct path bearing.
A yagi with a beamwidth of ~30 degrees is optimum.
Elevation on shorter paths (~10 degrees) may
yield better results – if anything it will reduce local noise.
Take Off Angles for x distance
Know your antenna
- Lobes
- Take off angle
- Probable Rx Stations
- Is it MS?
So what do I need?
To start• A transceiver or transverter/radio combination capable of TXing at the
desired frequency. USB with ~3khz passband
• Antenna – minimum 5 ele yagi @ 144Mhz
Dipole/vertical @ 50Mhz
Dipole/vertical @ 28Mhz
• Power – minimum 30 – 50 watt. 30 watts will work during a big shower.
• Frequency accuracy and stability – better than usual.
Must be within 100 -150 hz of center frequency. Rigs do drift and age.
• Audio Interface and key line between software/computer and rig
• Accurate computer time – please check this. Be a good neighbour.
• A path in the desired direction of communication
• Patience – and lots of it for 2m MS
More advanced
setups• Antenna 9 – 13 elements ideal for contacts made from VK1
• Mast head RX amp
• Balance the RX and TX gains of your system. Including audio stages.
• GPS frequency locking
• Heavy duty transmit/receive relays (keying every 15 seconds)
• Sequencing of amplifiers, RX amps and other devices. Hot switching
relays is not a good idea.
• Adequate cooling for your equipment – up to 2hours of 15 second
switching before 0800 local.
• High power license application - reflection of signals from a celestial
body
Which Program
should I use??
MSHV WSJT-X
VK Meteor Scatter
Operating Schedule
2 main activity periods within VK
Saturday & Sunday morning from 07:00
(Sydney/Melbourne time)
Duration ONE-TWO HOUR
Frequency 144.230 MHz (144.330 MHz) 50.230 MHz
Used for
coordinated QSOs
in differing modes
or when timeslots
conflict.
SaturdayVK1/3/5/7 First period Beaming North
VK1/2/4 Second Period Beaming South
Sunday
VK 1/2/3/5/7 First Period Beaming North
VK4 Second period Beaming South
Meteor Scatter Operating
Schedule
Nahh It still cant work!
If I’m transmitting in Canberra and the
other Guy is in Brisbane
How come my signal isn’t mixed up with
all the other VK1 and VK3 stations?
I don’t want to double with the other
station TXing….. “I’ll wait my turn”
GEOSPECIFICITYAnd other small factors
Other factors include –
-Small variations in stations original
frequency
-Small variations in TX stations
location
-Doppler
-Randomness of scatter
Why are there
only meteors at dawn?
Bugs on the Windscreen
OTHER BANDSOn a given meteor-scatter path the duration of a ping is
proportional to the inverse square of operating frequency.
432 MHz (λ1/3 x 144 MHz)
Ping duration αλ² (1/9th of 144 MHz)
Signal strength αλ³ (1/27 of 144 MHz -15dB)
432 MHz
144 MHz
OTHER BANDS
50 MHz (λ=3 x 144 MHz)
Ping duration αλ² (9 x 144 MHz)
Signal strength α λ³ (λ27x 144 MHz
+15dB)
What’s New & Where Next?
New Modes ISCAT PSK2K MSK144 MSKMS
New Platforms MSRX WSJT-X MSHV
Mixed Propagation MS/ Tropo-ducting
MS/Es
MS/TEP
Etiquette• Check your system clock – time.is
• Everyone (Locally) to transmit in the same period
• Everyone (Locally) to receive at the same time
• Losing 3 seconds of RX time due to a local transmitter equates to
20% of the RX window gone. Of which time a meteor could have
come through.
• If you want to contact a station outside of the guidelines or mode
being used – QSY to 144.330 Mhz
• Ask on the Logger if you cannot tell what mode and TX/RX period is
being used.
• Generally stop at 0800 local. Very high signal levels within CBR
region will interfere both ways. Give the AE guys a go !
In Conclusion
Meteor Scatter using digital signals can achieve terrific DX
capability even with “Dead Propagation” on VHF
Regular QSO’s out to 2000 Km on 144 MHz are possible
Can be achieved with “normal” equipment, Antennas
and Power
Not really a “weak signal” mode at all
Spectacular results during a Meteor Shower
REFERENCESMeteor Scatter: How Much Antenna is Too Much?
https://physics.princeton.edu/pulsar/k1jt/AntBk22_Meteor_Scatter.pdf
Check you time
https://time.is/
PSK Reporter – Map View
https://www.pskreporter.info/pskmap.html
VKLOGGER – Spot and Chat
http://www.vklogger.com
MSHV Software
http://lz2hv.org/mshv
WSJT-X Software
http://physics.princeton.edu/pulsar/k1jt/wsjtx.html
Computer Time Syncing
https://www.maniaradio.it/en/bkttimesync.html
http://www.timesynctool.com/
POWERSDR
TX in Sh. Mode On.
POWERSDR, MSHV, WSJT-X and
VKLOGGER
Recommended