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