Meteor-Scatter

by Waldis Jirgens VK1WJ Date: 14th October 2012

Meteor scatter is a propagation mode that exploits the trails of meteors during atmospheric entry to establish brief communications paths between radio stations up to 2,500 Km distance.

Each day lots of space rocks called "meteors" enter the earth's atmosphere. When these meteors begin to burn up, they create a trail of ionised particles in the E layer of the atmosphere that persist between a fraction of a second and up to several seconds. These ionisation trails can be very dense and thus useful to reflect radio waves. Thus we have very short band openings caused by meteors burning up in the atmosphere.

The frequencies that are used for MS contacts range from 28 MHz to 440 MHz . On 10m pings are 25 times longer than on 2m and the signal strength is 120 times higher than on 2m. On 70cm pings are 10 times shorter than on 2m and up to 30 times weaker. In praxi 6m, 2m and sometimes 70cm are used for MS. Most MS communication however is done on 2m.

To exploit the very short band openings you have to pack a lot of information into a very short time span. In praxi this is done by using the FSK441 digital mode.
This mode is available in the WSJT digital modes program:

WSJT by K1JT is freeware and provides besides FSK441 also JT2, JT4, JT64, JT65, JT6M and (in versions 7 only) WSPR.
Current versions:   wsjt_9.0r2136_i386.deb for Linux and  WSJT9_r2574.EXE for Windows. URL to download: physics.princeton.edu/pulsar/K1JT/

The package for LINUX is a DEBIAN package, I have it installed under Mageia (an rpm based system) as follows:
  1. Convert the package to a tgz one by executing:
    ar -x wsjt_9.0r2136_i386.deb rendering two tar balls control.tar.gz and data.tar.gz

  2. Unzip and untar these. The control tarball contains only a small file called control.
  3. The important part of control looks as follows: Depends: python-tk,python-imaging-tk,python-numpy,libsamplerate0 This shows the dependencies. python-tk is irrelevant for Mageia. Install the others (Mageia rpms)!
    Pitfall:
    WSJT does NOT work with python-numpy-1.6. If you happen to have that one, you have to install version 1.5.1 as follows:
    [waldis@waldis_main linsoft]$ rpm -q python-numpy
    python-numpy-1.6.1-2.mga1
    [waldis@waldis_main linsoft]$ su
    Password:
    [root@waldis_main linsoft]# rpm -e python-numpy --nodeps
    [root@waldis_main linsoft]# rpm -i python-numpy-1.5.1-5.mga1.i586.rpm
    [root@waldis_main linsoft]#
  4. The data portion gives you a subdirectory WSJT9 containing the whole WSJT package.
  5. Move this directory to a suitable location and then create a shell script to CD to that directory and execute wsjt there, mine looks like:

    #!/bin/bash
    cd /home/waldis/AR/software/WSJT9
    ./wsjt
    exit 0
There are also older versions available from K1JT's site.

Having installed the program there are a few things to consider, before you go on air:

First of course starting up the program. The start-up screen (generating the GUI) looks like:
Terminal

Then setting the ubiquitous parameters (as callsign, time-zone etc.)

Sequences to use for FSK441 (Australian de-facto standard, internationally there are many variations):
1. Calling CQ:
CQ Owncall
2. Answering a CQ:
Callsign/report Owncall
3. Answering a report sent to you:
Callsign/Rreport Owncall
4. Answering such an R-prefixed report:
Callsign/RRR Owncall
5. Answering such an RRR:
Callsign/73 Owncall
*** Note that the QSO is officially finished and valid once the RRR has been received. The 73 is just a courtesy gesture to notify the QSO partner of this fact ***

This exchange format can be achieved with the following settings in "Options":
Options menu

What Report to Send?
A report consists of two numbers. 1st one: Duration of the ping, 2nd one: Signal strength.
First Number
 0 = less than 40 ms (does not happen in praxi)
 1 = 40 to < 100 ms
 2 = 100 to < 1000 ms
 3 = greater than 1000 ms
Second Number
 6 = 0 to 10 dB
 7 = 11 to 16 dB
 8 = 17 to 22 dB
 9 = greater than 22 dB

Pitfalls:
  1. Note that your TX frequency must be within 400 Hertz of your QSO partners. Some TRTX frequency displays can be out by several 100 Hertz on VHF/UHF! Many people lock their VFOs to GPS (see various Gippstech presentations).
  2. You must also decide which station "sends first" meaning in the first 30 seconds of each minute (if you use 30 second intervals which is standard). If you use 15 second intervals "sending first" means sending the 1st and 3rd 15 seconds of each minute.
  3. To get the timing right it is common practice to use the NTP protocol via the Internet to synchronise the PC clock.
    You can also listen to BPM, WWV or WWVH (Hawaii) on 5, 10 or 15 MHz, have the PC clock set to the next minute, and apply the setting as soon as you hear the full minute beep - if you don't have internet access.

FSK441 is done on Saturdays and Sundays between 5 and 8 AM. as a "gentlemens' agreement". There is however nothing to stop you to arrange skeds for whenever and wherever you want, just keep in mind that the early morning is the best time to encounter meteors. FSK441 is not for the impatient. A QSO can take more than 1 hour to complete!

Hardware Used:
This varies considerably. At the moment I use an FT857 with a VLA200 PA delivering 100W output and a 10 element yagi - NO masthead pre-amp. This is a bit more than the entry level. I have used 20W output plus a 10 element and also 50W output plus a 5 element yagi (working VK3, 4, 5, 7 and ZL3TY). The "Big Guns" use up to 4 stacked 10 element yagis, legal limit as output and masthead pre-amps.
Antennas: Click to play video
Rig: Click to play video

Saturday Schedule:
5:45 to 7:00 VK East trying to work ZL on 144.330.VKs TX SECOND, ZLs TX FIRST. Regular contacts are achieved with ZL3TY in Greymouth. I have heard only ONE ping from a different ZL! Exception: Rex VK7MO can regularly work into Christchurch.
7:00 to 8:00 on 144.230 VK7, VK3 and VK5 beaming towards the N and NE and TX FIRST, whereas VK1, 2 and 4 beaming towards VK7 - VK5 and TX SECOND.

Sunday Schedule:
6:00 to 8:00 on 144.230 VK7, VK1, VK2, VK3 and VK5 beaming towards the N and NE and TX FIRST, whereas VK4 beaming towards VK1, 2, 3, 5, 7 and TX SECOND.

This is how the screen looks after you just started out:
Main Screen

This is more than 1 hour later:
Main-1h later

FSK441 in action: Click to play video

An alternate method of notification that the QSO is finished - via the VK-logger website. You MUST NOT exchange any QSO data there until the RRR has been received:
Regulars

The MS regulars are all online - see top right corner:
Options menu

This is SpecJT, an option to see pings in real time and decode them before the automatic decode does that at the end of the interval. Here we see a 17 dB burn from VK3AMZ on the 22/9/12:
SpecJT

How pings sound:
     

A feature of the VK-Logger - VHF/UHF contacts:
Contacts

Another feature of the VK-Logger - Flight Radar - good to spot possible AE contacts. Note that FSK441 is not the best mode for AE. I had numerous SSB contacts with Jim VK3II that started out as FSK441. When I saw him and when it was my turn to TX I switched "Auto Off" and called him in SSB, completing the QSO in less than 30 seconds:
Flight Radar

Return to my Digital AR page
Return to my home page