It's called meteor-scatter, or just MS, when communication is held via the traces of meteors penetrating earths atmosphere. The meteors are everything from dust-particles to larger stones, but could also be as large as asteroids!
As most people know it's not likely that the earth-population would survive a direct hit of an asteroid, but calculated over a year it's believed that earth atmosphere is hit by thousands of tons of smaller meteors. Whenever a particle hits the atmosphere there will be an ionisation in the atmosphere and this area can reflect radio-signals.
This phenomena is so reliable, it's sometimes called "poor mans satellite". It's used both commercially as by the military. There are systems in the world with a single beacon-transmitter with a couple of kilowatts output power. When terminals beyond the horizon hear this signal there is a useful channel. The terminals then transmit on another frequency, hereby sending their information.
This channel is useful for a short time, everything between tenths of a second up to nearly a minute depending on the velocity and size of the meteor. Since the usable time is short and impossible to predict only burst-communication is used. It can be short data-packages or brief talk-messages.
Voice communication via meteor-scatter
At some occasions the earth travels through large trails of dust originated from old comets, we are then talking about a "meteor-shower". A shower can sometimes be very intensive and we then call it a storm.
During a storm there are good possibilities for the communication-channel to be "open" for minutes and really usable for voice communication!
It must be pointed out that a storm is not necessary for voice-communication via meteors, one only have to repeat the transmitted message several times and have a large portion of patience - and luck.
One famous meteor-shower with a sharp peak and has giving pretty good "storms" recent years is the "Leonids".
Here you can listen on a QSO between me and G4FUF the 18th of November 2000.
If you haven't tried meteor-scatter or VHF-communication this is what happen;
The recorded length is about 24 seconds but the burst was more than one minute long! I have chosen this recording since it shows how clear one must speak. I think G4FUF really speaks clearly and keep a good "calm" speaking speed. (To keep calm during an occasion like this is not really easy, remember they will only occur a couple of times during your lifetime!)
- G4FUF call DL6UAL and gives him his signal-report. (DL6UAL is not heard.)
- The increasing volume the first ten seconds indicates that I turn my antenna towards Great-Britain.
- After the QSO between G4FUF and DL6UAL, G4FUF calls QRZ, ie the same as CQ.
- Unfortunately I did not record my own voice, but my call is about three seconds long.
- G4FUF respond with my call and report. His transmission is about four seconds long.
- I send my report and acknowledge during about three seconds and after G4FUF's acknowledge the QSO is finished!
- Afterwards G4FUF calls QRZ again.
Morse communication via meteor-scatter
In the "early days" morse code was transmitted with the help of tape-recorders where the code speed was increased by playing the tape on a higher speed than recorded. This can still be done, but nowadays computers are most often used.
Digital communication via meteor-scatter
Some will say that morse-code is as digital as "digital" communication. Surely true, but I wanted to have these separated.
A way of digital communication is the WSJT, Weak Signal communication by K1JT. Four different tones are transmitted and all letters are built up by three tones each transmitted in a sequence. The short message is transmitted in a sequence of 30 seconds and then this changes to the other station. It's important to synchronize your computer to a reliable time-standard. I usually use GPS, but time-systems as the DCF77 works well too - and much cheaper!
It has been showed that this is very effective and has truly "blown life" into meteor-scatter! Even during normal conditions it's very likely to be able to work stations far away in a way very similar to commercial systems.
Here you can listen on a burst from a QSO between me and Serge, UT5JCW, the 15th of August 2002.
To decode the file properly you must download WSJT.
If you don't get it right the first time you try to decode this message, then try with some different settings for W and S. For me it was ok when I used W=40 and S=1.
I received Serge with my antenna about 30 degrees "wrong", ie I could not put my beam exactly into his direction since I had very much noise there. It's not necessary to have the beam in exactly right direction since we'll never know how the signals are scattered from the meteor-track, but I think that one should try - at least if you're working QRP. (This is really a science of it's own and many pages are written about the scattering and the scatter is depending on the velocity and direction of the meteor.)
The distance between Serge and me is about 1870km and I used 25W and a 15element yagi. This really shows how powerful WSJT is, but also that it's not always that easy as some hams think!
17.6 seconds into the file the decoding is perfect; 26 SM7OVK UT5JCW 26.
The QSO took about 40 minutes to complete and I'm sure that we were both quite exited, since we first had decided to test for 30 minutes, but we carried on... Thanks Serge!
Future of amateur-radio meteor-scatter?
Is it possible for radio-amateurs to get a beacon, similar to the system described in the beginning of this page?
This could be a possibility to improve the effectiveness of the WSJT system. We do after all transmit continuously for 30seconds and there might not be any meteor during this period. If the transmitting-station also listen on a FM-transmitter in the neighbourhood of the receiver-station this could trigger the transmitter and we then only transmit when there is a meteor.
The receiver, receiving the FM-signal, should be a SSB/CW-receiver as a PCR1000 and when there is a meteor there will be a "ping" from the center-carrier. This ping will be decoded by a fast PLL, could be made with a NE567 or similar.
The PLL then triggers a gate opening the sound to the transmitter. (The transmitter is already set into transmit-mode by the WSJT-software.) The gate could be a CMOS-circuit as 4066.
I have not yet tested this, but if anybody is interested I'm willing to give it a try, "who dare wins"!