Meteor Scatter: Reinforcement from outer space

It is worthwhile not only for radio amateurs, but also times with the whole family to observe such shooting star showers optically. To do this, you should look for a place in the region that is as dark as possible. Unfortunately, the light pollution in densely populated areas is enormous, so it is difficult to find a place that is sufficiently dark. Helpful are maps on the Internet, which show the degree of light pollution, e.g. https://www.lightpollutionmap.info oder https://darksitefinder.com/. Or ask the local astronomy group, where they go for observation... No matter if you look at the shooting stars, listen to them or use them actively as reflectors - we wish you a lot of fun and "Clear Skies".

As a radio amateur you always try to bridge as large distances as possible by radio. To do this, we can use almost any means: good antennas, sufficient power, some knowledge of physics - and special phenomena in the ionosphere. This is exactly what happens in the so-called meteor scatter. The ionosphere is the upper layers of the atmosphere, the thin skin of air that surrounds the Earth. Usually, solar radiation creates an electrical charge (ionization) at certain altitudes, which in turn causes radio waves to reflect off these ionized layers. Thus, under 'good conditions' (= suitable ionization), we can reach other radio amateurs at great distances with manageable effort.

Now, there are other mechanisms besides solar radiation that can generate an electric charge of the ionosphere. One such effect is meteors entering the Earth's atmosphere. When they do, the small pieces of rock heat up so much that they burn up - we can see a shooting star. As they burn up, heat is generated, and this energy also creates an electrical charge (ionization) in the thin air of the upper atmosphere. And this is strong enough that radio waves are reflected! So exactly what we want. The difference to normal reflections in the ionosphere: These reflecting meteor trails often exist only a few seconds, whereas the usual E- or F-layer reflections can exist for hours or days.

Meteors occur every day, but there are annually recurring dates when they can be seen (and heard by us) in clusters. The origin are comets, which orbit around the sun and which have lost many dust particles and smallest stone chunks in the course of the millennia. These remain on the orbit of the comet. The earth crosses these orbits every year at the same time, the comet dust hits the atmosphere and burns up - a meteor shower is created.

Some of the strongest meteor showers of the year are:

The Quadrantids from late December to mid-January.
The Perseids with the maximum in the middle of August.
The Geminids in the first half of December.

The name comes from the constellation from whose direction the shooting stars seem to come. The amount of appearing shooting stars is very different and also varies every year, but in the best times and in dark places on earth you can see 40 to 50 shooting stars per hour. To be heard and usable by radio amateurs are usually many more meteors, because even those that leave no visible trail are often large enough to create an ionization trail that can reflect our radio signal. The band of debris and dust that such a comet leaves behind is quite wide. That is why meteor streams often last several days. Some have a pronounced maximum, others are more evenly distributed over time. The best time for shooting stars and for us radio amateurs is the second half of the night, roughly from midnight until about 6 o'clock in the morning. This has to do with the movement of the earth around the sun - at night the dark side of the earth moves into the dust stream, thus the probability to be hit by these small particles increases. But also at any other time there are quite usable meteors, just much rarer. These are then fast moving meteors that are fast enough to 'catch up' with the Earth, and those that happen to lie in the path of our planet.

How it works:

Meteor Scatter is done only on the VHF and UHF bands (6m, 4m, 2m and 70cm). On shortwave, the reflections are also visible, but are masked by other effects. The most commonly used frequency band is 2m. The challenge in radio operation over meteor scatter is that the reflecting ionization tracks exist only for a few seconds up to (in rare exceptions) 1 minute. So you have to fit all data for a QSO (a radio connection) into this randomly occurring reflection as fast as possible. In former times this was done by telegraphy (Morse code). With a tape or later by computer a Morse text was sent out very strongly accelerated (400 to 600 characters/minute!). On the receiving side, a tape recorder was used which recorded at high speed. After a fixed period, the tape was played back at a much slower speed, the received Morse code was decoded, the answer was quickly formulated and then sent out at high speed. This procedure cost a lot of time and required strict adherence to radio discipline (who transmits, who hears when). In addition, a fairly high transmitting power and a good antenna were absolutely necessary for this procedure. It was hardly necessary to start with less than 300 to 500 watts, and the antenna had to be a large Yagi for VHF.

Modern times digital

Thanks to modern digital technology, the requirements for operation via Meteor Scatter have become much smaller. The reason lies in the software development and in the nowadays cheaply available, very powerful PC hardware to run this software. The secret is the modulation technique. For example, very robust techniques were developed long ago that require only an extremely small signal-to-noise ratio to be decoded reliably. The origin is space travel with the need to safely receive extremely distant space probes, which can only transmit with low transmission power, on earth. This only achieves a low data transmission speed, but it is better than not being able to receive scientific data at all. The extreme example are the Voyager probes, which are far outside the orbit of Pluto (distance 22.9 billion km) and transmit with a transmission power of little more than 20 watts. Here, NASA's Deep Space Network receives data at a few 100 bit/s (bit, not kilo- or megabit!). This is made possible by extremely sophisticated modulation technology and very large antennas, at least on Earth.

So it needs more than just a good antenna ... but even without this it is not possible. For scatter operation on 2m band the 9 Element 2m Yagi from YU1CF (Antenna Amplifiers) is suitable. For the 6m band the 5 element LFA3-HG Yagi from InnovAntennas can be used. To make the best use of the band openings, which occur for a short time and sometimes only for a few seconds, a good preamplifier is helpful in addition to the antenna. Here the SP200 as well as the SP600 offer amplification on the 2m or 6m band for the corresponding frequency ranges of 144-146 MHz or 50-52 MHz.