Meteor scatter
| Meteor scatter | |
|---|---|
| Also called | MS |
| Reflector | Ionized trails left by meteors about 80–120 km (50–75 miles) up |
| Range | Up to roughly 1,400 miles |
| Signals | Bursts lasting a fraction of a second to a minute or more |
| Operating | |
| Bands | Mainly 6 m and 2 m |
| Main digital mode | MSK144, in WSJT-X |
| Best time of day | Around dawn, local time |
| Best dates | Major showers such as the Quadrantids, Perseids and Geminids |
Meteor scatter (MS) is a way of making VHF contacts by bouncing signals off the trails of ionized gas that meteors leave as they burn up in the upper atmosphere. Each trail lasts only a moment, so signals arrive as short bursts, or pings, rather than a steady signal, but they can connect stations up to about 1,400 miles apart on the 6-meter and 2-meter bands at any time of year. With modern digital software, a station with 100 watts and a single Yagi can take part, not only during the big showers.
How it works
Millions of meteors, most no bigger than a grain of sand, enter Earth's atmosphere every day at between about 7 and 45 miles per second. As each one burns up, at heights of roughly 50 to 75 miles, it leaves a narrow trail of ionized gas that can be miles long. A radio signal striking the trail at the right angle is scattered back toward the ground far away. Most trails spread out and fade within a second or so; a large meteor may leave one that lasts a minute or more.
Because the trails sit at about the same height as the E layer of the ionosphere, the geometry resembles that of sporadic E: the longest paths are about 1,400 miles, limited by the curvature of Earth, and very short paths are difficult. Lower frequencies reflect more strongly and for longer, so 6 meters produces more frequent and longer bursts than 2 meters. 10 meters works by meteor scatter too, and well-equipped stations reach 222 and 432 MHz during major showers.
When to operate
Meteor rates follow a daily cycle. They are highest around dawn, local time, when your side of Earth faces forward in its orbit and sweeps up meteors like a car windshield in the rain, and lowest around early evening.
On top of this steady background of random meteors come the annual meteor showers, when Earth passes through debris left along the orbit of a comet or asteroid. The most useful for radio include:
| Shower | Peak (approximate) | Notes |
|---|---|---|
| Quadrantids | January 3–4 | Strong but brief; the peak lasts only a few hours |
| Arietids | Early June | A daytime shower, invisible to the eye but strong on radio |
| Perseids | August 12–13 | Reliable, with good activity for days around the peak |
| Geminids | December 13–14 | Often the strongest shower of the year |
Peak times shift a little from year to year, so check a current meteor shower calendar.
Operating
Meteor scatter contacts use timed, alternating transmit and receive periods, so each station knows when to listen. During its turn, each station sends the same short message over and over, waiting for a trail to carry it. The exchange follows a fixed sequence of call signs, then a report or grid square, then confirmations, and the contact counts only when both stations have received everything. That can take a few minutes on 6 meters and much longer on 2 meters.
Most meteor scatter today uses MSK144, a mode in the free WSJT-X software, the same program used for FT8. MSK144 packs a complete message into a burst of 72 milliseconds and repeats it continuously, so even a brief ping can deliver the whole message, and the software decodes pings too weak to hear. It replaced an older mode, FSK441. Accurate computer time is essential.
Before digital modes, operators sent high-speed Morse code, recorded and played back far faster than anyone could send by hand, and some still work SSB in short overs during the big showers, when bursts of voice can be loud and clear.
Contacts are either scheduled, arranged in advance on internet chat pages with an agreed frequency and time, or random, made by calling CQ on a recognized meteor scatter frequency. WSJT-X lists the usual frequencies; check the current band plan as well. On 6 meters, 100 watts and a small horizontal Yagi are enough to start; on 2 meters, more power and a longer Yagi pay off.