Using Meteor Scatter Propagation on VHF

This is one of a series of “Notes” I published on Facebook. Since Facebook has discontinued the Notes feature, I am publishing that series here on my blog.

Note: I may add illustrations later, but want to get this out before the peak of the 2017 Perseids meteor shower.

You’re staring into the night sky when all of a sudden a streak of light appears. It’s caused by a meteor burning up as it enters the Earth’s atmosphere at high speed. It may be no bigger than a grain of sand but it makes quite a show. There may very well be a ham radio operator somewhere trying to bounce a signal off that meteor trail.

Since the 1950s, VHF ham radio operators have been using ionized meteor trails to reflect their signals beyond normal everyday range. While the tools and methods used have changed over the years, meteor scatter remains a popular method of communication. I mentioned this propagation mode only briefly in previous VHF weak signal operating primers, so let’s take a closer look at it.

What is meteor scatter good for? It’s not a ragchew mode. At 50 MHz the ionized trail may only be capable of reflecting the signal for a fraction of second, or it could be up to a couple of minutes in extreme cases. The higher you go in frequency, the fewer meteors capable of supporting propagation and the shorter the signal duration. At 144 MHz anything over 30 seconds is relatively uncommon but some may last a minute or so. There are still fewer meteors capable of supporting propagation at 222 MHz. Only the biggest and fastest provide very brief propagation at 432 MHz. Most of the time, several meteors will be needed to complete a “minimum QSO”. So just what use is meteor scatter? Using special techniques, it is possible to work stations over distances up to 1400 miles. Meteor scatter is a good way to get more states, grid squares, or just make some nice longer distance contacts on VHF. It can be fun and exciting!

Let’s define what we mean by “minimal QSO”. Long ago it was decided that a valid contact needed to demonstrate some basic level of capability to exchange information (communicate) over the air between two stations. The agreed upon standard was that for a QSO to be valid the following information had to be exchanged in both directions: call signs, signal report (or other piece of information such as a grid square) and acknowledgement that the report was received. This means that if I am trying to make a QSO with W1XYZ, I must hear his call sign and my own. I must hear a signal report and I must hear some confirmation (usually “roger” or RRR) that he got the signal report I sent him. W1XYZ must receive the same information from me.

In meteor scatter you don’t hear the other station all the time. Far from it! Signals come and go erratically in short bursts. In order to make maximum use of available meteors and prevent both stations inadvertently transmitting at the same time, a special operating procedure has evolved. Stations take turns transmitting. In North America the transmit and receive periods are usually 15 seconds each. This requires accurate clocks. During a scheduled QSO attempt, both stations initially start out sending call sings over and over during their assigned 15 second periods. When one station copies call signs, that station will start sending a signal report with call signs. Assuming the other eventually copies both call signs and a signal report he will send acknowledgement that he got his report (usually just R) and a report. When all of that is copied at the other station he sends RRR. The QSO is technically complete when this RRR is copied but since the station sending it has no way of knowing it has been heard, typical procedure is for the one who receives RRR to send 73. Reception of 73 lets the other know all is complete. If you end up sending RRR and never receive a 73, you won’t know if the QSO is complete unless you check with your QSO partner by some other means such as email or an internet chat site. If he got the RRR it is a valid QSO. The honor system is very much in play here. This sounds far more complicated than it actually is. You get used to the process after a few QSOs. The process for a non-scheduled contact (where one station was calling CQ) is similar. Theoretically, using 15 second transmit/receive periods, a QSO can be completed in just over a minute. On 50 MHz it sometimes works that way. On higher frequencies it usually takes longer and sometimes even after 20 or 30 minutes there haven’t been enough meteors to complete the QSO exchange.

In years past, using SSB or CW the procedure followed that form exactly. Once a QSO progressed beyond a need to hear call signs, they were omitted from the transmissions. Most of the time this worked OK. One could often tell from the voice or speed and “fist” that the correct station was being copied. With digital modes, call signs or an abbreviated form of them is usually sent at each stage of the QSO along with whatever info is required at that point. This helps to make sure you are copying the intended station and not someone else.

You may be thinking this sounds like a lot of work just to exchange enough information to log a contact. Maybe you wonder what is the point. To the person who just likes to talk this method of communication makes no sense. But for those who enjoy a challenge, are chasing states or grid squares on VHF or just looking to do something few hams even realize is possible, meteor scatter can be very interesting and rewarding! There is a thrill in that signal suddenly appearing out of nowhere. Completion of any given QSO attempt is by no means guaranteed. Some attempts succeed, some fail due to insufficient number of meteors capable of supporting propagation or other factors. Every completed QSO feels like an accomplishment — because it is!

Meteor scatter has both predictable and unpredictable qualities. Sporadic meteors (those not associated with any particular meteor shower) are best in the morning hours around dawn and shortly after. Relative velocity is also usually higher in the morning unless the meteor is on a path almost parallel to that of the Earth. There are enough of these sporadic meteors to permit QSOs on 50 MHz every day of the year. Winter can be tough going on 144 MHz but most of the year every morning works to some extent. Several major meteor showers each year provide greatly enhanced opportunities on those bands along with the possibility of 222 and 432 MHz. Most notable are the Perseids in August, Leonids in November, Geminds in December and (though of very short duration) Quadrantids in January. There are several other meteor showers that don’t compare to those but nevertheless elevate meteor counts well above the sporadic rate. Regardless of season, time of day, or the presence of a meteor shower, exact meteor rates, burst duration and timing can never be known. You may get 30 bursts in a 10 minute period and not a single burst in the following 10 minutes. You never know. This unpredictability adds to the fun and challenge. During meteor showers there are optimal times of day for specific directions. This has to do with geometry of the intended communication path and the meteor trail angles which change as the Earth rotates. This was much better known and utilized years ago than it is now. Most operators today just take their chances at whatever time they feel like operating.

What kind of station do you need to work meteor scatter? On 50 MHz, 10 watts to a three element yagi will get you started. 100 watts will do quite well. I have made meteor scatter contacts to more than 1000 miles on 144 MHz with 25 watts and a six foot long yagi, but it is not easy! 100 watts to a 12 foot yagi is a good minimum setup to aim for on two meters. If you are looking to break into the extreme distances, 1300 to 1400 miles, you will need more power and a larger antenna. At 222 MHz, 150 watts to a good long yagi (say something on the order of a 20 foot boom more more) is advisable as a minimum, and at 432 MHz you’ll probably need several hundred watts and a monster yagi or array of several yagis.

WSJT-X software running MSK144 mode is the default for meteor scatter work at the present time, but modes tend to change in the modern era. MSK144 transmits data at such a high rate of speed that call signs plus grid square or call signs plus signal report can be received in a burst as short at 72 milliseconds! This allows QSOs to be completed using much smaller meteors (hence a greater number of them) than SSB or CW did in the past. Almost always this is just what you want but on rare occasions there can be a down side to new methods. You can’t shorten the 15 second transmit/receive periods “on the fly”. It won’t work. So if you get a long meteor burst, say lasting a full 15 seconds, you may only get one piece of QSO information through on it; possibly two if it overlaps the station transmit periods sufficiently.

I am going to digress for a moment to add a couple of historical notes. These may illustrate some of the rare magic that meteor scatter operators never forget.

On SSB (and CW to a lesser extent), an alert operator could “pounce” with a very short transmission if he was hearing the other station right at the end of a 15 second period. This sometimes allowed for a quick back and forth with the whole QSO being completed on one meteor trail. One was always on high alert, ready to pounce! Back in the 1980s I was running a SSB meteor sked with a station in Missouri, about 1250 miles away. We suddenly got a long burn and abandoned the 15 second sequencing to rapidly complete the exchange. I was immediately called by another Missouri station who had been listening in. I worked him and then a third, all on one meteor!

Making meteor scatter QSOs at 1400 miles is usually quite difficult, but it can be done. One time I was running a 144 MHz meteor scatter schedule with a station in Greenland, a distance of just over 1400 miles. This would have been a new country for me on two meters and a new personal distance record. At the time, very high speed CW meteor scatter was the normal method in Europe, while SSB was the standard in North America. European high speed CW was so fast it had to be recorded and then played back at slower speed for copy, even among the very best CW operators. One minute transmit and receive periods were used. The Greenland operator (visiting from Denmark) was set up for high speed CW. SSB was the standard in North America at the time, so I had no means to record and play back CW at lower speed. The Greenland operator agreed to transmit at 40 wpm which I could copy by ear. I was using a memory keyer to send at 100 wpm, slow by the European standard but was the best I could do. As it happened we got almost no short bursts at all and the QSO was not progressing. Suddenly he popped out of the noise and I heard him for a full 45 seconds! That is very uncommon at this extreme meteor scatter distance, and was all the more unusual since I have a small hill in that direction blocking extreme low angle signals. There was nothing I could do. Because of the automation and method, we were stuck with the one minute transmission periods. Had we been doing SSB or even conventional speed CW using shorter periods, with operators doing all the decision making in real time, this would undoubtedly have been a complete QSO. We might have squeezed everything in using MSK144 with 15 second transmit/receive periods. Nothing more was heard during our schedule, so I did not get my new country or personal distance record. However this was an exceptional event and exciting even without a QSO in the log to show for it. In all my years working meteor scatter I have never heard another long burst like that at 1400 miles. I did work Greenland on EME (moonbounce) years later.

Getting back to the present, let me introduce a few more relevant points.

Antennas are generally pointed toward the station you want to work, but the optimum path can be skewed a few degrees to one side or the other. The WSJT-X software calculates suggested headings. It also helps keep you on track during the QSO process because it knows what you should send next based on what you have received. There are pros and cons to digital modes, but at least I don’t lose my voice for three days after the Perseids and Geminids meteor showers!

Meteor scatter can be used at any distance less than the 1400 mile theoretical limit, but under about 600 miles it becomes considerably more difficult with fewer and shorter bursts. This is even more apparent if you have a high antenna or one that has a narrow vertical lobe such as stacked yagis. Being able to elevate the antenna a few degrees above the horizon can help with the shorter distances. 700 to 1100 miles is the easiest range although this may vary somewhat for different antenna patterns, height, etc.

Various online chat pages and scheduling tools are an aid in finding stations to run schedules with. ON4KST chat and Ping Jockey are the most widely used. If you just want to make random contacts (calling CQ or responding to CQs), there are MSK144 calling frequencies for that. In North America, these are 50.260 on six meters, 144.150 on two meters. There is activity on 50.260 almost every morning. It seems random activity on 144.150 has decreased significantly in recent years but some CQs can occasionally be found. QSOs can be completed on the calling frequencies when things aren’t too busy. During periods of high activity there is a procedure for calling CQ on the calling frequency, announcing where you are listening for calls. When you hear someone calling on your listening frequency, you move your transmitter there to complete the QSO. Helpful advice on operating procedures can be found in the WSJT-X User Guide and other references, but if possible you may want to find a local elmer who knows the ropes to help you get going. MSK144 works well with strong stable signals too, so you can test with a local station.

If you have six or two meter capability and are looking for a new challenge or just a change of pace, give meteor scatter a try! It’s not your average ham radio communication but it can be quite rewarding. If you don’t already have it, download the WSJT-X software, version 1.7.0 or later. You will need a computer with a sound card and some type of radio interface. Then listen on 50.260 in the mornings to get a feel for what meteor scatter is all about. Here in the northeast U.S. at least, most activity tends to be between the hours of 6 and 9 AM outside of major meteor showers, and possibly any time of day or night during showers.

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