Wednesday, 9 August 2017

After Es, why not try meteor scatter with MSK144?

As the Es season starts to wind down, my mind turns to meteor scatter.

Anybody on the VHF bands who uses modes like JT65, PSK, JT9 or FT8 already has all of the basic system to use the MSK144 mode.
2 metre band MSK144 activity seen on PSK reporter on 9 August 2017
When I was first licensed meteor scatter seemed exotic and very difficult. So it was in the 1970s. Only the kings of the hobby tried meteor scatter. I also became aware that these stations tended to use pretty high power. The text books suggested that commercial meteor scatter stations used hundreds of kilowatts and huge high gain antennas. So it looked to be out of my league.

The real game changer for me was the arrival of personal computers running data modes via audio tones. We now have the WSJT-X suite which offers MSK144, the latest solution to the meteor scatter mode battery. MSK144 can also be found on MSHV, and both these suites can be downloaded via the links on the right of this page.

Now anyone who is used to the other WSJT-X modes can try meteor scatter. My long held view that lots of power and large antennas were needed has been proved wrong. Whilst a simple dipole or loop is not going to work, I found that using about 100 Watts and an HB9CV got me round Europe reasonably well. A few simple improvements - going to 200W and a three element yagi certainly helped a bit more - but not too much.

As it says in the WSJT-X User Guide:-

Meteor-scatter QSOs can be made any time on the VHF bands at distances up to about 2100 km (1300 miles). Completing a QSO takes longer in the evening than in the morning, longer at higher frequencies, and longer at distances close to the upper limit. But with patience, 100 Watts or more, and a single yagi it can usually be done.

Not just the modes have changed over the years, so have the radios. These days most rigs are rated at full power output for FM use. They often have several multi-speed fans. MSK144 has 15 second tx segments which makes appreciable difference compared with the longer tx periods we used to use. This gives two rx cooling segments in each minute, which the rigs seem much happier with. Frequency stability has improved out of all recognition, though I have added the optional TXCOs to my Yaesu and Kenwood rigs.

You can listen to the VHF bands and hear meteor "pings" - short bursts of scattered radio signals. They are not all weak. At their peak periods pings can be remarkably long, up to a  minute or two and come in sustained bursts. However, the more common individual ones are not so strong and last for fraction of a second. In this situation, adding more power or pre-amplification does very little for communication during the peak moment but might lengthen the time you can hear the signal as it fades away. What MSK144 does is to further improve the ability of data modes to cram the necessary information into a short enough time to be decoded at the other end. 

There is a lot of variation in meteor activity between times of the year and also between times of the day. The meteors strike the Earth every day, but there are periods when large groups arrive over a period of a day or so, and these are called "meteor showers". Despite what you hear, you can work meteor scatter at any time of the year, not just on the few days of the meteor showers. It gets harder between mid January and April, but it can still be done. And generally the period between 06:00 and 12:00 local time is probably best.

So all this means that anybody who can work other data modes can probably try meteor scatter. However, meteor scatter requires a different operating technique. Whilst there is a lot of complexity about the mechanics of communicating via meteors, and a lot to do with the meteors themselves, the purpose of this posting surrounds getting started. I am going assume that you know or can read up about the concept of meteors and scatter, so I am not going to cover that.

What I am saying is based on the IARU Region 1 meteor scatter rules - other parts of the world will have their own systems which may be different.

Here are my 11 key suggestions for converting to meteor scatter:-

1) Be patient


There is huge variability in the numbers of particles hitting the Earth. Breaking this down annually, the number is so low between mid-January and the end of March that I often work almost nobody. By comparison the peaks during the "showers" can provide contacts almost continuously

It takes patience to get the right conditions to pass the necessary information back and forth to constitute a QSO. MSK144 is a masterpiece of software design in which the data stream is carefully honed to convey the information quickly enough to get through a very short opportunity while the ion trail caused by the meteor is in the right place. MSK144 is very good at it, but you still need the meteors to be in the right place, so often you have to wait.

During a shower burst you can have a quick QSO. At more normal times you might send CQ for ten minutes and hear nothing. Then you hear a reply during a short ping on the 10th minute. You send your report for ten more minutes and hear nothing until the end of another (say) seven minutes when you get your report back.

So you have to be ready to just keep sending your message and waiting to receive the other one. It can be a bit frustrating and when you are neurotic (like some we could mention) you begin to think that it is all your fault; perhaps your antenna has collapsed, or you have drifted off frequency, or gone into a trance.

It stands to reason that QSOs tend to be longer at times when there are fewer meteor pings. So during showers it is much easier to get replies. The daily cycle runs so that meteor strikes are at their peak around 06:00 local times and least around 18:00. But it is still possible to work stations at all times if you have the time to devote to it.


2) Stick to the correct segment.
By convention, in Region 1 those beaming East or South transmit "second". This means that they listen for the first 15 period between 0 and 15 seconds), transmit in the second (15-30), then of course listen in the next (30-45) and transmit in the next (45-60). This is indicated in that they listen in the red quadrants and transmit in the green below:-
The IARU Region 1 meteor scatter minute
Obviously the station they are working to the East of them is beaming West and therefore doing the opposite. Doing so avoids interference to nearby stations. This is why dipoles, verticals and omni-directional antennas of all sorts are not very popular on meteor scatter.

The minute is divided into four quadrants of 15 seconds each. From the start of the minute these are 00 to 15 seconds (first), 15 to 30 (second), 30 to 45 (first again) and 45 to 60 seconds (second again). Then the next minute starts. So, you alternate between transmitting and receiving segments. If I was beaming East or South I would listen 00 to 15 and again 30 to 45 seconds, and transmit 15 to 30 and 45 to 60.
Note the "Tx even/1st" box ticked - I must have been beaming West
The reason for this arrangement is simple. It means that any stations in your area who are beaming in the same direction as you will all be listening at the same time. Otherwise, if stations transmitted during random segments you could find a local station transmitting while you were trying to listen.As the signal fills your receiver passband that would bring everything to a halt.

This system is not perfect. For example, at what point does "East and South" become "West and North"? Things get a bit blurred round the edges but in general it all works well. It would be impossible to use meteor scatter if everyone just transmitted at will. We will see the consequences of all this later.

It seems simple to transmit in the right segment relating to your beam direction, but it is very easy to get it wrong as I know only too well.

3) Don't waste time calling on the wrong segment
Not only will you annoy everybody around you if you call on the wrong segment, it does not really work either.

This is very easy to do by mistake. Whilst you may have ticked the box correctly, WSJT-X invites you to be quick and double click on the other station's callsign to enter their details and reply. Doing this will also set your tx period to the opposite of the station calling, which could well be the "wrong" one for you. I have been guilty of this by mistake.

Just clicking the callsigns and replying indiscriminately will get you into hot water with other local operators. Random calling works on Es with FT8 and JT65, but not on meteor scatter - regardless of mode.

4) Keep your PC clock accurate
Obviously this whole system falls down if stations fail to keep their station clock accurate. There are two commonly used systems for PCs, Dimension4 and Meinberg. No doubt similar software is available for Macs and other operating systems.

As a default Windows only checks the time when it is started up. This is not frequent enough as computer clocks are not very accurate and the errors over a long operating session would be too great for our purposes. There are various arguments for and against either Dimension4 and Meinberg. But still, either of them is vastly better than no clock synchronisation at all.
Meinberg working away - these are supposedly UK time sites but they are anything but.
 If your clock goes out of synchronisation you will probably drift gently out of the correct segment. This is not good because if you are trying to work someone part of your signal will be impossible for them to hear as they will be transmitting then. Also, this misplaced snatch will turn up in the receivers of those stations around you who are straining to hear weak signals. Not good.


5) Get on the right frequency
Just because your VFO says that you are on, say, 50.280, that does not mean that it is accurate.

Both WSJT-X and MSHV software suites provide variable settings for "FTol", or frequency tolerance. If your frequency is not accurate you have to hope that the other station (1) is on the correct frequency, and (2) has their FTol setting wide enough to decode you. Better still, get on the right frequency yourself, reducing the risk of falling outside the other station's FTol range.

The reason why FTol is variable is to allow for different computers in use by each station. The advice is to run the widest FTol which you can. Widening FTol increases the demands placed on your computer's processor.  WSJT-X comes with MSK144 set for narrow FTol (+- 20Hz) and the notes advise operators to increase this as far as possible providing their computer processor has the capacity to cope. You cannot rely on the abilities of the computer at the other end so get on the right frequency to start with.

If your rig does not have one, add a higher stability TCXO oscillator. To find out if you need one, a simple thing you can do is to look at the frequency recorded by the software from received stations. Good local stations should be a guide. Doppler shift tends to vary the dx stations by 10 or 20Hz each time, but it is still interesting to see if you are roughly right ...
OH7TE is close to 1500 so he might decode me if he could hear me (he couldn't hear me anyway)
 If most of the frequencies you see are spread evenly on either side of 1500 you can be pretty sure that you are more or less right. If all of them are above, or all of them below, or the differences are more than about 50Hz in many cases, it might be worth calibrating your frequency.

The other (not recommended) way to find out that your frequency is not accurate is to go on anyway and find that nobody is replying to your CQs.

6) Get off the right frequency
That sounds odd given the last suggestion (5). This time I am assuming that your VFO is correctly calibrated and stable, but the frequencies you want to use are very busy.

It is best to get off the "centres of activity" frequencies as soon as possible. You can do this easily by using that frequency as a "calling frequency". The standard approach is to call CQ and give the working frequency you want to use in kHz. For example here I am calling on 70.170 and listening on 70.712.
In WSJT-X, the rig VFO is set to 70.172, the TX CQ to 170 and settings to "Fake it"
In the example above the message sent is "CQ 172 GM4FVM IO85" and WSJT-X changes the VFO on every over to send that message on 70.170 but revert to 70.172 for reception. So if any station wants to call me they only have to turn their VFO to 70.172 and carry out a normal QSO. As soon as I hear a call on 70.172 I uncheck the box beside "Tx CQ 170" and a normal simplex QSO results. This keeps 70.170 clear of long drawn out QSOs.

MSHV does it differently, using the split VFO arrangement in most rigs, but the effect is the same in terms of the message and the outcome.

The frequencies in common use for MSK144, as far as I can see, are 50.280, 70.280 and 144.370. I cannot comment on the "rightness" of these centres of activity. I know that 50.280, for example, is not in accordance with the Region 1 band plan. I am just reporting on what I see.

People seem to be more likely to use a different working frequency if there is a lot of activity, and it is more common on 2 metres where contacts often take longer.

70.170 is an interesting case. During the periods when German stations have access to the 70MHz band it becomes a sort of multi-purpose calling frequency. I have heard CW, SSB, JT65 and FT8 on it. However, when there is no Es or tropo propagation it becomes a sort of meteor scatter calling (and working) frequency.

7) Consider the Hot Bearing
No, not your big ends knocking, Hot Bearings in this case are alternative beam headings. Strictly speaking the direct beam heading between your station and a dx one will not work well for meteor scatter due to the scattering pattern. The ideal heading varies during the day and with the distance between the two stations.

Luckily both WSJT-X and MSHV calculate the "Hot" angle once you enter the locator square of the other station. This can be either a "Hot A" or "Hot B" angle, but the distinction does not matter for our current purpose.
MSHV suggesting a Hot A bearing of 134 rather than the direct angle of 118 degrees
It is worth considering the Hot angle and trying it. Personally I follow the advice given to me by Bryn, G4DEZ (SK), who suggested aiming "somewhere in between" direct angle and Hot Bearing. In my case, with modest gain antennas, the beamwidth is not narrow anyway and my telescopic tube masts introduce some slack, so my antenna angles are not very precise.

WSJT-X marks these Hot Angles simply as A and B and there is little in the guide to explain what they mean. I suspect that not knowing about the Hot Angles is the cause of many missed contacts.

8) Don't assume that MSK144 only works during the mornings of meteor showers.
As I write this the Perseids shower is due to peak in three days time. Already the bands are busy. The Perseids is a long lasting shower so it is not sensible to limit yourself to the peak couple of days.

These showers can be great fun but meteor scatter propagation is possible every day of the year. It is also possible at any time of the day. It is just that sometimes it gets harder. We like harder. Harder is character forming. Easy is fun but you don't learn much.

The major showers are listed on sites like this:-
https://stardate.org/nightsky/meteors


Whilst the average shooting star observer needs to pick a shower period listed on these sites to see anything interesting, we in the radio world can find meteor trails at any time of the year (and in daylight too!).

Associations like the RSGB and ARRL list major showers in their propagation predictions.

Be aware that the Southern Hemisphere is affected by different shower patterns. If you happen to live in the Southern Hemisphere expect everybody to just assume that you live in the Northern Hemisphere. It is like your national radio society assuming that you live within 25 miles of their office. It comes with the territory of living where nobody expects you to. An unusual place like "Somewhere in the World". Golly gosh.

Anyway, 06:00 outside a shower period is likely to be as productive as 18:00 during a shower. And 18:00 at any time is better than not getting on the bands at all.

9) Use the most up to date software.
For some reason I cannot understand, several 2m meteor scatter operators still use the technically inferior FSK441 modes. Personally, I prefer a mode that works better, and MSK144 is that mode.

MSK144 uses 15 second transmit periods, which is remarkable to see in operation during a strong meteor shower. QSOs are over in a minute. Also, there is none of the panic with FT8 over getting the right macro running at the start of the over - you can change the macro at will during a segment. So if you are sending CQ on  MSK144 and you see that someone has called you, you just change your tx message mid-transmission and if the conditions permit it will be decoded at the other end.

I have an old copy of "the Amateur Radio Operating Manual", dating from 1991. The meteor scatter procedures in there are mind boggling. They are complex way beyond the rather fiddly methods described above. We do not know how lucky we are. I had forgotten most of it, and luckily now you can forget all of it.

10) Try the different bands
The days when "VHF" was simply assumed to mean 2 metres have gone. 4m if you have it is great for meteor scatter. 6m is good too. The bands have different feels to them. On 2m the pings are shorter and a lot of QSOs are pre-arranged. On 4m and 6m the signals tend to last longer and everything is much more relaxed.

11) Have fun
You don't need a kilowatt linear. You don't need a big antenna. If you already have a beam and WSJT-X you already have the setup. If you can do JT65 or PSK you can do MSK144.

Even if you just turn on and start you are not likely to fail completely. Keeping to the suggestions above will improve your strike rate. But if all you do is tune in and listen I bet you will find it fascinating.

See you during the Perseids.

73

Jim

GM4FVM