Thursday, 21 September 2017

8 Sept aurora and "above the MUF" propagation with FT8, JT9 and JT65

Olli, DQ8BHA, whose blog is listed on the sidebar, writes some very interesting material. His description of the 8 September aurora is worth reading (remember to use the back arrow to return here!).

http://www.dh8bqa.de/major-x9-solar-flare-aurora-all-around/

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Thanks to David, GM4JJJ, for alerting me to an article by Carl, K9LA, in October 2017 QST magazine entitled "Understanding Propagation with JT65, JT9 and FT8".

This article brought me to one of those "D'oh!" moments. Suddenly things which should have been obvious fit into place and I realise that I should have worked this out myself.

The article explains that the ability of the slow WSJT-X modes to receive signals "below the noise level" means that we can work stations using these modes when the bands are closed. Now that was sweeping statement by me. SOMETIMES. Let us think about why this can happen.

It is well know that these modes (and WSPR) can successfully decode signals which are below the level of noise in our receivers. In fact, so can good CW operators using their ears. The seemingly odd outcome arises both from the fact that the superb modes devised by Joe Taylor and his merry band can makes sense of extremely weak signals in this nether region, but also the way we define noise is rather arbitrary.

When your WSJT-X software shows that you have decoded a signal at -20dB, that relates to the noise factor for the SSB filter, and in reality it is not 20dB below what you can hear. However, make no mistake, it is a lot below what you can hear, just not quite 20dB. Let us take, for the sake of argument 10dB below what you can hear. Imagine that. Think of a signal that needs to be 10 times louder for you even to hear it, and then imagine decoding the weak version. Pretty impressive.

The fact is that the minimum signal to noise ratio required for reception of SSB is higher than that required for CW, which in turn is higher than that required for, say, JT65.

You may think of it this way. You are working a nice distant dx station just as the band closes as the MUF falls. In other words, rather than being below the "maximum usable frequency" (MUF), you now find yourself operating above the MUF. Whilst on SSB the signal would have faded into the noise, and you can no longer hear it on the loudspeaker, on FT8 or JT9 you are still about to complete the QSO. Magic. Except that it happens all the time if you use FT8 or JT9 (or JT65 or WSPR). You just keep completing QSOs where you cannot hear the other station in your loudspeaker.

However, there is another way to look at this. For an SSB operator the band has closed. They cannot make a QSO as the MUF has fallen and "the band has closed". But you, as a data mode operator can still work people. What you are doing is using what is called "above the MUF" propagation.

In effect, using these data modes has made an otherwise closed band stay open for longer.

Let us have yet another take on this. When I started on data modes back in the 1970s I used RTTY. I might be appalled by that mode these days, but it was cutting edge then when nobody had a PC. RTTY was (should be past tense) a mode which basically replaced the microphone with a bulky, oil-spewing, unreliable, clattering electro-mechanical beast. You did not get any extra performance out of this contraption, it just meant that your QSO got printed out instead of spoken. Unlike RTTY, WSJT-X slow modes are not just a text-based replacement for voice or CW. They out-perform SSB by being able to be used successfully in conditions where phone, RTTY and CW would not work at all.

In the 1970s, during any opening, my RTTY success directly mirrored by SSB success. If the band was "open" I could use SSB or RTTY. If the band was "closed" then both stopped working. But the WSJT-X slow modes continue to work. So how does that happen? Surely the F-layer (or the E-layer) is either bending the signals back to earth, or it isn't. How can using different mode make a band open?

Let us go back to basics. The diagrams are my own (copyright!) handiwork, not to scale and can be enlarged by clicking on them. The QST article is based on 28MHz and F-layer propagation, but there is no reason why the same principles would not apply to other bands or E-layer propagation. For this purpose though I will stick to the same example as the article.

When the band is "open" the ionosphere bends (some of) the signal back down to Earth in the well known way. The classic diagram shows band open ...

... (above) where you would expect to find propagation between A and B, and (below) closed, when you would expect nothing to happen between A and B ...
If this was all there was to it, everything would be as we expect. But once again the simplistic diagrams we all used to learn radio theory let us down.

The diagrams above show the F-layer as if it is a thin line which either reflects (band open) or refracts (band closed) the radio signal. In reality we would have no propagation at all if that was the case. The F-layer could never reflect radio signals at the angles we transmit them. The F-layer is not a mirror, it is a layer of ionised gas which has a structure of steadily varying density. This variation in density results in a very large number of small refractions of the signal, gradually bending it down until it is almost horizontal, and only at that angle is there one, small, reflection which returns the signal via a whole series more of refractions.

So almost all the work of returning our signals to Earth is done by a large number of refractions. Let us look at a diagram of how the F-layer would look - and this is definitely not to scale - when the band is open ...
The signal follows the green line inside the F-layer. It starts to bend as soon as it enters the F-layer, refracted by the changing density it passes through. It is almost as though the F-layer was made up of a series of very thin layers on top of each other, each with a different density.

What nobody told us in radio school was that every time one of those refractions takes place, there is also a reflection. This has been known for hundreds of years in optics, and light is just a different wavelength of electro-magnetic energy from radio, so the same principles apply. The Fresnel equations can calculate the relative strengths of the reflection and the refraction. The other basic optical principles apply too - so the angle of the diffraction will depend on the relative difference in density, but the angle of the reflection will still be the same as the angle of incidence. Which means that actually we get something like this ...
Why did nobody tell us about this? In the real world of radio the many reflections are small in relation to the strength of the eventual main signal. Not only are they low in relative strength, they are directed slightly differently and sometimes out of phase. So  in the world of 20 metre band SSB you often never notice them. They do reach Earth, but they are weak enough to have been considered irrelevant.

In fact, given the noise handling ability of your radio you might never hear them. But JT65 can.

And JT9, FT8 and WSPR can hear them too. WSJT-X slow modes can successfully decode signals well below what we can hear. You might correctly take that to mean that they can hear weaker stations when the band is open, but it can also mean you can work stations when otherwise the band is closed and you can hear nothing but noise on the loudspeaker.

Moving on from the time the band is open until when it is closed we would get this diagram for the ionosphere ...
This is what we knew: it explains why we hear nothing when the band is closed. But the weaker reflected signals are still directed towards Earth, as shown below...


These weaker signals will pass through the F-layer, though they may be bent a bit in the process, and some will reach the ground. If they are WSJT-X slow modes they can be detected down to much lower levels than would be possible for voice signals.

The result of this is that before the bands open, and after they close, the weak signal modes should be able to decode signals we cannot hear above the noise. We need to re-think our existing assumptions. Most MUF predictions are made on the basis of a conventional SSB radio with about 100W and a dipole or small beam. The QST article suggests that a path of almost 3,000km, a single F-layer hop, would be open for an SSB contact at 28MHz (obviously) with the MUF of 28MHz. In fact this could be done on low power, with 100mW of CW doing the trick. But of course once the MUF falls below 28MHz this path is lost and the band is considered to be closed.

The article goes on to suggest that CW using a narrow filter could keep the path open at 28MHz at 10W even if the MUF falls to 25MHz. So, operators are already using "above the MUF" propagation. However, using FT8, JT65 or JT9  this path would be open with the MUF of around 23MHz. So the ten metre band would sound dead, SSB would be possible on fifteen metres, but data operators could operate on the otherwise "closed" ten metres. CW operators might get away with the WARC band on twelve metres.

The significance of this is that the MUF rises to 23 MHz far more often than it reaches 28MHz.

The fact that WSJT-X data operators are making stacks of contacts when the band is open is already clearly demonstrated. But this other fact shows what some of us had already noticed - these modes can make contacts possible on an otherwise "closed" band.

It could be said that there is confusion over our own figure "maximum usable frequency". For practical reasons we have set this figure by taking the measured critical frequency using near vertical incidence reflections and multiplying it by a constant which produces a figure which works for SSB and the receivers we all normally use. However, the better sensitivity of these WSJT-X modes alters the constant to be applied. What we call "MUF" is really the "Maximum workable frequency for easy SSB contacts".

In a sense it is silly to talk about "above the MUF" contacts as F-layer propagation should be impossible above the MUF by definition if it is really the maximum usable frequency. However, I bet that the term MUF will continue in use to mean the frequency at which those easy F-layer QSOs start happening.

I avoid the easy contacts and go for the difficult ones. But you knew that already.

So what happens if the MUF is much lower, and the F-layer basically disappears? Does this "above the MUF" propagation disappear? Not totally. At that point although reflection more or less stops, even at a very low level, scattering from the atmospheric molecules will still occur and produce just the sort of weak signals which JT modes love. Ionoscatter has been known for years too, but it usually requires high power as it produces weak signals - something which JT modes are ready to help with.

I should have seen this coming. I knew that these modes can receive much weaker signals than the human ear. What I had not thought about was that they could in effect outwit the conventional calculation of "maximum" usable frequency. None of this is new - Isaac Newton (1642-?1726) knew about reflections during refraction in light. The people who made my camera or my glasses spend a lot of time trying to minimise the effect by applying coatings to the lenses. However, our radio educators thought fit not to remind us about it. As so often, the standard diagram in the radio text books is over simplified. Oh yes, it was over simplified on this blog too ... mea culpa.

When I started using WSPR I told some old timers about the results I was getting. Their immediate reaction was that it is was impossible and somehow WSPR must be using the internet rather than radio. When I assured them that WSPR was all radio over the whole route from my antenna to the other station's antenna they were very sceptical. Now I know what was happening. More recently as WSJT-X modes became more popular on 6m, several of us have been finding paths open when the band is otherwise "closed".

As always, more investigation is required.

This is my stumbling attempt to explain this. I encourage you to look up the much clearer explanation by K9LA in QST if you can. I hope to put it to more use soon.

And thanks again to GM4JJJ for putting me on to this. It explains a lot of what I have been experiencing but not understanding.

I wonder how often stations turn on, listen to the band, hear nothing, and switch off. What would happen if they tried calling CQ on FT8?

73

Jim
GM4FVM

Thursday, 14 September 2017

Did I miss an aurora?

I have been in Blankenberge which, as is well known, is in Belgium. It is customary in this blog to show the means of transport I used at the end of my trip (how did that come about?). Anyway here is a tram at De Panne, which was as far as we got before heading back to Blankenberge...
Tram at De Panne 09 September 2017
We did use trains which were more comfortable and rather faster to reach Belgium in the first instance.

The journey back from De Panne was, at 115 minutes, the longest time I have ever travelled in one tram. We broke the journey on the way out, but as we were tired on the return we decided to do the whole thing in one trip. Result - seriously numb bums. Almost as bad as the plastic seats on Euskotren from Bilbao to Irun via Donostia.

Anyway, it was clear to me that all my recent talk of the "end of season wind-down", and me decamping to Belgium, doesn't stop auroras happening. If I learned anything in statistics class (did I learn anything in statistics class?) it was that anything with a distinct probability, however small the probability, will happen sometime if you wait long enough. Like motorcycle accidents and unexpected pregnancies, if the basic requirements keep being met, then eventually even an unlikely outcome will occur, given enough time. So we shouldn't be surprised, and that also explains the scars on my leg, my broken upper jaw, and other things like me being here in the first place.

I have gone on about this before. The "Carrington Event", the most violent solar storm seen and recorded (so far), occurred in 1859. When I was at school we were told it was a "once in a hundred years" event, so we have better expect it soon. Now we are told that it was a "once in 400 years" event. We shall see. "Once in a hundred years" floods seem fairly common these days.

The aurora on 8 September was a good one. Not in the Carrington Event category, as one of those would threaten power systems and satellite communications, but good all the same. As we have not had a good aurora for some time, and as I missed it (boooh-hoooh), I am lucky to be able to draw on the reports of others to describe what it was like. Mike, GM3PPE is about 30km South West of me in IO85, David GM4JJJ is about 90km North-West of me in IO86, and both gave me accounts of the event. Thank you to both of them for allowing me to quote from their reports.

The basic plan for aurora is to be on alert for anything untoward happening. Mike was able to send me this email on 6 September which was very accurate in predicting the events of the 8th.
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"I was on 15 meters this morning working stations on FT8 when suddenly at 0910Z all signals disappeared.  The same on the other HF bands.  I thought my rig had broken, or the antenna fallen down!  Then 30 minutes later all signals back.  A massive event on the sun.  Middle of the day another total radio blackout.  Apparently the biggest solar X class solar flare for several years.  It looks like there was an accompanying CME in our direction, which augurs well for a big Au event over the next 24 to 36 hours."

After the aurora Mike sent this report "6 meters started buzzing at lunchtime and closed to Au contacts mid evening. Kp went up to 7 and the geomagnetic records went purple.  I have never seen that happen with previous events.

I worked about 40 stations all over the UK and Europe, with some even on SSB.  Signals were very strong with some peaking 59A on my K3.  Towards the end of the event some signals start going Es, with hardly any Au buzz at all.  LA8HGA was particularly noticeable for this effect."
" ... the Au opening ended quite abruptly for me at about 1830Z - as you say, quite early.  In terms of DXCC countries, I worked G, GM, GW, EI, ON, LY, SM, F, DJ, PA and LA, making a total of 21 squares.  Not a bad haul for one day on 6 meters!"
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Quite right Mike, and well done on that. 21 squares on 6m is remarkable and once again it proves what can be done on VHF.

SSB can be useful during auroras, even if the distortion makes it difficult to use voice. There is a large band of amateurs who never use CW, and during an aurora they can only be reached on phone. If I need the square I can use almost any mode I need to, however difficult that might be.

Mike sent me a link to the British Geological Survey site:-

http://www.geomag.bgs.ac.uk/education/current_activity.html

This certainly shows the 8 August event in context (and shows the purple bar graph which was a new one on me too) ...
BGS "Current Geomagnetic Activity" chart for Lerwick taken on 14 September 2017
Click to enlarge if necessary (as always).

Note too that geomagnetic activity had another smaller peak later in the week and there may be some more action to come. The fact that you often see possible warnings of auroral events when nothing actually appears is part of the joy and the frustration of the hobby. This time who knows?


David, GM4JJJ sent me these useful illustrations of his operations:- 
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2m Aurora Map showing worked squares with 500km intervals in red

4m Aurora showing worked squares with 500 km intervals in red

OH SLICE meteor Radar showing the solar flare attenuation at 36.9 MHz on the day before Aurora at around Noon. 
latestMeteorCount.png

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Thanks and congratulations David, well done.

It takes a fair amount of determination to work stations on 2m during an aurora. The Doppler shift is greater as the frequency increases. This makes life harder.

Clearly 8 August 2017 was a "big" aurora in every way. 

I am sorry I missed it. I used to work in Belgium and I always enjoy practising my rusty Vlaams (and indeed Dutch and French, if I can admit to that too). 

En waarom niet? Een fles Kwak voor GM4FVM!


Thanks for all the information and let us see if there is another aurora round the corner.

73

Jim
GM4FVM

Friday, 1 September 2017

31 August Es and the end of the season wind down

Here, as I gaze over my estates from the lofty heights of the old stone tower at the end of the West Wing, I see the workers toiling in the fields to save the wheat crop ...
Harvesting the wheat as seen from GM4FVM's QTH on 27 August 2017
Actually, there does not seem to be too much toil involved sitting up there in the cab of the harvester watching the machinery doing its work.

If I really did have a West Wing with a stone tower on it, I would have attached another antenna to it long before now. Especially if it had lofty heights.

No, this week I have been watching the field behind the house being sucked clean of all its produce, then straw baling being completed. The straw bales have already been removed and no doubt ploughing and drilling will be complete within days. Who knows what crop will be pushing up next year?

When it comes to harvest time I start thinking of Autumn, and the end of the Es season. Time for me to review the Summer and then batten down the hatches for Winter.

This year I feel that I have overdone things over the Summer. I think that it is time for a break from operating and use the opportunity to spend a bit more time with my other projects.

Most of my amateur radio life has been marked by upsurges and downswings in activity. I am not an operator with just a rig and a bit of wire, but nor am I someone who invests all his time and money in this hobby. I move around the middle ground, sometimes getting too much involved and having to step back a bit. So this is time for a step back.

The Es season is over, the Christmas VHF Contests are over the horizon. Time for a measured reaction. The Autumn promises more Es, more aurora, more meteor scatter, and more tropo. So bring it on, as I am not going hunting for it.
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 31 August produced a nice Es opening.

I knew it was coming towards the end of the week because the RSGB VHF propagation report said there wasn't going to be one then, but "at the head of the week" and it would "struggle" due to "weak Jet Streams".

So, of course with this promise I reckoned that if they say it will happen weakly at the beginning of the week I should start looking for a strong one at the end of the week. I find that is the best way of treating these reports, and it has always worked for me.

I am not saying that Jet Streams have nothing to do with Es (though that is what I think, but it is hard to prove a negative), but what I can say with fair certainty is that using them for prediction does not work. Relying on the predicted Jet Stream to base an Es prediction is always wrong here.

Jet Streams might be implicated in Es (I doubt it) but if this is the track record of making predictions based on them, what I have seen over the last year or so makes the predictions look laughable.
Es as reported by DXMaps at 21:18 on 31 August 2017.
I had a number of nice contacts, including I6FLD, IK4ISR, IZ8IBC, SP7QJF and SP8NR on 50MHz, and returning regulars DD3SP and OK2BRD on 70MHz.

Actually Sandro, DD3SP was an interesting one on 4m as I worked him first with meteor scatter on MSK144 at 13:16. I guessed that would be my last German station on 4m for this year, as their temporary authorisation ended on 31 August. But then I worked him again on SSB on Es at 20:32. I also worked Jiri, OK2BRD twice, both on Es. First by FT8 at  20:37, then again on SSB at 20:45.

It is notable that the last QSO was at 22:55 and I only stopped because I needed some sleep. This bout of Es was generated by a geomagnetic storm caused by a coronal hole. There was no widespread aurora, though I did hear the usual Northern Ireland beacons over the previous day or so. I often see this Es pattern repeat itself during positive polarity coronal hole disturbances. Perhaps today we will get some negative polarity material from the Sun too, and maybe an aurora.

10m Es was pretty good as well...
10m Es on WSPR, 31/8/17. Presumably Mauritius was F layer, but you never know!

A great day of Es to round off the season, so to speak. I will miss the German stations on 70MHz even though, due to conditions, they have not been as prevalent as previous years. I already miss Italian stations who we have not heard on 4m for several years.
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It definitely has been a busy Summer and I am in need of a bit of a break. Never mind the radio, a brilliant Tour de France (Rigobero Uran was brilliant) was star of the season. Now the battling of Contador, Nibali and Aru are keeping me welded to the television and La Vuelta Ciclista a Espana. Not just cycling, but cricket has been superb too, plus of course Masterchef Australia. What a Summer.

I am not going QRT, just taking a bit easier. There is plenty more for this blog, or so I hope anyway.

73

Jim

GM4FVM

Sunday, 27 August 2017

2017 Es season - not that bad? Aurora springs to the rescue.

I wrote this over the past few days. It started off being a piece complaining about poor Sporadic E conditions. As the piece developed, it turned out that things were not as bad as they had seemed.

What was bugging me was that on the 70MHz band (4 metre band), I had only had one Es QSO so far in August. Normally I would have had many more, and I can often work up to 8 DXCC in August, whereas of course in 2017 it was just one. I moaned about this in my last posting, and I went off and got the figures out of the logs to prove it.

Of course, it was probably just random variation (and not the weather and definitely not the jet stream). As I was finishing off my blog there was a small opening on 4m. I worked two stations in 4m, both in EA. One was on SSB and the other on FT8. That was followed the next day by a short opening into OH with two stations worked. For a while, the OIRT interference made it look like the "good old days" of Radio Gdansk...
OIRT broadcast stations at GM4FVM on 27 August 2017

So I have decided to re-write my downbeat piece as a review of the good things that have happened recently. And why not?


I can hardly complain about the 2017 Es season as a whole, even if August has been relatively poor. Six trans-Atlantic contacts on six metres on six different days so far this year. These cross Atlantic paths are (we believe) multiple hop Sporadic E. Ron, WB3LHD, went so far as to send a very striking QSL card direct ...
QSL Card received direct from Ron for 6m FT8 QSO on 29 July 2017
We do have sea eagles not far from here, plus kites and buzzards overhead, but that is quite a bird. Even the slightest squeak from any large bird sends Katy out of the garden and into the shack for shelter, so I have kept Ron's card out of her very sharp cat vision.

However, none of those NA QSOs were in August.

I suppose in this respect I am "old school". I really like receiving an unexpected QSL card through the post. After I sent the card back (direct) Ron sent me a screenshot of what the QSO looked like from his end. Unfortunately I did not take a screenshot at my end.

Nor can I complain about working 7K2KF in Algeria recently. I view this as a new continent. Sure, I have worked Madeira and the Canary Islands on 6m, which count as Africa, and had many 2-way spots with CN8LI on WSPR, but I have never before had an actual QSO with a station on the African continental mainland itself.
7K2KF on 6m at GM4FVM on 25 August 2017
I am not sure why this has taken me so long as the CN8LI spots prove that the path is open quite often. 2162km to 7X2KF is not far in 6m terms. It seems that the "FVM equations" are the problem, with Egypt, Tunisia, Libya, Algeria and Morocco all within easy range but not very active. The issue here is not about the level of Es, but more about the level of activity. Or so I suspect.

It also depends how the weekends fall in the month. Conditions are always better at the weekend. Of course, this is not true, but it seems to be. There are more stations around, they make more noise when the bands open, and that gets others involved.

I have also had a few QSOs into France - which is a great place for me to find new squares on 6m. France was late to release the 6m band, and then at first only part was opened up. Now it is easy to work French stations but they are still few and far between. Given the size of France, just about everybody starting up is in a new square for me.

However good things have been on 6m, 4m has not been good for weeks. I have to conclude that it is probably just normal statistical variation. Up here at 56 degrees North I am towards the edge of the strong Es. Stations in the Mediterranean get much more, and the further North you go the less we benefit from it. So it might reach us here on 6m, but the ionisation might just be too weak to work at 4m from here. A few days like that and it makes all the difference.
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If Es levels may be down (and reading the above, they probably are not down), auroral activity is definitely down.

I wrote a long piece about auroras to illustrate them, but I still have not posted it.

There were more auroras over the last couple of years, and fewer recently. ("Please, no more figures Jim", they cry). That is probably due to the well established pattern the auroras peak in the two years after a sunspot maximum.

Like meteors, auroras do not go away just because it is not a maximum period for them. The various sites suggested that a coronal hole might have been active for the previous two days, but nothing exciting was predicted for 23 August. Suddenly my 10m WSPR monitor showed a blast of noise which filled the waterfall right across the screen. It must have been fairly wideband but I did not see it on the higher bands...
Wideband noise burst on 10m before the aurora on 23 August 2017
This was followed by me hearing the beacons on 2m in Northern Ireland, plus the 4m beacons on  Syke and in Northern Ireland. Interestingly the 4m NI beacon is now running PI-RX mode and I could compare the signal direct and via aurora, depending on which way I turned my beam antenna.
GB3CFG beacon near Carrickfergus while beaming directly at it (tropo)
GB3CFG beacon while beaming North (aurora). PI-RX is decoding despite the Doppler distortion
I must say something more soon on this blog about PI-RX beacons. Let us say now that unlike almost every other data mode, PI-RX works during an aurora. Looking at the comparison above, between direct and via aurora, it is amazing that PI-RX can make anything out of it at all.

Beacons were all very well, but what actual stations could I hear. As usual, not many.

I managed to work one station each on 4m and 6m. They were both LA9BM. Leif and I seem to find ourselves in this position quite often - the band is open but there is nobody else to work. Not quite though, he worked a few more, including OH0CO. I had heard OH0CO over the past few days via meteor scatter but he did not hear me, and I did not hear him on aurora. Aland Island would have been a new DXCC on 4m and 6m, but not a new square.

Anyway, I worked LA9BM on 4m and 6m using CW, and not even using my pre-programmed QSOs using the keyer memory. All done old style with a keyer and brain power. I did hear a couple of other stations but their CW was far too fast for me to try to work. Why does anyone use fast CW during an aurora when signals can be distorted and hard to copy?

I like a good aurora. Even if I only got to work one station on two bands, this one was better than nothing.
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73

Jim

GM4FVM



Monday, 21 August 2017

MSK144 and The Perseids

Well, the Perseid meteor shower has been and gone for this year.

After I wrote the eleven points about MSK144 and the Perseids David, GM4JJJ added another. I will re-post it here:-

Might I add a number 12 bulletin point?

In MSK144 there is a checkbox marked 'sh'. This allows a short-format message format to be used.

The user guide explains:
For operation at 144 MHz or above you may find it helpful to use short-format Sh messages for Tx3, Tx4, and Tx5. These messages are 20 ms long, compared with 72 ms for full-length MSK144 messages.

It also makes plain that on 50 and 70 MHz sh is not useful as the pings are of much longer duration anyway.

What is important to remember is that on 144MHz, you need to know if the other station is using sh or not, failure to use the sh setting if he is using sh will result in no decode even when a strong burst is received.

Another point is that if sh is used, there is a greater chance of false decides, so once you have detected the other station it is best to use RIT to get your RX frequency as close to his transmitter frequency as you can and then narrow FTol.


Thanks for that David.
"Sh" is accessible by clicking a box. SWL mode is for listening to the Sh messages of others

I might even add point number 13.

13) Think about AGC?
On the face of it, AGC should be turned off, especially on 2m metres. Meteor scatter pings are short events and they tend to be shorter the higher you go in frequency. AGC will cut your receiver gain as soon as a ping is detected, and therefore seems like a bad idea for a mode which depends on momentary signals. You receiver gain may remain lowered as the ping trails off, and thus you might miss the weakest part of a vital ping.

In practise I find that this is not an easy decision to make. Using my IC-7100 and IC-7300 the initial AGC action is very deep. However, the recovery time is adjustable and you can make it very fast indeed. At the fastest setting the response is good and it seems to help in some cases.

I would therefore suggest that it might be a good idea to try the AGC on and off for trial periods. To some extent it will depend on your rig. Slow acting AGC is almost certain to be detrimental, but fast AGC might work depending on the equipment. If in doubt, I would suggest turning it off.
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I am a bit worried that listing 13 points makes meteor scatter with MSK144 look very difficult. It is not difficult. Why not try it and see?
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Just because the Perseids are over, there is no need to wait for another shower to try meteor scatter propagation.

About 40,000,000 kg of material collides with the Earth every year. Whilst during a shower the particles may be bigger and there may be more of them, this is still only about 4 times the average for a normal day. When I say bigger, maybe golf ball sized, rather than the size of your thumb nail or smaller. But even a speck of dust can produce an ion trail as it falls to Earth and compresses the atmosphere in front of it, producing heat, light and ionisation as it progresses. Either the "burned up" particle is reduced to a speck of material which falls gently through the lower atmosphere, or, more likey for the ones that interest us, they are vapourised entirely by the intense heat.

Any object large enough to remain a significant size and reach the Earth's surface is called a meteorite. If we are ever going to be on the receiving end of a large meteorite then, believe me, the effects it might have on radio propagation will the be the last thing we are interested in. So the small ones are our main interest, and they fall all year round.

Is random meteor scatter a reliable method of communication? Take my QSOs with Henning, OZ1JXY. Since 2014 I have worked Henning by meteor scatter 61 times, at all times of the year and at all times of the day. That is reliable meteor scatter communication over a fairly short distance - 732km. During the same period I have worked Henning only two times on Es and once each on aurora and tropo. Anyone who suggests that meteor scatter is confined to a few days of the year needs to look at the performance of that link (not even a sked, all of it random answers to CQ calls).
OZ1JXY blasting in on FSK441 on 1 October 2016, outside a recognised meteor shower

There is enough "stuff" falling into the atmosphere, be it space dust from far-off stars, emanations from the Sun, space debris, or whatever, to keep a good QSO going all year round (though in February the going gets tough).

The Perseids shower is formed by the Earth crossing the dust trail left behind by a previous pass of the Swift-Tuttle comet. As we pass through the path of the comet we cross the material it left behind. Thus we have a predictable event to take into account. Random meteor trails are not as dense, but they are capable of producing surprising results for the amateur. And they occur almost all the time if you have the patience to wait.
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Given the many advantages of MSK144 over previous formats, I am surprised to see so many stations on 2m still using FSK441. I will not go into the reasons for this, but they are just plain stupid. The justification used by one or two of these people is keeping MSK144 off the table for the rest of us.

For many operators, all they do is follow the pack, which in this case means sticking with FSK441. Nevertheless, for the few operators who drive this piece of numb-skullery, the basic object of resisting the spread of MSK441 is their belief that changing mode will damage their success. It won't.


There is a sort of meteor scatter neurosis which develops amongst operators. I know, I have had it too. The other station seems never to have heard you, though you can hear them (or vice versa, it doesn't really matter which). Therefore, the fault is clearly your antenna, their antenna, the software, your sound card, the phase of the Moon, ..., perhaps this new mode will reduce my QSO potency. This is human nature, given the characteristics of a mode that depends on tiny wisps of signal. But, meteor scatter communication depends on probability. You are waiting for a randomly timed event to happen. The gaps between hearing the other station are --- random. Who'd have guessed it? There is no need to blame your rig, or MSK144 for it, nor anything else. Mind you, when you are sitting there waiting for a signal, you might think of everything under the Sun.
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Here the Perseids produced a few interesting contacts here.

6m MSK144 - LX1JX, S59A, SM6A, and SO3Z
4m MSK144 - DF1AN, DF3XZ, DF5VAE, DJ9YE, DK5YA, DK6AO, DL4KUG, DL9YEB, GD0TEP, OH7TE, ON4FI, OK1DIG, OZ1JXY (of course - twice), OZ1MFP, OZ6GH, PA3ECU and YL2CP,
2m FSK144 - SM2CEW and SM7THS

With 6m squares now being less sought after by me (I already have quite a lot), I have been looking for new ones and not calling ones I have. On the other hand, most of the 4m contacts were from stations hunting out my square, IO85. I do not think that I live in a rare square on 6m, especially as it has Edinburgh City in it. However, on 4m there are not many active operators, hence it is more in demand.

With 2m I stood out for a while by sticking to MSK and working no-one as a result. I had a few QSOs on FSK but that was it.

Two new countries for me were provided by LX1JX on 6m and YL2CP on 4m. Many years ago Jack, LX1JX (JO30, 843km) was my first LX station on 4m (on FM!) but it has taken a while to track him down on 6m. YL2CP (KO27, 1674km) had to have a lot of patience to work me as we had a number of attempts over two days. Because YL have only recently gained 4m he was much in demand and had to keep switching to other stations who kept calling him. We did it in the end though.
=========================================
All this talk of meteor scatter has made me think about how reliable it is, and how unreliable Es has been for me this year. I must look all that up and see if I am imagining it.

73

Jim

GM4FVM

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

Thursday, 27 July 2017

More on FT8, WSJT-X1.8.0-rc1 and imaginary band conditions

Well, I have had a lot more chance to work with FT8.

1) When FT8 does work

Included in my activity has been more time on 40m which was good fun as it included a QSO into VK and then I missed this ZP9 because I had to go out and quell a cat fight in the garden (don't ask, it involves a "Squeezy" bottle full of water - not to wet the cat but to cause it to find a close shave enough to leave the premises). ZP9 on 40 would have been a new one...

ZP9CTS missed on 40m at GM4FVM on 23 July 2017
Still, VK will do nicely.

In operation it is fairly easy to cut out an entire 30 seconds of otherwise missed DX opportunity by being quick to reply to calls.

I leave the PC pointer over the second line above the bottom (once the "Rx Frequency" box has filled - before then you have to pick the lowest blank line). It takes a bit of care to put it over where the other station's callsign will appear. Then I resist the temptation to click as soon as their callsign is decoded (on the line below). This is because my reaction time is not quick enough to click on that before the callsign moves to the line above.

 It certainly works if you click it within 2 or 3 seconds. Here is what the result looks like, showing that the next CQ was interrupted by the reply within two seconds and the other station received it fine ...

I have decided not to get steamed up about the superfluous 73 which often happens. Yes, I could hang over the spot with my pointer ready to click if I failed to get a 73. This might save 30 seconds. So far I cannot see the need to do it. It is worth doing it when getting replies to CQ calls as otherwise people can get fed up and stop calling.

2) When FT8 does not work

I have had a series of mysterious failed contacts where my reply was not decoded at the other end even though we were strong signals in both directions.
LA7DFA not decoding me on 6m for 20 minutes. Click to enlarge if necessary.
I was calling LA7DFA all this time and he only copied me once. After I got his report I sent mine but he did not decode that at all. This went on for twenty minutes. You can see that I missed his messages quite a few times too, even though I could see a big signal on the waterfall. Signals were strong enough and Per sent me several emails about it as things went on. There was little that we could do about it. Eventually Per suggested that we move to meteor scatter and once we had sorted out an "FTol" settings issue with MSK144, the QSO was instant. Hardly surprising as I could hear Per clearly.

This failure and a few others like it are rather mysterious. It does not seem to be a timing issue and I have switched back and forth between Meinberg and Dimension 4 several times which makes no difference. Signal strength is not an issue. Usually the other station has decoded my CQ and perhaps my reply. Drift does not seem to be involved. Sometimes I have decoded their message once, but not again. Sometimes it passes, other times it goes on for ages (though the example above is extreme).

A bit of a mystery that situation. I see others seem to be affected too. I still feel that I must be doing something wrong.

3. When nothing works (or so I imagine)


Between 1 July and 27 July 2017 I worked only 4 stations outside the UK on the 70MHz band.

This seemed so bad I decided to compare it with 2016, when the figure for the same period was 5.

Then I checked 2015, and then it was 7.

So four is not so bad. I do not recall July being quite so bad on 4m.

On 6m, by comparison, in 2016 I worked 18 stations and in 2017 I worked 55. So July is not so bad on 6m, and certainly not when I can rattle through the contacts on FT8.

Ah, the good old days. When July was full of 4m DX and the world was well ordered.

What went wrong?

73

Jim
GM4FVM