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.

EDIT:- I soon discovered what I was doing wrong. If you look at the screenshot you will see that Per was 400Hz or so off my frequency. I later moved my frequency down by 90Hz using the "offset" setting in WSJT-X. Not perfect but better. It does not help that WSJT-X download includes a default setting for FTol or 20.

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?




  1. Hello Jim, had this in several occassions. Although after 3 or 4 times back and forth eventually the decode happened. Very strange? Luckely most of the time FT8 works like a charm. Never made any QSO in MSK144, tried to recieve some once and did but calling CQ did not help. 73, Bas

  2. Bas. Thank you for that. Very useful information. I am trying to understand this. OK about MSK144, I hope to write osmething about this soon. 73. Jim

    I have tried, but i have so many failed QSO with it. I admit, they are quickly failed QSO, but failed all the same.
    Love it on 6m -will use it on higher HF bands if it is quiet, otherwise, JT65 still seems to work better.
    Just wish more folk would use JT9.

  4. Dale.
    JT9 is a much under-rated mode. I find it better than JT65 but actually finding up somebody to work is a different matter.