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Author Topic: Can't decode FT8, but can decode JT65 signal  (Read 6210 times)
AA2UK
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Posts: 309




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« Reply #15 on: September 18, 2017, 05:01:08 AM »

My observation, Timing is critical w/FT8 more so than JT65 modes.
Bill AA2UK
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AJ8MH
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Posts: 253


WWW

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« Reply #16 on: September 18, 2017, 06:07:43 AM »

Here is a very rough check of timing.  Look at your waterfall while in monitor.  All signals should start and stop on the horizontal lines.  There should NOT be a space or overlap.  There is one exception.  After your CQ, a station may answer you, but be slow to return.  You will see a space and the signal may not decode.  On his second answer to you, his signal should start and stop on the horizontal lines.

Keep in mind that if timing is off by 1 second, the space or overlap may be difficult to see on the waterfall.
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W1VT
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Posts: 2489




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« Reply #17 on: September 18, 2017, 06:48:39 AM »

DT, the signal’s time offset in seconds relative to your computer clock.

If everyone is close to 0.0 seconds in the DT column, your clock is fine.

Zack W1VT
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K0UA
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Posts: 1371




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« Reply #18 on: September 18, 2017, 06:55:29 AM »

All of these questions, pale beside the larger question:  How can he be receiving and decoding JT65 signals, and not FT8 signals?  It would seem to me this would have to be program related.  How could the levels be off?, how could the timing be off?, How could he be on the wrong sideband?,  How could anything about the selection of the sound card be wrong?  how could you possibly decode JT65 signals and not be able to decode FT8 signals?   When FT8 was invented, we all had to do exactly zero to start receiving them.  Just upgrade the same software we all used for some time on JT65 and JT9 and MSK144.  It just magically took off and worked. And there is no good reason it should not work for him.

Confused in Branson... Huh
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AA2UK
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Posts: 309




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« Reply #19 on: September 18, 2017, 07:18:05 AM »

I guess the assumption is that he is using WSJTX and not WSJT to receive JT65?
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K0UA
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Posts: 1371




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« Reply #20 on: September 18, 2017, 07:21:23 AM »

I guess the assumption is that he is using WSJTX and not WSJT to receive JT65?


yeah, that thought crossed my mind too, but he said he was using WSJT-x

This one has me pretty stumped.  And that is a feeling I don't really care for a lot. Smiley
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AA2UK
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Posts: 309




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« Reply #21 on: September 19, 2017, 07:14:28 AM »

HS0ZIB any updates if so what was the problem?
Bill, AA2UK
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K0UA
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Posts: 1371




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« Reply #22 on: September 20, 2017, 07:08:15 AM »

Any news on this?  Enquiring minds really need to know.  Smiley
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N6YFM
Member

Posts: 502




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« Reply #23 on: September 20, 2017, 10:08:49 AM »


My clock sync program syncs with an external time-server every 5 minutes, so that's not the problem.


Don't be so sure.   I have done approx. 4000 QSOs on JT modes, and my personal experience is that
FT-8 is slightly more sensitive to time sync than JT-65.

I run the NTP time package, and it does NOT get any more accurate than that, yet, 3 separate days
this year when I booted up and got on the air NOTHING would decode.   In looking at the NTP diagnostic
console, it seemed that the system had associated to a bad remote clock server, and time was just a
slight touch too far off for JT8 to decode.    Removing the linkage to that remote NTP server and
restarting the NTP time program fixed it, and decodes started happening right away.

If your receive audio is somewhere between 50 and 60dB on the vertical bar indicator,
and you are tuned to an FT8 frequency in the WSJT-X program, and the program is controlling
your rig OK via CAT control  (for USB DATA mode), and you are not seeing decodes, then
you 99% sure have a clock problem.

I would suggest uninstalling your current choice of time sync software, and install an
alternate package, then compare your PC clock, including seconds, to a GPS clock like
your cell phone, including seconds.    Being even 1 second off can cause trouble.
You want to be within millisecond accuracy.    NTP packages provide that.

And, as Zack said;
DT, the signal’s time offset in seconds relative to your computer clock.
If everyone is close to 0.0 seconds in the DT column, your clock is likely fine.


Neal
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VA3VF
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Posts: 806




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« Reply #24 on: September 20, 2017, 06:18:42 PM »

I switched to GPS timing permanently, and DT now is usually between 0.0 and 0.3s. There are exceptions, specially CO stations, in the 1.5 to 2s. This is much better than when I was using NTP.
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AA2UK
Member

Posts: 309




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« Reply #25 on: September 21, 2017, 04:56:13 AM »

I run D4 most stations w/in 0.2 secs on DT
AA2UK
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IK6IOQ
Member

Posts: 2




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« Reply #26 on: September 21, 2017, 07:05:24 AM »

Install BktTimeSynk by IZ2BKT and you will decode FT8.
73
Marco - IK6IOQ
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VA3VF
Member

Posts: 806




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« Reply #27 on: September 21, 2017, 07:29:47 AM »

Install BktTimeSynk by IZ2BKT and you will decode FT8.
73
Marco - IK6IOQ

Aside from the fact that BktTimeSync can use a GPS receiver, how is it different from D4 or any other NTP clients? I used D4 until last week, before switching to GPS timing, even at home.

As for GPS use, BktTimeSync has some incompatibilities with uBlox 7 based GPS receivers. These are the cheap GPS dongles available on eBay, and the one I use. The author of BktTimeSync made an entry on his blog saying he was to acquire one of these, to try and figure out what needs adjusting.
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HS0ZIB
Member

Posts: 598




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« Reply #28 on: September 23, 2017, 03:56:36 AM »

Sorry for not updating.

I can't give an update because the authorities disconnected my antenna....  Even though I am not transmitting (ham radio banned since 1962 in Myanmar), they also decided to come into my room and disconnect my receive antenna...   Cry

And I got stopped whilst riding my dirt-bike to teach at an orphanage today - I was stopped by the police for the umpteenth time ..... told I wasn't allowed to ride on that road, had to make a 20 mile detour on rough roads to reach the kids.

Not a good day today.  Not a good week either for my ham radio efforts over here.  Angry

Still, better luck next week.

Oh, I'm using WSJT-X RC2 to receive my signals.  And yes, I can't figure out why the JT65 signals decode just fine and the FT8 signals don't!!  Weird...
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VA3VF
Member

Posts: 806




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« Reply #29 on: September 23, 2017, 07:08:28 AM »


I can't give an update because the authorities disconnected my antenna....  Even though I am not transmitting (ham radio banned since 1962 in Myanmar), they also decided to come into my room and disconnect my receive antenna...   Cry

And I got stopped whilst riding my dirt-bike to teach at an orphanage today - I was stopped by the police for the umpteenth time ..... told I wasn't allowed to ride on that road, had to make a 20 mile detour on rough roads to reach the kids.


Very sorry for the kids, but it's time to bail out.
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