Upgraded - Massive drop in performance

[iwanders73]

Hi, been running a AIS system for about 2 months. Live in Greenwich London, about a mile away from the Thames. Started off with an old SDR dongle, and a small are aerial, and once I know I could pick up stuff I upgraded to a Shakespeare AIS aerial on a pole on the side of the house (top of aerial about 10m high), a FM blocker, a 162 LNA, 12m cable, RTL-SDR Blog V3, and a PI3. For the last 2 weeks it's been running great. During the day getting between about 8-10 messages per second, and at the peak of the day over 120 ships. At night the message and ship count goes down (less boats on the river), but a few times I have got ships towards France in the english channel, and towards Netherlands in the north sea. Looking at the all station list, I was quite often about 5th in the UK for messages and also ships.

Anyway, yesterday I was securing the 12m cable to the wall with cable clips (just a few as still need to sort a few things out), and after all was still running uk.

I then decided to upgrade the AIS software (via the web page System menu), think I was on V62, Version details started v0.62-62, after the upgrade I was still on V62 but version details stared v0.62.94 (I think). Anyway as soon as the AIS software restarted I had a massive drop in performance. Messages was about 4 per sec, and ships was only about 50. Rebooted the pi, and made sure everything was secure (it was), but no difference.

I had been running a Gain of 20, so thinking there were some internal software decoder changes I played around with the gain (setting it higher and lower), but again no difference. Tried turning off BaisT, and then back on, but still the same (there is a green light on the LNA, so assume its still working ok).

I then updated AIS again by using the From Source menu option. I am now on v0.62-105-g2f827edc, but again, no improvement.

Here you can see the drop. -20 is about when I did the first software update, and -10 is when I shutdown / rebooted and checked all connections.

And this is from the main AIS Catcher web stats for my station (the drop at about 16:30 is when I was securing the cable).

Any thoughts / ideas. Any major changes in the code between sub version -62 and the current versions that may explain the massive drop in performance.

Ian.

[iwanders73]

So, some more testing. Tried turning BiasT off, and powering LNA via USB. No difference. Removed FM block, No difference. Removed LNA, messages / ships dropped even more. Replaced RTL-SDR Blog with a Airspy Mini, No difference (maybe a bit worse). Removed LNA and used a FlightAware orange SDR (that has a built in LNA), No difference (again maybe a bit worse).

So, thinking maybe the 12m cable got damaged when I attached the few cable clips. But as can be seen from my 1st graph above, all was ok for a while (until I did the software update), so thinking unlikely. However to rule out, I will disconnect the Pi from downstairs and take it to bathroom window and try and connect it directly to the LNA output, and if that still shows no difference maybe directly to the bottom of the 3m cable that goes up the pole to the aerial.

Otherwise was thinking maybe re-image the PI and re-install the AIS Catcher software. Not sure if it possible to install a previous version (such as the 0.62-62 that was working ok).

Also, not sure if it's related, but it seems that since the software update yesterday, the PPM charts aren't showing anything (well they are flatlined at 0).

Ian.

[iwanders73]

So, updated software again via the System tab, and it's now at v0.62-111-g8de30389, and it's seems back to as I would expect. Messages per min have been be averaging about 10 per sec. And Ships about 100 per min. The PPM graph is also now working again.

Here you can clearly see when I did the update, the jump back up.

Was it some kind of bug?

Keep up the good work.
Ian.

[jvde-github]

There is a piece of the code that finds the precise center frequency of the messages that are coming in, I switched that off by accident in the main branch. There are quite a lot of ships not sending on the precise center frequency so those were missed. Your observation of ppm = 0 was spot on and linked to the root cause.

So program versions 0.62-89 to 0.62-105 were impacted and had reduced reception. Apologies for sending you on a chase but enjoyed reading the story of your station.

[iwanders73]

Thanks for the explination, glad it's sorted. And apart from the "if it's not broke, don't upgrade!" the other thing to remember is don't change 2 (or more) things at once. If I had waited a day or so before updating the software, then that would have pointed straight away to a software issue, rather then possible hardware due to the fiddling around I did with the aerial wire and cable clips!!!

If you interested, here's my station - https://aiscatcher.org/stations/details/2185