AIS reception, RTL-SDR vs Vesper XB-8000

[JSantos]

Real world tests of AIS sdr receivers, targeted for sailors are scarce. You might find these results helpful.

Two systems
1 – SDR – 4 elements collinear antenna rigged up close to the mast/spreader à rtl-sdr V2 dongle à Macbook, 10.11.6, rtl_ais (default parameters), OpenCPN 4.4.0
2 – VESPER – commercial VHF antenna on a stern rail à Vesper XB-8000 transponder à Macbook, 10.11.6, OpenCPN 4.4.0

Bed test
Sailing boat moored in a marina, 1 mile from the sea shore, no direct line of sight to the sea; 3 miles away from a commercial harbour with no direct line of sight and with a busy city area between; must of the AIS class A used as targets for this test were underway to or from that commercial harbour; 24 hours test with both systems always on, samples at random intervals, balanced consecutive trials of 6+6 minutes for the 2 systems ; temperature near the rtl- sdr dongle, 21-25 ºC.

Results
Data quite stable across the 24 hours test. Descriptive statistics of 2 samples in the attached file. VESPER clearly outperforms SDR in all recorded parameters: nº of targets, maximum range, warm up time to reach the maximum target number, refresh rate of an AIS target. Connecting the SDR to the commercial VHF antenna drastically reduced range (to only nearby moored vessels up to 0,3 miles). Same performance of Vesper regardless of the type of antenna. Playing with the gain and sampling rate of the rtl_ais decoder, not done here, might help achieving better performance. With a clear line of sight, the RTL performance should be far better, anyway. Of course, there is not an “always best” performance standard for an AIS system; Therefore, the performance of the SDR, in this test, with default parameters, might be more than enough, or not, for a given skipper/goal/navigation area.

In sum
SDR might be useful both as a backup to our boat and as the standalone system for delivering or chartering other boats for a few days. In a previous 1200 miles passage the VESPER needed to be rebooted, to overcome AIS or Wifi troubles, about once per day. It is unlikely to achieve a better reliability with an SDR. So, for an intensive use, particularly if in hot areas, better to buy a spare rtl-dongle and of an improved design.

Fair winds.

Bw
Jorge

[barnakiel]

Yep. The temperature compensing chipset is worth the extra buck.

A dongle could in fact work better than a commercial unit (in the rarified environment of a laboratory). The real difference is how they are put together and protected from knocks, water and other factors.

The dongle is a fine toy for a hobbyist and better than nothing in a boat. But not a substitute to a well built commercial grade unit.

I may be building an rtl based wifi ais node later this year or early next year. I will report back here how it delivers against a SH VHF/AIS combo then (this is what we have onboard).

Thanks for sharing!
Cheers,
b.

[rgleason]

Congratulations on getting signals with the Rtl-Sdr, I've found dAISy receiver much easier and better, but there is a 2 channel dAISy HAT receiver now....

[jeffrobbins]

Originally Posted by JSantos

In a previous 1200 miles passage the VESPER needed to be rebooted, to overcome AIS or Wifi troubles, about once per day.

Hi Jorge,

Glad to hear the XB-8000 performance was good but this is not normal so I'd like to get that sorted out for you. First thing is to check that you've got the latest firmware installed. You'll find the latest release at (http://support.vespermarine.com). If that's the case and you are still having any problems at all, then please contact our tech support at support@vespermarine.com or flick me an email so we can get to the bottom of whatever's going on.

Thanks,

Jeff

[JSantos]

Hi Jeff,

I'll check the firmware and also check in the next sailing voyage if the problem is solved. I'll keep you informed.

Thanks for your concern.

Bw
Jorge

[Snore]

Originally Posted by jeffrobbins

Hi Jorge,

Glad to hear the XB-8000 performance was good but this is not normal so I'd like to get that sorted out for you. First thing is to check that you've got the latest firmware installed. You'll find the latest release at (http://support.vespermarine.com). If that's the case and you are still having any problems at all, then please contact our tech support at support@vespermarine.com or flick me an email so we can get to the bottom of whatever's going on.

Thanks,

Jeff

I was having similar problems. After wrestling with it for a few months, it came down to brief voltage dips.

When the AP was working hard on low batteries, the voltage would drop. All the other electronics would hold up fine, the NMEA 0183 Vesper to Garmin chart plotter was fine. But the Vesper WIFI would truncate a sentence and cause the iPad running iNavx to error out and lose connection.

A big part of the issue on my boat is the relatively power hungry Ray wheel pilot versus a ram below decks. I would imagine any large DC power demand could pull the voltage down enough to cause this error.

Cheers

[jeffrobbins]

Originally Posted by Snore

When the AP was working hard on low batteries, the voltage would drop. All the other electronics would hold up fine, the NMEA 0183 Vesper to Garmin chart plotter was fine. But the Vesper WIFI would truncate a sentence and cause the iPad running iNavx to error out and lose connection.

Something you could try to see if it might help... perhaps you are getting an additional voltage drop in the power cable. If you extended the supplied power cable try increasing the diameter of the extension cable. The XB doesn't draw a lot of power 99% of the time so voltage drop is minimal but when the XB transmits at the same time as the AP is working hard, perhaps that's causing a significant enough voltage drop.

[Snore]

Jeff thanks for the input. I ran a direct wire (<10') from the AIS to the battery (with fuse).

Using whatever gauge wire you guys recommended. I am away from the boat for a few weeks, but will jump in some #10 when I get back and post results. Should be another week.

Bill