New AIS receiver: dAISy-catcher #563
Replies: 5 comments 24 replies
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Hello 👋 I worked with Jasper on this project, mainly working on the hardware while Jasper did his DSP magic. Based on side-by-side tests, performance is comparable to running AIS-catcher with a good SDR like the Airspy HF+. At the same time, the dAISy-catcher uses about half the power of just the SDR, and that's with doing all the compute heavy work on the receiver instead of the host computer. My favorite feature of the dAISy-catcher is the precision timestamps, though we're still looking for a good real-world application for that data. Triangulation is an obvious one, but it turned out to be trickier than expected due to the impact of topography and atmospheric conditions. The below plot shows how time-of-arrival (Y-axis) correlates with distance (X-axis), but also the differences between AIS transponders. The dotted line is expected time based on speed of light. 
Happy to answer any questions. You're also welcome to contact me by email (see profile) if you want to pitch an interesting, resource-limited project that needs a better AIS receiver, or have an application for the precision timestamps. |
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Hi Jasper & Adrian, Great news. I just ordered one yesterday to replace a dAISy HAT and Uputronics LNA running on a RPi5. Thanks, |
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This picture is with the 16mm stand-offs, which leaves a bit of room above the active cooler for the air to circulate. If the circuit board would expand over the ports on the right, it would sit flush on top of the USB ports with maybe 0.1-0.2mm to spare. The plastic body of the 2x40 header provided with the 16mm kit is the same height as the more commonly available double-shrouded stacking headers with long pins. For comparison, the dAISy HAT sits 11mm above the circuit board of the Pi. |
I just ordered one yesterday for a Raspberry pi 3. I got the 11mm standoffs, should I have ordered the 16mm? Anyone know of a case for a model 3 that would fit a daisy catcher in a hat configuration? |
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11mm works fine if you don't have a heat-sink or active cooler on the Raspberry Pi CPU. The dAISy-catcher with 11mm stacking header will fit into most Raspberry Pi cases that accommodate for a HAT. Though you may have to drill a hole for the antenna connector. I think the Raspberry Pi 4 case you ordered will also work for a Pi 3. The side panel for the Ethernet/USB jacks can be reverted to match the rearranged ports on the Pi 4 vs Pi 3. |
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The tallest part of the dAISy-catcher is the GPS header. With the 16mm header, the dAISy-catcher sits ~10 mm above the USB ports. 
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Thanks for taking the time to post the detailed pictures—they were very helpful. I'm planning to use a Raspberry Pi 3 since it produces considerably less heat than a Pi 4/5, and the performance should be more than adequate for running dAISy-catcher. This receiver will eventually be installed at a friend's house about 30 minutes away, so reliability is more important than raw performance. I'm running Raspberry Pi OS Lite with Tailscale for secure remote SSH access, which should let me perform software updates and maintenance without making the drive. I'm hoping that will let me keep everything in a compact plastic case without needing active cooling. Do you think a fan is necessary in the HAT configuration, or have you found |
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Just ordered one, should arrive any moment, looking forward to difference with RTL-SDR v4 |
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yes, sorry I missed that. working now. If I compare my two stations I have two examples -11 for RTL-SDR v4 and -85 for dAisycatcher for a ship a couple of km's away |
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I was looking for the plot, to see the lower bounds of signal level to get an idea of the noise floor (technically the signal strength of the weakest AIS messages received, actual noise floor is a few dB lower). With a high noise floor, a more sensitive receiver wouldn't improve results. The lower bound of the signal level plot should be below -100 dBm, ideally below -105 dBm in an RF quiet setup. 
(here a change in the setup introduced a lot of noise, which bumped up the weakest signal levels by over 10 dBm) Though your strong signal reminds me, that I should cut a new firmware version for the dAISy-catcher. There's a bug in v1.0 where very high signal levels (-43 dBm) can be reported as a very low signal level (-114 dBm). |
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Here is the plot of the daisy-catcher 
And this of the rtlsdr v4, so that plot is a bit weird, those values can't be correct 
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Looks like your weakest messages with the dAISy-catcher are around -97 dBm, with the peaks below that every few minutes due to the bug I've mentioned above. You also have a lot of traffic with very high signal strength. I guess you're located right at a harbor. An alternative explanation is, that a strong local transmitters keeps the 16 dB front-end attenuator permanently enabled, which will impact sensitivity at the low end. Is the red CH2 LED turned on permanently, or only flickering occasionally? Do you use an external amplifier? If so, try without. I'd like to send you an external filter to see if that improves things. If you're up for it, send an email to the address in my profile. I found the signal level chart not very useful for the RTL-SDR. I think in this case the chart just represents the magnitude of the IQ data as received by AIS-catcher, not accounting for any amplification and (automatic) gain control happening in the SDR hardware. With the dAISy-catcher, the magnitude of the IQ data is corrected for the amplification, attenuation and automatic gain control happening in the frontend, representing the signal strength at the antenna port within about +/- 1 dB. |
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I don't see the red CH2 light on, the red CH1 does flash sometimes. I've done some testing with the antenne a bit more outside and that helps a lot in the distance, would have to check that with the RTL side by side to make a fair comparions. I'm in a quite busy environment indeed, station ID 3321/Kogeka |
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Same antenna. Top is dAISy-catcher, bottom is Nooelec NESDR SMArTee v2 SDR + Uputronics 162MHz Filtered Preamp. 
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Interesting distribution. Looks like most targets are far away, mixed with a few local ones at -60 dBm. |
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Still testing before I move the AIS station to it's permanent location, but saw some impressive Tropospheric Ducting this morning, 450+ miles. The daisy-catcher is exceeding expectations. Rasberry Pi 3 with ais-catcher and daisy-catcher, temporarily connected to my roof top comet GP-3 dual band ham radio antenna. I'm blocked to the west/ocean by hillsides, but do have a path to the ocean down a narrow valley to the south. I'm seeing ships 450 miles away, AIS is only 5 watts! There was a heavy overcast this morning, ideal conditions for tropospheric ducting. |
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Looks good! Unfortunately we rarely get any ducting up here in the PNW. Small nit: AIS class A is 12.5W, and 2W for class B. Checking Wikipedia, there seems to be a newer Class B that's using SOTDMA and is 5W. |
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I believe AIS-catcher let's you identify a transponder using SOTDMA technology. 
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I have the opportunity to install a daisy-catcher on a commercial tower on a hillside overlooking the Pacific. Would the filter listed at wegmatt add any value? Any suggestions or tips for installation? We will be using an existing retired VHF ham radio antenna fed to the shack with hard-line. The raspberry pi/Daisy catcher will be installed in a cabinet shared with VHF and UHF ham radio repeaters.
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The dAISy-catcher has an integrated filter and amplifier, so not sure an additional filter would help unless you have noise around. Being on a tower, that could be a potential issue? 
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Really looking forward to see what coverage you get from that tower. Do you have a RF spectrum/waterfall from that location? Are there any continuous transmitters on that tower? And if so at what frequencies? |
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Hi all,
just want to point out a new AIS receiver we developed together with Wegmatt, the dAISy-catcher. More information on specs and documentation can be found here. The idea was to combine the advantages of an SDR-based AIS receiver (reception quality, flexibility) with the advantages of a hardware solution (plug-and-play solution as either USB serial receiver or Raspberry Pi HAT, low power consumption, accurate signal levels and timestamps, and AIS-tuned filters for robustness).
The new device can be run with AIS-catcher using serial device as input driver.
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