The AIS receiver described in this article is an update to an earlier version that revealed some issues in the print layout. Since I had to place an order for some other PCB projects anyway, I let this corrected version run along and also took the opportunity to add an extra Si4362 (or Si4463) to the design for dual channel simultaneous AIS-receipt.
With the EZRadioPro Series, Silicon Labs provides an attractive family of receiver and transceiver chips. They have a good performance, low power consumption, integrated synthesizer for the sub-GHz (119-1050 Mhz) range, while with their QNF20 they are small in size but still possible to solder by hand. Moreover, they are easily available and can be purchased for low prices on eBay and AliExpress (per piece but also as a module where the crystal can also be used). There are many manufacturers that supply similar ICs but most of them are limited to the UHF range or even, within that, only the ISM bands (433 and 866 MHz). Few alternatives remain that cover the VHF area and - more specifically - the two AIS channels 161.975 MHz and 162.050 MHz. In this design there are two pieces placed on the print, each with its own crystal. Where in my first version the receiver switched channels alternately, there is now real simultaneous reception and therefore fewer AIS messages are missed. For a general introduction to AIS and the design choices made in the design, see the original article: AIS-receiver with Silabs Si4362 | Si4463 radio chip and STM32 processor
Despite the extra receiver chip, I was able to reduce the dimensions of the PCB a bit further, while maintaining the RS422 interface with the MAX3438. The same goes for the LNA with the AT3543 pHEMT mosfet sandwiched between two bandpass filters. It has now become clear to me that the extra amplification with the AT3543 is not an unqualified success. This is because blocking from the FM broadcasting band can soon be lurking. See the following article I devoted to it: An alternative matching network for the SI4362 | Si446x LC-Balun at AIS frequencies. Incidentally, the mosfet is connected by a capacitor of a few pF, which results in a 5th order bandpass filter is created and that is certainly not a superfluous luxury. For a next version I would probably switch to one or two SAW filters. For example, the TA0395A or TA0289A from Tai Saw Technology Co. Ltd.. The datasheets can be found in the downloads of this article and the TA0289A can be obtained from the webshop of Tindie.
As I mentioned by my first version: The design is derived from the dAISy project by Adrian Studer which was based on Texas Instrument's MPS430. It was published at the time on the Energia 43oh but that forum is now dormant but the original source can still be found at Github. All credits goes to him.
Here below you can find the circuit diagram, source code, gerbers and other production files
Some notes to the source code: Parts of the code are generated with the STM32CubeMX version 6.5.0.code generator which can be obtained from STMicroelectronics at https://www.st.com/stm32cubemx. The current source does not rely at the (in-)famous STM32 HAL Library but at the STM32 LL (Low Level) library instead, in my opinion a considerable improvement. From within STM32CubeMX the code generation can be targeted to various compiler vendors including Keil. Keil's free MDK-Lite Edition version of their Microcontroller Development Kit can be obtained from their website at https://www2.keil.com/mdk5/. The configiration file for the radio chip - 'uFlexDual4362_l.h' - is generated with the "WDS GUI Version: 3.2.11.0", the Wireless Development Suite", from Silicon Lab which can be downloaded from their website at https://www.silabs.com. All modifications to the original source are "as is", and are just made for 'fun and education' without any commercial intentions.
Schematic
Downloads
