YO3ITI • Alauda Projects

SA818 radio node – version 2.0

By AP, 

            
I was pretty busy since August 2024 with a lot of other tasks, mostly job-related and did not have too much time for DIY and tinkering. And this included my SA818 project.I cannot believe how fast time flies and seems the speed is increasing as I am getting older. However, december was a nice month, a little more relaxed so I found some time to burn on my hobbies. And I did a redesign of the august 2024 version of my SA818– and CM108-based radio node.


In January 2026 I ordered the improved version from jlcpcb.com with many new parts, including a SMD 40-pin header and SA818 pre-assembled by them. This is version 2.0 and I dare to say it simply runs flawlessly.


The node, assembled on a Raspberry Pi Zero W2 board. Antenna is a Linx 430 MHz, high efficiency professional antenna I got from Mouser.


All boards came from jlcpcb in this format:




Probably the stencil for SA818 could not be accomodated on the smaller, final shaped, board so they chose this approach.


This version supports active cooling by attaching a 4-wire fan (with tacho and PWM wires). I designed the board with a MOLEX PicoBlade 4-pin 1.25mm pitch smd connector on the bottom of the board for convenience and fast connection of a fan. Also, it has an UFL connector for those that want to have a remote-ish antenna.


I had gathered some lessons learned from my last version and also tried a new approach to noise management that seems to work darn well: additional and improved power supply filtering and some pcb design tricks that simply make a huge difference. I am extremely pleased that I can use cheap switchmode 5V power supplies and there is not even a shadow of any hum or click or hiss. Modulation is good, not perfect. But this is a limitation of the SA818 and it’s crappy emphasis/de-emphasis filters. Anyway, this is the last CM108-based. I will completely drop this project and I will focus only on the I2S version. I think the CM108 version simply cannot be improved too much anymore but most importantly I want to focus on I2S, driver and dtoverlay support. I have in mind some other RPI Zero based projects that will benefit from high quality audio on I2S.


More to come. Some more pictures below:


		
		


WARNING !!! Please do not write me asking for KiCad files and samples. I do not sell these and definitely I will not share my work. I do not believe in the so called Open Hardware concept. This is just another way of stealing other people work and capitalizing on their efforts. People that asl for free lunch should at least have the decency to credit the authors – which they never do. You can at least make a small effort to learn new things – learning is good for your brains – and do these things by yourselves especially given the fact that these are not complicated projects. If you don’t like it, you can shove it. Thank you for your understanding.

                        
            

    


    




    
    

                        

                    

                        

                            
Raspberry LED error codes
By AP,  
While debugging a faulty RPi I had to find out what are the LED error codes. You might find these useful.


                            

                                
                                                                    
                            

                        

                    

                

                        

                    

                        

                            
Fan control with dtoverlay on Raspberry
By AP,  
Another day working a bit for my SA818 radio node project. Today I tried active cooling with a 5V fan driven from RPIs 5V rail and controlled from GPIOs with a MOSFET (2N7002).


                            

                                
                                                                    
                            

                        

                    

                

            







			
		
Comments are closed.


	

			

			

				
            
Related posts

                    

                
                

                

                    

                        
Using lsof
By AP,  
                        

                            Raspberry Pi | Raspberry Pi Zero W 2 | raspbian                        

                        
lsof command can show which processes are using which resources. This is extremely useful for troubleshooting. Basic syntax is: Without arguments, it lists all open files on the system (requires root privileges). Common Use Cases and Examples: Find which process is using a file: Find which process is using a port: The above command Lists […]

                        

                            
                                                            
                        

                    

                

                

                
                

                
                

                

                    

                        
NetworkManager connection priority
By AP,  
                        

                            network manager | radio node | Raspberry Pi                        

                        
I recently ran into an issue with my Raspberry-based radio node. I tried to connect to some othet WiFi access points and I realized that I had no idea how to set connection priorities if I have multiple candidates for connection. I was used with wpa-supplicant way of doing things which was just to add […]

                        

                            
                                                            
                        

                    

                

                

                
                

                
                

                
                

                

                    

                        
Schematic Parity Error
By AP,  
                        

                            kicad | PCB design | radio node                        

                        
I am already one week into the design of the PCB for my new radio node and today I discovered some schematic errors that I had to fix. Running the DRC (Design Rule Check[er]) KiCad threw some schematic parity errors which “occurs when there’s a mismatch between the schematic diagram and the physical PCB (printed […]

                        

                            
                                                            
                        

                    

                

                

                
                

                

                    

                        
I2S Raspberry Interface (4)
By AP,  
                        

                            CS4344 | CS5343 | I2S | radio node | Raspberry Pi                        

                        
More work today. Some wires got loose and I did some experiments with .asoundrc and ALSA settings. I added a 39 Ω ballast resistor on SDIN and SDOUT lines and put a ferrite core on both wires. The radio node works as expected, absolutely no issues with one exception, a periodic pop that is audible […]

                        

                            
                                                            
                        

                    

                

                

                

                    

                        
A Si5351 DIY oscillator project
By AP,  
                        

                            I2S | oscillators | SA818 | Si5351                        

                        
I have some Si5351 chips that I never used for any projects. I purchased them from Mouser, I believe for an APRS project, long-standing and overdue. That APRS project I started some time ago but I never completed and maybe I should strongly consider to complete. But this is another topic.

                        

                            
                                                            
                        

                    

                

                

                
                

                
                

                

                    

                        
I2S interface for Raspberry Pi (1)
By AP,  
                        

                            Cirrus | CS4344 | CS5343 | I2S | radio node | Raspberry Pi                        

                        
Today I managed to connect the Digilent Pmod I2S2 to a Raspberry Pi 4 and have all frequencies generated. This is part of an older project that I left abandoned for a while: a radio node built on Raspberry Pi and using Svxlink. As known, Raspberry boards do not have a proper audio interface and […]

                        

                            
                                                            
                        

                    

                

                

                

                    

                        
Beacon with SiLabs module
By AP,  
                        

                            433 MHz | 70 cm | beacon | DIY | SiLabs                        

                        
This is a beacon project started by my friend YO5VAE. He faced some issues while programming of the Si4463-based module and I thought I might give a hand. I resoldered the entire project on an empty Arduino shield to allow expansion of the project with some additional modules. Below are some pics, but probably the […]

                        

                            
                                                            
                        

                    

                

                

                

                    

                        
Ferrite beads
By AP,  
                        

                            DIY | eBay                        

                        
I ordered some ferrite beads for a RF circulator project I currently work on but these might also be very handy for the SWR bridge project. These are extremely efficient for RF supression, or at least this is what they say.

                        

                            
                                                            
                        

                    

                

                

                

                    

                        
Boards for prototypes
By AP,  
                        

                            DIY                        

                        
For low frequency projects, a fast way to prototype is using a bare PCB and scratch some dividers that allow “manhattan” style prototyping. I am especially very fond of this prototyping technique and I believe that PCB design should be avoided in the early stages of prototyping. Jim Williams was an artist in such designs. […]

                        

                            
                                                            
                        

                    

                

                

                

                    

                        
Electronics from China — Pixie CW
By AP,  
                        

                            DIY | electronic parts                        

                        
Power supply: DC 9v – 12v Antenna: 50 ohms, is not balanced, 7MHZ band, standing wave ratio below 1.8 Receive the static current: 10 mA @ 9 v Transmission power: 0.8W @ 9 v, 1.2W @ 12 v Frequency range: 7.023 MHz launch, receive 7.023-7.026 MHz (7.023 MHz crystals) Stray (harmonic) inhibition: – 20 db […]

                        

                            
                                                            
                        

                    

                

                

                

                    

                        
Electronics from China
By AP,  
                        

                            DIY | electronic parts                        

                        
I am pretty pleased by the outcome of my commercial endeavours on eBay. Purchasing seems to be a pleasure; until now — with just one exception — I was spared from any nasty experiences. After several small items that I ordered in part for my curiosity to evaluate speed and quality of shipments from chinese suppliers, I […]

                        

                            
                                                            
                        

                    

                

                

                

                    

                        
DIY Fridge Magnets
By AP,  
                        

                            DIY | fun | magnets                        

                        
I love fridge magnets. We love fridge magnets (my wife likes them too). This is how our fridge looks like: But we also love beer. And we have a large collection of beer bottle caps and coasters. So I thought to combine these and make the caps stick to the refrigerator. Now, what you need […]

                        

                            
                                                            
                        

                    

                

                

                

                    

                        
Logic Analyzer!
By AP,  
                        

                            DIY | Logic Analyzer | Objective-C                        

                        
…and not only software (maybe). OK, to keep things short, I got tired by limitations of my Saleae logic analyzer, especially on the software side so I decided to build one. This is my new project: a DIY logic analyzer that I will hopefully use to better extent in my other projects. First results promising. […]