A Si5351 DIY oscillator project

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.

What

These days I am doing a major revamp of my radio node that is working on a Raspberry Pi 4 but using an USB dongle for audio interface. I want to move that away from USB audio and implement the I2S interface that I tested some time ago. That is a much more elegant and compact solution. For those who don’t know, we have here, in YO, a very cool internet and repeater based network that works with radio terminals as “nodes”. A ham radio operator can choose from using a repeater (linked to this network) or a personal radio node to connect to the same network. These personal nodes are usually built either on Orange Pi or – much less frequently – on Raspberry Pi, using a SA818 or similar radio transceivers. Orange Pi is very popular because of its built-in audio interface that allowes bidirectional audio communication. This is lacking on Raspberry Pis computers. But I do not like OPi because of their other issues which I consider major and sufficient for me to be a “no go” for any project. So I went on the way of discovering I2S and means of audio communication as such on Raspberry Pi. This was a short intro. Just to put things a bit in their perspective.

Why

From this, to what I want to do: I2S interface on RPi and directly using a new radio stack implementation, getting rid of the SA818. That served and serves well but displays some issues that I really don’t like: aside from being bulky, I suspect there are some flaws in the design like timeouts and some issues with the firmware inside SA818’s μ-Controller. Not to mention that I do not need 1W of RF power for such a node. Don’t get me wrong, I can live with that but I want to try to improve a bit the way these nodes work, the audio, and their setup. So the logical step would be to go directly into using the chip inside SA818, the RDA1846, now obsolete, in a dedicated new transceiver that is completely designed and built by me. Including the PCB. The major advantage of this approach is being able to create similar radio nodes on any computer that supports I2S and with a minimal radio signature, I mean minimalistic approach on the transceiver design.

How

But this is rather challenging. I would have to deal, same time, with tweaking I2S (and this is a lot, believe me) with details of implementation of the RDA1846 and its cr@ppy documentation. Moreover, RDA1846 is obsolete, not manufactured anymore. I have only 10 such chips from a previous AliExpress buy and gift from a friend of mine, YO4ISC, another ham and one of the architects of this network I was talking about. In time, I have to find a replacement, but for now I could do only an initial small batch of 10 such nodes.

So I decided to split the concerns, so to speak, siplify matters and project. I will deal first with an SA818 implementation with I2S and, later on, I will go with chip simplification on RDA1846, in a separate project. However, for RD1846 I need an oscillator and this is where this Si5351 comes into picture.