The Australian regulator has allocated the band of frequencies from 915.1 - 927.9 for used as an ISM band. This band of frequencies is used by a range of systems including Drones, industrial equipment as well as a number of IoT type systems. To allow for interworking with Lora the Lora Alliance defined a series of 64 channels, each 200kHz wide with the first centred on 915.2MHz and the 64th centred on 927.8 MHz.
For LoraWan they went further and defined the “downlink” radio channels for a Gateway to communicate with a Node. For “uplink” from the Node to Gateway they divided the 64 channels into 8 blocks of 8 channels to match the design of the Semtech radio modules found in Gateways. These blocks (of 8 channels each) are now called FSB1 to FSB8.
For AU915 the uplink and downlink channels are
Being a bit small and making it easier to read, I’ve broken the image into sections
Bottom End of the ISM band
Middle Section
Top End of the band
The channels in light or dark blue are the uplink channels from the Node to the Gate
The light orange blocks are the downlink channels from the Gateway to the Node.
TTN in Au915 is located in FSB2 which means the Nodes transmit on all 8 channels from 916,8 MHz to 918.2 MHz. The gateway responds further up the band on 923.9 MHz
An important thing to realise is the uplink and downlink channels are different, they don’t overlap and are sufficiently separated not to interfere with each other. This is an important aspect for the operation of TTN which I’d ask you to remember as we will come back to later…
When we get to describe both versions of AS923 you will see the Node and Gateway communicate back and forward on the same channel. So there is a quite a distinct difference between the underlying operation and performance of AU915 and AS923. The same occurs in Europe on EU868 where I would bet they envy both the number of channels we have and the separation of uplink from downlink frequencies.