Dear Tony,
Thanks for the eye opening answer.
I know for a fact that the IMST IC880A gateway has only 2 SX1257 receivers which share the load of 8 channels and receive simultaneously from all 8 LoRa channels. Did you mean to say that a single SX1257 has multiple receivers inside?
I’ve always has this problem as to how could the SX1301 DSP know which IQ data correspond to which physical channel if the SX1257 RF front end is cycling through multiple physical channels time to time(dwelling through channels). Your answer makes me think differently. Thank you. However, your answer lead me to few different questions. Perhaps you may like to help me a bit further.
To my understanding, the IQ data sent from the SX1257 RF front end to the LoRa SX1301 DSP via a serial interface, I.E bit by bit. A standard LoRa gateway ( such as the IMST IC880A) has only 2 SX1257 front ends. I paste a diagram of the SX1257 internals below.
It seems to me from the diagram that the SX1257 can only tune to one PLL frequency at a time. I.e. It sends a single frequency quadrature clock (2 clock signals, 90 degrees offset) to the Mixer.
Now lets compute the channels in the 868MHz ISM Band. It has 8 channels 200KHz apart.
so that’s a total of more than 800KHz BW per each front end IC as the Standard gateway has to sample 8 channels.
So I am confused how these 2X SX1257 ICs manage to sample a BW of 1800KHz to capture all LoRa channels.
Please help.