us915 rx1 downlink frequency question

[Lawrence Griffiths]

We are trying to send downlinks to 50+ sensors that have been mis configured.
One thing we are puzzled by on us915 is the RX1 downlink frequency doesn’t correlate to the Uplink freq.

UL 905.300 SF9BW125
DL 927.500 SF9B5W00

We understand that DL BW is set according to RX1DROffset
E.g SF9B5W00 but we naively assumed that DL frequency would be identical to uplink Freq? Is this an issue or just another part of LoRaWAN unexplained detail?

Thanks
Lawrence

[Jason Reiss]

It is defined in LoRaWAN and explained precisely in the Regional Parameters specification. The downlink channel is correlated to the uplink frequency by using modulus 8 on the uplink channel index.

Downstream – 8 channels numbered 0 to 7 utilizing LoRa 500 kHz BW at DR8 to 845DR13) starting at 923.3 MHz and incrementing linearly by 600 kHz to 927.5 MHz

Both US915 and AU915 have eight downlink channels. They are 500 KHz width with 600 KHz spacing.

See pages 21 and 25 of LW1.0.3
https://lora-alliance.org/sites/default/files/2018-07/lorawan_regional_parameters_v1.0.3reva_0.pdf

[Lawrence Griffiths]

@jason thanks

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