TxPower 29 and RX2 window

ChirpStack (v4) Setup and configuration
1

Hello there, maybe I am off-topic since I don’t directly use ChirpStack but within new Helium console. Region EU868. Excuse me if it’s off-topic.

Chirpstack sends downlink with

spreadingFactor:12
power:29

Two questions.

  1. Power 29 is legal for Europe? I have the impression 16dB EIRP is the limit for nodes. I don’t remember for gateways. I suppose is the same?
  2. When joining downlink was in RX1, now it’s SF12 on RX2 window. There is a reason for that? SF12 and with power 29 creates noise.
2

ETSI defines which frequencies can be used in what way. The RX2 frequency (869.525 MHz) can be used with +30dBm EIRP maximum at a 10% dutycycle. So high-SF messages are usually moved to RX2 window since it means the gateway is allowed to transmit more of those (as the dutycycle on Rx1 is 1%).

1 Like
3

Nice info about 1% and 10% duty cycle, I forgot it. ETSI p.22

869,400 MHz to 869,650 MHz, 500 mW e.r.p., ≤ 10 % duty cycle

500mW I thing it’s 27dBm. So it seems fine?

4

That’s indeed the right document, thanks for linking it. I don’t really know how to calculate the dBm from the mW unit, but it’s somewhere around 30dBm, that’s what I remember. So yes, 29dBm should be right at the edge of what’s allowed.

To get back to your original question w.r.t. noise at SF12/TX29: that is indeed a known problem and overkill in most situations - there’s a valid reason why TTN promotes SF9 for Rx2 as that is usually plenty at TX29 to get the downlink delivered.