Hi,
I have some problem with RFM69HW module.
I wrote some code based on LOWPOWERLAB RFM69 library.
I have 4 modules that communicate without problems with FSK modulation and 57,6kbs baudrate (868Mhz, +20dbm mode).
Now I try avoid some collision when transmitting data. I`m checking RSSI before sending data like in LowPowerLab library.
When RSSI is above -90 dbm channel is busy and transmission is delayed.
LowPowerLab library code in this case is:
//
if (_mode == RF69_MODE_RX && PAYLOADLEN == 0 && readRSSI() < CSMA_LIMIT) //if signal stronger than -100dBm is detected assume channel activity
CSMA_LIMIT is set to -90dbm
//
That means, author of this code has RSSI lower than -90dbm (-100dbm in comment ?) when there is no RF signal.
In my case I have signal between -90 and -80dbm (depends from module) when is no RF signal (my CSMA_LIMIT is -90dbm).
This indicates to code that channel is still busy.
Additional, I can still receive proper packets when RSSI is about -90dbm.
I can move my CSMA_LIMIT for example to -70dbm
That means, when signal level is LOW, I can still receive packets, but I can`t recognize channel activity
My questions are:
What are practical RSSI values for RFM69HW when nobody transmit data (channel is free)?
Maybe I`m doing something wrong. Should be my RSSI values lower than -90dbm when channel is free.
Best regards,
TL