LowPowerLab Forum

Hardware support => RF - Range - Antennas - RFM69 library => Topic started by: evh on May 12, 2015, 07:15:20 PM

Title: OPTIMUM SENSITIVITY SETTING FOR RX?
Post by: evh on May 12, 2015, 07:15:20 PM

I am deploying 915Mhz HWs at 1200Baud.   It seems like I never get an RSSI that is weaker than about 90db.   I am hoping to receive packets that are down to 120db.  Is there a setting I should use to get maximum sensitivity?  I noticed one -90 setting for CMSA or some such thing in the .h file.  I changed that to 119, but it did not seem to have any effect.

Thanks for whatever you can tell me.
Title: Re: OPTIMUM SENSITIVITY SETTING FOR RX?
Post by: Felix on May 13, 2015, 10:51:53 AM
I am deploying 915Mhz HWs at 1200Baud.   It seems like I never get an RSSI that is weaker than about 90db.   I am hoping to receive packets that are down to 120db.  Is there a setting I should use to get maximum sensitivity?  I noticed one -90 setting for CMSA or some such thing in the .h file.  I changed that to 119, but it did not seem to have any effect.

You mean weaker stronger than -90dbm?
To change the RSSI threshold look for this line - note there is a formula involved, you might want to check the datasheet (http://www.semtech.com/images/datasheet/sx1231h.pdf) for more details:

Code: [Select]
/* 0x29 */ { REG_RSSITHRESH, 220 }, // must be set to dBm = (-Sensitivity / 2), default is 0xE4 = 228 so -114dBm