Low RSSI and Short range issue of RFM95W

[Kim]

Hello, I am using RFM95W transceiver module for a sensor data transmission between a two devices. Both have same module ie RFM95W.
Operating freq.   : 915.0 MHz
MCU                  : ESP32
Libraries            : RadioHead
Data Rate          : setModemConfig(Bw125Cr45Sf128); And setModemConfig(Bw125Cr48Sf4096);
Modulation Type : LoRa
Mode                 : Continuous Mode
Transmitting Power set to +13dBm.
Antenna             : ANT-916-CW-RCL-SMA, which is Omnidirectional Monopole 1/4-wave

We just used the example codes of RadioHead libraries for both Client and Server. YES it's the example codes!

However,
With SF = 128, I see an RSSI of about –80 dBm at a few meters in line-of-sight. When I move to roughly 30m with walls penetrated, RSSI falls to around –120 dBm, packets still get through but merely the bound.
To try and push the range further, I increase the spreading factor to 4096 (i.e. lower the data rate), yet under 50 m + penetrating floor, the RSSI drops even more—to about –135 dBm—and 80% of the packet lost.
For pins setting, we have not used G1~G5 on LoRa module, but we connected SPI-related pins and used G0 for interupt.
Can anyone help to figure these out? I can provide further info if needed.

[Kim]

Do I need to give a big reference ground plane for the monopole antenna?

[Felix]

Not sure what antenna you use but a 915mhz monopole is around 82mm, you'll need a GND plane (ideally disc) at its base that is equal in radius.
See this: https://lowpowerlab.com/guide/rf-best-practices/
PS I often say breadboards are one of the worst deterrents to entry level electronics enthusiasts. You'd be much better off with a board that is designed to host a radio module rather than try to airwire it around a breadboard. At the clock speeds these modules work signal integrity starts to matter and breadboards are a horrible way to build a reliable circuit that has any kind of data signals at clock speeds of any significant speed.