Pole1 Received Signal to Noise ratio report

Meshtastic Signal To noise ratio (SNR), importance and explanation

RF (Radio Frequency) NOISE

Think of this just like the noise you hear as it is "waves" just ones we can't directly hear

Just like Audio there is always an element of noise no matter how small. Those that remember tuning old FM radio's hearing all that hiss sound between radio stations.and on AM radio the hums crackles and pops. Some of this noise is natural from the atmosphere, even left over from the big bang. and these days much of it is man made in the form of interference from other electrical items radiating RF noise and EMF, EMI, RFI, Amateur Radio Hams refer to man made noise as QRM

Traditional Broadcast radio signals need to be strong enough to be above the noise but LoRa (inc Meshtastic) can work below the noise floor.

Taken from the LoRa Documentation

LoRa, or Long Range Area, is a technology that can demodulate signals that are below the noise floor, which is usually the physical limit of sensitivity. LoRa can demodulate signals that are -7.5 dB to -20 dB below the noise floor, but only at very slow data rates of ≤ 0.5 Kbit / s. If the data rate increases, the negative signal-to-noise ratio (SNR) will increase towards zero, or the bandwidth will need to be increased, which will increase the noise level. To help the receiver detect the preamble and sync word, LoRa uses a simpler up-down chirping that doesn't need to carry a lot of information. The goal is to make the preamble and sync word noticeable against the noise floor, and easy to demodulate with high accuracy.

Image below is very simplistic representation of a signal below and above the noise floor

SNR

SNR (Signal-to-Noise Ratio), often written as S/N, is the ratio of the received signal power to the noise floor. SNR is commonly used to determine the quality of the received signal.

SNR can be calculated using the following formula and is often expressed in decibels (dB):

SNR (dB) = Perceived_signal (dBm) - Pnoise (dBm)

If the RSSI is above the noise floor the receiver can easily demodulate the signal

So does SNR matter for Meshtastic

YES!!! its still very important

although it can work below the noise floor being above it or as near to zero the better as it will mean your signal will go further and more reliable for transmitting and receiving messages

In Meshtastic, signal-to-noise ratio (SNR) is a measurement of how strong a desired signal is compared to background noise. A higher SNR means a clearer signal, which can improve the quality and reliability of data transmission. SNR is usually expressed in decibels (dB), and a positive SNR indicates that the signal power is greater than the noise floor. A negative SNR means that the signal power is less than the noise power.

How Can you improve the SNR

• Increase Antenna Height (more hight = more might) also gets you away from possible QRM noise
• Higher Gain Antennas
• Reduce path loss (Specialist high frequency low loss coax shorten length)ensure high quality connections at every stage
• Reduce likely hood of picking up QRM (Noise) for base stations have your node in a metal screened box with external LoRa and Wifi/Bluetooth Antennas.Keep node away from other equipment. Ensure power supply is not sending noise to the node (use filtering Ferrite chokes etc. in the path)

Below is an image from Richard Wenner video explaining RSSI, SNR, Noise Floor and Margin see video

RSSI is approx -65 dBm the noise floor is approx -90 dBm. You can calculate the SNR as follows:-

SNR (dB) = Perceived_signal (dBm) - Pnoise (dBm)

SNR (dB) = -65 dBm -(-90 dBm) = 25 dB