Reference: https://meshtastic.org/docs/overview/radio-settings/#presets

What does the link budget, expressed in dB, actually refer to?

Does that mean I can expect to have a usable signal down to the RSSI listed as the link budget? e.g. LongFast will be usable down to -153 dB RSSI where ShortFast will need a received signal strength of at least -143 dB?

I’m debating on whether to deploy my mesh in LongFast mode (default) or ShortFast. I’ve received advice that, in the wild, ShortFast has “close enough” range to LongFast but with the benefits of being roughly 10x faster and reducing the airtime per client (which produces other benefits). They said terrain, height, and line-of-sight are more critical factors (which makes sense).

Looking at the link budget table, there’s also a 10dB difference between ShortFast and LongFast. I do know that the decibel scale is logarithmic, so that difference is fairly significant.

Basically, I need to make sure I’m understanding link budgets correctly so I can put the proper values into the site planner.

  • Admiral Patrick@dubvee.orgOPEnglish
    0·
    26 days ago

    I still don’t fully understand how it’s applied to the real world, but I’m a bit closer after reading this:

    https://lora.readthedocs.io/en/latest/#link-budget

    A link budget is the sum of all of the gains and losses from the transmitter, through the medium (aka free space), to the receiver in a telecommunication system. It is a way of quantifying the link performance.

    The receiver sensitivity is the lowest power level at which receiver can receive or demodulate the signal.