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Propagation notes

MigrationGetting from here to there-how and why

Two terms will show up if you are looking at nodes on your device, or more useful, one of the local meshsense stations:

  • RSSI: received signal strength (how loud do I hear you)
  • SNR: signal to noise radio (how noisy are the surroundings: library or noisy street)
The best metaphor for SNR I think is talking to someone in progressthe shower: you can hear them (high signal, low noise) while they cannot hear you (same signal, high noise).
There is also a phenomenon called "de-sensing" which means if a radio is transmitting near another radio, the gain (sensitivity) of the second unit is automatically decreased (AGC or automatic gain control)
What does this mean for Appleyour Wikiproject?
  • keep nodes that are not actively repeating mesh traffic in client-mute mode, meaning they hear but do not repeat
  • make sure any node in repeater/router mode cannot directly "see" another repeater, as they will simply echo each other
  • careful placement of repeaters and routers is critical: both repeat all traffic, so using router-late is a good option if you are not sure: it delays the repeating until another can respond
  • the only difference between repeater and router is the former does not show up on maps
Antennas:
See the article listed on the home page i543A9.for a detailed account of different antennas.
General thoughts:
  • Most antennas used are vertical quarter wave omni antennas or "whip" antennas
  • Higher performance antennas look like these, but are actually dipole antennas
  • Make a larger dipole, arrange it like a fish skeleton and you have a yagi antenna or yagi-uda beam antenna (n.b. yagi is "goat" in Japanese)
As a general rule, the longer the vertical omni antenna, the more disk-like is the horizontal propagation pattern
In my experience, mesh follows many paths, and using a yagi may seem like a great way to extend range, but be careful that the polarization of the antenna is setup correctly: 905 mHz uses vertical polarization, so any yagi should look like vertical elements to be useful.

Migrated from Apple Server Wiki. Original page ID: i543A9