Antenna testing

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How to test the OLPC XO antennas.

Why test them?

  • they may have been damaged by impact, misuse, or electrostatic discharge,
  • to classify laptops for repair,
  • to verify a repair,
  • to survey a site,
  • to find parts of a site that have low coverage.

Linux, GNOME or Sugar

  • connect to an access point,
  • use Browse, Firefox or Epiphany to visit a web page,
  • while transferring data, display the signal and noise values:
iwconfig eth0

Open Firmware

References

Link Budget

The link budget is the total gains and losses of a radio link.

For an OLPC XO using an access point, this is the sum of:

  • for the access point:
    • the transmit power,
    • the loss in the transmission line (the coax and connectors between the transmitter to the antenna, normally very short),
    • the gain of the antenna,
  • for the environment:
    • the loss due to distance,
    • the loss due to obstructions,
    • the loss due to noise, (from other radio transmitters),
  • for the laptop:
    • the gain of the antenna,
    • the loss in the transmission line (the coax and connectors between the antenna to the receiver),
    • the sensitivity of the receiver.

For two OLPC XO using an adhoc network, the link budget is the sum of:

  • for the first laptop:
    • the transmit power of the wireless card,
    • the loss in the transmission line (the coax and connectors between the transmitter to the antenna),
    • the gain of the antenna,
  • for the environment:
    • the loss due to distance,
    • the loss due to obstructions,
    • the loss due to noise, (from other radio transmitters),
  • for the second laptop:
    • the gain of the antenna,
    • the loss in the transmission line (the coax and connectors between the antenna to the receiver),
    • the sensitivity of the receiver.

See