Introduction

The activity was a hands on demonstration on the effects of physical and environmemntal conditions on wifi links. This demo was performed using a Metrix box linked to a wifi client over approx. 20m link. The link distance being short a step attenuator was used to simulate a longer hop distance. A 14.5 dBi gain Yagi antenna was used at the Tx while an 8.5 dBi directional panel was used at receiver. A portion of the received signal was tapped into a spectrum analyser using a directional coupler. At the receiver end Netstumbler tool was used to measure link performance in respect of the received signal strength indication (RSSI). The net objectives of this activity was to:

• Measure RSSI at different simulated environmental conditions i.e. unobstructed path, path over dry leafy environment, path over wet leafs.
• Measure RSSI at different simulated physical conditions i.e. near end- far end obstaruction using solid copper foil, meshed grill, wood, glass, packs of books and CDs.

Methodology

• Establish the link over an unobstructed path and measure the RSSI using the netstumbler and spectrum analyser.
• Measure RSSI with a solid copper foil over the path near the receiving antenna, at link mid-point and near the transmitting antenna.
• Measure RSSI with meshed grill over the path at the same points mentioned above.
• Measure RSSI with glass, wood board, packs of books and a pack of CDs.
• Position some dry leafs over the path and measure the available RSSI.
• Pour water over the dry leafs and measure the available RSSI.

Recorded results

Variances in RSSI were recorded with different obstructions introduced over the path as follows:

• RSSI of approx. -63dBm over clear path.
• A dip of 10 - 20 dB registered when somebody crossed the path. A total loss of signal was registered when 5 person stood over the path
• Total blockade of signal over obstructed paths using solid copper foil and meshed grill.
• No meaningful reduction in RSSI noticed with glass, wood, a plastic container and dry leafs over the path.
• A loss of 10 dB with 10 CDs held over the path, while there was a loss of 5 dB with a pack of books over the path.
• The RSSI fell by 15 dB when water was poured ovet the dry leafs.

Conclusions

• Glass, wood, plastics surfaces have no tangible effect on radio waves over a propagation path.
• Dry leafs may have little effect on the propagated wave.
• Both copper foil and grill had a reflective effect on the propagated wave. All the transmitted wavefront was effectively reflected by the two surfaces.
• The packs of CDs and books and a huge effect on the transmitted signal. An important lesson to learn here is never to instal APs behind CD or bookshelves as is common practice.
• There is obviously a huge effect on the propagated signal over water.

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