CP400P Wireless Communication and Networks

Comparing Meters

In order for collected data to have any value, they have to be independent of the specific instrument used. The purpose of this lab exercise is to see how consistent different meters are. Related to that is the meaning of signal strength indications on wireless devices. (Often these are given as a percentage, or indicated visually by a number of bars.) In this exercise you'll determine how these indicators relate to actual power measurements.

Objectives

1. To determine how consistent different meters are for the measurement of power in wireless systems.
2. To determine a correlation between signal strength indicated on a wireless device (such as a laptop) and actual measured power.

Equipment

• 2 wireless power meters
• laptop or other wi-fi device
  Since we're looking at wi-fi strength, not cellular signal strength, we can only use a smart phone if it has a wifi connection with a power indicator.

Procedure

Comparing meters

1. At the same point in the hallway, take a set of 10 measurements with each meter at their proper orientations for maximum sensitivity.
   
   
2. Average the readings as before, and see if the averages agree within their experimental uncertainties or not.
   
   
3. If they don't agree, try to figure out if there is something you should be doing differently, and try it and see if you are right.

Wireless device signal indicators

1. In order to get meaningful results, you'll need to start by determining the directionality of the wireless device antenna, just like for the power meter.
   Do this, and note how the device should be oriented towards the source for maximum sensitivity.
   
   
2. If power is indicated by a number of bars
   With one of the meters and your wireless device, move along the hall and record power readings at the transition point between different numbers of bars (e.g. 5-4, 4-3, etc.)
   
   
3. If power is indicated by a percentage
   With one of the meters and your wireless device, move along the hall and record power readings at 90%, 80%, etc.
   
   
4. Plot your results on a graph, and extrapolate to determine what power is represented by full bars or 100%.

Are the indicators linear? logarithmic?

Before you leave the lab, have the lab instructor sign your lab notebook immediately after your last entry.