How to Use Passive Directors for Improving Cell Phone Reception

When stranded in an area forsaken by cell phone towers, finding a way to place a call on your cell phone can be quite difficult. Fortunately, for those areas on the brink of losing cell phone reception, a couple lengths of copper wire can mean the difference between getting your message out and dropping your call. Popular among many radio enthusiasts, the concept of the yagi antenna can be easily applied to your internal cell phone antenna to improve both data and voice reception.

The yagi is a directionalized antenna which starts off as a dipole. Elements added, known as passive directors and reflectors are added in front of and behind, respectively, to improve the gain and overall quality of the signal in a single direction. If you've ever had a TV antenna on top your house, most commonly a variation of the log-periodic antenna, you know that when the antenna is pointed just right the reception improves considerably. This is because instead of wasting energy by radiating radio waves in all directions, the energy is focused into a single direction therefore increasing both the strength of the sending and receiving signal.

Things you will need:

Copper Wire

Something to measure with

Wire Cutters or Scissors

Tape, preferably electrical tape

Something to mount the directors on, such as cardboard or a stick. Thick or reusable twist ties work magic.

Constructing your cell phone directors:

Cell phones in the U.S. normally operate on or very close to two frequencies, 850 MHz and 1900 MHz. Everywhere else you will normally find 900 MHz and 1800 MHz. Why do we need to know this? Because this determines the length of the segments of copper wire you've somehow acquired. For this example I am going to be using 1900 MHz because it is being used more commonly for voice and data as opposed to 850 MHz which is more commonly used for authenticating and metadata. The formula we will be using will be 468/frequency (1900) = length of wire in feet for a half-wave. This brings us to .246. Round that up to .25 feet and you have an easy measurement, 3 inches.

Cut three inches from the wire and set it aside. This will be your first director. For the following directors, the formula used is length of director behind x .95 = following director. So plug in .25 feet and you get .2375 feet or 2.85 inches. This is the length of your next director. A third and final director will solidify your cell phone signal. Using this formula your third director will be 2.7075 inches. Exact measurements are helpful, but as long as you are close the effect will be the same.

Mount these three lengths of wire 1.475 inches apart with the tape. Make sure they are parallel to each other, on either the cardboard or the stick, and going from biggest to smallest. Try to keep the wires straight and parallel to each other. 

Place or mount this array 1.475 inches away from your cell phone and orient yourself to the closest tower. Move around a bit and pay attention to the levels of your reception. There should be an area with the strongest reception.

This is how you can use directors to improve your cell reception. You should be able to see a notable difference when the array is pointed into the right direction toward the tower. Hopefully you see an improvement of 7-8 dB, which could mean the difference between one bar and no bars.

Diagram:

I hope this picture makes the concept of cell phone directors easier to understand. Use it as a reference when constructing your cell phone director array. None of the elements are connected to each other. I chose not to include how they are mounted in the diagram to avoid possible confusion. Whether you mount them on a flat surface or perpendicular on a stick doesn't make a noticeable difference. Tape the ends of the wires to the top of your car if you need to. Do whatever you need to get that call out.

References

Poole, Ian (2010). "The Yagi Antenna". Radio-Electronics.com website. Adrio Communications, Ltd.. Retrieved 2011-03-29.