Cell Cellular Signal Strength

Question - what effects my ability to receive or send cellular signals?

 

Many things determine how your cell phone or cellular data phone will receive calls or data.

  1. Distance from base station antenna
    a.    The RF frequency used for cellular service are very high and act very much like light beams in that they propagate in a straight line - so being behind a hill/mountain, or over the curve of the earth will cut off the signal.

  2. Building construction -
    a.    If the cell antenna is located inside a building your RF will be degraded - by what degree depends on the materials in the walls of the building. An all metal building will the worst but at lot of building have steel reinforcing that will reduce the signal - to what degree will vary. The number of windows in a structure also affects reception. For example, a metal building with many windows admits more signals than a concrete building with only a few windows.  On the flip side windows with a metallic reflecting coating as in silver/gold will reduce the RF signal.

  3. Transmit Power -
    a.  The cell tower RF signal will be much stronger than your cell unit for a number of reasons. First they transmit with a higher power than your cell unit and they have very high gain antennas placed high as possible with no obstructions.
    b. Your cell unit will transmit with much less power and will be limited by the antenna - hand held units have very poor antennas - a fixed cell unit (as in a data unit) can use a much better antenna with more gain and/or directional and can be placed much higher as on a tower. (see section on antennas)

  4. RF Amps
    a.    Sometimes weak signals can be over come with a Intelligent Cell/Cellular amplifiers - signal booster but be careful you can over load the cell site tower which will not go well with your cellular carrier.

  5. Out of phase signals -
    a.    There are times when the RF signal is reflected off a hill/mountain or building. The strength maybe ok but there can be 2 paths to your receiver - one is direct and one is reflected off something (be it off a hill/mountain or building or even the ground - if your higher up). The reason for this if the two signals are received out phase with each other the modulation will affected and can be reduced/degraded.

     


other inputs

There are some other things to keep in mind when we talk about cell coverage.

GSM is based on another technology called TDMA (Time Division Multiple access). In a few words, users share a single radio channel by taking turns "talking" and "listening" on the frequency. CDMA (Code Division Multiple Access) works differently in that everybody "talks" and "listens" at the same time, the phone and the cell tower "tuning out" all other irrelevant signals. It's more complicated than that, but that's basically how it works.

Now, with GSM, the signal strength indicator is exactly that, a signal strength meter. So, the more bars you have, the stronger the signal you get from the tower is. You can rely on this to evaluate the signal penetration in a given building.

For CDMA though, it's different. The system is designed so that you can always add another phone on the tower, "talking" and "listening" on the frequency, but in the process adding "noise" to all other phones. So signal strength is not really important. The signal strength on CDMA cell phones indicates the signal to noise ratio (SNR), in other words, the signal quality. That means that you can stand in one spot for say, one hour, and see the indicator on your phone fluctuate between 0 and 4 bars constantly. The quality of the signal depends on how much signal is getting in the building, but also how many phones are in your vicinity. The more phones are present, the worse the signal is.

 


see very in-depth write up on antennas

see other cellular pages


ARC ELECTRONICS
a DCE Company

301-924-7400 x 17

e-mail Sales at drowe@data-connect.com

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