Wireless Technician's Handbook 2nd Edition / Edition 2 available in Hardcover
Wireless Technician's Handbook 2nd Edition / Edition 2
- ISBN-10:
- 1580533574
- ISBN-13:
- 9781580533577
- Pub. Date:
- 07/31/2003
- Publisher:
- Artech House, Incorporated
- ISBN-10:
- 1580533574
- ISBN-13:
- 9781580533577
- Pub. Date:
- 07/31/2003
- Publisher:
- Artech House, Incorporated
Wireless Technician's Handbook 2nd Edition / Edition 2
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Overview
This book:
>Focuses on testing concepts and procedures, and types of testing equipment, including spectrum analyzers and power meters and their applications
>Reviews AMPS, CDMA, IS-136, and GSM
>Includes charts technicians refer to daily and screen shots from common test instruments
>Surveys common problems with cellular and PCS networks and handsets
Perfect for field-based wireless technicians, this handbook is also an excellent reference for wireless engineers seeking an understanding of practical field applications, and newcomers to wireless communications. It's also a handy guide for non-technical business personnel seeking a better understanding of the technology and industry.
Product Details
| ISBN-13: | 9781580533577 |
|---|---|
| Publisher: | Artech House, Incorporated |
| Publication date: | 07/31/2003 |
| Series: | Artech House Mobile Communications Library |
| Edition description: | Second Edition |
| Pages: | 312 |
| Product dimensions: | 7.00(w) x 10.00(h) x 0.75(d) |
About the Author
Read an Excerpt
Chapter 1: Reviewing the Basics
1.4 Understanding PropagationThe process of transmitting signals into the air is called signal propagation. Understanding the concepts involved in taking a useful signal and sending it down a transmit path to an antenna and out into the air is an essential aspect of a technician's position. A useful analogy to this process is a water hose. If we turn the faucet on for a moment, we hope that all of the water will get to the nozzle and spray on our vegetable garden. Of course, all of the water usually won't make it. A small leak in the hose might send some of the water where we don't want it. A kink in the line might slow the amount of water down. If it's a large kink, it could stop the water altogether, and in fact send it back to the faucet (backwash) maybe causing more problems. Of course, the best way to make sure everything works well is to use the right diameter hose for the pressure you want.
RF is much the same (except that after a while of efficient watering we don't end up with plump tomatoes, but rather happy customers). We generally have an amplifier, our faucet, on which we attach a cable leading to the antenna-our nozzle. As we send our signal down the cable to the antenna, we hope that all of the power makes it through the route and out the antenna, but there are often reasons why this does not occur. For instance, a bad cable that was not shielded enough might have been used, or a connector might not have been tightened enough, or there might simply have been some sort of break in the transmission line or a flaw in the antenna.
One advantage in the RF world is that by using what is called an RF bridge, we canseparate what we are transmitting down the cable, and what is coming back the other way (the reflected power-the power that did not make it out). Chapters 7-10 of this book will give more detail on these testing methods.
It is also important to understand that different frequencies propagate differently. Generally, lower frequencies will travel much greater distances, but are also more susceptible to physical obstacles, such as a wall. Also, lower frequencies will propagate with a much wider footprint than higher frequencies; in other words, higher frequencies have more propagation loss than lower frequencies. Higher frequencies are much more directional (hence the use of microwave signals for line of sight point to point transmission systems). Thus, transmitting 50 W at 570 kHz is quite different than transmitting 50 W at 800 MHz. In cellular systems we take advantage of this directionality when we divide cells into sectors. This will be discussed more in Chapter 2.
The concept of fading also needs to be understood. Fading generally refers to the degradation of the signal at the receiver. There are four main fading effects related to physical conditions:
. Attenuation due to distance;
. Attenuation due to environmental features;
. Rayleigh fading;
. Multipath fading.
Naturally, as a receiver moves away from the transmitter, or places large objects between itself and the transmitter, the signal level will decrease and lower the call quality. When the subscriber moves a significant distance away from the transmitter, the fading that occurs is called large-scale path loss, since the attenuation is due to the distance. Shadowing generally refers to a type of fading that occurs when the subscriber moves behind a large object, or perhaps in a tunnel or the like (see Figure 1.8). These two fades are naturally an obstacle to all wireless systems, although some systems are able to overcome the problem more easily than others.
Multipath fading is another type of fading caused by interference between two or more waves which left the transmitter at the same time, but took different paths to the receiver, and thus arrived at the receiver at different times. This can cause the signals to have different phases as they enter the receiver, and this will cause a destructive process, lowering the actual received level. It should be understood that the multipaths can arrive in-phase, and thus they would add constructively, a sought after condition.
If the multipaths could somehow be demodulated separately, and then combined coherently, this would substantially improve the system. This is what CDMA-ONE does with its Rake Receiver. Problems in digital systems related to signals taking different paths to the receiver, and thus arriving at different delays, are also often called inter-symbol interference (see Figure 1.9)...