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Data Hacking

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78 Part I — Hardware Hacks<br />

For more information on Belden cable, check out the Belden website at http://bwccat.<br />

belden.com/ecat/jsp/index.jsp.<br />

Many people don’t realize that lower-loss cable usually means thicker cable. The thicker the<br />

cable, the harder it is to get it around bends.<br />

Connector Losses<br />

It’s not just the cables that attenuate; the connectors do too. Generally, each connector adds<br />

about 1.5 dB of signal loss into the system. However, if you are using cable with 75-ohm resistance<br />

on a 50-ohm system (these figures will be marked on most cables that you use, while<br />

connectors are sold with a particular resistance value stated), then this figure goes up to 3 dB.<br />

This combination is therefore considered to be a poor match and not recommended for GPS.<br />

One example of a 75-ohm cable from Belden is the RG59.<br />

Adding a connector at each end of the cable means you are looking at a minimum of 3 dB<br />

attenuation of signal, which alters the maximum cable lengths that you can have. Depending<br />

on whether your cable/antenna setup has one connector or two, you can figure this value into<br />

your calculations directly, as shown in the following table.<br />

Cable (with connectors) Max Length Using Max Length Using<br />

High-Gain Antenna Low-Gain Antenna<br />

RG8 110 45<br />

RG213 75 35<br />

RG142 40 15<br />

RG58 30

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