Data Hacking

Carrying a GPS Signal via Cable
Chapter 4 — Antenna Hacks
You’ve already learned that cables that are too long or have unnecessary connectors cause signal
loss — but how much signal loss? The following sections outline some of the variables that
affect the answer to this question.
How Much Signal Do You Need?
Before we look at the losses, let’s look at how much signal you need to get to your GPS in
order for it to work.
For a high-gain (high-sensitivity) antenna (roughly 35 dB), most receivers can function properly
with 12 dB +/- 2 dB attenuation (signal loss) from the antenna to the receiver input.
For a lower-gain (low-sensitivity) antenna (those in the 26 dB region), most receivers can function
normally with 6 dB +/- 2 dB attenuation from the antenna to the receiver input.
Cable Losses
There is significant signal loss through a cable. What we are interested in is the signal loss at
1575.2 MHz. The following list of four different cable types shows the average signal loss
you’ll encounter (derived from data on www.belden.com):
RG8 (Belden 9913F), 100ft: 7.5 dB attenuation
RG213 (Belden 8267), 100ft: 12.0 dB attenuation
RG142 (Belden 84142), 10ft: 2.0 dB attenuation
RG58 (Belden 8919), 10ft: 2.7 dB attenuation
Therefore, putting the preceding information into context, the following table shows the maximum
length of cable that you should be able to use.
Cable Max Length Using High-Gain Max Length Using Low-Gain
Antenna (feet) Antenna (feet)
RG8 150 80
RG213 100 50
RG142 60 30
RG58 40 20
The better quality cable (generally, “more expensive”) you use, the lower the attenuation and
the less the signal loss. However, higher-quality cables cost more. If you want less attenuation
over greater distances, the only option available to you is to spend the money.
You can also find rigid and semi-rigid cables that have better specification, but these will
undoubtedly cost extra and the gains you get aren’t going to be massive.
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