Global Positioning System Reference
In-Depth Information
Figure 6.1
The electromagnetic spectrum.
6.1.1
Frequency, Wavelength, Bandwidth, Power, and Noise
Each color of light and each oscillating radio signal have a frequency
f
measured
in cycles or oscillations per second for which the unit is Hz (hertz). It has a
wavelength
λ
, which is related to light speed
v
, as shown in equation (6.1):
f
=
v
/
λ
(6.1)
In general, however, most radio systems operate over a band of frequencies,
since when a single frequency is used to carry any information it is
“modulated”—continuously modified in amplitude, frequency (or both).
Modulation creates extra frequency components either side of the original
“carrier” frequency. The more information that is sent, the greater space these
extra frequencies (known as sidebands) occupy in the electromagnetic spectrum
(see Figure 6.2). The frequency space occupied is called the bandwidth of the
signal, and radio channels are allocated so that each channel occupies its own
band without interfering with adjacent channels allocated to others. Bandwidth is
a very important characteristic in positioning. The greater the bandwidth (in Hz),
the more power (in Watts) is needed to transmit and the more accurate is any
resulting timing measurement. There is always a limit to transmitter power
because of power supply, heat generated, human safety, devices used, and
