Doppler shift is
an apparent change in frequency (or wavelength) due to the
relative motion of two objects. Either one or both of the
objects may be moving with respect to the ground. Radar
systems exploit the Doppler shift to provide an indication of
relative speed. When the two objects are approaching each
other (closing), the Doppler shift causes a shortening of
wavelength - or increase in frequency. When the two
objects are receding from each other (opening), the Doppler
shift causes a lengthening of wavelength - or decrease in
frequency. For a Doppler
radar system to measure speed, an accurate sample of the
original phase of the transmitted signal must be maintained
for comparison against the reflected signal.
Fixed
Transmitter with Moving Target ,
where all units must be kept constant (c=speed of
light)
Moving
Transmitter with Moving Target ,
where all units must be kept constant (c=speed of
light)
FREQUENCY
BANDS
30
Hz
300
Hz
3
kHz
30
kHz
300
kHz
3
MHz
30
MHz
300
MHz
1
GHz
2
GHz
3
GHz
4
GHz
8
GHz
12.5
GHz
18
GHz
26.5
GHz
30
GHz
40
GHz
300
GHz
>300
GHz
ELF
VF
VLF
LF
MF
HF
VHF
UHF
L-Band
S-Band
SHF
C-Band
X-Band
Ku
K
Ka
EHF
Millimeter
ELF =
Extremely Low Frequency
VF =
Voice Frequency
VLF =
Very Low Frequency
LF = Low
Frequency
MF =
Medium Frequency
HF =
High Frequency
VHF =
Very High Frequency
UHF =
Ultra High Frequency
SHF =
Super High Frequency
EHF =
Extremely High Frequency
DTMF
FREQUENCIES
Dual-Tone, Multiple
Frequency tones for touch-tone phones. When a keypad
button is depressed, a dual-tone signal is
transmitted according to the table below. For
example, if the "5" is depressed, then
both a 770 Hz tone and a 1336 HZ tone are sent
simultaneously. On the receiving end, the tones are
discriminated and decoded.
,
where all units must be kept constant (c=speed of
light)