User's Manual

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FSK
Microwave Motion Sensor
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odule
HB180 Users Manual
V1.0
0
ST Electronics (Satcom & Sensor Systems) Pte. Ltd.
29 New Industrial Road, ST Electronics Paya Lebar Building, Singapore 536213
Tel: [phone] Fax: [phone] Email: [e-mail]
Website: www.agilsense.com (
Regn
:
199103901W
)
8. Output Signals
FSK Doppler shift – The two-channel IF terminal outputs two Doppler shift signal when movement is
detected. The magnitude of two-channel Doppler Shift is proportional to the reflection of the
transmitted energy and is in the range of microvolts (µV).The phase difference between these two -
channel signal included the distance information, basing on the phase difference can attain the distance
between the target and the radar detector. The formula is as follows:
Two high gain low frequency amplifiers are usually connected to the IF terminals in order to amplify
the Doppler shift to a processable level (see Annex 2). Frequency of Doppler shift is proportional to
velocity of motion. Typical human walking generates Doppler shift below 100 Hz. Doppler frequency
can be calculated by Doppler equation in Annex 2.
The Received Signal Strength (RSS) is the measured voltage of the Doppler shift at the IF output. The
RSS figure specified in the technical data sheet is the level of a 25 Hz Doppler shift, generated from the
modulated microwave signal received at the receiver antenna, The received microwave signal is
attenuated to 93 dB below the transmit microwave signal from the transmit antenna of the same unit.
The 93dB loss is the total losses combining two ways free space loss (82.4 dB for 30 meters at 10.525
GHz), reflection loss and absorption loss of the target, as well as other losses.
This RSS figure can be viewed as an approximation of the output signal strength for a human at 15
meters away walking straight to the module at 1.28 km/hour.
Reflection of a human body is varied with the size of the body, clothing, apparels and other
environmental factors; RSS measured for two human bodies may vary by 50%.
Circuit designer must take note of the maximum and minimum Received Signal Strength (RSS)
specified in technical data sheet, when designing the amplifier. Sensitive deviation between modules
has to be considered when setting amplifier gain or alarm threshold. On-production-line gain
adjustment may be necessary if a narrow window for triggering threshold is required.
Noise - The noise figure specified in the technical data sheet is the noise measured in an Anechoic
chamber, that shields the unit-under-test from external interference, as well as reflections from surfaces.
Hence, the figure is only representing the noise generated by the internal circuit itself.