Features
MPS-4100 product guide • • • 1 - 3
Operating frequencies and polarization
Six selectable modulation frequencies allow multiple sets of MPS-4100 to be used
in either a stacked or linear configuration. Selecting different modulation
frequencies prevents crosstalk between different units located in the same area.
The Planar Linear Array Antenna transmits the microwave signal in either a
vertical or horizontal polarization depending on the orientation of the antenna
assembly. The output polarization can be changed by rotating the antenna
assembly 90 degrees. This reduces interference between multiple units mounted
in close proximity to each other.
Vertical polarization = Narrow Beam;
Horizontal polarization = Wide Beam;
default setting = Narrow Beam.
The Transmitter and Receiver in a microwave link must use the
same modulation frequency and antenna polarization.
Built-in AGC
The received RF amplified signal is processed by an automatic gain control (AGC)
amplifier enabling the amplifier output to be held to a constant level, regardless
of the Transmitter-Receiver separation distance (maximum TX-RX separation
distance = 183 m {600 feet}). The amplifier output is applied to a phase-locked
loop (PLL) detector which operates as a narrow bandpass filter at the selected
modulation frequency. The Receiver’s modulation frequency is selected to match
the modulation frequency of the Transmitter, while rejecting spurious signals and
other Transmitters.
PLL circuit
The PLL detector output is a voltage level which is held constant under normal
conditions by the slow-acting AGC loop. Rapidly changing signal strength caused
by a target moving into the microwave beam is not affected by the AGC loop and
causes an AC signal to appear at the PLL detector output. The signal is amplified,
filtered and compared with upper and lower alarm threshold voltages. Whenever
a signal exceeds either threshold voltage, an alarm is generated. The gain of the
signal amplifier may be adjusted with a Sensitivity potentiometer on the circuit
board. The signal bandwidth, affecting the MPS-4100 response to moving targets,
may be set to Fast or Slow with a PCB jumper. The Slow setting detects human
intruders (default setting) and the Fast setting detects moving vehicles.
