RXM-900-HP-II Linx Technologies Inc, RXM-900-HP-II Datasheet - Page 13

• Manufacturer Part Number: RXM-900-HP-II
• Description: RECEIVER RF 900MHZ 8-CH PACK
• Manufacturer: Linx Technologies Inc

Specifications of RXM-900-HP-II

• Frequency: 902MHz ~ 928MHz
• Sensitivity: -95dBm
• Data Rate - Maximum: 50 kbps
• Modulation Or Protocol: FM, FSK
• Applications: Home / Industrial Automation, Remote Access, Security Alarms
• Current - Receiving: 18mA
• Data Interface: PCB, Through Hole
• Antenna Connector: Through Hole
• Voltage - Supply: 2.7 V ~ 16 V
• Operating Temperature: 0°C ~ 70°C
• Package / Case: 18-SIP
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Features: -
• Memory Size: -
• Other names: RXM-900-HP2; RXM-900-HP2

RSSI CIRCUIT
The HP Series-II receivers are equipped with an on-board Received-Signal-
Strength-Indicator (RSSI) circuit. RSSI is useful to check for channel occupation,
and interference as well as signal strength determination.
The RSSI circuit provides a DC voltage which is logarithmically proportional to
the incoming signal strength present at the RF input pin. The RSSI circuit has a
voltage range of about 800mV to 2.5 V and a dynamic signal range of better
than 60 dB.
Figure 5 on p. 3 shows the RSSI output versus input signal strength. This graph
is a characterization only and is adapted from measurements made from a small
sampling of receivers. The RSSI response is different for every FM-IF chip, and
is therefore different for every HP Series-II receiver. Calibration parameters are
stored on-board to compensate for this variation.
Figure 6 on p. 3 shows the RSSI response time with an input power of -80dBm.
This graph basically shows how long it takes the RSSI voltage to respond to an
instantaneous increase in output power. If the carrier is AM modulated, or OOK
modulated (in the case of data), the RSSI pin can be used for demodulation.
If your application requires that you accurately measure the incoming signal
strength (distance measurement, for example), then you must calibrate the
RSSI circuit on a receiver-by-receiver basis.
The calibration process is simple. Using a signal generator, inject a -40dBm
unmodulated carrier into the receiver and measure the RSSI voltage.
Repeat the same for an input signal level of -100dBm. This is known as a
two-point “slope” calibration.
To determine the slope of the RSSI response, use the following equation:
M=60/(V2-V1)
Where
Using this slope, you can determine the signal strength for any RSSI
voltage using the following formula:
SS=M * (V
Where
If you are using a microprocessor with an A/D converter, this process can
easily be achieved in software. If not, it can also be achieved using standard
analog measurement circuitry.
NOTE:
M=slope in dB/volts
V1=the voltage measured at -100dBm
V2=the voltage measured at -40dBm
SS=signal strength in dBm
M=previously determined slope
Vm=measured RSSI voltage
1
-V
MAKING SIGNAL STRENGTH MEASUREMENTS
WITH THE RSSI CIRCUIT
m
) +100dBm