Applications information
Power supply requirements
The NiM1B have built-in regulators, which deliver a constant 3.3V to the transmitter and the receiver circuitry
when the external supply voltage exceeds 3.3V. This ensures constant performance up to the maximum
permitted rail, and removes the need for external supply decoupling, except in cases where the supply rail is
extremely poor (ripple/noise content >0.1Vp-p). The unit will continue to function with a 3v supply, but power
output will fall
TX modulation requirements
The module is factory-set to produce the specified FM deviation with a TXD input to pin 14 of 3V amplitude,
i.e. 0V “low”, 3V “high
If the data input level is greater than 3V, a resistor must be added in series with the TXD input to limit the
modulating input voltage to a maximum of around 3V on pin 14. TXD input resistance is 100k to ground,
giving typical required resistor values as follows:
Vcc
3V
3.3V
5V
Series resistor
-
10 k
68k
220k
9V
RX Received Signal Strength Indicator (RSSI)
The NiM1B wide range RSSI which measures the strength of an incoming signal over a range of 50dB or
more. This allows assessment of link quality and available margin and is useful when performing range tests.
The output on pin 11 of the module has a standing DC bias of up to 0.5V (approx.) with no signal, rising to
around 2.0V at maximum indication. (Vmin-Vmax) is typically 1V and is largely independent of standing bias
variations. Output impedance is 56k. Pin 11 can drive a 100A meter directly, for simple monitoring.
Please note that the actual RSSI voltage at any given RF input level varies somewhat between units. The
RSSI facility is intended as a relative indicator only - it is not designed to be, or suitable as, an accurate and
repeatable measure of absolute signal level or transmitter-receiver distance.
Typical RSSI characteristic is as shown below:
Figure 4: RSSI level with respect to received RF level at NiM1B antenna pin
Radiometrix Ltd.,
NiM1B transceiver data sheet
Page 8
RADIOMETRIX [ RADIOMETRIX LTD ]
