Power supply requirements
The standard RX3G requires a regulated 5V supply with ripple content <100mVpk-pk
However, built-in regulator in the regulator version RX3G delivers a constant 5V to the
module circuitry when the external supply voltage is 5V or greater, with 40dB or more of
supply ripple rejection. This ensures constant performance up to the maximum permitted
supply rail (16V max.) and removes the need for external supply decoupling except in cases
where the supply rail is extremely poor (ripple/noise content >0.1Vp-p).
Note, however, that for supply voltages lower than 5V the regulator is effectively inoperative
and supply ripple rejection is considerably reduced. Under these conditions the ripple/noise on
the supply rail should be below 10mVp-p to avoid problems. If the quality of the supply is in
doubt, it is recommended that a 10F low-ESR tantalum or similar capacitor be added
between the module supply pin (Vcc) and ground, together with a 10 series feed resistor
between the Vcc pin and the supply rail.
Received Signal Strength Indicator (RSSI)
The module incorporates a wide range RSSI which measures the strength of an incoming
signal over a range of approximately 50dB. This allows assessment of link quality and
available margin and is useful when performing range tests.
The output on pin 5 of the module has a standing DC bias in the region of 0.5V with no signal,
rising to around 1V at maximum indication. The RSSI output source impedance is high
(~100k) and external loading should therefore be kept to a minimum.
To ensure a fast response the RSSI has limited internal decoupling of 10nF to ground. This
may result in a small amount of ripple on the DC output at pin 5 of the module. If this is a
problem further decoupling may be added, in the form of a capacitor from pin 5 to ground, at
the expense of response speed.
Typical RSSI characteristic is as shown below:
1100
1000
900
800
700
600
500
400
300
200
-130
-120
-110
-100
-90
-80
-70
-60
-50
RF input level (dBm)
Radiometrix Ltd
RX3G data sheet
page 4
RADIOMETRIX [ RADIOMETRIX LTD ]
