Radiometrix Ltd, TX3A & RX3A Data Sheet

page 8

RX3A Received Signal Strength Indicator (RSSI)

The RX3A receiver incorporates a wide range RSSI which measures the strength of an

incoming signal over a range of 60dB or more. 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 of typically 0.25V with no signal,

rising to 1.1V at maximum indication. The RSSI output source impedance is high (~50k

Ω) and

external loading should therefore be kept to a minimum.

Typical RSSI characteristic is as shown below:

RSSI (V)

0

0.2

0.4

0.6

0.8

1

1.2

-120

-110

-100

-90

-80

-70

-60

-50

RF input Level (dBm)

Fig.7: RX3A RSSI response curve

To ensure a reasonably fast response the RSSI has limited internal decoupling of 1nF 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. For example, adding 10nF here will increase RSSI

response time from 100µs to around 1ms. The value of this capacitor may be increased without

limit.