Radiometrix Ltd

KRX2

page 5

Function S0 =1

Message repeated....

75ms: end of message

120ms: function activated

Start of new message

S0 Output

RXD

Received Signal Strength Indication (RSSI)

The KRX2 module incorporates a wide range RSSI that measures the strength of an incoming signal

over a range of approximately 60dB. This allows assessment of link quality and available margin and is

useful when performing range tests.

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.

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

Ω) and external

loading should therefore be kept to a minimum.

To ensure a 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 at the expense of response speed, in the form of a capacitor from pin 5 to ground. 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.

Figure 4: Timing diagram – showing action upon receiving a message with S0 = 1

Figure 5: Typical RSSI response

200

300

400

500

600

700

800

900

1000

1100

-130

-120

-110

-100

-90

-80

-70

-60

-50

RF input level (dBm)