User's Manual

MaxStream 9XStream™ Wireless OEM Module Manual v2.8

Confidential and Proprietary, ©MaxStream, Inc. 2001

Application Notes

Why does Sensitivity Matter?

Receiver sensitivity is the lowest power level at which the receiver can detect a

wave and demodulate data. Sensitivity is purely a receiver specification and is

independent of the transmitter. As the wave propagates away from the

transmitter, it attenuates as the distance increases. Lowering the sensitivity on

the receiver (making it more negative) will allow the radio to detect weaker

signals, and can thus increase the transmission range. Sensitivity is vitally

important since even slight differences in receiver sensitivity can account for

large discrepancies in the range. To better understand this relationship, the

following example is provided.

Example: Compare the MaxStream 9XStream module (with-110

dBm sensitivity) to a commercial radio receiver with a

sensitivity of –90 dBm. The Friis transmission formula

can be used to calculate received power (or signal

strength) at any receiver location under line-of-sight

conditions. This formula is given by

P(r) = received power (mW)

P(t) = transmitted power (mW)

G(t) = gain of transmit antenna (linear)

G(r) = gain of receive antenna (linear)

F(s) = fading margin (linear)

λ = wavelength (meters)

r = distance between Transmitter and Receiver (meters)

The following values were used to compare the range

limitations of these modules:

P(t) = 100mW

G(t) and G(r) = 2dB, or 1.585 linear

λ = 0.333 meters

F(s) = 21 dB, or 125.89 (experimentally determined)

The table below demonstrates the power received at the

receiver over the specified range between the TX and RX

antennas, assuming line-of-sight conditions.