Question 10.5: DYNAMIC RANGES A receiver has a noise figure of 7 dB, a 1 dB...
DYNAMIC RANGES
A receiver has a noise figure of 7 dB, a 1 dB compression point of 25 dBm (referenced to output), a gain of 40 dB, and a third-order intercept point of 35 dBm(referenced to output). If the receiver is fed with an antenna having a noise temperature of T_{A} = 150 K, and the desired output SNR is 10 dB, find the linear and spurious free dynamic ranges. Assume a receiver bandwidth of 100 MHz.
The noise power at the receiver output can be calculated using noise temperatures as
N_{o} = GkB[T_{A} + (F − 1)T_{0}] = 10^{4}(1.38 × 10^{−23})(10^{8})[150 + (4.01)(290)]= 1.8 × 10^{−8} W = −47.4 dBm.The linear dynamic range is, from (10.55), in dB,
LDR = OP_{1dB} − N_{o} = 25 dBm + 47.4 dBm = 72.4 dB.
Equation (10.60) gives the spurious free dynamic range as
SFDR = \frac{2}{3} (OIP_{3} − N_{o}) − SNR = \frac{2}{3} (35 + 47.4) − 10 = 44.9 dB.
Observe that SFDR ≪ LDR.