Question

QUESTION 1 (25 MARKS) a. A block diagram of a small private radio station is shown in Figure Q1(a). Operating at a frequency of 550 kHz, the station receives a full AM signal with 260 mW of power. The minimum and maximum bandwidths required by the system are 100 kHz and 200 kHz. If the surrounding temperature of the system is 18 °C, calculate the following: i. Noise Figure, NF for the system. (CO2: PO2 - 2.5 marks) ii. Noise voltage, V, at the input if the antenna resistance is 0.50 ΚΩ. (CO2: PO2-2.5 marks) NF =3dB L=3dB TA N Pre-selector RF amplifier Mixer IF Filter Audio Section 5 G-20dB NF:-1dB G=30dB L=348K NF = 4dB L-15dB Local oscillator Figure Q1(a)

Answer 1

دان را Noise figure of the system have u devices so NE NFI Nf₂-1 + Noz + Nfu-l Glanz द. Gill But in this formula all valued x in h8می not in dB Se will convert them in Nounol ratio NA -4aß 20log (NF) 40B 4/20 so, NE 1.585 Similarly G. zelzo 1 G → 31.623 3/20 1.412 20 aze -z = - o.107

Dato Nou to I-122 15 Gu - 5.623 Now, for RF amplifiers, NF2 is not given. its temperature given & we know that → LNE 1 + Tho d NE 348K L8°c = (18+ 273) K 348K (18+273)k Nf₂= 2. 196 Now put all values in formello NF 2.7995 t Overall Noise figure of system

Date 3 وتل Noise voltage un S4 KTBR where Ke bolte mann's constant 1-3881023 JK Here R z 0.5 K2 To (Nfu) (8+273) (2.1995-1) T- 523-654K Be min look itz Brat 2ookHz we have 2 Noise Noise voltages for a Bandwidth SUKT B min R Vn min min 1-2 Yv un (4KTB max R max 1.Tu max