Introduction

Radio receivers work within short, FM, and medium wave ranges. Medium wave ranges between 530kHz- 1700kHz while short wave goes up to a range of 30MHz. Before the introduction of the FM wave ranges, medium and long waves were the main waves that were used in the radio industry. Today they are still used due to the offering of the long range of channel accommodation as compared to FM waves. In this article, our main focus is the FM receiver and we are going to learn how we can build a simple FM receiver.

FM radios adopt a transmission process called frequency modulation. Here, the audio signals are modulated using high frequencies and then transmitted at very high frequencies.

Working of the Receiver

The block diagram above is a good illustration of how the receiver works. The FM signal is received by the radio antenna and pushed into the RF amp which is a VHF amp that is tuned to FM bands and rejects any other type of frequencies. From RF, the signals move to the mixer which does the work of mixing the input signals with another one from the local oscillator. This is the tuning and at the end of the tuning, we end up with two brand new frequencies that is the incoming signals with and without the frequencies from the local oscillator. One is known as the intermediate frequency that is sent to the FM detector which will convert the frequency to voltage and do the extraction of the audio modulation and get amplified by the AF amplifier.

The Required Components

BT1, 1 1.5V Battery_Cell Battery:BatteryHolder_Keystone_103_1x20mm Single-cell battery

C1, 1 20p C_Variable Capacitor_THT:CP_Radial_D4.0mm_P1.50mm Variable capacitor

C2, 1 5p CTRIM_Small Capacitor_THT:CP_Radial_D4.0mm_P1.50mm Trimmable capacitor, small symbol

C3, 1 22p C_Small Capacitor_THT:C_Disc_D3.0mm_W2.0mm_P2.50mm Unpolarized capacitor, small symbol

C4, C7, 2 100n C_Small Capacitor_THT:C_Disc_D3.0mm_W2.0mm_P2.50mm Unpolarized capacitor, small symbol

C5, 1 10n C_Small Capacitor_THT:C_Disc_D3.0mm_W2.0mm_P2.50mm Unpolarized capacitor, small symbol

C6, 1 33n C_Small Capacitor_THT:C_Disc_D3.0mm_W2.0mm_P2.50mm Unpolarized capacitor, small symbol

C8, 1 10n C_Small Capacitor_THT:C_Rect_L7.2mm_W2.5mm_P5.00mm_FKS2_FKP2_MKS2_MKP2 Unpolarized capacitor, small symbol C9, 1 100uF CP_Small Capacitor_THT:C_Disc_D7.5mm_W5.0mm_P10.00mm Polarized capacitor, small symbol

L1, 1 L_Small L_Small Inductor_THT:L_Radial_D6.0mm_P4.00mm Inductor, small symbol

L2, 1 2.2uH L_Core_Ferrite_Small Inductor_THT: L_Radial_D6.0mm_P4.00mm Inductor with ferrite core, small symbol

LS1, 1 Earphone Earphone Connector_Stocko:Stocko_MKS_1651-6-0-202_1x2_P2.50mm_Vertical Earphone, polarized

Q1, 1 BF199 BF199 Package_TO_SOT_THT:TO-92_Inline 50mA Ic, 25V Vce, NPN Radio Frequency Transistor, TO-220

Q2, Q3, Q4, 3 BC547 BC547 Package_TO_SOT_THT:TO-92_Inline 0.1A Ic, 45V Vce, Small Signal NPN Transistor, TO-92 R1, 1 470k R_Small_US Resistor_THT: R_Axial_DIN0207_L6.3mm_D2.5mm_P10.16mm_Horizontal Resistor, small US symbol

R2, 1 10k R_Small_US Resistor_THT: R_Axial_DIN0207_L6.3mm_D2.5mm_P10.16mm_Horizontal Resistor, small US symbol

R3, R5, 2 1M R_Small_US Resistor_THT: R_Axial_DIN0207_L6.3mm_D2.5mm_P10.16mm_Horizontal Resistor, small US symbol

R4, R6, 2 4.7k R_Small_US Resistor_THT: R_Axial_DIN0207_L6.3mm_D2.5mm_P10.16mm_Horizontal Resistor, small US symbol

R7, 1 56k R_Small_US Resistor_THT: R_Axial_DIN0207_L6.3mm_D2.5mm_P10.16mm_Horizontal Resistor, small US symbol

RV1, 1 10k R_POT_US Potentiometer_THT: Potentiometer_Bourns_3266W_Vertical Potentiometer, US symbol

SW1, 1 SW_DIP_x01 SW_DIP_x01 Button_Switch_THT: SW_PUSH_6mm_H4.3mm 1x DIP Switch, Single Pole Single Throw (SPST) switch, small symbol

The FM Radio Circuit

Above is the complete circuit for our design and how every component should be interconnected to end up having our FM radio work.

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