The availability of inexpensive integrated circuits capable of implementing receiver functions makes it possible build a simple radio receiver with surprisingly few parts. RF and IF amplifiers, mixer/oscillator combinations, product and FM detectors, and audio amplifiers can be combined to build miniature AM or FM receivers.
The purpose of this experiment is to learn more about receivers, and the application of integrated circuits to their design, by building an AM receiver for the broadcast or lower (20 QST (Feb 88 p 14, Nov 91 p 51), 73 (Feb 88 p 28, Jun 90 p 30, Apr 91 p 26, Oct 91 p 8) and Radio Electronics (Jan 91 p 56) have particularly appropriate hints on construction and selection of components.
This is an advanced project and not for those without previous wiring and component selection experience. It should be built on a circuit board that encourages both short lead lengths and ground paths effective at radio frequencies.
A typical schematic is drawn below. Actual parts values and circuit configuration will depend on the frequencies you wish to receive. High-frequency construction techniques, including short lead lengths and careful bypassing and grounding, will be required for successful operation of the completed circuit. Construct and de-bug the receiver and demonstrate it to the class and the teacher.
|C1, C4, C11, C12: depend on frequency||R1: 1000 Ω variable|
|C2, C5, C10, C14, C16, C17: 0.1 µF disk||R2: 100 Ω|
|C3, C6, C20: 10 µF 10 V electrolytic||R3: 1.5kΩ|
|C7, C8: XC approx. 50Ω at required frequency||R4, R6: 10kΩ|
|C9: XC approx. 100Ω at required frequency||R5: 4.7 Ω|
|C13, C15: 0.047 µF||T1, T2: 10.7 MHz IF transformer,|
Mouser 421F123 or equivalent
(green core, 7:1 turns ratio)
|C18, C19: 100 µF 10 V electrolytic|