Aviation Band Receiver Schematic Diagramshows a schematic diagram of the Aviation Receiver--a cool heterodyne AM (Amplitude Modulated) assemblage congenital about four IC's: an NE602 bifold counterbalanced mixer (U1), an MC1350 beeline IF amplifier (U2), an LM324 cloister op-amp (U3), and an LM386 audio amplifier (U4).
In operation, an antenna that plugs into J1 picks up the AM signal. That arresting is again accompanying through C1 to a three-section, tuned-filter arrangement consisting of L1-L5 and C2-C6. Signals in the 118-135Mhz VHF (Very High Frequency) ambit are accompanying through C7 to a VHF transistor (Q1), area the signals are amplified. From there, the signals are fed through C8 to the ascribe of U1 (the NE602 is a bifold counterbalanced mixer), which in this appliance serves as a bounded oscillator. A capricious inductor (Local Oscillator L6) and its associated capacitor arrangement set the bounded oscillator abundance 10.7-MHz college than the admission 118-135MHz signals. A affability arrangement , consisting of varactor diode D1 and potentiometer R1, allows the local-oscillator abundance to be acquainted beyond about 15MHz.
The 10.7-MHz aberration amid the accustomed arresting and the local-oscillator (LO) abundance (i.e., the Intermediate Abundance or IF) is achievement at pin 4 of U1 to a 10.7-MHz bowl clarify (FIL1). The clarify is acclimated to ensure a attenuated canyon bandage and aciculate arresting selectivity.
The achievement of FIL1 is amplified by Q2 and again fed through C16 to U2 (an MC1350 IF amplifier), which, as configured, additionally offers Automatic Accretion Ascendancy (AGC), as we'll see shortly. The amplified 10.7-MHz IF arresting is ailing application capricious agent T1. The AM audio is again demodulated by diode D2. After that, the audio is fed in arrangement through four sections of U3 (a LM324 cloister op-amp).
Note that a allocation of U3-a's achievement arresting is fed aback through resistor R25 to the AGC-control ascribe of U2 at pin 5. That arresting is acclimated to automatically abatement the accretion of U2 back able signals are present or to automatically access U2's accretion for anemic signals. That keeps the achievement aggregate of the ambit aural a adequate alert ambit behindhand of the backbone of the admission signals.
The receiver ambit additionally contains a squelch ambit that is controlled by potentiometer R3, which is acclimated to annihilate accidental babble beneath a called beginning level. Back appropriately set, the squelch ascendancy around eliminates accomplishments noise, so that all you abreast are admission signals that can be brought up to a accessible level. Potentiometer R2 controls the all-embracing aggregate fed through C26 to U4, an LM386 low-voltage audio amplifier. Due to the all-embracing architecture and squelch control, the audio achievement is absolutely low in accomplishments noise, and yet it's able of active simple communications apostle or earphones to accomplished aggregate levels.
