Hey friend, if you have ever wanted to pull AM broadcasts out of thin air with nothing more than a single CMOS IC and a few passive parts, this CD4049-based AM radio circuit is pure electronics magic. I have been building radio projects for decades as an engineer, and designs like this one The star of the show is the CD4049AE hex inverting buffer, running on just 6V, turning medium-wave signals into clear audio for a pair of 32-ohm headphones. No dedicated RF chips, no complex tuning—just clever use of CMOS gates as amplifiers and detectors. In this guide, I will dissect every section of the schematic, list the exact components, walk you through the build step by step, and share the tweaks that make it perform reliably. Whether you are a beginner or a seasoned builder, this project will have you listening to talk radio or sports in an afternoon. Let’s get into it.

Why Build a CD4049 AM Radio?

AM radio might seem old-school next to FM or streaming, but the medium-wave band (530-1700 kHz) is still alive with local stations, especially at night when signals bounce off the ionosphere. This circuit stands out because it uses a common logic IC in an analog role. The CD4049 has high input impedance, decent gain at RF frequencies, and can drive low-impedance loads directly. I love it for four reasons. First, the parts cost is under $5. Second, it runs on two or three AA batteries for weeks. Third, the tuning is simple—just a variable capacitor and a hand-wound coil. Fourth, it teaches core radio principles: resonance, detection, and audio amplification without jargon. I have used similar setups in emergency kits or for teaching kids how invisible waves become sound. If you want a pocket-sized receiver that actually works, this is it.

Analyzing the CD4049 AM Radio Circuit

The schematic breaks into five stages: antenna tuning, RF amplification and buffering, detection, AF filtering, and audio output. The CD4049 contains six inverters; five are used here, with the sixth left unused. Let’s follow the signal path.

Antenna and Tuning Network

The antenna (ANT) connects to a parallel LC tank: variable capacitor C1 (100 nF trimmer, labeled 100n but likely 10-100 pF range) and inductor CL (80 turns of 35 SWG wire on a 10 mm former, ~220 µH). A 0.1 µF coupling capacitor (C1 in parallel) feeds the tank to the first inverter input. This resonant circuit selects the station—peak resonance at f = 1 / (2π√(L×C)). With 80 turns on a 10 mm former, inductance is roughly 220 µH, so tuning range with a 365 pF variable would cover 500-1700 kHz. The note says “100n,” but in practice, use a 10-365 pF polyvaricon or trimmer.

RF Stage: Inverter 1 as High-Impedance Buffer

Pin 7 of the CD4049 connects to the tuned circuit via R1 (2 MΩ). This ultra-high resistor biases the CMOS input to mid-rail (~3V) while presenting minimal load to the tank. The first inverter (pins 7-6) operates in linear mode as a high-impedance RF amplifier. CMOS gates have a voltage gain of around 30-40 dB at 1 MHz when biased properly. Output at pin 6 couples through C5 (220 pF) to the next stage.

Detector Stage: Inverter 2 as Diode Detector

The second inverter (pins 5-4) is configured for envelope detection. D1 (1N4148) is shown in the feedback path, but the schematic places it across the input—standard practice is to use the inverter’s ESD protection diodes for detection. C3 (100 nF) and R3 (100 kΩ) form the envelope filter, extracting audio from the AM carrier. The detected audio appears at pin 4.

AF Filtering and Gain

Pin 4 feeds the third inverter (pins 9-8) via C2 (10 nF) and R2 (10 kΩ). This stage provides additional voltage gain and filters RF remnants. Output at pin 8 goes to the fourth and fifth inverters wired in parallel (pins 3-2 and 11-10, outputs tied at 12 and 15) to increase current drive. R4 (100 kΩ) biases these gates. C6 (100 nF) decouples the supply locally.

Audio Output

The paralleled outputs drive C4 (220 µF electrolytic) to a stereo 32-ohm headset (2x 32 Ω). The capacitor blocks DC, and the low output impedance of paralleled CMOS gates (~100 Ω) matches the headphones nicely. Power is +6V from a battery, with C5 (220 µF) and C6 (100 nF) filtering the supply rail.

How It Works in Detail

1. The LC tank resonates at the desired station frequency.
2. Weak RF voltage (~µV) appears across the tank.
3. First inverter amplifies it 30-40 dB.
4. Second inverter rectifies via internal diodes, C3/R3 demodulates.
5. Remaining inverters amplify audio ~60 dB total.
6. Paralleled outputs deliver ~10 mW into 32 Ω—plenty for headphones.

The CD4049 works here because its transition frequency is high enough for 1 MHz, and the square-wave transfer characteristic clips the carrier, aiding detection. Biasing at mid-rail keeps it linear for small signals.

Key Components You Will Need

Here’s the exact shopping list. All are standard and cheap.

• IC: CD4049AE (or HCF4049UBE) DIP-16 – $0.50
• Variable Capacitor: C1 – 10-365 pF polyvaricon or two 100 pF trimmers in parallel – $1
• Coil: CL – 80 turns 35 SWG (0.2 mm) enameled wire on 10 mm former (ferrite rod or plastic tube) – $1 wire
• Capacitors:
  • C1 (coupling): 0.1 µF ceramic
  • C2: 10 nF ceramic
  • C3: 100 nF ceramic
  • C4: 220 µF 16V electrolytic
  • C5: 220 µF 16V electrolytic (supply)
  • C6: 100 nF ceramic (decoupling)
• Resistors (1/4W):
  • R1: 2 MΩ
  • R2: 10 kΩ
  • R3: 100 kΩ
  • R4: 100 kΩ
• Diode: D1 – 1N4148 – $0.05
• Power: 6V (4x AA battery holder) – $1
• Headphones: 32 Ω stereo (old earbuds work) – $2
• Misc: Perfboard, wire, antenna wire (1-2 m), switch, enclosure

Total cost: under $10. Wind the coil tightly—loose turns lower Q.

Step-by-Step Guide to Building the AM Radio

Let’s assemble it. Breadboard first, then solder to the perfboard.

1. Wind the Coil: Take a 10 mm plastic tube or ferrite rod. Wind 80 turns of 35 SWG enameled wire in a single layer. Scrape enamel from ends. Inductance should be ~200-250 µH.
2. Build the Tank: Connect C1 (variable) across CL. Solder 0.1 µF in parallel if using a small trimmer. One end of the antenna the other to the ground.
3. Place the CD4049: Insert into the breadboard. Connect pin 8 to +6V, pin 16 to ground (note: CD4049 pinout is NOT standard 14-pin—check datasheet).
4. Bias and RF Input: R1 (2 MΩ) from tank hot side to pin 7. Antenna to tank via 0.1 µF.
5. Couple Stages: C5 (220 pF) from pin 6 to pin 5. D1 cathode to pin 5, anode to ground (or omit and rely on internal diodes).
6. Detector and Filter: C3 (100 nF) from pin 4 to ground, R3 (100 kΩ) parallel. C2 (10 nF) from pin 4 to pin 9.
7. Audio Amplifiers: R2 (10 kΩ) from pin 8 (output) to pin 9 (input). R4 (100 kΩ) from +6V to pins 3 and 11. Tie pins 2 and 12, pins 10 and 15 together.
8. Output: C4 (220 µF + to tied outputs, – to headphone jack tip/ring). Ground to sleeve.
9. Power Supply: C5 (220 µF) and C6 (100 nF) across +6V and ground near IC.
10. Test and Tune: Power on. Extend the antenna. Slowly rotate C1. You should hear stations as hisses turn into voices. Adjust R1 if needed (1-4.7 MΩ range). Peak volume with coil tap if weak.
11. Enclosure: Mount in a small plastic box. Add a knob to C1, antenna jack, headphone jack, and power switch.

Build time: 1-2 hours. My first version crackled until I scraped the coil ends properly—clean connections matter.

How the Circuit Performs in Real Use

With a 1-meter wire antenna indoors, you will pick up strong local stations (10-50 km). At night, DX reception reaches hundreds of kilometers. Audio is mono, slightly muffled (AM bandwidth ~5 kHz), but clear for talk and music. Current draw is ~5-10 mA, so four AA batteries last 50+ hours. Sensitivity is surprisingly good—comparable to cheap transistor radios. Selectivity depends on coil Q; a ferrite rod improves it. Add a 1 kΩ pot in series with C4 for volume control if desired.

Common Issues and Fixes

• No Sound: Check power polarity, IC orientation (pin 1 mark), coil continuity.
• Only Hiss: Tank mistuned—rotate C1 fully. Try a different antenna length.
• Motorboating: Add 100 µF across the supply. Keep audio and RF grounds separate.
• Weak Audio: Parallel another inverter section or use 16 Ω phones.
• Oscillation: Add 100 pF across R1 or shorten leads.

Test with a signal generator if possible (1 MHz AM modulated with 1 kHz tone).

Safety Considerations

Low voltage, low risk. But soldering irons are hot—use a stand. Avoid shorting batteries. If adding an external antenna, keep it away from power lines.

Why Build Instead of Buying?

A $5 pocket radio works fine, but building teaches resonance, detection, and CMOS analog tricks. You can modify it—add a regenerative stage, solar power, or speaker amp. It is a gateway to more complex receivers.

Wrapping It Up

There you have it, friend—a complete guide to this brilliant CD4049 AM radio. From the hand-wound coil to the paralleled CMOS output, every part plays its role. Build it tonight, tune in tomorrow, and enjoy the airwaves. For more radio projects, check out the FM receivers and transmitters on a2ahelp.com. If you pull in a station from another state, let me know—I live for those stories. Happy tuning!