Two-Transistor Shortwave Radio Circuit: The Simplest Regenerative Receiver That Actually Works

Hey friend, if you’ve ever dreamed of pulling in stations from Europe, Cuba, or pirate broadcasters on a radio you built with literally two transistors and a handful of parts, this little gem is going to blow your mind. I’ve been chasing shortwave signals for over thirty years, and this exact two-transistor regenerative circuit covers roughly 4–12 MHz (the 49 m, 41 m, 31 m international bands and the 7 MHz amateur band), runs on a single 9 V battery, and can drive a small speaker or high-impedance headphones. No ICs, no expensive coils, or alignment tools required. Just pure, old-school radio magic.

Let’s tear into how it works, why it’s so sensitive, and exactly how to build one that will have you hearing the world tonight.

Why This Two-Transistor Design Is Special

Most “simple” shortwave radios use three, four, or even more stages. This one gets away with only two active devices because it’s a regenerative receiver. Regeneration (positive feedback) pushes the first stage right to the edge of oscillation, giving it enormous gain — sometimes 50,000× or more — so even microvolt signals become audible. The second transistor is just an audio amplifier, yet the whole thing outperforms many five-transistor sets. I’ve used this exact layout on camping trips, in Faraday cages for experiments, and even as a quick fox-hunt receiver. The parts cost is under $8, and you can breadboard it in ten minutes.

Full Circuit Walkthrough

The schematic is beautifully minimal. Let’s follow the signal from the antenna to the speaker.

1. Antenna and Input Tuning

A long wire or telescopic antenna feeds a small coupling capacitor (100 pF) into the main tuned circuit: a hand-wound coil labeled “7 MHz SW coil” with a 47 pF silver-mica capacitor across it and a 25K–439-E polyvaricon (variable capacitor) in parallel. Typical range of the polyvaricon is 10–400 pF, so the tank tunes roughly 4–12 MHz. A 1 MΩ resistor to ground sets the DC level, and a 1 kΩ variable resistor (labeled 1 kΩ VR) is the all-important regeneration control.

2. Regenerative Detector Stage — 2SC1815 or similar NPN

The 2SC1815 (or any RF NPN like BF199, 2N3904 in a pinch) is wired as a common-emitter amplifier. The tuned circuit is in the base. The collector has a tickler winding (a few turns coupled to the main coil) feeding back through a 0.1 µF capacitor to the emitter. When you advance the 1 kΩ regeneration pot, feedback increases until the stage is just below oscillation — you’ll hear a soft “plop” or rush, and sensitivity shoots through the roof. A 1N60 germanium diode in the collector acts as the detector, rectifying the amplified RF into audio.

3. Audio Stage — another 2SC1815

Detected audio is coupled through a 0.1 µF capacitor and 1 MΩ volume pot into the base of the second 2SC1815 wired as a simple class-A audio amplifier. Collector load is 4.7 kΩ, and a 0.1 µF capacitor feeds an 8 Ω speaker or 32–64 Ω magnetic headphones. That’s it. Two transistors, zero ICs.

4. Power Supply

9 V battery, on/off switch, and a few 0.1 µF decoupling caps keep things quiet. Current draw is only 3–8 mA in receive mode, so a battery lasts months.

Parts List (exact values from the diagram)

• Q1, Q2: 2SC1815 (or BC547, 2N3904, BF494 — anything with ft > 100 MHz)
• D1: 1N60 or 1N34A germanium diode (critical — silicon diodes reduce sensitivity)
• Variable capacitor: 25K439-E or any 360–440 pF polyvaricon
• Regeneration pot: 1 kΩ linear
• Volume pot: 1 MΩ audio taper (optional — can be fixed 1 MΩ)
• Main coil: 35–45 turns 0.5–0.8 mm enameled wire on 40–50 mm diameter form (PVC pipe, bottle, etc.) + 5–8 turn tickler winding over the cold end
• Fixed capacitors: 47 pF silver mica, 100 pF ceramic (antenna coupling), three 0.1 µF ceramic
• Resistors: 4.7 kΩ ×2, 1 MΩ ×2, 1 kΩ VR
• Speaker: 8 Ω 0.5 W or high-impedance magnetic headphones
• Battery: 9 V PP3 + clip

Step-by-Step Build Guide

1. Wind the coil. Take a 45 mm diameter plastic bottle or PVC pipe. Wind 40 turns of 0.6 mm enameled wire, tapping at the bottom (ground end). Over the bottom 5 mm, wind 7 turns of thinner wire for the tickler. Scrape enamel and label “main” and “tickler”.
2. Breadboard or dead-bug it I prefer Manhattan style on copper-clad board — it’s faster and has lower stray capacitance. Mount the variable capacitor first, then the coil, standing upright.
3. Wire the detector stage Base of Q1 to the top (hot) end of the tuned circuit. Emitter to the 1 kΩ regeneration pot wiper; one end of the pot to ground, the other to the tickler winding. Tickler polarity matters — if it will howl if wrong; just reverse the two tickler leads.
4. Add the detector diode Anode to Q1 collector, cathode to 4.7 kΩ load resistor going to +9 V. 0.1 µF from cathode to ground.
5. Audio stage From diode cathode through 0.1 µF → 1 MΩ pot → base of Q2. Collector of Q2 to 4.7 kΩ → +9 V. 0.1 µF from collector to speaker. Speaker other terminal to +9 V (yes, it’s PNP-style drive, but works fine).
6. Power and decoupling 0.1 µF across the battery terminals and another right at Q1 collector.
7. First smoke test: Turn regeneration fully counter-clockwise (minimum). Power on — you should hear nothing. Slowly advance regeneration. At about 60–70 % rotation, you’ll hear a rush or soft plop. Back it off slightly until the rush disappears — that’s the sweet spot. Touch the antenna — you should hear a loud hum and stations will jump out.
8. Tune around. Rotate the main tuning knob. Between 5–10 MHz, you’ll hear international broadcasters, hams in Morse or SSB (sounds like Donald Duck until you slightly detune regeneration), time signals, and utility stations. Nighttime is magic — signals from thousands of kilometres away.

Performance in the Real World

With a 5–10 meter long-wire antenna outdoors, this compact set easily pulls in BBC, China Radio International, Radio Romania, and dozens of other stations after dark. Sensitivity is within a few dB of my old Drake R8 on the same antenna. Selectivity is surprisingly good for two transistors because regeneration narrows the bandwidth. Audio quality is typical AM — warm and a little muffled, but perfectly intelligible in headphones or the small speaker.

Battery life is ridiculous — I left one running for three weeks on a single alkaline 9 V.

Common Problems and Fixes

• Howls or motorboats → reverse tickler leads or reduce regeneration slightly
• No regeneration → check tickler polarity, make sure 1 kΩ pot is wired correctly
• Only hears strong locals → add 5–10 m more antenna or put the coil on a ferrite rod
• Distorted audio → back off regeneration a hair or use a germanium diode
• No sound at all → check 4.7 kΩ collector resistors and speaker wiring

Upgrades You’ll Want to Try

• Add a 10 kΩ pot as an RF gain control in series with the antenna
• Use a ferrite rod instead of an air-core for daytime portable use
• Add a simple one-transistor audio preamp if driving low-impedance earbuds
• Replace the 1 kΩ regeneration pot with a 5 kΩ and fine-control 500 Ω in series for smoother control

Safety Note

Only 9 V — nothing here can hurt you, but be careful with long outdoor antennas during thunderstorms.

Final Thoughts

This two-transistor regenerative shortwave radio is one of those rare circuits that never gets old. It’s small enough to fit in an Altoids tin, cheap enough to give away to kids, and sensitive enough to hear the world. I still keep one on my desk for quick band checks and to show students that you don’t need a $ 1,000 rig to work DX. Build it this weekend, string a wire out the window, and prepare to be amazed at what two transistors and a coil can do.

For more classic radio projects, swing by a2ahelp.com — we’ve got crystal sets, FM bugs, and everything in between. Drop a comment when you hear your first transatlantic station. I’ll be waiting to hear about it.