Tuning FM Radio on a 3D Printer Heatbed – Jeff Geerling

On May 28 2026 a visitor from Repkord asked a deceptively simple question while we were tinkering in the studio: Can a 3D printer’s heatbed act as an antenna? The heatbed on a Prusa Core One is a large copper‑clad PCB with a dense grid of traces, and those traces look a lot like a dipole when you squint. In theory any conductor can radiate or receive RF if it’s the right length and you feed it enough power.

The experimental setup

I pulled out the family’s NanoVNA – the pocket‑sized vector network analyzer that hobbyists use to sweep S‑parameters and plot SWR. The NanoVNA’s port 1 was connected to the heatbed’s copper plane via a short coax lead, while port 2 was left open to act as the reference. The printer was powered off, so the bed was just a passive metal sheet.

The NanoVNA hooked up to the Core One heatbed. The image shows the typical Prusa Core One heatbed layout, which resembles a meandering antenna.

Sweep results

The NanoVNA performed a 10 kHz‑to‑3 GHz sweep. The SWR trace showed several shallow notches, the most pronounced at:

Frequency	Approx. SWR	Observation
43 MHz	2.1:1	Near the lower end of the FM broadcast band (88‑108 MHz) but still a clear dip
130 MHz	1.8:1	Directly inside the FM band – this is the sweet spot for local FM stations
1 GHz	2.4:1	Likely a harmonic of the bed’s trace length

The notches are not razor‑sharp; the heatbed is not a purpose‑built antenna, so the Q‑factor is low. Nevertheless, the dips indicate that the bed presents a lower impedance at those frequencies, which is exactly what you need for reception.

Real‑world reception test

Armed with the data, I tuned a cheap FM receiver to the 130 MHz notch while the heatbed was still connected to the NanoVNA. The receiver was placed a few centimeters from the bed, and the antenna lead was simply clipped onto one of the copper traces.

Within a mile of KYKY‑FM in St. Louis (30 kW ERP) the signal came in clean enough for stereo playback. The audio was a bit tinny, but the station’s RDS data decoded without error. At 43 MHz the reception was weaker, as expected for a band that sits below the standard FM range.

Why it works (and why it’s not ideal)

• Low‑resistance DC design – Heatbeds are engineered to carry several amps of DC with minimal voltage drop. The copper traces are wide and short, which reduces resistance but also makes the structure electrically short relative to RF wavelengths.
• Distributed capacitance – The dense grid creates a capacitive mesh that can support standing waves at specific frequencies, giving rise to the observed notches.
• Lack of matching network – A dedicated antenna would include a balun or matching network to transform the impedance to 50 Ω. The heatbed presents a wildly varying impedance, so the SWR never drops below ~1.8:1.
• Power handling – Since we are only receiving, the bed’s power rating is irrelevant. If you tried to transmit, the traces would quickly overheat and the printer’s firmware would shut down the bed.

Practical takeaways for homelab builders

1. If you already have a Prusa Core One (or any printer with a large PCB heatbed), you can experiment with it as a makeshift antenna. Just keep the coax short and avoid powering the bed while measuring.
2. For reliable FM reception, add a simple matching stub – a quarter‑wave piece of coax or a small ferrite choke can bring the SWR down to ~1.2:1.
3. Don’t count on it for transmission. The bed’s low‑impedance DC path will short any RF power, potentially damaging the printer’s MOSFETs.
4. Consider integrating a dedicated antenna port in future printer designs. A 3.5 mm jack wired to a spare copper trace would give makers a ready‑made RF test point without compromising the heating function.

Build recommendation

If you want to turn your 3D printer into a low‑cost FM receiver station, follow this checklist:

• Printer: Prusa Core One or any printer with a copper‑clad heatbed (≥200 mm × 200 mm).
• Measurement tool: NanoVNA‑E or NanoVNA‑F (10 kHz‑3 GHz sweep).
• Coax: RG‑174 or RG‑316, ≤30 cm, with a BNC‑to‑SMA adapter for the NanoVNA.
• Matching stub: 1/4‑wave at 100 MHz (≈75 cm of 50 Ω coax) with a ferrite choke at the feed point.
• Receiver: Any FM dongle or cheap radio that accepts an external antenna.
• Software: Use the NanoVNA’s built‑in sweep viewer, or export CSV data to VNA‑Plotter for deeper analysis.

Bottom line

A 3D printer heatbed is not a replacement for a professionally tuned antenna, but the experiment proves that the copper mesh can pick up strong broadcast signals when you give it a proper feed point. For the homelab enthusiast who already owns a Prusa, the extra hardware cost is near zero, and the fun of turning a printer into a radio receiver is priceless.

Stay tuned for the next experiment – maybe a Wi‑Fi‑enabled print bed that doubles as a low‑power transmitter for IoT devices.