FAQ
TL;DR: For cochlear links, the external-to-implant hop often uses a 1.8 MHz carrier; “not anything that would be directly processable by the human ear.” Build around near‑field pickup and audio amplification, not a 20 Hz–20 kHz RF receiver. [Elektroda, george gonzalez, post #21668023]
Why it matters: If you design for audio‑band RF, you’ll miss the actual carrier and hear only noise. This FAQ helps hobbyists plan workable pickup, filtering, and amplification for implant-adjacent audio monitoring.
- Typical implant link example: 1.8 MHz carrier with amplitude‑coded digital control for 16 electrodes. [Elektroda, george gonzalez, post #21668023]
- Audible target band: Approx. 20 Hz–20 kHz; use audio‑path filtering and speakers. [Elektroda, Alex Blanco, post #21668008]
- Loop/coil pickup is preferred to avoid far‑field broadcast interference. [Elektroda, Ruben Proost, post #21668015]
- Receiver input goes to the antenna; output feeds a speaker or recorder. [Elektroda, Frank Bushnell, post #21668017]
- Untuned ULF projects hear everything in‑band; add selective filtering to target signals. [Elektroda, Steve Lawson, post #21668018]
Quick Facts
- Typical implant link example: 1.8 MHz carrier with amplitude‑coded digital control for 16 electrodes. [Elektroda, george gonzalez, post #21668023]
- Audible target band: Approx. 20 Hz–20 kHz; use audio‑path filtering and speakers. [Elektroda, Alex Blanco, post #21668008]
- Loop/coil pickup is preferred to avoid far‑field broadcast interference. [Elektroda, Ruben Proost, post #21668015]
- Receiver input goes to the antenna; output feeds a speaker or recorder. [Elektroda, Frank Bushnell, post #21668017]
- Untuned ULF projects hear everything in‑band; add selective filtering to target signals. [Elektroda, Steve Lawson, post #21668018]
What does “receiving 200 Hz–20 kHz” actually mean for this project?
It refers to the desired audio band your speaker should reproduce, not an RF carrier in that band. Cochlear links commonly ride on a higher‑frequency carrier, so design for audio extraction after near‑field pickup, not for an RF receiver at 200 Hz–20 kHz. [Elektroda, george gonzalez, post #21668023]
Do cochlear implants transmit audio directly at audio frequencies?
No. An example shared used a 1.8 MHz carrier with amplitude‑coded digital control for the implant electrodes. That carrier powers and controls the implant; the raw RF is not directly listenable as sound. “Not anything that would be directly processable by the human ear.” [Elektroda, george gonzalez, post #21668023]
So how should I pick up the implant’s external signal?
Use a small loop or coil placed near the implant’s external coil to couple the magnetic field. Feed that into a low‑noise audio amplifier and then into a speaker or recorder. This near‑field approach minimizes unrelated broadcasts. [Elektroda, Ruben Proost, post #21668015]
Can I just use a long straight copper wire as the antenna?
A straight wire is not ideal here. For low frequencies and near‑field coupling, use a loop or coil across the two antenna terminals. Wire is cheap, so you can test loop sizes and turns to maximize pickup. [Elektroda, Frank Bushnell, post #21668020]
Where do I connect antenna and speaker on a simple ULF receiver board?
Connect the loop/coil to the input terminals marked for the aerial. Connect a speaker or attenuated line to the output terminals. This lets you monitor or record what the front end captures. “The input terminals connect to the aerial.” [Elektroda, Frank Bushnell, post #21668017]
Will an untuned ULF receiver isolate my implant’s signal?
No. Untuned front ends hear everything in their passband. Add selectivity after the pickup, such as a tunable notch or band‑pass filter, to suppress unwanted tones and hum while passing desired audio content. [Elektroda, Steve Lawson, post #21668018]
What is AFSK, and is it relevant here?
AFSK is Audio Frequency‑Shift Keying—digital data encoded as two audio tones. If your system used an RF carrier, AFSK could reduce acoustic interference. For pure near‑field audio monitoring, focus on magnetic pickup and audio amplification instead. [Elektroda, David Adams, post #21668006]
How wide should my filter be if I use an RF IF approach?
If you truly demodulate an RF carrier, speech‑grade AM needs about 10 kHz audio, while wider hi‑fi needs more. One suggestion used 455 kHz IF cans and noted SSB is easier to filter narrowly. Match bandwidth to your content. [Elektroda, Rodney Green, post #21668014]
Can I tune specific frequencies on the Stormwise‑style ULF project?
That project is broadband. Add an active tunable notch or band‑pass stage after the preamp to target a particular tone region. Insert it between the detector and audio amp to shape what reaches the speaker. [Elektroda, Steve Lawson, post #21668018]
Is the 20 kHz upper limit useful for everyone?
Not always. One contributor noted few adults can hear 20 kHz. Designing for 15–18 kHz often delivers similar perceived quality while easing filter and amplifier demands. That tradeoff can simplify your build. [Elektroda, Frank Bushnell, post #21668007]
Any risk of picking up unrelated radio stations or hum?
Yes. Far‑field RF and mains hum can leak in. “Use a magnetic coupling rather than RF to avoid picking up radio stations all day.” Keep loops small, shield the preamp, and use notch filtering for 50/60 Hz. [Elektroda, Ruben Proost, post #21668015]
How do I physically try a coil pickup quickly? (3‑step)
- Wind 20–50 turns of enamel wire on a 3–5 cm former.
- Connect the coil across the receiver’s antenna input.
- Place it near the external implant coil and adjust distance/angle for strongest audio. [Elektroda, Frank Bushnell, post #21668020]
Who can confirm the exact carrier and protocol for my implant?
Ask your implant manufacturer or clinical team for the link specs and approved accessories. They use test receivers and coils and may share a compatible monitoring schematic or antenna details. This saves guesswork. [Elektroda, Frank Bushnell, post #21668020]
Does the chosen Stormwise ULF receiver fit this goal?
It can amplify very low‑frequency fields, but your implant may use a higher RF carrier for power and data. Without matching the actual link method, results may be weak or noisy. Verify the link before investing more. [Elektroda, Alex Blanco, post #21668016]
Can I route the receiver output to a recorder instead of a speaker?
Yes. Use the output terminals and add attenuation if needed to meet line‑level. This helps capture sessions for later analysis or adjustment while avoiding clipping. [Elektroda, Frank Bushnell, post #21668017]
