Parts list for building a radio to receive 200 Hz–20 kHz audio signal range

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How can I build a receiver to pick up a 200 Hz–20 kHz audio signal, and what parts do I need?

You can't pick a generic 200 Hz–20 kHz signal with an RF receiver until you know the actual carrier frequency and modulation, so the first step is to identify the transmitter details before choosing parts [#21668005][#21668007] One reply notes that a cochlear implant link may use a 1.8 MHz carrier with amplitude-coded digital modulation, which is not something you would listen to directly [#21668023] For an implant, magnetic coupling is suggested as a better approach than a normal RF antenna: use a coil on an amplifier, and on the receive side use a coil into a microphone-input style front end [#21668015] If you really are receiving a low-frequency/ULF signal, the posts suggest a loop or coil antenna rather than a simple length of wire, and on the receiver the input terminals go to the antenna while the output can drive an auxiliary speaker or recorder [#21668017][#21668020] If the signal is actually on a higher-frequency carrier, one suggested design is a band-pass filter around 455 kHz using standard AM IF cans, with bandwidth chosen for AM or SSB as needed [#21668014] The practical next step is to get the implant or transmitter specifications, or a circuit diagram, from the manufacturer or medical team before buying parts [#21668007][#21668017]

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#1 21668004 10 May 2013 09:58

Alex Blanco Alex Blanco

Anonymous

Post #1
21668004 10 May 2013 09:58

I am trying to build a radio to receive a 200 hz - 20 kHz audio signal. The signal frequency is the most important thing for this project.

Can anyone give me a starting point as to what specific parts I would need (breadboard, operational amplifier, capacitors, transistors, resistors, antennae, etc..) for this frequency range?
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#2 21668005 10 May 2013 11:21

Steve Lawson Steve Lawson

Anonymous

Post #2
21668005 10 May 2013 11:21

So, do you mean that you want to receive an RF signal that is modulated with a 200 hz – 20 kHz audio signal [because you can't receive audio energy with an RF receiver]?

If so, what type of modulation? What carrier frequency?

If not, then do you mean receive an RF signal in the 200 hz – 20 kHz range?

If so, what kind of signal? Continuous Wave [CW], modulated? Or is that irrelevant?
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#3 21668006 10 May 2013 12:42

David Adams David Adams

Anonymous

Post #3
21668006 10 May 2013 12:42

As Steve said are you transmitting these frequencies via a high frequency carrier - or just want to receive an audio signal - which in that case just build an audio amplifier with a mic input. If you are then I would look for circuits that can do AFSK - at least that way you would cut down on sound wave interference - somewhat
#4 21668007 10 May 2013 14:37

Frank Bushnell Frank Bushnell

Anonymous

Post #4
21668007 10 May 2013 14:37

Hi Alex,
It would help if you can give more details of the nature of your project. When we can see what you are trying to accomplish, we can give more detailed advice.

When you say, "The signal frequency is the most important thing for this project.", do you mean the audio signal or the radio signal ?

Are you trying to build a high fidelity radio receiver ? This would usually go down to about 20 Hz. And 20 kHz is a frequency that very few adults can hear.

Your starting point is to clearly define the functions you require the radio to perform, such as to be receiving speech or music or digital data, The second is to obtain a circuit diagram, then you will have a list of parts to buy.
#5 21668008 10 May 2013 15:56

Alex Blanco Alex Blanco

Anonymous

Post #5
21668008 10 May 2013 15:56

Some background -

I have a cochlear implant. It is a transmitter and receiver. It transmits the external audio signal from my surroundings and I receive audio from my medical team. The reception signal falls between the 20 hz - 20000 hz range, because this is the audible range of the cochlea.

http://bit.ly/1952vmo

So essentially what I am trying to do is broadcast this signal over an external speaker. I do not wish to transmit any signal, just receive the audio signal from this range of frequencies.
#6 21668009 10 May 2013 16:01

Steve Lawson Steve Lawson

Anonymous

Post #6
21668009 10 May 2013 16:01

So, how does the audio get from the implant, to whatever the "medical team" is using to receive it?

And/or what do you mean by "receive audio from my medical team"? Receive it how?
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#7 21668010 10 May 2013 16:16

Frank Bushnell Frank Bushnell

Anonymous

Post #7
21668010 10 May 2013 16:16

This may be useful to help everyone in this discussion :

http://en.wikipedia.org/wiki/Cochlear_implant#Parts_of_the_cochlear_implant
#8 21668011 10 May 2013 16:31

Frank Bushnell Frank Bushnell

Anonymous

Post #8
21668011 10 May 2013 16:31

Alex, does your implant operate something like the one shown in Wikipedia ?

If it does, I think what is needed is something like a loop antenna over your ear to pick up the signal from the external part (the signal that goes to the inner implant), and amplify it, possibly broadcasting it by radio like bluetooth to another receiver, so that it can be heard by other people.

Have I got the basic idea of what you want ? Please correct any misunderstanding I may have.
#9 21668012 10 May 2013 17:15

Alex Blanco Alex Blanco

Anonymous

Post #9
21668012 10 May 2013 17:15

Essentially, it does not work on Bluetooth though. It works by transmitting and receiving *longwave* radio frequencies, somewhere in the 20 - 20000 hz range

(the medical team is located in Brazil, so shortwave frequencies like Bluetooth wouldn't transmit far enough. Also, my implant is wireless, differing from the wiki page. But the idea is the same).

So I was hoping to just intercept, for lack of a better word, the radio signal and broadcast it over a speaker on my makeshift radio, which would be receiving the same frequency signal as my implant.

I know its complicated, but any help would be appreciated.
#10 21668013 10 May 2013 18:09

Frank Bushnell Frank Bushnell

Anonymous

Post #10
21668013 10 May 2013 18:09

Thanks Alex, here is a diagram of how I understand the situation.
Please correct any mistakes.

P.S. You say your medical team is in Brazil, so where are you ?
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#11 21668014 10 May 2013 19:31

Rodney Green Rodney Green

Anonymous

Post #11
21668014 10 May 2013 19:31

Hi Alex.
The other coments are important for us to know, but (assuming HF carrier), you will need a band pass filter, and you can do this at 455kHZ, with a few standard AM IF cans from transistor radios. I have built such a receiver for Hi Fi AM (10 kHz band width). If you can use SSB, then a filter of 20 kHZ bandwidth is easy, but you may need to go somewhat higher in frequency for an AM signal as you wil need a filter of 40 kHz bandwidth. I will watch this space for your comments.
#12 21668015 11 May 2013 04:48

Ruben Proost Ruben Proost

Anonymous

Post #12
21668015 11 May 2013 04:48

For an implant it would make more sense to use a magnetic coupling rather than rf to avoid picking up radio stations all day. In that case you just need a coil on an amplifier to do the job. For the receiving end same thing. A coil on a microphone input.
#13 21668016 25 May 2013 19:13

Alex Blanco Alex Blanco

Anonymous

Post #13
21668016 25 May 2013 19:13

Thanks to everyone for their help. Here is where I am right now.

This is the radio I decided to build. http://www.stormwise.com/project1.htm.

It is capable of receiving ULF frequencies. I've built and mounted the circuit. But I am not sure what the next step is, or if this circuit will even serve my purpose.

1.) What are the input and output used for? Are they just grounds, or do I need some input to be able to receive ULF waves?

2.) Where do I connect the antenna - and how do I build a ULF antenna?

3.) How do I tune into specific frequencies - can I add a tuning mechanism to the circuit?

Thanks!

And to the curious, I am located outside of Philadelphia. The waves are not AM or FM, they are ULF waves which can be transmitted longer distances and are propagated through the Earth's surface. Again, I just need to receive the audio from the implant.
#14 21668017 25 May 2013 23:10

Frank Bushnell Frank Bushnell

Anonymous

Post #14
21668017 25 May 2013 23:10

The input terminals connect to the aerial (antenna) that picks up the signal, the output terminals are for an auiliary speaker or (possibly with attenuation) for recording the signal.

The home page of the site (http://www.stormwise.com/) sells the antennas, or go down to the "LIST OF Do-It-Yourself VLF RADIO PROJECTS:" section. If you contact the site operator he might provide help.

Also, you could google "ULF antenna construction" (or similar terms) for home build designs.

This circuit is intended to receive all signals in its frequency range. If your transmitter only broadcasts at audio frequency, this receiver might do what you want without tuning.

We would need further information on your transmitter to figure out any other circuit details, but I would think that either your medcal team or the implant manufacturer would be able to supply that information. They might even be able to give you a suitable circuit diagram to build.
#15 21668018 26 May 2013 02:01

Steve Lawson Steve Lawson

Anonymous

Post #15
21668018 26 May 2013 02:01

Perhaps you could use an "Active Tuneable Notch Filter" to add frequency selection to this circuit:

http://books.google.com/books?id=-sE7JVywygQC...SMy4GwBw&ved=0CGIQ6AEwBQ#v=onepage&q&f;=false
#16 21668019 26 May 2013 08:38

Alex Blanco Alex Blanco

Anonymous

Post #16
21668019 26 May 2013 08:38

Would a normal copper wire antenna suffice? Just a length of copper wire ~100 ft?
#17 21668020 26 May 2013 17:24

Frank Bushnell Frank Bushnell

Anonymous

Post #17
21668020 26 May 2013 17:24

There are two antenna terminals, so the antenna will be some kind of loop or coil.

Try googling "low frequency antenna construction" or "low frequency aerial design" or similar.
For short ranges, a fairly small loop or coil might work.

Ideally, the antenna in your implant would be the ideal shape, if you can get the specification from the manufacturer or your medical team. I would expect that they have aerials and conventional receivers for testing the transmitter/implant system.
The manufacturer's design team would probably be delighted to help you, and quite possibly provide a circuit and antenna design inforomation.
#18 21668021 26 May 2013 20:30

Alex Blanco Alex Blanco

Anonymous

Post #18
21668021 26 May 2013 20:30

Could I use a length of copper wire and solder a dual wire output to the end?
#19 21668022 27 May 2013 15:00

Frank Bushnell Frank Bushnell

Anonymous

Post #19
21668022 27 May 2013 15:00

My general knowledge of antennas is minimal, but I would think it needs to be a loop from one terrninal to the other at low frequencies. You can read up on it.
But, wire is cheap, experiment and see what happens !
#20 21668023 30 May 2013 13:40

george gonzalez george gonzalez

Anonymous

Post #20
21668023 30 May 2013 13:40

I used to work with cochlear implants. The signal used by the implant we were using between the microphone and the implant was a 1.8MHz carrier with amplitude coded digital modulation on it. The carrier was used to power the implant and the digital codes encoded which electrode, out of 16, was to be stimulated and at what current level. Not anything that would be directly processable by the human ear by listening to the signal.
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Topic summary

✨ The discussion centers on building a radio receiver capable of capturing audio signals in the 200 Hz to 20 kHz range, specifically related to a cochlear implant system transmitting wireless signals within this frequency band. Clarification was sought on whether the goal was to receive modulated RF signals carrying audio or directly receive audio frequency signals. The implant transmits longwave (ULF) radio frequencies rather than Bluetooth or typical AM/FM bands, with the medical team located remotely. Suggested components include a bandpass filter (potentially at 455 kHz IF for AM), operational amplifiers, coils or loop antennas for magnetic coupling, and active tunable notch filters for frequency selection. The use of a loop or coil antenna is recommended over simple wire antennas to avoid interference and improve selectivity. A referenced ULF radio project circuit was tested, with questions about antenna connection, tuning mechanisms, and input/output usage. It was noted that the implant’s carrier frequency might be in the MHz range with amplitude-coded digital modulation, implying the received signal may not be directly audible without demodulation. The importance of obtaining detailed transmitter specifications from the implant manufacturer or medical team was emphasized to design an appropriate receiver and antenna system.
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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]