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Human voice Spy

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ChArLyZzZ

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Hey guys,
if we build a transmitter on the same frequency of the human voice (i guess it's 20 KHz), its only job is to send a carrier. Then we build a receiver to detect this carrier, and get out the information from the signal which in this case is just the human voice. Do u think it might works? does it have any sense?
:)
 
Will it work? - No
Does it make sense? - No

I assume that you mean a radio transmitter. So you are going to transmit an unmodulated carrier, listen to it on a receiver, and you will hear nothing.
A bit of noise maybe, but no intelligence.

JimB
 
ChArLyZzZ said:
Hey guys,
if we build a transmitter on the same frequency of the human voice (i guess it's 20 KHz), its only job is to send a carrier. Then we build a receiver to detect this carrier, and get out the information from the signal which in this case is just the human voice. Do u think it might works? does it have any sense?
:)

First off, the human voice is from 20hz to, well im not sure exactly how high, but some people can hear up to 20khz (like me :lol: ). i have no idea what youre talking about :lol:
 
Let's see.
Connect a microphone to a very high voltage audio amplifier connected to an extremely long antenna wire. That is your "transmitter".

To receive it you could try connecting an extremely long antenna wire to a high gain audio amp.

I don't think you will hear the transmitted voice. You will hear mains hum like mad, and noises from electrical appliances being turned on and off. Your "receiver" will probably also pickup a jumble of AM radio stations.

Radio communication systems use a high frequency carrier so that they can be tuned and so that their antenna is a reasonable length.

I don't know how many Ghz my new cell phone operates at, but its antenna is only about 2cm long. It records, transmits and receives voices, music, pictures and videos (built-in digital camera). It has a built-in speakerphone and radio that it can record. It can go on the internet and download, upload, record and play pictures, videos and MP3s. It can record, transmit and receive data using IR. And it is tiny and cheap!
My daughter got it and another one for her for "free". She pays a small fee each month and we can use them on evenings and weekends for unlimited local calls at no charge. After a few hundred hours each month of calls during business hours they charge an arm and a leg. :lol:
 
Have you ever seen the size of radio astronomy satellite dishes? Ever wondered why they have to be so huge? Well, antenna sizes have size limitations binded by the laws of physics. To be able to transmit or sense a signal, the transducer size has to be a sizeable fraction of the signal wavelength.

If you check out the electromagnetic spectrum, the human voice (usually capped at 4kHz for telephony systems) lies in the extremely remote end of the radiowave band. Using the speed of light in free space, that comes up to a wavelength of 75km. Try building an antenna tens of kilometers long. Even at 20kHz, you'll need a transducer of at least a few kilometers in size.

If you can achieve that, it may work.
 
well i dont think my backyard will help:) you know it might be a good idea, we can then listen to the whispering of the astronauts in the space :D i'll go to sleep:)
 
Hi ChArLyZzZ,

If i read your post correctly, you mean to transmit just the voice
audio as a wireless radio transmission straight into the ether ...
... and see if you can pick it up ... ?

Well, yes. You can. They used to do this in the engine rooms of ships
but that was a long time back now, the headphones were also ear-muffs.

Reception was rough, filters were used to reduce the higher
frequencies, and the distance carried was not great as i recall.

They were like a primitive cheap walkie-talkie, but all on one band.
Haven't seen one for many years.
I think the aerial was just a trailing wire a few feet long, tucked
in the boiler suit.

Best of luck with it, John :)
 
john1 said:
Well, yes. You can. They used to do this in the engine rooms of ships
but that was a long time back now, the headphones were also ear-muffs.

I had a brief flirtation with such a system many years ago.

If I remember correctly, the system worked on a magnetic loop rather that radio.
Around the engine room was a loop of wire, which was fed from a reasonably powerfull audio amplifier.
In the headphones was a coil of wire connected to a small amplifier which drove the headphone speakers.
Streching the headphones to put them on operated a microswitch to turn on the battery to power the amplifier.

I believe a similar sort of system is in use in places like cinemas so that deaf people can hear the sound in their hearing aids.

JimB
 
Hi JimB,

I think your recollection of those old headphones is better than mine.
I only came across that system years ago on a very old boat.
It used a very tiny vaccuum tube in the headset, almost no other
components apart from the batteries required.

I think i was mistaken about it being like a walkie-talkie .....
I don't remember any microphone or switching involved at all.
It must have been just for reception, not for sending.

Which fits with what you say about cinemas (movies),
and the trailing wire that i recall may have been for a battery pack,
not an aerial at all !

And as you say, magnetic induction not radio waves, which kind of
limits the range from the sending loop to about a room or so.

I only recall them because i was so struck by the simplicity of them.
Haven't seen anything like it since.

Regards, John :)
 
John1

The things I am thinking of definitely had a transistor amplifier, it certainly wasnt a valve. I cant remember where the batteries fitted, but unless you knew what they were, the thing just looked like some very up-market ear-defenders. In fact these were military things onboard a warship.

JimB
 
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