Audio transmission through the ground

[4pyros]

Look here;
https://caves.org.uk/radio/comms_in_caves.html
and here;
https://www.scavalon.be/avalonuk/technical/radio1.htm

 

[unclejed613]

the complete series of Speleonics Magazine can be found here: http://www.caves.org/section/commelect/drupal/speleonics

 

[killivolt]

the complete series of Speleonics Magazine can be found here: http://www.caves.org/section/commelect/drupal/speleonics

Something like this would be impossible in urban areas, if I read this correctly? I have a power line in my back yard 30feet away. I was wondering about this about a week ago, but didn't want to start something.

Is there a way of jamming the hum and embed a code in it, rather than producing radio wave transmission?

 

[unclejed613]

you could hypothetically use a transmit/receive frequency of between 500hz-3khz and use one of the following programs as a text terminal using the soundcard in your computer. such mid-audio band transmissions should be relatively free of power line interference.

http://www.w1hkj.com/Fldigi.html

http://www.digipan.net/

**broken link removed**

with an audio amplifier driving an antenna coil or stakes in the ground, and the receiver just being a second set of stakes or coil fed into the input of the sound card microphone input, you would have an audio band electromagnetic transceiver. for some of these modes, you want to keep the distortion as low as possible, so you a) don't want to overdrive the amplifier, and b) want as good a quality amplifier as you can manage. you will want to make sure the "antenna" impedance is at least 8 ohms to keep from tripping the protection circuits present in most modern amplifiers.

with stakes, you could place the transmitter stakes about 20 feet apart, and position the receiver stakes inline and also 20 feet apart (so that your line of stakes is 40 feet long and use the stake in the middle as a common ground between transmit and receive). for dry soil (like we have here in Colorado) you can insure good conductivity by soaking the dirt along the whole 40 foot line with salt water. likewise, the transmitter'receiver at the other end of the link would be set up broadside to the first station.