Stuart France
Active member
Why not use radiolocation gear? Most cave electronics nerds focus on getting maximum depth or station separation, but making a miniature low power transmitter that?s good for only a few metres could be useful too. It can be driven via a timer so as to turn some hours or days in the future, run for a while, and then turn itself off to protect its battery from deep discharge.
On the far side of the gap you would need a corresponding receiver since the transmitter is not generating audio signals that you can hear. With a directional aerial you can determine bearing and inclination of the one set relative to the other, telling what direction to dig and how far.
We did this many years ago concerning a potential Aggy-Daren link over a distance of about 25 metres, but obviously it can be scaled down much further for shorter potential link-ups.
What I?m talking about is a transmitter that is based on feeding a reasonable looking sine wave into a miniature power inductor wound on a bobbin ferrite an inch across something like https://www.farnell.com/datasheets/3606590.pdf which will create an oscillating magnetic field that is ?easily? picked up a few metres away with a directional antenna such as a loop or even another of these bobbins as the receiver loop (suitably driven) to triangulate it.
I suppose if you fed your transmitter inductor with 198KHz pulsed at some audio frequency like 256Hz then you would hear a middle-C tone of a piano and get directionality into the bargain with a common-or-garden kitchen radio tuned to Radio 4 long wave as your receiver set on the other side of the dig (assuming your kitchen radio has a ferrite rod antenna). This is not difficult to do on an evening with a PIC processor costing a pound...
On the far side of the gap you would need a corresponding receiver since the transmitter is not generating audio signals that you can hear. With a directional aerial you can determine bearing and inclination of the one set relative to the other, telling what direction to dig and how far.
We did this many years ago concerning a potential Aggy-Daren link over a distance of about 25 metres, but obviously it can be scaled down much further for shorter potential link-ups.
What I?m talking about is a transmitter that is based on feeding a reasonable looking sine wave into a miniature power inductor wound on a bobbin ferrite an inch across something like https://www.farnell.com/datasheets/3606590.pdf which will create an oscillating magnetic field that is ?easily? picked up a few metres away with a directional antenna such as a loop or even another of these bobbins as the receiver loop (suitably driven) to triangulate it.
I suppose if you fed your transmitter inductor with 198KHz pulsed at some audio frequency like 256Hz then you would hear a middle-C tone of a piano and get directionality into the bargain with a common-or-garden kitchen radio tuned to Radio 4 long wave as your receiver set on the other side of the dig (assuming your kitchen radio has a ferrite rod antenna). This is not difficult to do on an evening with a PIC processor costing a pound...