On Monday, October 14, 2013 6:59:41 PM UTC-7, Jeff Liebermann wrote:
On Mon, 14 Oct 2013 10:10:57 -0700 (PDT), Frank Krygowski

wrote:



So: Anyone know the easiest way to determine the exact location

of such a buried coil?



The compass, stud finder, and divining rod will not work. What you

need is a coil resonant to the operating frequency, some kind of

detector, and an indicator. The problem is that the frequencies used

vary from 10 Khz to as high as 200 Khz. That means either a broadband

detector, or a tunable coil.

http://en.wikipedia.org/wiki/Induction_loop



If you have a smartphone of some flavor, you can probably use one of

the oscilloscope apps to act as the amplifier, detector, and display.

Something like this:

https://play.google.com/store/apps/details?id=com.nfx.noscpro&hl=en

There are also various "ghost finder" and "EMF detector" apps that are

basically LF (low frequency) signal detectors. For example:

https://play.google.com/store/apps/details?id=com.superphunlabs.emf&hl=en

https://play.google.com/store/apps/details?id=com.codebros.emffree&hl=en

They use the phones magnetic sensor as a LF pickup coil. I have no

idea of the operating frequency range or sensitivity, but methinks

it's worth trying.



Otherwise, I would build a resonant pickup coil, setup a tuning system

(switched caps and tuning capacitor), mount it on a wooden stick, and

plug the coil into the microphone input. Then use an oscilloscope

application to view the signal. If the signal is low, add a battery

powered audio amp. If you want, I can throw something together (time

permitting) and see what it produces.

So, is there a cell phone app for triggering the loop?

-- Jay Beattie.