Pulse Star II intriguing search loop

[Claude]

I found the universal search loop from Pulse Star II (tb Electronic) very intriguing. You can put it in various shapes. I wonder on what principle is this working, where are the windings? How do you achieve the 300mH or so needed for a PI? By only having a double wired cable shorted at one end, the other connected to the circuit?
Here is the link:
http://www.tb-electronic.de/prodinfo/ps2/univcoil/unien.htm
Let's have a discussion on this.

[Carl]

Re: Pulse Star II intriguing search loop

It's possibly a multi-coil cable, maybe 4 or 5 conductors. They would be wired to form a series loop, with each end going to the circuitry.

- Carl

[proscan]

Re: Pulse Star II intriguing search loop

Carl is right, definitely.

Beside the loop does not have to have such high inductance (300mH).

Most likely it has 3 orders lower one, i.e. 300uH.

proscan

[Claude]

You think all loops are indepentently connected?

Thanks for these answers. You think they designed the circuit with 3 or 4 independent coils of one turn or just one coil but the ends of wires are connected at the end, forming like extremely elongated turns?

[Eric Foster]

Re: You think all loops are indepentently connected?

Hi Claude,

There may be a bit of confusion here and I will try to sort it out. I made flexible coils for the Superscan PI detector that I used to make. The coils were made from 12 way cable with each conductor made up of 16/0.2 strands. The wires in the cable are all colour coded which makes connecting into a coil easy. Say I wanted to make a 1m square coil; I would then cut a 4m length of cable. The outer sheath would be stripped back a few cm. at each end to expose the individual conductors and their coloured sleeves. Take the red lead at one end as the start of the coil. Go to the other end and bend the cable around to give a circular coil initially. Strip the insulation off this second end of the red lead and join it to another colour wire at the start end, say yellow. Go to the far end of the yellow lead and join it to another colour at the start end, say orange. Continue this procedure, always joining to a new colour to avoid getting a shorted turn. Measure the inductance as you go and stop when the required figure is reached. Any unused conductors will have no effect. Each join should be sleeved with heat shrink to avoid shorts. I used to do all of this joining so that it was inside a plastic potting box and then take the coax cable out through a cable gland. The whole joint would be potted in epoxy to give a neat finish. The finished coil can be either a 1m square, 0.5 x 1.5m rectangular, or whatever you wanted.

For smaller coils for use with detectors running at higher sensitivities, I have used multicore data cable with aluminium coated mylar shield with drain wire. Connecting all the ends is a bit tedious, as I think it was 24 way that I used, but you can make a good shielded coil this way by connecting the drain wire to the ground of the coax braid.

Eric.