Making a Coil from a USB cable?

[bklein]

I have a spool of 24G solid core insulated wire to make a 10" coil. I used 22 turns for ~262uH. I have some really long USB2.0 cables that have a spiral wrap of an aluminum/mylar foil with a ground wire as well. As I have a bunch of these USB cables, the next coil I make will use the signal wires as the insulation is probably better than my solid core 24G wire has. Anyway, I took the foil and spiral-wrapped it around the coil, leaving a gap as I see recommended. Any issue with then using the ground wire and wrapping it around the foil and then tying it to one of the coil wires?

I've read that some have used such USB cables as the feedline. Would you then recommend using the signal wires (green/white) as the hot and Vbus/ground as the ground? Should the shield and its ground wire then connect at the pcb ground and then leave the shield and its ground wire open at the coil side - or would it be better to connect them along with the Vbus ground to the coil ground(s), thus grounding the shield at both ends of the USB cable?

[bklein]

Thanks for all the great responses!
I tried the usb cable as described (but with ground shield connected to coil shield) and it worked better than my water-compromised feedline. I took the original aluminized mylar off a similar cable and wrapped it around my coil, grounded it, and left a gap. I noticed that this ended up having a bit of ringing in the rx signal and needed a bit of a readjustment of the damping resistor to eliminate it. I also tried a RG-58/U cable and didn't notice much of a difference - my preference would be the USB cable because it is thinner... I also have USB3.0 cables to try sometime...

Barry

[WM6]

Thanks for all the great responses!
I tried the usb cable as described (but with ground shield connected to coil shield) and it worked better than my water-compromised feedline. I took the original aluminized mylar off a similar cable and wrapped it around my coil, grounded it, and left a gap. I noticed that this ended up having a bit of ringing in the rx signal and needed a bit of a readjustment of the damping resistor to eliminate it. I also tried a RG-58/U cable and didn't notice much of a difference - my preference would be the USB cable because it is thinner... I also have USB3.0 cables to try sometime...

Barry

Good idea Barry. Probably using USB cable you can lower parasitic capacitance too in comparition with usual wound coil, because of not straigt wire line in cable and thicker insulation of wire.

[satdaveuk]

Am i right in thinking you will continue with the farady cage from the usb3 cable directly around the RX coil with no joins , then do another shield for the TX using another another run from usb cable.
Keep them in that order.
If thats correct sounds a good Idea most certainly worth the experiment oviousy dont make a full loop , the usb3 cable if made by belkin etc is a good cable thicker with more strands and better screen than usb2, keep in mind use your red as the hot wire, got more strands slightly thicker.

You know as well as me less joins mean less problems far as performance and fucture faults.

Let us know how you get on

Regards

[satdaveuk]

sorry may not have read your post correctly if its pulse induction, as a guess I would use the red as your hot wire slightly thicker with a few more strands and the screen as a return, if your talking about Induction balance type use the known wiring as Red TX hot= start, screen TX return, Green RX start, white, RX return, Black often n/a but sometimes used as a TX return, leaving your screen for earth bonding via faraday shields


If you mean actually winding a PI coil go for the red and black as your windings because you need the thickness, you stated that your using .24 solid at the moment, work out the diffrence because stranded wire has different parameters by quite alot, saying that supose if it was me maybe try everything, them who dares wins noble prizes.

Maybe we are on totl cross purposes but maybe help to someone who knows

Regards

[Tepco]

I made few coils using UTP (not USB) cables and i was disappointed whit performance. Fact that wires are twisted together will actually increase coil capacitance even more, in combination whit very tight shield, and another problem is high resistance, making large coils for more powerful detectors unpractical. I suppose USB cable will suffer from same issues (but i not tried yet)

[bklein]

My fault - my thread title is incorrect. Should have read Making a Coil FEEDLINE, not coil. My main intent was to replace my corrupted feedline. I then made two coils with around 22G plastic insulated solid wire. One of them I took another such USB cable, split the plastic jacket off, took off the shield braid, and unwrapped the aluminized mylar shielding. I wrapped the aluminized mylar around one of the two coils - so I had one shielded and one unshielded coil (that I could switch in and out). The shielded one was a bit less impervious to the various emissions from my work area but the flyback response had some ringing in it that the unshielded coil didn't have - this took a readjustment of the damping resistor to bring down a bit. I didn't see a big difference between them as far as target detection and in fact the detector still sucked as far as that goes. I got so frustrated with the detector and the large amount of time I have spent trying to get it up to even the performance of the Clone PI that I sent it to Whites for repair. I had replaced both cmos IC's, the mosfet, the pots, the feedline and even the coil. The feedline swap was the biggest improvement but RG-58/U was just as good. Perhaps though there were improvements in capacitance that I didn't really care about in this stage - as all I was interested in was performance seeing a quarter or a dime. I did see a little difference in flyback time between the original coil and my two (mine were faster) but so much in the same ballpark I didn't care.

[Jose]

I performed the coil to the Pulse Delta, UTP cable, with good performance. The delay is 20 usec, with Scotch tape Blindage No. 24.
Best Regards
Jose

[Tepco]

I know it works well, i did the same. 4 turns UTP, 28cm, everything inside connected in series. But try other configurations, can work even better!