PI Mono Coil Cable question

[yatahaze323]

Hey everyone,

I've finish building a 10 inch 3dss 329uh mono coil for my Minipulse plus rev D and I need to decide on a cable to connect the coil to my minipulse. I've got a lot of different cables that I would like to use to connect the coil to the box, but I'm unsure which would work best. Here's a list of the different wires I currently have:

campbell scientific p/n 9922 -20 AWG, 1-Twisted Pair Santoprene Cable - https://www.campbellsci.com/p9922
RG-59 coax (unsure if the core is solid or stranded)
RG-58 coax (unsure if the core is solid or stranded)
Speaker hookup wire 16 awg, https://www.amazon.com/dp/B006LW0W5Y..._fhYsCb6VRC60V
Speaker hookup wire 20 awg, similar to the above
XLR microphone cable

Not sure if this matters but I will be using this minipulse and coil at the beach and in the salt water to find coins and jewelry so I probably won't be operating it at 10us or under.

Any advice is appreciated!

Thanks!

[bklein]

Bill Lahr told me to use RG58CU. This is stranded. I found a spool of 150500 Ancor marine grade 100’ for $46 on ebay. Going to try it on a dual field coil I’m swapping the cable on. West Marine has it for less than a dollar a foot too.

[MartyJ1963]

@Yatahaze,,,,When I make my 3DSS mono coils I always measure 33" f which ever wire I'm building the coil with and I start the coil from the 33rd inch. I measure the iinductance after 5 full sets of turns and try for 300uh. When the coil is 300uh I measure 33" inch again and then I twist the 2 long wires together at 3 twists per inch,,,this way, the coil wcable is part of the coil. I have never needed to shield them. All I do then with the cable is wrap it with electrical tape then I cover it with 1/4" inch Spiral wrap,,,then I wrap the spiral with one more layer of electrical tape. My minipulse REV-D and REV-E both have 3dss coils at 300uh and I get small targets very clearly at 12"-14" and bigger targets a lot deeper. I build 3dss coils for all my PI's and never had issues,,,I find they work better than the bundle wrapped-copper enamelled wire coils that need shielding. Hope this helps. Marty

[bklein]

http://www.geotech1.com/forums/showt...ax-good-enough

found this discussion.
really interested to learn what type of cable is used on TDI and the new pi detectors coming out soon.

[yatahaze323]

Thanks guys for your reply's.

MartyJ1963: For my future pi coils I can try this, for my current coil the start and end wires are much to short so I'll have to use something else to attach the coil to the detector box. I have a few questions with this technique. Using this method have you taken your coils in salt water? If so have you noticed any water getting inside the taped up wire? How long have these wrapped wires lasted for you?

bklein: I saw that thread awhile ago but thank you for posting it. I took a read through it again and it gave me a good idea of what to look for.

[MartyJ1963]

Hiya Yatahaze,,,,I have tested my coils in shallow salt water, and No, water does not get inside. The coil cable and coil wire is one continuous cable. I use 16 stranded normal hook-up wire that is 0.5mm in diameter. The wire is rated at 600v and PTFE Coated. By being one cable the wire has no solder joints for the coil to see and the wire has less capacitance which helps the speed of the coil. When I have finished building my coil I wrap the coil in 2 layers of paper medical tape. Then I wrap the coil in cotton fabric that is 3/4 of an wide. I make a centre piece for the inside of the coil (for the ears to sit on) , out of 6mm plywood and drill tiny holes around the edge. I use waxed cotton thread (the type for sewing Tents, camping equipment etc,,,) to sew the piece to the coil. The waxed thread is waterproof and does not break easily so a lot of tension can be applied. I then put a coat of fibrglass resin on to the coil. When it's dry I apply another coat. I build up the layers gradually giving each layer time to cure. When I have time I will make a PDF document , with photo's, on how I do this. Hope this helps. Regards,,,Marty

[homefire]

RG-58 Stranded is the BOMB. Wish I had a pile of the stuff. Meets most any RF needs I ever have as well. You can even run WiFi Amps with the stuff. https://www.amazon.com/Stranded-Copp.../dp/B01HDFS0WY

[bklein]

I bought this: https://www.amazon.com/Ancor-150510-...+marine+rg58cu

[sinclairuser]

I like the audio coax, 2 insulated twisted wires with a separate shield, so you have options too two separate wires one for + and one for - that are a twisted pair(good for pi, and another shield braid that can be separate or connected to -.
you can get different strands too, one type has 4 wires two twisted pairs and braid, good for twin coils for pi, there is a version 3 pairs as well.
another reason I like it is its soft some coax is horribly stiff, this is not the only downside is its expensive on a roll, but DJ equipment outfits and some audio specialists sell it by the meter, so you just buy what you need for your project when you need it and then its not that bad.

[bklein]

I used some Mogami cable like this for a few Excal coil repairs but am a bit worried at the soft jacket compared to the originals.
Has anyone reading this seen performance differences per choice of cable - does pF/ft really matter?

[samsearcher]

How do you measure the inductance whilst winding the coil Marty? Do you cut a much longer length than is needed, or probe (with a pin) through the insulation?

[godigit1]

here is the TDI cable each wire has a seperate shield.

[MartyJ1963]

Hiya Samsearcher,,,,,Depends on what type of coil I'm winding and what Inductance I'm wanting. Usually, If I'm making a 3dss coil and I'm wanting an inductance around 300uh I wrap the wire around the form so it's done 35 full complete revolutions then I measure it by slicing a small space in the insulation and measuring wth the LC Meter. I know that when I'm using 0.5mm/16 strand pvc coated wire that my inductance will be pretty close, if not exact after 35 full turns. I always use the same wire for my PI Coils cos' they've always given me good results. Hope this helps. Regards,,,Marty EDIT:- I forgot to mention that when I reieve the wire I order, I always rewind it onto a 'net-making spool' (like for making fishing nets) so it can easily pass through the centre of the 3dss coil form,,,saves me a lot of hassle and I don't have to cut it until I reach my intended Inductance. Marty

[kt315]

i have for release two types of soviet made coax cable. one is more hard. not chinese quality and fake copper.
i will send 1.80-2.0m to whom want to probe it for 8euro.

[nickel_n]

that may help. I got the info from an ML "Dust bin" 18"coil.
the coil was used with the SD2000 and it was one of the very early coils that they made.
it is labelled as fallows
AUSTEC cables 75 ohm Air spaced Co Axial UV Stabilised