DIY 2wire low EMF cable from 4wire cable - Page 1
Forum section: electronics / general

author: meandeev
author_rank: Regular Contributor
timestamp: March 26, 2022, 12:06:16 pm
content: I have shielded 4 wire PTFE insulated cable, 2 pairs of wire are twisted to each other.Similiar to picture from wikipedia:I want to make my own low EMF cables from this with gold plated lugs.What is the best way to make 2 wire cables out of this?Should I cut 2 wires - if yes, which?Should I crimp 2 wire in parallel - if yes, which,red-black and blue-yellow orred-yellow and blue-black orred-blue and yellow black?

author: marks2c
author_rank: Contributor
timestamp: March 26, 2022, 08:09:29 pm
content: Please ignore this (answering a different question):Sorry, a cable with two twisted pair cables cannot be made in a low-EMI'quad' cable.The guts:* Common-mode rejection cancels out signal that is the same in both the +ve and -ve conductors.* Conductors in exactly the same place would have exactly the same signal induced in them... but unfortunately they'd also be joined together.* Quad cable 'fudges' this by having a helix spiral of four conductors with the conductors opposite each other joined together. The beauty of this is that the 'average position' of both pairs of conductors is in the middle of the cable (ie the same place) and so if the magnetic field is linear perfect cancellation is achieved.EDIT: fixed my cognitive issue: the question asked was EMF not EMI...

author: RoGeorge
author_rank: Super Contributor
timestamp: March 27, 2022, 10:15:37 am
content: - crimp red and yellow together- crimp blue and black together

author: marks2c
author_rank: Contributor
timestamp: March 27, 2022, 04:46:21 pm
content: Quote from: RoGeorge on March 27, 2022, 10:15:37 amHi RoGeorge, I'm really happy to be wrong here, and keen to learn how the effective induction loop area gets to be reduced compared to that of a single twisted pair?

author: RoGeorge
author_rank: Super Contributor
timestamp: March 27, 2022, 05:23:42 pm
content: I didn't say crimping the two twisted pairs in parallel will lower the noise. The parasitic EMF in each pair is the same, except the total max allowed current will be higher (lower resistance).I was aiming to lower the resistance at least, but I'm not experienced in metrology. At a brief look it seems that crimping the two twisted pairs in parallel will half the resistance while keeping the same noise as a single pair. Isn't that so?

author: marks2c
author_rank: Contributor
timestamp: March 27, 2022, 07:40:50 pm
content: Thanks RoGeorge: an EMF question, not EMI. Fixed my incorrect post above.

author: martinr33
author_rank: Frequent Contributor
timestamp: March 27, 2022, 07:58:39 pm
content: 1) For low EMF, you will need "pure red copper" spades (that's the phrase to search for outside of specialist suppliers). The best gold plated ones use a silver interlayer, much less good ones use nickel. By far the majority of gold plated connectors are brass.You can tell the difference in the construction - nickel underplated spades are mirror shiny. Gold over silver looks flat.2) One twisted pair is enough for low thermal and low noise measurements. With two twisted pairs, you can measure two sensiive signals with less concern about RF loops across two leads. Single pair cables are much more useful.The high dollar Fluke low thermal cables are a single 22GA shielded twisted pair in a PTFE jacket.

author: guenthert
author_rank: Frequent Contributor
timestamp: March 30, 2022, 02:41:38 am
content: Related, I was once (~2017) told that in Germany you "only" get STP Ethernet cable. I was quite surprised as while I think it's possible to get such in the USA, I haven't seen it. Neither at Fry's (R.I.P.) nor any office or data center (left coast only) I've been to in the last 25 years. There it's always UTP, be it patch cable or fixed installation. What's the whole story?