# Twisted Pair (EMI Cancellation)

Discussion in 'General Electronics Chat' started by AutoNub, Nov 10, 2011.

1. ### AutoNub Thread Starter Member

Oct 14, 2011
44
1
Hello,

I am putting together a wiring harness schematic for outsourcing to reduce company labor costs, and we adhere to strict electromagnetic radiation standards. One of the techniques we use to reduce EMI is twisted pairing for cancellation.

I'm curious, though, is there a standard for the ratio of twists per some measure of length? For example, 2 twists (two complete loops) per inch? How much of a difference does the frequency of twisting have on the EMI? Can you twist too much? Any details would be appreciated.

Thank you!

2. ### t06afre AAC Fanatic!

May 11, 2009
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Unless the signal is truly diferential. I doubt you will see any improvments in radiation from the cable.

3. ### AutoNub Thread Starter Member

Oct 14, 2011
44
1
All of our products have to pass MIL-STD-461 and 462 testing. We know twisted pairs improve our test results by reducing EMIs, but for the sake of outsourcing the construction of our wiring harnesses, I'm wondering about the amount of twisting necessary to achieve optimum results.

4. ### #12 Expert

Nov 30, 2010
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7,339
I think I saw, "5 turns per foot" in reference to Cat5 cable.

5. ### AutoNub Thread Starter Member

Oct 14, 2011
44
1
Thanks for the information #12. One thing I'm wondering is if there is a linear relationship between the number of twists per unit of length. For example, if you have twice as many twists per inch, would the EMI be reduced by twice as much? I doubt it is exactly linear, but I'd be surprised if someone didn't actually put together some calculations and/or measurements and maybe a graph of some kind showing these relationships.

6. ### #12 Expert

Nov 30, 2010
16,703
7,339
I am not equipped to measure EMI, but apparently you are. Set up a test and do the work. The results will probably be about the law of diminishing returns and best measured in decibels.

7. ### AutoNub Thread Starter Member

Oct 14, 2011
44
1
We do have a non-certified anechoic chamber for our preliminary testing prior to sending out for official testing, which I could use to conduct some experiments and compile some data to establish some relationships specifically addressing twisted pairs. I was simply wondering what data was already available on the subject. Posting on forums is usually an effective strategy to supplement my learning.

8. ### wmodavis Well-Known Member

Oct 23, 2010
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150
I just googled "twisted pair emi reduction" and found lots of references. You'll have to sort through to find what if any are helpful to you.

9. ### AutoNub Thread Starter Member

Oct 14, 2011
44
1

I've been google surfing since about an hour prior to my creation of this thread. I have found lots of interesting material, but nothing quite satisfactory yet. I'm thinking it is time to close this thread .

Thanks again.

Oct 2, 2009
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