The differing twist lengths are engineered to minimize crosstalk between the pairs. If all of them have the same number of twists per inch then you will find that the same wires tend to be next to each other down the length of the cable. If instead you have each of them have a different number of twists such that over the length of the cable the amount of time each is in contact with each other tends to be more even, reducing crosstalk.
I suspect in some cases having two separate links running through the same cable will hurt performance because you will get crosstalk from the other link which you may not be able to cancel out using an echo canceller. Probably depends on the length and specifics of the link. On Tue, Jan 28, 2020 at 8:33 PM Ken Hohhof <af...@kwisp.com> wrote: > Each pair has a different number of twists per inch. In Cat5 and Cat5e > cable I observe the green and orange pairs, which are the data pairs, have > the tightest twists. I don’t remember if Cat6 is similar. This leads me > to believe the blue and brown pairs may have inferior crosstalk > performance. But GigE uses all 4 pairs for data, so my theory is probably > wrong. I guess the important thing is that none of the pairs have the same > number of twists. > > > > The reason I mention this is sometimes I see people assert that if you > split a Cat5 cable into 2 as is being discussed, it will hurt the > performance. > > > > *From:* AF <af-boun...@af.afmug.com> *On Behalf Of *Forrest Christian > (List Account) > *Sent:* Tuesday, January 28, 2020 5:24 PM > *To:* AnimalFarm Microwave Users Group <af@af.afmug.com> > *Subject:* Re: [AFMUG] Cambium POE Splitter > > > > This is actually pretty simple: > > > > Split the CAT5 into two, two pairs per radio, put the pairs on the data > line. At the bottom use a 24V gigabit capable injector which puts the > power on the data pairs. We have a couple at PacketFlux, Chuck makes a > couple, and there are others available. The goal here is to get the 24V > riding the data line along with the data. So effectively you have two > 10/100 capable links up with power on them. > > > > At the top, you reverse the process.... get a device which will pull the > power off of the data pairs, probably one of them from Chuck. (See > 800-GigE-PoE as an example). Plug the cable from the bottom in the PoE > port, then build yourself a cable for the radio which puts the extracted > power on 4,5,7,8 and the data pins where they belong. > > > > You could also use a single midspan Gigabit PoE injector at the bottom > with power on all 4 pairs, then remove it using a similar one at the top. > Then your long CAT5 stays unsplit, and the splitting and PoE mess is all > in a single cable harness. To do this you'd take two cat5 cables, and > then wire the 1,2,3,6 pairs from each cable into a single RJ45 (putting one > on 1,2,3,6 and the other on 4,5,7,8) which gets plugged into the non-PoE > side of the extractor. Then the remaining 4,5,7,8 wires you'd connect to > the power which came out of the PoE extractor at the top. The bottom > harness would be similar but for simplicity you can just put 24V in the > injector and not connect 4,5,7,8 on either CAT5. Now I think about this, > this is what I'd probably do and just use a single 800-GigE-PoE top and > bottom. > > > > On Tue, Jan 28, 2020 at 9:17 AM Matt <matt.mailingli...@gmail.com> wrote: > > I have a case where I need to power up two separate Cambium 24 volt > SMs on rooftop but only need 100base to each. Its very difficult to > run the second wire at this location which I need. Anyone know of way > to split the cat5 at bottom and top to do this? Not likely but > thought I would ask. > > -- > AF mailing list > AF@af.afmug.com > http://af.afmug.com/mailman/listinfo/af_af.afmug.com > > > > > -- > > - Forrest > -- > AF mailing list > AF@af.afmug.com > http://af.afmug.com/mailman/listinfo/af_af.afmug.com > -- - Forrest
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