Bob,
Thanks for that.
Yes, I have measured the skew, because of the twists per inch (pitch?) the tighter the twist the longer the wire physical length as well. I read that a maximum of 50nS/100 meters was the limit that the hardware was able to correct.
But for sure you can measure the difference.
Geoff
toggle quoted message
Show quoted text
On 8/23/2023 5:02 PM, Bob Ecclestone VK2ZRE wrote:
Hi Geoff,
You probably already know this, but each pair in a Cat6 cable has a different "twist rate" to minimise crosstalk, so the VF for each pair will be slightly different.
Try it with a piece of scrap cable. Measure the electrical length of each pair, you will find it will be slightly different for each pair.
I was involved with a startup VDSL broadband internet provider in the early 2000s and we used custom made, multiple pair Cat5 cable for the "last mile" (10, 25, 50 & 100pr).
We ended up characterising each pair in each cable size to help with fault finding. As with coax, the VF varied slightly along a cable and across batches, but it got us in the ball park to locate a fault.
Cheers...Bob VK2ZRE
On 24/08/2023 7:14 am, Geoff Peters - AB6BT wrote:
Sigi,
Yes, I have a piece of CAT6 cable to test. I removed the jacket at 1 foot intervals for about an inch. I will test by cutting 1 wire at a time at each location and see what I measure.
Geoff
On 8/23/2023 2:02 PM, Siegfried Jackstien wrote:
take 10 inch of speaker wire.. that should show almost similar numbers.. if thats the case then yes you can trust it
dg9bfc sigi
Am 23.08.2023 um 22:52 schrieb Geoff Peters - AB6BT:
Roger,
I sent a reply but it hasn't shown up so here's take 2...
In this case, what I'm trying to determine is the minimum distance I can measure to a fault.. I used 4.8mm to simplify this discussion, I'm not sure what you mean by "only in steps of 1 so this is the limiting factor." . I understand that the actual distance/step is VF dependent.
For example, I have a CAT6 cable with an open green wire. I have calculated the VF as I know the physical length of the cable, 300 feet/91.44 meters.
Using a NanoVNA-H4 I measure the distance to the fault at about 240mm.
So the question is...can I trust that number?
Geoff
