ranvier Posted August 27, 2011 Share Posted August 27, 2011 Hi all, I'm trying to find in vain, a device that can measure a coaxial cable propagation delay that can return a value of * ns/m. If anyone came across such a device and know the brand and model, I would really appreciate u sharing this information. Thank you! Link to comment Share on other sites More sharing options...
ramdram Posted August 27, 2011 Share Posted August 27, 2011 As I recall the "mu" of co-axial cable is specified. The "mu" as I recall was the percentage of light speed the propagation wave would travel down the cable. The example I recall is the "mu" of old, lossy TV feeder which was, approximately, 0.67. Modern feeder would be around 0.97 or so. You may be able to calculate your desired result from the length of the feeder and derive a figure from that. But, obviously, it would be a bit "ball park" I suppose. I would speculate further such kit would be a tad on the dear side, and, not found in a "retail outlet" on the "High St". Link to comment Share on other sites More sharing options...
pritch Posted August 27, 2011 Share Posted August 27, 2011 Sounds like TDR territory to me. I couldn't name a specific product that'll give you a time rather than a distance to the end of the cable, though. Link to comment Share on other sites More sharing options...
Jivemaster Posted August 27, 2011 Share Posted August 27, 2011 TDR will give figures sufficient for a comms utility company to dig a hole right on a fault to repair it. As it's time based then there must be propagation speed in the calculation to get distance. TDR is also used to check faults in computer cabling so there may be a hirer somewhere local to you. Link to comment Share on other sites More sharing options...
ranvier Posted August 27, 2011 Author Share Posted August 27, 2011 Hi hi, thanks all for the replies. Yes indeed, I understand we can derive the propagation delay using velocity of propagation which is - delay in ns/ft = (1.016 x Length of cable in feet) / VOP (in percentage) Link to comment Share on other sites More sharing options...
dbuckley Posted August 28, 2011 Share Posted August 28, 2011 When you use a TDR you enter into the machine the velocity factor of the cable, the TDR measures the time, and calculates the distance. Link to comment Share on other sites More sharing options...
timd Posted August 28, 2011 Share Posted August 28, 2011 When you use a TDR you enter into the machine the velocity factor of the cable, the TDR measures the time, and calculates the distance. But if you know the distance, you could guess a sensible velocity factor, see what the machine thinks the distance should be and work back to the actual velocity factor, and then test again using that to check. Link to comment Share on other sites More sharing options...
pritch Posted August 28, 2011 Share Posted August 28, 2011 "Sensible" potentially being 1 if the machine allows it, as it simplifies the maths by a small amount! Link to comment Share on other sites More sharing options...
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