Chasing RF Cables

[Mike H]

1 hour ago, rpasetto said:

The first thing I tried was shorting one end of cable while using Ohm meter to check other end.  with one of the two it showed non-zero; I later tried using a cable tester like the one Mike H had recommended earlier.  The other cable-end in front cabinet never had continuity with the rear one, or with any other cable-end I tried; same with the cable end in rear cabinet.   

But for sure, one pair of cable ends which did check out good are now failing the test using the cable tester.  More checking to follow.

.. Rick P 05 Sig Conquest

Make sure there are no splitters in the circuit or that will give you false readings.

[rpasetto]

Update:  After reading a few articles about calculating cable lengths using capacitance measurements I figured I'd give that a try.  Using the only one of my multimeters which has a capacitance scale I took more measurements.  The front-to-rear cable which used to work, the "B" cable to my DISH receiver, measures about 146 pF at the connector in front cabinet.  At 16.2pF / ft that comes to about 9 feet.  Measurement of the other cable end in the front gave 143pF, also about 9 ft.  So if the measurement and calculation is correct, the break would be around 9ft along the cables toward the rear.  

I decided to check some known cables to see if the readings are consistent with the 16.2pF/ ft.  Checked 10 ft cable gave 59pF for about 6 pf/ft; a 20 ft cable 202 pF, about 10pF /ft.   Then checked a longer cable, 24.5 ft. The reading was 286pF, about  11/7pf/ft.   So it could be the meter is only accurate at higher capacitance levels or the length of the leads affects readings or both.  With all this I think the break could be somewhere between ten and twenty ft. from the front.. maybe in the ceiling. 

[quick_tox]

Using pico-farads to calculate cable length.  Interesting. Did you use an analog or digital meter?

[rpasetto]

@Mike H:  A splitter might be responsible for the readings of the "unknown" cable.  That is the one for which the other end was not found.  However for the cable that was successfully working until a few days ago, I doubt that there was a splitter on it. 

 

@quick-tox:  It's a digital meter, apparently not very accurate at low capacitance ranges given the non-linearity the measurements have shown.