Testing quality of coax cable connection?

Hi folks

I’m looking for some advice. I’ve a video capture solution deployed to a few sites. The composite (CVBS) video signal is transferred across the rooms over coax cable terminated with BNC connectors.

On some sites the video capture cards intermittently lose the video signal. I’m investigating a number of options but one thing I’d like to rule out is poor quality cabling / termination.

I’ve looked at BNC cable testers but they seem to be basic works/doesn’t work testers.

Are there any common ways to test the quality of a coax connection?

thanks

Rather than buying a test system that you feel will meet your demands (whatever they may be), I'd suggest buying some quality replacement cables and if the faults persist then it wasn't due to the cables.

You need a TDR, that will tell you whether there are any continuity issues and the approx. location of the fault.

Simplest, visual inspection and wiggle the cables especially near the connections and see if the video feed is interrupted.

$$, Buy new cables as jackrae said!

$$$$, Use a TDR which is $$$$$ and probably way more complex than you want to know or understand.

JasonC0x0D:
$$$$, Use a TDR which is $$$$$ and probably way more complex than you want to know or understand.

Thanks folks, that was my suspicion.

The existing cabling is in-wall and a loose cable across the room isn't an option other than in the very short term (medical environment) otherwise I'd definitely have replaced them.

The joys of a very intermittent problem :frowning:

Thanks for the help

What kind of coax is installed? Cables should have their designation printed on them - you can then look
up the specs for the cable.

A quick search suggests RG59 cable is good for 100m runs.

What sort of BNC connectors are involved - soldered or crimped or what? Properly soldered connectors
are reliable, but they are hard to solder well, it takes practice.

JasonC0x0D:
$$$$, Use a TDR which is $$$$$ and probably way more complex than you want to know or understand.

It should be pretty easy to rent one:
https://www.conres.com/test-equipment/product-category/cable-analyzers/

A good fast oscilloscope and a pulse generator will do the job too, just drive the line via a 75 ohm resistor from
the pulse generator and look at the voltage at the sending end (obviously disconnect any sensitive equipment
from the other end) You should only see a single reflection from the very end (if its open or shorted), or if
the end is 75 ohm terminated you should see no reflections.

MarkT:
A good fast oscilloscope and a pulse generator will do the job too, just drive the line via a 75 ohm resistor from
the pulse generator and look at the voltage at the sending end (obviously disconnect any sensitive equipment
from the other end) You should only see a single reflection from the very end (if its open or shorted), or if
the end is 75 ohm terminated you should see no reflections.

That's an interesting option. I've just ordered a Diligent Analog 2 Discovery (30 MHz, 100 MSPS) which has both functions. I'll experiment with that.

Thanks

That does not sound fast enough for short cable runs. a foot of cable is a ns, and you can only sample 10 ns per point.

I said a good fast oscilloscope, you need nanosecond resolution (1GSPS or better) really. And fast probe(s) of course.