Ask The Trades - Print Page

Ask The Trades
https://www.askthetrades.co.uk/cgi-bin/yabb/YaBB.pl DIY Forum >> Alarms, Phones, Aerials, CCTV & Datacomms >> Testing coax https://www.askthetrades.co.uk/cgi-bin/yabb/YaBB.pl?num=1209710618 Message started by greg on May 2^nd, 2008, 7:43am

Title: Testing coax
Post by greg on May 2^nd, 2008, 7:43am

What is the best way to test coax for damage, ie nailing

Cheers

Title: Re: Testing coax
Post by Twobarrows on May 2^nd, 2008, 11:50am

Delay Time Reflectometry (I think, it's been a long time since I've done it - decades!).
You will also need a sillyscope, which most people don't have.
Basically you send a pulse down the (unterminated) coax & you can see the reflection from the end of the cable and also any anomolies. Depending on the length of the cable you can isolate a problem to within a couple of feet.
However, if you've stuffed a nail into it it's probably easier & cheaper to just replace it entirely (with decent quality coax)!
Good luck....

Title: Re: Testing coax
Post by pryantcc on Jan 11^th, 2010, 2:35pm

It may be too late, but......

If your nail has connected the shield to the conductor, you can check it very cheaply. Unplug each end of the section you want to test. Use a digital multimeter (beeps when you connect both probes together) to make sure there is no connection between the outer braid and centre conductor.

Put one probe on the braid, the other on the centre. If you get a beep, it's bad.

This only tests electrical connectivity, not the quality of signal delivered, etc as the oscilloscope tests above would do.

Title: Re: Testing coax
Post by Lectrician on Jan 11^th, 2010, 3:19pm

The oscillator method is used to determine where the damage is in terms of cable length - Not beneficial if you do not know the cable run to locate the damaged part. It is used regularly by the telecomms engineers such as BT, and occasionally by electrical distribution network operators.

If you just want to know if you have a fault or not, do as said in the post above (low ohms between the braid and conductor is NOT good!).