Coax Cable Tester: Match the Instrument to the Question
Quick answer / TL;DR: Short answer: use a continuity tester to find opens and shorts, a signal meter to measure level and quality at the outlet, and a time domain reflectometer to locate a fault along a buried or inaccessible run. Continuity alone does not prove a cable is usable, since a corroded connector passes DC and blocks high frequency.
Three coaxial families: BNC for CCTV, F-type for TV, N for RF – each with its impedance.A coax fault is usually one of three things: an open, a short, or excessive loss.
Different instruments answer different questions, and buying the wrong one leads to a tester that confirms continuity on a cable that still will not work.
This article covers the three measurements, the instruments that make them, and the order in which to use them.
The three questions are whether the conductor is continuous, whether the cable is shorted, and whether it passes signal with acceptable loss.
A cheap continuity tester answers the first two and says nothing about the third.
That is why a cable can test good and still fail in service.
Instruments and Questions
| Instrument | Answers | Limitation |
|---|
| Continuity tester | Open or short | No loss information |
| Cable mapper | Which cable is which | No loss information |
| Signal meter | Level and quality | Needs a live signal |
| TDR | Fault distance | Interpretation needs practice |
| Certifier | Loss and return loss | Expensive, for installers |
The TDR row is the one that saves hours on a buried run, because it reports the distance to the fault rather than merely that one exists.
The certifier row is the professional instrument, and it is the only one that proves a cable meets a performance standard rather than merely conducting.
A Practical Order
Start with continuity, because an open or a short is quick to find and common.
Then measure at the outlet with a signal meter, which tests the whole chain rather than the cable alone.
Then, if the fault is in an inaccessible run, use a TDR to locate it before digging.
Replacing a buried cable without locating the fault is the expensive version of the same diagnosis.
Common Faults
- A connector with a stray shield strand shorting the centre
- A corroded connector passing DC but not signal
- A crushed cable with a partial short
- A wall plate with a poor internal connection
- A splitter port damaged by a bent centre pin
Real-World Applications
A cable tests continuous and still fails. The connector is corroded and passing DC while blocking signal, and replacing it resolves the fault.
A buried run fails. A TDR locates the fault within a metre, and the repair is a joint rather than a new cable.
A wall plate is the fault. Continuity passes through it, and a signal measurement at the outlet shows the loss.
A splitter port has a bent centre pin. The cable tests fine and the port is replaced.
Standards and Verification
Coax performance is specified by the cable manufacturer per frequency, and certification instruments test against the applicable cabling standard.
Verification is a level and quality reading at the outlet, plus continuity where a fault is suspected.
Test at the outlet rather than at the cable. The outlet is where the user's problem is.
Interpreting a Reading
A signal meter reports level and quality, and the two together indicate whether the problem is loss, interference or overdrive.
A high level with poor quality suggests distortion, while a low level with poor quality suggests loss.
A reading taken at the outlet includes the whole chain, which is why it is more useful than a cable-only test.
Where the reading is good and the television still fails, the television's tuner is the remaining element.
That is worth checking before replacing cable that measures correctly.
Recording the reading at commissioning gives a baseline, which turns a later degradation into a measurable change.
Without a baseline, a system that has always been marginal is indistinguishable from one that has failed.
A short note of the reading and the date is enough, and it costs a minute during installation.
That minute is repaid the first time a fault needs diagnosing.
When to Call It
A fault in an accessible run is usually faster to fix by substitution than by measurement.
A fault in an inaccessible run justifies the instrument, because the alternative is destructive investigation.
That distinction decides whether buying a tester is worthwhile for a given installation.
For domestic work, a signal meter at the outlet and a spare cable answer most questions.
For installations with buried or concealed runs, a reflectometer pays for itself the first time it locates a fault.
The decision is about the cost of the alternative rather than about the cost of the instrument.
Where the run cannot be replaced economically, measurement is the only sensible first step.
Where it can be replaced quickly, replacement is the measurement.
Where the instrument is borrowed, recording the readings in the installation notes is what makes the next diagnosis a comparison rather than a fresh start.
Related reading: Coax cable signal loss — blogs/news/coax-cable-signal-loss
Related reading: Coax adapter — blogs/news/coax-adapter
Related reading: Coax cable in-wall rating — blogs/news/coax-cable-in-wall-rating
Frequently Asked Questions
Will a continuity tester prove my cable works?
No. It only shows the conductor is continuous and not shorted.
What finds a fault in a buried cable?
A time domain reflectometer, which reports the distance to the fault.
Why does a good cable fail in service?
A corroded connector can pass DC and block high frequency signal.
Do I need a certifier?
Only if you must prove performance to a standard. A signal meter is enough for diagnosis.
Sourcing cables for a project, a store, or a private-label line? Contact our B2B sales team for specifications, certification evidence, and volume terms – FOB and CIF options available. Request a quote or sample.
