[EE]: Contact Fault Locator to provide audible feeback

[Justin Richards]

Interested if anyone has suggestions for building a contact fault locator
circuit that would provide audible feedback as RF cables and connectors are
wiggled and tapped.

These cables terminate in Combiners and Transformers with a DC input
impedance of around 0.4 ohms and between 50 - 500 ohms impedance for their
usable frequency range . A multi-meter is useful for finding faults but
has some drawbacks. It is slow to update and a little difficult to use in
the field with sun, flies, rain, dust etc.

Not really sure where to start. Perhaps injecting a sine wave of a given
frequency which could be distorted as the faulty connectors are knocked.

Any suggestions are warmly welcome. See below if keen for additional info.

Cheers Justin


As a Telstra tech we used a contact fault locator QD750017 (some are
selling on Ebay at present) to test any coax cables that we manufactured.

These coax cables carried up to 140Mb/s so it was important that we made
quality connectors.

To test, both ends were connected to the tester and then the cables were
tapped with a piece of nylon as part of the knock test.

The tester produced audible feedback and were excellent at detecting
connectors that were not 100%.

I currently help maintain a network that utilizes thousands of RF
connectors.

We have various methods to determine faulty connectors and components
including

System self diags (Slow and fails to pin point failure)
Spectrum Analyser with tracking generator (Cumbersome but effective)
Multimeter (Very effective but with slow visual feedback can miss faults)

Recently while on repair duties I recalled the contact fault locators and
am now curious how to build such a circuit.

[Richard Prosser]

I'm wondering if the capacitance of the cable could be used as part of an
rf (or audio) oscillator circuit. The rf signal could be mixed with a
'fixed' frequency signal at a close frequency & the difference signal sent
to a speaker or headphone. Should be quite sensitive to contact problems
but might be a bit tricky to cover a wide range of cable lengths.
50ohm coax has a capacitance of up to 100pf/m so longer cable lengths could
have high enough capacitance for direct audio oscillation.


A TDR approach would work also, but I'm not sure how to produce an audible
output.

A capacitance bridge circuit could be used, fed from an audio tone source &
adjusted to balance prior to the test.

RP

Post by Justin Richards
Interested if anyone has suggestions for building a contact fault locator
circuit that would provide audible feedback as RF cables and connectors are
wiggled and tapped.
These cables terminate in Combiners and Transformers with a DC input
impedance of around 0.4 ohms and between 50 - 500 ohms impedance for their
usable frequency range . A multi-meter is useful for finding faults but
has some drawbacks. It is slow to update and a little difficult to use in
the field with sun, flies, rain, dust etc.
Not really sure where to start. Perhaps injecting a sine wave of a given
frequency which could be distorted as the faulty connectors are knocked.
Any suggestions are warmly welcome. See below if keen for additional info.
Cheers Justin
As a Telstra tech we used a contact fault locator QD750017 (some are
selling on Ebay at present) to test any coax cables that we manufactured.
These coax cables carried up to 140Mb/s so it was important that we made
quality connectors.
To test, both ends were connected to the tester and then the cables were
tapped with a piece of nylon as part of the knock test.
The tester produced audible feedback and were excellent at detecting
connectors that were not 100%.
I currently help maintain a network that utilizes thousands of RF
connectors.
We have various methods to determine faulty connectors and components
including
System self diags (Slow and fails to pin point failure)
Spectrum Analyser with tracking generator (Cumbersome but effective)
Multimeter (Very effective but with slow visual feedback can miss faults)
Recently while on repair duties I recalled the contact fault locators and
am now curious how to build such a circuit.
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