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

On 26 May 2018 at 19:25, Justin Richards <justin.richards@gmail.com> wrote:

> Interested if anyone has suggestions for building a contact fault locator
> circuit that would provide audible feedback as RF cables and connectors a=
re
> 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 thei=
r
> 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 inf=
o.
>
> 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.
> --
> http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
> View/change your membership options at
> http://mailman.mit.edu/mailman/listinfo/piclist
>
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