Coax Cable Tester

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Completed Coax Cable Tester


This is a simple circuit that can be used to test all those coaxial cables that we have or make. It only uses a few components and will test if the cable is OK, has any shorts between screen and inner and if both screen and inner are continuous. The circuit is shown below along with components required.

Note: switch shown in “SHORT TEST” position.

Designation Value
R1, R2 680R, 0.25W
D1, D2 LED, Green
D3 LED, Red
SW1 DPDT Switch
CONN1, CONN2 To suit


  1. Item MUST be built in plastic box. (See NOTE below)
  2. Other connectors can be placed in parallel with CONN1 and CONN2 to give more universal DC testing of cables.
  3. LEDs can be mounted in holders to ease build.
  4. Designed to work from PP3 battery or other 9V source. Resistors R1 and R2 can be re-calculated for other supply voltages.
  5. Additional switch can be placed in +9V line to provide an ON/OFF function.

NOTE: Box must be of an insulating material otherwise the connector screens are shorted together and braid test will give a false reading.


  1. Plug cable to be tested between CONN1 and CONN2.
  2. With switch in position shown it is in “SHORT TEST”. If there is a short the red LED D3 will be illuminated showing a cable fault.
  3. Switch to other position. This is “CONTINUITY TEST”. If centre core is intact then D2 will illuminate green, if screening is intact then D1 will illuminate green at the same time. If only one LED illuminates then there is a cable fault denoted by which LED is not illuminated.

Internal construction of Coax Cable Tester


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