Determining the place of interruption (shorting) coaxial cable capacity meter

It is relatively rare, that the coaxial cable will break at some point. However, especially in winter, coaxial cables are rigid due to low temperatures and coaxial is interrupted due to bending., or short-circuits. Few people have another coaxial cable in reserve, but almost everyone has a capacity meter (or milliohmeter).

How to find a place, where the coaxial cable is broken, or shorted?

1. Coaxial cable broken

We will need a capacity meter with a range to determine the point of interruption 2 to 20 nF (according to the cable length) and measuring band. Such a meter is, for example, part of some more expensive multimeters.

Disconnect the coaxial cable from all devices. We use a capacity meter to measure the capacity from both ends of the cable. For example, from the end, which we connected to TCVR - we measure 180 pF (denote as C1) and from the end, which has been connected to the antenna 120 pF (denote as C2).

We calculate the break point of the coaxial cable according to the formula:
D = C1/(C1+C2)xL [m; pF, pF, pF, m]
Where D is the distance from the coaxial break point to the TCVR, C1 and C2 are the measured capacitances and L is the total length of the coaxial.

In this way we can locate the point of interruption very precisely and eliminate the defect by cutting out the damaged section and joining good parts. Interruptions near connectors and locations are most common, where the coaxial passes through the wall (window).

2. Coaxial cable shorted

To find the place, in which the short circuit occurred we will need a milliohmeter and a measuring band.

Disconnect the coaxial cable from all devices. We measure the resistance from both ends of the cable with a milliohmeter. For example, from the end, which we connected to TCVR - we measure 0,8 ohmu (denote as R1) and from the end, which has been connected to the antenna 0,04 ohmu (denote as R2).

We calculate the break point of the coaxial cable according to the formula:
D = R1/(R1 + R2)xL [m; ohm, ohm, ohm, m]
Where D is the distance from the coaxial break point to the TCVR, R1 and R2 are the measured resistances and L is the total length of the coaxial.

I deliberately chose a large disparity of resistances in the example, because in 99% In some cases, there is a short circuit in the connectors, where usually “lost” the braid wire rests on the live conductor. Therefore, after detecting a short in the coaxial cable, we first check the connectors.