If you need to find the bad spot (short) of a coax cable then the MFJ-259 will help you find that. You will need to know the velocity factor of the coax cable being measured. Often times this is a know measurement from the manufactor.
Follow the steps below.
1. Connect the coax to the MFJ-259 input.
2. Turn on the MFJ-259 and start at the lowest frequency range. Watch the RESISTANCE METER for a dip reading (zero ohms) and record the frequency.
3. Continue moving up in frequency to find a second dip, which should be twice the first (recorded) dip frequency.
4. Calculate the position of the short: Divide 492 by the first dip frequency (in MHz) and multiply the result by the velocity factor of the coax cable being measured. The result should be