[TowerTalk] USING MFJ-259B TO DETERMINE LENGTHS OF COAX

[Greg Best]

I have several lengths of RG8 (and other types) coax that are more than 25 years old and i am trying to sort good stuff from stuff to throw away.  Most of them are over 100 feet. I have used my MFJ-259B using the distance-to-fault feature to try to determine the length.  I tested one coax that was 30.5 feet exactly to see if I can get reliable figures for the length. The MFJ-259 indicates it is only 29.4 feet after multiplying the displayed length times the appropriate velocity factor. In this case, it was RG-142 with teflon dielectric.  The only potential I see for any error is how the coax is terminated.  The manual says to just leave the coax unterminated on the other end when the measurement is made.  But it also says, that more accurate measurements might be obtained if it is terminated in a resistive bad match as opposed to a reactive bad match. 
Does anyone have experience with this and found a reliable method? 
On the good side I have checked some of the coax lengths and found that the loss measurement feature of the MFJ-259B tracks within 0.1 dB of the measurement made with a professional quality tracking generator and spectrum analyzer.
GregN9GB