[TowerTalk] Tuner SWR won't stay down

[Patrick Greenlee]

I recently had a problem where the SWR would "go crazy" frequently but 
seemingly at random.   After "getting lucky" in a trouble shooting 
session I found a defective RG-8X jumper.  In the middle of its length 
there was a section about 3-4 inches long where the center conductor was 
not centered in the dielectric.  The center conductor "wandered" around 
and was right at the edge of the dielectric and in one very small place 
was right at the surface where it touched or nearly touched the foil 
wrapped around the dielectric under the braid.

The jumper repetitively passed the ohm meter test showing good 
conductivity everywhere it was supposed to and not conducting where it 
shouldn't. However when a dummy load was attached to one end and the 
antenna meter to the other the meter's indications were just weird and 
uninterpretable.  Of course the same test setup with another jumper 
showed the expected 50 ohm reading independent of the freq. Subsequent 
to these tests I cut the jumper in half and by chance found the defect 
within an inch or so of the first piece I started cutting off little bits.

I saved a couple inch piece of just the dielectric with errant center 
conductor showing the worst of the defect and an adjacent sample of a 
couple inches showing a well centered center conductor at one end and 
the other end with the center conductor at the edge of the dielectric.  
I am keeping these samples as a reminder.  I have had lots of coax 
experience, nearly 55 years, but never had this problem before.  I will 
not have it again as all coax I buy with connectors installed will be 
tested with the antenna meter and or TDR and ditto for coax I put 
connectors on.

Prior to this experience I would have been skeptical that a jumper 
passing the ohm meter test could be so weird with RF. Seeing is 
believing. I hope reporting this incident may save someone some grief 
should they encounter a "funny" section in a piece of coax.

Patrick   NJ5G