I use the method often. Your results will vary depending upon several factors including the voltage level at which you perform the insulation test, type of dialectric, and what kind (and how many) arrestors may be inline. Generally speaking you should be able to perform a good high resistance test across the center conductor referenced to the shield conductor or a known ground to which the shield is connected but I would use the shield. Remember, this is a DC test of insulation resistance and isn't foolproof. Moisture intrusion may only conduct if the dialectric is saturated at some point but light condensation may conduct at all especially at lower voltages. If this is air dialectric Heliax with a convenient connector at some low point you may want to carefully disassemble that connector, inspect the copper for oxidation from pooling moisture, then reassemble. In my experience a meggar test is little more than an indicator of definite line failure (water intrusion or physical damage) but the test is worth the few minutes it takes to perform. Gary
dallasreact112 wrote: > I have access to a spare run of about 150' 1-1/2" heliax at a repeater > site. It goes from the "Radio Room" to the roof. There is no antenna > connected to it. I would like to verify if it still any good. > Obviously, hooking it up to a TDR would be a preferred method of > verification. Next best method probably would be hooking it to a > transmitter with a Bird thruline at the transmitter and a Bird > termaline at the end on the roof. I could then verify SWR and verify > actual transmit loss. Lacking that, I wonder if a megger, which I do > have, might be of use? If I were to suspect if the heliax is bad due > to moisture incursion, one might be able to see a low resistance path > between the center conductor and outer shielding. Has anyone tried this? > Is there a spec, or reasonable approximation for insulation resistance > center to shield per 100 ft or the like? > > 73 and Thanks > > Bernie Parker > > K5BP > > > Yahoo! Groups Links > > >
