Kim Elmore wrote:
>I'm not sure Towertalk is the right forum, but here goes:
>
>I'm using PL-259s outside to connect transmission lines (Belden 9913)
>that run up the tower to my antennas to the underground lines that
>run to the shack. Obviously, the PL-259s are connected through a
>barrel connector (which has a number designation I've forgotten).
>Everything is Amphenol and I've soldered more PL-250s than I can
>count, all with an American Beauty 100 W iron.
>
>Twice I have experienced one of the PL-259s becoming open. These have
>been outside for about two years and I live in Oklahoma, so while we
>see about 35" per yrar of rain, it tends to come in good sized
>amounts with extended dry periods in between. Disconnecting and
>reconnection doesn't affect the problem and bending around the
>transmission line has no effect: I have to actually re-solder the connectors.
>
>This has happened only to my HF transmission lines: there's no
>problem (so far) with my VHF/UHF lines. There is no warning and no
>prior symptoms. Using a tuner, I can sometimes of feed a little power
>to the system and see things change with 100 W power applied but the
>match is unstable and nothing ever becomes normal. The connectors are
>exposed and are not sealed with any sort of tape or flooded shrink
>tubing. When I look at them, the solder still looks good, but to
>reestablish connectivity I must re-solder them.
>
>I'm currently planning to replace connectors exposed to weather with
>N-connectors, but I've never seen this before, even though I've had
>connectors outside before that have lasted for many years with no
>problems. Has anybody else experienced this?
>
>Kim Elmore, N5OP
>
>
Kim, I am wondering if this might be a fatigue failure of the solder.
With 9913, the center
conductor can move axially during diurnal thermal cycles since it is not
captured tightly by
the helical insulating chord that suspends it inside the shield. Perhaps
the diurnal push-pull
force between the center conductor and the inside surface of the PL-259
center pin could
over time cause the solder to fatigue and crack. I know I have seen
cheap N-connectors
fail that were installed on 9913 when the center conductor migration
caused the
uncaptivated connector center pin to retract from the mating plane of
female connector
(the center pins are captivated on the better connectors).
73, Mike W4EF..............
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