[TowerTalk] C4 40 Meter Coax Repair

[Jim Reid]

Aloha,

Got super info from Press Jones,  The Wireman about the LMR-400:

"Have been following the sad tale with interest and sympathy - glad to
hear that the antenna is repaired.
There is little doubt to me that the coax is destroyed. LMR400 will not
take a kink under load and re-straightening. The AL center conductor is
tough and no doubt cavitated the dielectric, which would not re-form upon
straightening. Further, the bending and tension is likely to have opened
the copper surface of the conductor which would create serious
aberrations in the RF carrying capability of the surface. Fracture of the
whole conductor would cause arcing, as well, where a tiny shard of copper
could still maintain rcv continuity."

My great helpers,  Jim,  WH6FG (who loves to be up on towers with
his trusty safety belt) and John,  WH6EY, (Jim's ground support guy)
were back at  4 o'clock Easter Sunday afternoon to make a quick
coax replacement.  I took another length of LMR-400 from one of
my verticals.   Will have to have Press send me some PL UHF
males to cut and repair the remains of the LMR-400 to get my
back-up vertical going on the high bands again,  hi.

Jim went up the pole,  unscrewed the damaged coax,  and had a lot
of water pour out of the connector on him!,   even though well taped with
Scorch #23.  However,  as it had rained heavily for several days
after the "fall",  and the coax was hanging straight down,  we
decided that may be how the water got in.  Anyway,  Jim decided
we should warm the Force 12 B-1 balun SO-239 connectored balun end
to attempt pulling any more water out of that area and to thoroughly
dry the connector.  When all appeared dry,  Jim screwed on the replacement
length of LMR,  taped,  and then used The Wireman's coax seal,  very
sticky stuff,  then more tape.

Now for the RF test.  Sure enough,  the arcing,  or whatever problem seems
"almost" gone!  Well,  why not all gone?  No trace of a problem now at
50 watts,  but, just noticeable,  "ffffffp.......fffffffp" sounds at the
onset and close of
words on SSB at 100 watts out,  but no detectable distortion of any
sort on a 100 watt 40M CW signal ---curiousor and curiousor.

We had guys monitoring the signals both right out front of my QTH on
a truck mounted mobile rig,  and also a couple down on the Big Island
of Hawaii -- all gave exactly the same report as above.

Will A/B the antenna with my long wire which will tune up on 40 this
afternoon to be sure what we are hearing is not a rig/shack set-up
ground problem or RF pick up directly from the antenna.  BTW,  with
the MA-550 down,  the radiator element is just about exactly 50 feet
on the diagonal from the rig set up in the shack.  One fellow speculated
the RF field from proximity pick up of just 50 feet could be a source
or trouble-- is that possible with what I believe I have as a good RF
ground here?  It is a long way back via 450 ohm ladder line to where
the long wire (600 feet) antenna is placed,  so essentially no chance of
an intense,  near RF field being a problem from that one,  I should think.

We decided to button up the project for now,  and see if after a little
use if some residual water,  in the balun(?),  might be the problem,
and might go away.  Otherwise,  guess should consider replacing
the Force 12 B-1 balun.  Do not know if it is possible for water,
from inside the SO-239 socket to  get inside the B-1 balun,
or into the coax inside.  If possible,  that might be a problem which
only replacing the balun,  rather than a period of use,  could fix.

Status for now.

73,  Jim,  KH7M
On the Garden Island of Kauai



--
FAQ on WWW:               http://www.contesting.com/towertalkfaq.html
Submissions:              towertalk@contesting.com
Administrative requests:  towertalk-REQUEST@contesting.com
Problems:                 owner-towertalk@contesting.com
Search:                   http://www.contesting.com/km9p/search.htm