Hi Jim
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 rx continuity.
Let us know if we can help in any way. BTW, the 259B is supposed to have
TDR capability - haven't tried it for that purpose, but it might be
interesting. We've used our TDR to present scope pics of damage points on
coax.
73,
Press
On Sun, 4 Apr 1999 14:19:10 -1000 "Jim Reid" <jreid@aloha.net> writes:
>Aloha,
>
>Well, the Saturday morning repair to the broken boom of the
>C4 only took 6 hours!! Most of the time was spent taking
>down the remnants of the antenna, then literally driving into
>each boom half the splice tube -- very heavy Al tubing which
>must have been 1 or 2 mils larger in OD than the 2" boom
>tubing ID of the C4! Anyway, C4 is all repaired and back up
>on the MA-550, which is, of course, still collapsed down to
>20 some feet high. Unfortunately, found at the top, that it
>appears the upper section of the tower fell with enough force
>to bend its way further down than the stop which was supposed
>to stop it, hi. That repair is for some other day.
>
>Now, the back part of the broken C4 boom was dangling some
>8 feet above the ground, hanging suspended by the LMR-400
>coax running up to the 40 meter Force 12 dipole. Noticed it was
>"kinked" or sharply bent at the bend from where it was dangling
>from one of the US Tower coax support rings up on the tower.
>And, it must have had quite a bit of stretching force when it
>stopped the antenna back part from the fall.
>
>Thought nothing of it really, used a bit of finger action to reshape
>the coax back to round, and put the antenna back up after the
>boom splice was installed.
>
>40 meter element now "hears" great, but on transmit, much
>crackling and distortion occurs, almost sounding as if RF
>arcing is occurring per fellows on the Hawaii Afternoon net
>yesterday. Don't know the innards of LMR-400, but is it
>possible it was permanently damaged in some way --
>stretch of the inner conductor, crack in it, or now the outer
>conductor is permanently pinched in toward the inner, and
>arcs. This "arcing" occurs even with only 50 watts output!
>
>I hope the problem can be solved by replacing the coax,
>and that some problem to the 40 meter dipole, unnoticed
>yesterday when all was at ground level, has not occurred.
>Visually the dipole, linear loading, matching coil, etc.,all
>appeared just fine.
>
>Can it be a damaged coax that would cause these symptoms?
>Arc was too fast to see any impact on my vswr indicator, but
>guys on the net reported their S-matter reading seemed to
>actually increase during or immediately after the crackle
>sound, or arc, or whatever it is.
>
>73, Jim, KH7M
>On the Garden Island of Kauai
>
>
>
Press Jones, N8UG, The Wireman, Inc., Landrum, SC, 29356
Sales (800)727-WIRE(9473) or orders@thewireman.com
Tech help (864)895-4195 or n8ug@thewireman.com
http://www.thewireman.com and the WIRELINE bargain page
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