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Re: [TenTec] Eagle problem?

To: Discussion of Ten-Tec Equipment <tentec@contesting.com>
Subject: Re: [TenTec] Eagle problem?
From: Robert <rmcgraw@blomand.net>
Reply-to: Discussion of Ten-Tec Equipment <tentec@contesting.com>
Date: Fri, 16 May 2014 18:47:03 -0500
List-post: <tentec@contesting.com">mailto:tentec@contesting.com>
I had 3 pieces of 1" braid in place to bond the rotating mast to the sleeve at 
the top of my tower.   A lightning strike burned all 3 into.  Balled ends on 
the strands confirmed this.

73
Bob


Sent from my iPhone

> On May 16, 2014, at 6:04 PM, Stuart Rohre <rohre@arlut.utexas.edu> wrote:
> 
> Jim, don't we all use Flukes now?  :-)  I do have several at home and work.  
> I was remembering a discussion of a rig fault where the pin intended for 
> grounding, had not been grounded at the radio connector entry to chassis.
> 
> Good point you make about low ranges needed for ohms measuring.  There are 
> some good build it yourself low ohms measuring circuits out there, to extend 
> the range of an ordinary meter.  The Graf (author) series of circuit diagrams 
> books includes at least one.  The ham magazines in last 40 years had one or 
> more.
> 
> In the midst of measuring things, most good troubleshooting includes a 
> thorough visual inspection to see how things are bonded and grounded, and if 
> the circuit board is providing the connection to chassis.
> Unfortunately, we had not done a pre service inspection of the following 
> radio incident:
> 
> For high current faults, we have seen a Yaesu 5100 that had RF connection to 
> circuit board and its DC negative power line to same circuit board at other 
> end of chassis.  A lightning event on the tower induced shield current down 
> the coax to the radio , across the circuit board, vaporizing part of the 
> ground copper, and then to the DC negative line which returned to AC third 
> pin and power supply chassis.
> 
> The bonding was done by an experienced power plant engineer, but it provided 
> an extra return path through that circuit board trace, that caused severe 
> damage to the trace.  Luckily, that radio has survived that, with a bus bar 
> now bonding DC negative to the coax connector shell external to the chassis.  
> (No longer relying on the radio circuit board traces.)  The radio worked even 
> after losing part of the board copper, but only if the coax was connected, 
> which was grounded to the tower and earth providing a return through the AC 
> third pin.  That observation prompted us to open the radio, which then showed 
> the missing trace.
> 
> As for braid failures, literature about high current faults has stated that 
> braid can blow apart in a near direct strike, as little shards of wire.  
> Indoors in someone's shack that could cause injury, or put small shorts into 
> places hard to find.
> 
> Copper flashing could be used in place of braid.  The use or either was to 
> provide low inductance through wide flat conductors used for bonding 
> equipment together.
> 
> Stuart Rohre
> K5KVH
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