[TowerTalk] The hunt for a feedline fault - update

[David Gilbert]

Normally I would (and my wife, sons, and friends will tell you that I 
normally double and triple check everything), but at the time I didn't 
have either an 80m antenna I was happy with or a good KW dummy load.  I 
should have switched one of my other antennas to that run of Heliax to 
do a high power test.  Everything looked good at 100 watts ... it was 
only when I hit it with 1500 watts that it flinched.

I guess I was just over confident.  Luckily the price I'm paying for it 
this time is minimal.  ;)

73,
Dave   AB7E



On 11/8/2019 7:26 PM, Wes Attaway (N5WA) wrote:
> David .... I am not by any means criticizing you, but why not just test any
> new coax run and all the fittings before you cover up and seal everything?
>
> It seems like this would make things a lot simpler, in the long run.
>
> In any event, I am glad that you spotted the area of the fault quickly.
>
>     -------------------
> Wes Attaway (N5WA)
> (318) 393-3289 - Shreveport, LA
> Computer/Cellphone Forensics
> AttawayForensics.com
>     -------------------
>
> -----Original Message-----
> From: TowerTalk [mailto:towertalk-bounces at contesting.com] On Behalf Of David
> Gilbert
> Sent: Friday, November 08, 2019 6:01 PM
> To: Towertalk
> Subject: [TowerTalk] The hunt for a feedline fault - update
>
>
> To repeat the situation here ... I have roughly 150 feet of 1/2 inch
> Heliax from the tower to just outside the shack, a good quality LF4-50A
> connector to make the transition to about 20 feet of BuryFlex coax for
> the rest of the run, and a high power fault somewhere in the line.  The
> procedure I described earlier told me that the fault was probably 23
> feet from the shack end of the feedline, which strongly pointed to a bad
> job by me installing that connector.
>
> Before doing a bunch of digging, I decided to repeat the procedure
> except from the tower end of the Heliax.  The readings were a bit less
> consistent (no doubt due to the much longer length to the fault), but
> they ranged between 145 feet and 151 feet, with an average of 148 feet
> ... again pointing to the same location.
>
> So I dug up that feedline starting at the house and working until I
> found the splice between the BuryFlex and the Heliax, which indeed was
> just over 20 feet from the shack end of the BuryFlex.  As soon as I
> removed the outer vinyl tape and the thick stretchy silicone inner tape
> the connection came apart in my hands.  The interior of the Heliax
> connector was literally as black and sooty as the chimney of my wood
> burning fireplace.  It looked awful.
>
> So the fault has been found and the location was as predicted. Given
> that I had made eight connections like that and totally messed up one of
> them, it seems my QC defect level for that particular task is about
> 125,000 PPM.  Gotta do better.
>
> By the way, I was wrong when I said earlier that TLW was telling me I
> had a dead short.  The graph only made it look like that, and a more
> careful look at the axis dimensions said that the dips for each
> frequency were always about 28 ohms resistive at the low power of my
> analyzer ... which makes more sense than a short for a fault caused by a
> high power RF arc over.  I find that even more impressive (the data, not
> my error), since it means that the location of even non-absolute
> anomalies (neither open nor short) could potentially be found by this
> method.
>
> Hope this is useful to somebody.
>
> 73,
> Dave  AB7E
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