Jim:
An Ultrasonic detector/receiver/whatever is not always going to sound off
even though the pole being scanned is definitely the source of the
interference. As Mike pointed out, there are many reasons why an ultrasonic
detector won't respond. There are no "likely indicators that an LA is bad"
other than the obvious visual clues like a blown out ground connection or
an obviously loose or broken clamp or stinger (wire connecting the LA to
the primary conductor.)
Over the years I have found my Radar Engineers Model 250 produces a
meaningful response about 50% of the time. I know from my direction finding
that I have most assuredly located the source pole/house/structure but the
ultrasonic detector doesn't allow me to pinpoint precisely or at all what
specifically might be the source. While I will always scan a pole with the
ultrasonic detector I am not surprised when I don't get any useful
indications.
Keep in mind that an ultrasonic detector responds to the sound being made
by an arc. That's all it does. If the arc is being produced inside a
lightning arrester, transformer or other device/container the sound may not
be detectable outside the offending device. However, (obviously) the RF
produced by the arc is radiating well enough to allow a successful locate
based on direction finding techniques. Not getting a useful indication with
the ultrasonic detector means that a step by step troubleshooting method
will be needed to pinpoint the exact source.
An ultrasonic detector will usually allow you to pinpoint:
1. Blown lightning arrester grounds that are arcing against the bottom of
the LA
2. Arcs occurring between a washer and a bolt head, nut and washer, bolt
or screw and crossarm brace or any other external arc that can be "seen"
and heard by the ultrasonic transducer.
3. Some Neutral crimp connections that have begun to arc.
It doesn't matter anyway. Your only course of action is to report the
offending pole to the appropriate utility and stay on top of the matter
until they fix the problem. Try as best you can to arrange to be present
when the utility crew works the pole so you can use your RF direction
finding gear to assure the crew they have or have not resolved the problem.
Very likely the crew will assume the LA is bad and often they are. But the
problem could just as easily be something related to the LA like the clamp
on the primary that feeds the LA or the LA bond (ground) wire being too
close to a metal mounting bracket or the bond wire is arcing against a
staple that has worked itself out of the pole somewhat. Each of these could
produce an arc that only your DF gear can hear. Most crews will appreciate
knowing for certain they have resolved the problem because most crews are
neither trained nor equipped to be able to do that themselves.
Congrats on the successful find. Hopefully the resolution effort will
happen soon and be equally successful.
Good luck!!
73,
Frank N. Haas KB4T
Utility Interference Investigator
Florida
On Sat, May 23, 2015 at 6:49 PM, Mike Martin <mike@rfiservices.com> wrote:
> Jim,
> Not exactly, that is more the indication that the U-S can't detect the
> source for anyone of many reasons. I'm not implying it can't be a LA.
> The sensitivity of that unit is a big factor and since you're dealing with
> line of site it possible the source isn't detected because it can't see it.
> The freq your using is a good frequency to use but make sure its your
> source and not just a source.
>
> Mike @ RFI Services
> ( Replying from a mobile device)
>
> Jimk8mr--- via RFI <rfi@contesting.com> wrote:
>
> >I've located a bad pole by RF DFing at 432 MHz. It has, however, no
> >detectable noise using a W1TRC ultrasonic receiver. Is this a likely
> indication
> >of a bad lightning arrester?
> >
> >
> >73 - Jim K8MR
> >_______________________________________________
>
>
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