Thanks for adding to the discussion Don.
That reminds me I forgot a couple of important details so I'm
replying on-list to add them.
I hadn't thought about using a spectrum analyzer even though I'm
well aware of the increasing high frequency component as you get
closer to the source. The bloom sounds like an even quicker way to
get very close to the source than the variable frequency method
(assuming, perhaps, there aren't too many overlapping noise
radiations from multiple sources).
I forgot to add I have been using a UHF FM link to hear audio from
my home receiver in the field. In early stages with multiple noise
sources being heard at home and in the field I couldn't sort one
from the others by ear. I could sort them pretty well at home where
I had the scope and felt that having one in the field would have
saved me countless hours of frustration. In later stages comparing
by ear started to be useful, though with some of the steady noises
it was difficult to know for sure if I had the right one. I also had
(and still have) many sources in the field that I do not hear at
home on any band. I'm leaving them alone. It's amazing that I have
one not more than 500 feet several of my antennas. Loud on HF
through 135 MHz as I pass by it, deafening on ultrasound, but not a
whisper of it at home.
I would agree most folks may not need the ultrasonic unit but I owe
mine a huge debt of gratitude and will never be without one -
preferably the most capable one I can get my hands on. It saved my
bacon this summer. The power company had been out and wrote a work
order to address multiple problems. Three months had passed and the
work had supposedly been completed, yet I still had noise from all
but one of those poles. Nothing I said about my RF observations was
convincing him to come out and check again. He was doing everything
possible to convince me I couldn't possibly have power line noise
any more and whatever I was hearing must be generated in a home and
radiated from power lines. I wouldn't have been the first to go down
in flames dealing with this company. I was losing the argument big
time until I asked him to kindly explain why I could be hearing
ultrasound from a particular insulator and the changing sound
pattern matched up perfectly with audio from the home receiver over
the UHF link. He was back out here in 2 days, and 3 work days after
that every one of those poles had been rendered absolutely silent.
73,
Paul
On 01/05/2013 02:41 PM, Don Moman VE6JY wrote:
Similar observations here Paul in my never ending battle to keep on top of
the noise situation in my rural area - mainly 14.4 kv distribution and
some 25kv 3 phase stuff.
Many sources top out above 135 mhz but well below 450 so a yagi in between
is certainly helpful. Like a ch 13 tv yagi or something for UHF mil
aircraft.
In the vehicle I often like to use an old (i.e. analogue and inexpensive)
spectrum analyser like some of the portable Texscan CATV ones. Mine is the
VSM-1 which covers up to 300 mhz so that coupled to a little whip on the
vehicle is almost always enough to get you to the nearest pole or two as
you drive by. The AVCOM PSA 65 I have is also OK but one wants something
with a really wide RBW so you gather lots of the noise energy and in my
experience the cheap and dirty Texscan gives me the best noise "bloom" as
you drive by the pole. Depending on ambient light it can be tough to see
the screen and still drive safely so fortunately they also have a wide band
video out jack that can be used to drive a amp'd speaker.
To zero in a bit closer I use the ICOM R-10 and a Create 50-1300 mhz log
with the rear elements removed to make easier to get in the vehicle. It's
"OK" but the pattern is not as nice as a single band yagi. But with this
setup I can almost always tell the utility which pole is the culprit and
they take it from there.
I have some ultrasonic stuff and the power guy has the Radar Engineers unit
- the hand held dish style and these are generally NOT helpful in finding
much other than in maybe 1/3 of the cases confirming the findings that we
are on the right pole. I think on many of the sources the arc is weak
enough that there's not much ultrasonic energy. I have seen it not work
enough that I wouldn't spend much energy or money on this route.
The one ultrasonic device you want the power guys to have is the hot line
sniffer from RE and that can (in their hands, not yours) pinpoint the exact
hardware.
The most challenging noise situation that I have experienced is the faulty
transformer (all from brand new units) with a micro arc inside the can.
TONS of LF noise around 80 and 160m but nothing at VHF, nothing ultrasonic
as everything is in the can. And as you know, the noise at lower
frequencies can travel a LONG way and you'll get noise peaks at corner
structures etc, all trying to mislead you. When you don't see any obvious
source in the normal fashion and there's still plenty of noise then you
have to start suspecting the transformer. Getting the utility to drop the
primary is about the only way to tell. On the one case I was
most familiar with they even listened with a mechanics stethoscope to the
case but no arc noise. Keep in mind that many will NOT arc when the power
is connected back on for several minutes or hours so don't let this mislead
you. Obviously the utility doesn't want to change out a good transformer
so don't let this trick you. And the new one could be bad, altho I haven't
had that piece of bad luck - yet! Once the first bad transformer was
identified and replaced, proving I was right, it became a LOT easier to
convince them in future bad transformer cases.
I have not used the o'scope much at all for noise signatures. I prefer to
rebroadcast my noise from home on a very low power tx so I can hear it
while I'm at the suspected source. It is easy to find all kinds of noise
when we go looking around but one should focus on the noise that actually
bothers you first. In a perfect world we'd like to clean up everything but
with costs and manpower issues being a big issue with the utilities it's
best to stay focused on the problems that affect you and save some good
will and budget for the next one.
73 Don
VE6JY
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Stew Perry Topband Distance Challenge coming on December 29th.
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