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
On Sat, Jan 5, 2013 at 4:44 PM, N1BUG <paul@n1bug.com> wrote:
> I've been following this discussion with interest. I spent the summer
> tracking down more than 20 sources of power line noise. As an offshoot of
> that I've made it my mission to help clean up RFI in my little corner of
> the world. I've been slowly drifting away from DXing and this has turned
> out to be my new area of interest.
>
> Since this topic is perhaps of interest to topbanders, and since my
> experiences seem to vary somewhat from the typical reported here so far, I
> thought I would take a moment to share some observations. I should probably
> note I was dealing with a mix of 13.2 kV distribution lines and 46 kV
> transmission lines. My hunt was made more challenging by the fact I had
> multiple sources in a relatively small area and could often hear more than
> one at a time even with directional antennas and attenuation.
>
> My tools this summer were 135 MHz AM receiver with 3 element yagi and step
> attenuator; LF/MF/HF/VHF/UHF AM receiver with DF loops for low bands and 7
> element yagi for 445 MHz; ultrasonic receiver with dish.
>
> Low frequencies, eg. AM BC or 160 meters were *occasionally* useful in
> locating a general source area. Sometimes the area identified turned out to
> be an area of *radiation* but the noise was *generated* elsewhere. Often
> the relatively close proximity of multiple sources made low frequency
> tracking useless.
>
> VHF was always useful in finding a source area, 80% of the time resolving
> it to a single pole. The sharp, deep null at exactly 90 degrees off axis of
> the yagi proved very useful for confirming a source structure. Poor
> resolution/accuracy of signal strength metering was perceived as a problem.
>
> UHF was very helpful in a few areas where the noise was particularly
> strong at VHF and/or signal strength so close over a span of several poles
> that VHF could not pick the source pole with high confidence. So far,
> experience indicates this is more likely to happen on the transmission
> lines. They're a bear. Again, poor or no signal strength metering (signal
> below AGC threshold) was perceived as a problem.
>
> The first ultrasonic unit tried was a waste, finding something at only 10%
> of RF noisy poles. The second unit was able to hear something from about
> 60% of the same 21 poles. The figures are averages over more than 10 runs
> with each unit. The two were also tested on a spark signal range under
> somewhat controlled conditions. These things are definitely not created
> equal!
>
> To date I have identified and had the power company fix almost everything
> I have worked on. The remaining open case involves a short section of a 46
> kV transmission line which is extremely perplexing due to the specific
> nature of the issue (details on request). Just when I starting thinking I
> was getting good at this, I came up against this one.
>
> If I were doing this strictly for myself these tools would be more than
> adequate. Since I'm not and I only have so many hours in a day I have
> several upgrades on my wish list:
>
> HF/VHF/UHF AM receiver with wider bandwidth better signal strength metering
>
> Log periodic dipole array covering ~100 to ~900 MHz for frequency agility
> while maintaining some directional properties
>
> Portable oscilloscope for observing noise signatures in the field (I'm
> hoping it helps sort out overlapping source radiations)
>
> Yet another upgrade of the ultrasonic unit.
>
> Comments are welcome, even if it's to tell me I'm clueless! :)
>
> 73
> --
> Paul Kelley, N1BUG
> RFI Committee chair,
> Piscataquis Amateur Radio Club
> http://www.k1pq.org
> ______________________________**_________________
> Stew Perry Topband Distance Challenge coming on December 29th.
>
_______________________________________________
Stew Perry Topband Distance Challenge coming on December 29th.
|