Topband: Power Line Noise (long)

[Garry Shapiro]

Brad,

While there are many noise "profiles", the typical profile for arcing 
insulators on a power pole is that the noise will have a 120Hz buzz, and 
will have a spectrum that monotonically decreases with increasing 
frequency. How high it can be heard indicates how far away the source 
is. Such noise is amenable to listening at 130 MHz. If you can hear it 
into UHF, you are probably close enough to eyeball the offending pole, 
or to shake a guy wire and hear a result. (The power company does not 
want you shaking guy wires, or beating on poles with a hand sledge, but 
I routinely do both, and so do the linemen.)

The mechanism of the noise begins with an arc, which can be very small, 
in an insulator, particularly one with a clevis pin arrangment. It can 
also originate with loose spans and connectors, or with (wet) branches 
contacting a bare HV wire, arcing capacitor banks, etc. Out west, the 
crossarm supporting these insulators is typically wood, braced with two 
metal braces affixed to the pole using a lag bolt through one end of 
both braces, a washer and spring. Over time the bolt can loosen in its 
hole due to expansion and contraction of the wood and the hardware 
oxidizes. Now you have rabbit ears in which current can be induced from 
HV primaries--and a diode detector. In turn, this arrangement couples 
into the distribution line spans and re-radiates. The fix is to tighten 
all loose wires and hardware and perhaps to replace the insulators.

If the noise you hear on 160 is continuous, frequency-wise, but rolls 
off quickly within the HF band, it is unlikely to be due to arcing on a 
pole, unless it is quite distant. Dimmers, touch lamps, shorted doorbell 
transformers, fish tank heaters and thermostats of all kinds have been 
shown to generate such noise, which is conducted from the 
source--usually within customer premises--back out to the power lines 
and re-radiated. Cheap Chinese lighting, e.g. pole lamps with dimmers, 
are notorious. /The utility is not responsible for noise originating 
within customer premises/. You will have to locate the source and deal 
with the neighbor. The neighbor is no less responsible for Part 15 
incidental radiators than the power companies, but you are on your own.

If the noise you hear appears as a discrete noise-modulated signal, and 
especially if it repeats at uniform frequency intervals, it is probably 
emanating from an electronic device, also within customer premises. You 
may, for example, observe a noise repeating every 20, 40, 60 kHz or so, 
usually unstable. As high-tech consumer electronics products have become 
ubiquitous, these noise types are now becoming dominant. Common sources 
particularly include cheap switching power supplies in plasma TV's, 
laptop computers, battery chargers, low-voltage track lighting, etc. 
Noise suppression components are left out, for cost reasons, and the 
industry mouthpieces, e.g. the Electronic Industries Association, 
suggest but do not mandate inclusion of noise suppression components in 
either electrical or electronic products. This is absurd, because the 
inclusion of a few cents worth of ferrite beads in dimmer can suppress a 
good deal of the noise. I have found that there are "good" and "bad" 
dimmers--which I learned by buying an assortment and testing them. I 
learned that the cheapest dimmer at the hardware store has no 
suppression components, but the same dimmer with these beads costs 50 
cents or a buck more but gives better  performance. Most consumers, not 
knowing or caring, just buy and install the cheapest unit. I keep some 
"good" dimmers around for such cases, and have replaced a half dozen in 
the neighborhood. I have no dimmers in my house.

If the noise repeats at larger intervals, it could be coming from your 
router--I once ran all over my neighborhood searching, only to find the 
culprit --an unshielded LinkSys router---sitting on my operating table. 
Certain frequencies seem most likely, such as 14030 kHz, +/-, which may 
be a harmonic of the crystal oscillator driving the device. Again, the 
power company is not obligated to fix it.

For your 1815 kHz noise, the best way to find it is with a small loop, 
balanced properly to give a deep null perpendicular to the plane of the 
loop. I use a 100kHz marine Loran loop I picked up at a swap meet and 
moved up to 160m. For the noises that extend well past HF, start with a 
mobile rig on 10m and get as close as you can. Then, if you have an H/T 
that covers aero mobile (AM), as with the 130 MHz setup you described, 
and get closer. All the better if you have UHF gear. The old trick of 
using body-shading with a rubber duck to get some directivity can help.

With my local utility, I learned that middle managers' bonuses were tied 
to how little of their budgets were spent, that they rotated through 
jobs every two years, and that outages were fixed by another department. 
Thus they were totally disincentivized to spend money on preventive 
maintenance, much less repair.

If the power company is not responsible, you are on your own. See K9YC's 
website for info on chokes--your best hope is to prevent the noise from 
conducting back out of the house on the 120V power leads or on telephone 
or cable lines. If the noise is a direct radiator, as from an unshielded 
router, you may have to replace the device.

In my experience, one can quickly become proficient at finding sources. 
Getting the power company to respond is the real challenge. When Riley 
Hollingsworth was the FCC enforcer, he whipped utilities into line in 
many cases. The Bush FCC seemed (IMHO) more interested in cheerleading 
dubious technologies such as BPL (Broadband over Power Lines) than in 
enforcing Part 15. The current FCC has a new enforcer in Gettysburg 
(Laura L. Smith). It remains to be seen what Ms. Smith will do in this 
area. As for customer premises, YMMV. If you have a good relationship 
with your neighbors, enlist their cooperation.

Over the past 16 or 17 years, I have fought these battles with my local 
utility and my neighbors. It can be maddeningly frustrating. If you can 
cultivate a relationship with people in the utility, do so. I tired 
early of managers telling me I was costing them money---it was, after 
all, their capital equipment, not mine, that was at fault. Right now, I 
am awaiting action on a pole that I went to like a homing pigeon and 
handed off to a company noise guy, who filled out a tag. That was months 
ago---anything and everything has priority for repair. This is typical, 
even if the folks you directly deal with are sympathetic. My next step 
is to contact FCC, but that is no panacea.

GL

Garry, NI6T

Brad Anbro wrote:
> Hello T-B'ers,
>
> I have power line noise at my QTH that is causing me a
> lot of grief on 160 meters. At 1.815 Mhz, the noise is a
> continuous S9, when the rig is in the AM mode. The 
> noise is not as noticeable on 80 meters.
> --------------------------------
>
> If anyone has any ideas on how I can pin-point the
> exact source of the noise, I would sure appreciate
> the information. Thank you in advance.
>
> 73, Brad, N9EN
>
>
>