[RFI] Noise sniffer article in QST - WW3S
EDWARDS, EDDIE J
Thu, 24 Jan 2002 09:11:59 -0600
Leon's mention of using a hand-held yagi is right on the mark. It's the
only way to hunt PL-noise that is "Conducted" along the line because of
Standing Waves along the line. We use the Oak unit here to find the
right pole. Then we use UE Systems Ultrasonic detector to determine
what item on the pole is generating the noise.
Here's something I answered a question from someone in Southern Cal
Edison's territory a little while back that explains polarization and
Line noise intensity and propagation is variable depending on
the frequency you are listening on. The higher you go in freq, the
closer you have to be to the source to hear the noise. And the lower
you go in freq, the farther away from the source the noise can be picked
Also, noise as it propagates down the lines can display standing
wave characteristics so that at the spot your vertical is sitting may be
seeing a "peak" in the vertical position, while it is then a "null" in
the horizontal position which may be why the portable doesn't hear
anything there. In another spot in either direction along the line the
opposite will be true. But even at a null a "minimum" of noise can
still be heard. If not, you may not be hearing pwr line noise at all
but something else.
Another thing to keep in mind. You can only hear line noise or
other impulse noises on an AM (or SSB) Rcvr. You CANNOT hear it on FM
There are 3 ways noise is propagated: (1) Direct Radiation from
the source. This can be picked up at very high freqs (100Mhz & up) on
AM. (2) Conduction on a transmission (or Power) line. This re-radiates
the noise energy all along the transmission line since it is not
balanced nor shielded! (3) Induction onto other lines (power, phone,
cable) which can then re-radiate and conduct the noise to new and
exciting locations like your ham shack!
Tip number one: Ensure you have a very good station ground.
This will rule out noise problems caused by a poor or improper ground.
Go to http://www.polyphaser.com and look at their tutorials under
"Technical Info" if you need more info in this area.
Tip number two: Buy the "Interference Handbook" by William R.
Nelson, WA6FQG who is a retired RFI Investigator from (get this!) SCE
Company! Perhaps you could suggest that the new SCE RFI guy buys this
book as well, if he doesn't already have one. You can buy it at ARRL or
CQ bookstores or even at many Ham shops. Read Chapters 4, 5 & 6
thoroughly! You can read 1-3 later if you find time or interest! The
later chapters cover other RFI topics but some of these are out-dated
and the ARRL's RFI Handbook is better on these topics.
The new ARRL "RFI Handbook" has a good chapter on electrical
line noise written by an RFI guy from NE Utilities. It's much better
than the info in the old book "RFI: How to find it & fix it".
Tip number three: The only way to get the noise fixed is to
either locate the noise yourself, or get the SCE guys to find it, and
then have SCE fix the problem. Unfortunately, along with supposedly
lower priced electricity, deregulation has also brought lowered
services. The RFI investigator is usually the first to go in many
deregged utilities across the nation. They are not spending money on
equipment and training like they used to when they got dozens of calls
each day before cable TV came along. Now the only complaints coming in
are from Hams and CBers. No one else uses wireless "AM" rcvrs anymore.
If you're having problems getting SCE to get going, first make
sure it is in fact power line noise and not SCR devices. Then track it
down using your car's AM radio to narrow down the gross vicinity of the
source. Ignore the peaks and nulls and just look for increasingly
stronger peaks. Once the peaks start getting weaker, that indicates
you've driven past the source or the sources main conduction "FEED". Go
back and drive at 90degree angles from the Peak-Peak location repeating
the process. This will get you "in the neighborhood" of the source.
After doing this you will probably see how difficult this can be
and have some empathy for the poor RFI guy at SCE who probably doesn't
have anymore training at this point than you! %^O
de ed -K0iL
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Ed Edwards, Communications Engineer
2-Way & Paging Systems
Omaha Public Power District
4302 Jones Plaza
Omaha, NE 68105-1099
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> -----Original Message-----
> From: email@example.com [SMTP:firstname.lastname@example.org]
> N4ZR is correct in suggesting an AM receiver in the aeronautical band.
> One of the nicer professional models made for Utility Companies and
> Cable Companies to use in policing noise was manufactured by Oak
> Industries in Illinois and used a frequency of approximately 260MHz
> and employed an S meter to measure noise intensity. It also used a
> small 5 element yagi hand carried that would alow the operator to
> rotate the antenna through both horizontally and vertically polarized