Line Noise Tracking Expedition, Power Line RFI - Tracking it down

*** Power Line Interference Report ***

Reporting Station: Jim Poll, WB5WPA

Location: Allen, TX AM Mode: 5 dB over S9 SSB mode: S7

Interference: Line rate (60 Hz mains) raucous buzz on 75M at S9+5 dB level in AM mode, S7 in LSB mode (See Note 1 in Appendix) and observable up through 10M (29 MHz)

Onset date: 4-10-2008 (Thur.) Youtube video w/arcing: http://www.youtube.com/watch?v=uhaMJD57QwAFixed: 4-26-2008 (Saturday, noted to be absent when driving by the pole about 1 PM)

Perhaps due to: Storm/lightning and/or high wind damage occurring the night of 4-09-2008 (Wed.) into the morning hours of 4-10-2008 (Thursday)

Source located date: 4-11-2008 (Fri) power pole found with air gap between fuse assembly hot-side metalwork and 'hot' wire from phase (wire from phase broke or worked looseand is not making physical contact). Pole number: 2254-522-7168located on south side of McDermott across from 201 E. McDermott (church).

Station Equipment:● Icom IC-756PROII ● ½ Wave Dipole above roof, cut for 75 Meter band (3.900 MHz)● ½ Wave 10 M (28.5 MHz) Ringo-style antenna w/3 ground radials 15' above ground

Analytical Equipment:● Hewlett-Packard Spectrum Analyzer:● 8557A Spectrum Analyzer Plug-in, Range: .01 - 350 MHz● 853A Digitizing Display

Youtube video http://www.youtube.com/watch?v=ozzp4RW5G54 showing pulses (on a TEK 453 display)

Direction Finder● Sears Model 2278, AM/FM/SW Portable Radio; SW1 covers 2 – 6 MHz and SW2 6 - 18 MHz.

SW1 band uses internal ferrite rod as antenna as well as the telescopic whip. Radio has an analog signal strength indicator/meter (Note 3 in Appendix for use of this radio to DF signals).

● Silva Map Compass Youtube video showing DF technique http://www.youtube.com/watch?v=EUxkXSVCYxg

Additional Observations:

1. The signal can heard in the reporting party's driveway/QTH on the AM Broadcast band on a car radio on a clear frequency like 1610 or 1650 kHz. The signal source can also be heard on a consumer-grade SW receiver in the range of 2 to 7 MHz using only the radio's stock antennas.

2. The signal source was determined to be the same signal as that received at the reporting party's QTH by two methods: a) The signal was noted to be continually received during the DF efforts to initially locate it on 4-11-2008 and b) via a remote base using a 80 Meter radio tied to a 440 MHz link. This technique allows reception of the offending signal at the pole -and- a relay of the signal from the reporting party's QTH from the 80 M radio via the 440 MHz radio link allowing for direct coincidence - comparison of the signals via their audible signature using the human ear.

Page 1 of 11 Power Line Interference Report TXU/ONCOR pole # 2254-522-7168

http://www.youtube.com/watch?v=uhaMJD57QwA

http://www.youtube.com/watch?v=ozzp4RW5G54

http://www.youtube.com/watch?v=EUxkXSVCYxg

Narrative

Wednesday night/Thursday morning's storms resulted in some broken tree limbs and a raucous buzz on the HF bands. To the right is what the Icom shows (notice the scalloped envelope on the spectral display; this is due to the offending noise source). (See Note 2 in Appendix)

To make a long story short, I made use of a battery-powered ferrite loop-stick equipped AM/SW receiver (lower right), initially following a compass bearing of 280 to 290 degrees (as indicated from the QTH) for what seemed like the LONGEST time west until the compass indicated the nulls to have swung through North – I then backtracked and walked North and found a hot 'area', but not the specific pole yet, until more walking and some 'local' bearings were taken.

The area turned out to be south of the downtown area ... this is a little over a mile away! (Does anyone have the statistics on how many power poles there are in an urban area within a 1 mile radius?)

After one or two 'false'/premature conclusions I finally found the actual source. And heard it. High-frequency noise issued by arcing is weird stuff. One needs to point one ear in the direction of the noise source then one can hear it. Or use a hand as a 'reflector' (not a cup) to hear it with one's head pointing forward to the noise source.

To the right is what a spectrum analyzer tuned to 2.75 MHz showed. This was found to be close to the frequency of maximum pulse amplitude on the Spec An and later on a tunable AM/SW receiver used to track this signal down. Peak signal level was greater than -50 dBm for the RBW (Resolution Band-Width) used.

Spec Ref. Level, Span and RBW setting validation:

Ref Level = -20 dBmFreq Span = 100 kHz/DIVRBW = 30 kHzTrigger = Line

A narrower RBW would more closely resemble a communications receiver's BW, but the intent here was to show clearly the presence of a pulsed noise source, and a 30 kHz wide BW does this nicely.


Flat map of area. Location of offending power pole and Amateur Radio receiving site shown:

A 'flat map' doesn't really do this story justice, it doesn't show 'the mass of humanity' and the associated infrastructure nearly as well as a Google satellite image; the buildings the houses, the streets and the highways. Too bad power poles don't show up too ... the thin line below traces the line-of-sight path from the source pole to the affected receiving site:


Here's a little fuller presentation of the sat view; the black marks show the course I first walked to find the area where the offending pole was located. During this 1st walk I was following the course of the indicated 'null' on the battery-operated portable radio, 280 to 300 degrees magnetic until the last bit :

As I walked north on Cedar from Ellis - lots of poles in the area – which one's the problem? The signal was VERY strong in this area.

Shown below is the intersection looking NNW across McDermott and north on Cedar; McDermott is running left and right and Cedar up and down ... the stop sign seen here is for northbound traffic on Cedar.

Zooming in (below) looking north on Cedar we see: a) pole with 1 transformer, b) pole with a riser and three phase being sent somewhere; c) adjacent to the two-story building further up (but not shown) is a pole with 3 transformers delivering 3-phase into that 2-story building:


Looking a little to the left from the previous picture (NW) we have two more poles, the pole on the left has a single transformer on it: --- picture -------->

But that's not what I checked first.

Instead I checked the poles on Cedar first, past the church and then I circled back to the West (circling the church complex and parking lot) and ended up then checking the poles across the street on McDermott shown here -->

Across from the First Baptist Church at 201 E. McDermott, is where the strongest signals were observed when 'sampling' the signal strength near the pole ground wires.

This is the technique I use to 'nail it down to one pole' after locating 'the area' where the noise is originating. Position the radio about 6 inches from the wire and note the signal strength; I don't think anyone can gage the signal 'strength' by ear so a meter which is driven by the radio's AGC line is a must.

Right: The lone 'pole pig' power pole across from the church.

Hardware, from left to right (ignor-ing the three insulators and phases on the top of the pole cross arm) we have:

● transient/lightning arrestor● transformer and ● fuse/disconnect assembly:


This is where I had very strong indications on the pole with the lone pole pig (pole on left in picture on top of previous page).

The picture to the right is the signal strength meter on the Sears AM/FM /SW radio indicating this strong signal:

The offending pole number:

Mid-day picture; didn't realize until later while going over the pictures that there was a gap between the top fuse holder and the wire (phase wire) that should have been clamped tightly in the upper set of fuse holder jaws like the bottom wire is:


The wire's insulation looks odd too. I didn't notice the gap and the wire-not-being-connected aspect until I later analyzed the photographs as it is difficult to interpret the image appearing in the small viewfinder of an electronic camera:

Analysis of above photo: Photo shows the top of the fuse assembly.

The wire (with the melted-looking insulation) should normally be residing in the jaws/clamps to the right of the end of the wire, but instead looks to have been broken due to mechanical flexure over time and perhaps 'blown' free during Thursday morning's storms.


This photo was snapped early the following morning. The outline of the bare wire with 'cooked' insulation can clearly be seen against the morning sky unattached to the top of the fuse/disconnect assembly:

The camera was lucky to catch this arc JUST when it was 'flashing over' during a peak of the applied 60 Hz AC sinusoid appearing on 'the grid' – this arc was not photo-shopped in:

A short video clip can be found on youtube.com. This video was taken the same morning and it shows the unattached wire arcing; the sound has kind of a higher-frequency buzzing:




Update: On Saturday 4-26-2008, the noise was noted to be absent. Later in the week a visit was paid to the site and here's what was observed -

a) Dualie wheel tracks (characteristics of a bucket truck) backing up to the area of the pole:

b) The wire was found re-attached:


Appendix

Notes

1. Icom 756 Pro-II 75M S-meter measurements made with a) no Preamp selected and b) no Attenuation selected

2. To get a single clean 'paint' of the envelope for pictures on the 756 Pro-II BRIEFLY connect the antenna then disconnect after one screen paint otherwise that area on the display will be overwritten again and again!

3. DF Procedure using ferrite-loopstick-equipped Sears Model 2278 radio:

a. Choose frequency with strongest signal between 2 and 6 MHz as the loopstick antenna is active for SW on this band only; do not raise telescopic whip.

b. Orient/rotate the radio on a central vertical axis looking for a minima (a null) in the 'buzz' or noise level. If several noises can be heard, note the minima for the noise under observation (it is possible at a particular locale more than one noise BUT they usually have different audible 'signatures') Note the compass bearing for the null; the radio position at this point represents an ambiguous compass bearing until resolved for the 180 degree ambiguity.

c. Change position and repeat. Convergence occurs when multiple intersecting lines cross the same general area. A higher freq can be used to reduce 'coupled field' effects as opposed to radiated wave when close to the noise source.

d. Local pole-pole measurement of noise signal strength with the radio's signal strength meter is performed to identify the pole with the offending hardware.

This short youtube.com video demonstrates how the signal 'null' is found and used to determine the direction of the signal source: http://www.youtube.com/v/EUxkXSVCYxg . Notice how the buzzing sound is nulled by turning the radio and the sound is minimum when the radio sits on-a-line to the source .

- End -


http://www.youtube.com/v/EUxkXSVCYxg



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Line Noise Tracking Expedition, Power Line RFI - Tracking it down