Power Line Interference

[halo fan]

Do power lines interfere with GPS signals? I was under power lines, near a tall (20 ft) concrete wall and the direction finder on my etrex legeng kept bouncing around pointing in different directions. Not sure if it was the wall or the power lines. Any ideas?

[Kerry.]

Power lines can, depends on the voltage but I'd be looking for other reasons first.

 

The wall could also be an issue (and/or) depending on how close you were to it and the affect it might have been having on a critical part of the sky, at that particular time.

 

Could also be totally unrelated and be interference from some other source. Without looking at and eliminating first the affect of the wall as an obstruction it can be difficult to put the finger at any specific cause.

 

Cheers, Kerry.

 

I never get lost everybody keeps telling me where to go

[+Dave_W6DPS]

The electromagnetic field around power lines can cause some local disturbance, and the physical characteristics of transmission lines can cause some interesting effects, as well. These usually show up only directly under the lines, or within the footprint--the area they could hit if they fell over.

 

The multiple reflections of the lines can cause the GPSr to jump around as described. So can the reflections and/or shielding from the concrete wall, due to the steel reinforcing inside it.

 

Adding the effects of both in the same area may be what really did your GPSr in. Most modern GPSr units have anti-falsing and interference rejection features, but they can only do so much. If you have false (reflected) signals and a high ambient noise level, it can confuse event he best of GPSr units.

 

You might want to back off a 100 to 150 feet from the power lines and see if you can get a fix on what your GPSr is pointing at. Most localized disturbances won't reach that far.

 

Speaking as a fellow Angels fan, and employee of the company the field is now named for, I hope you won't find too many places where the lines cause problems. Of course, having the wall and/or other propagation problem causing structures around our lines doesn't help.

 

Good luck!

 

Dave_W6DPS

 

My two cents worth, refunds available on request. (US funds only)

[+Prime Suspect]

quote:

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Originally posted by halo fan:

Do power lines interfere with GPS signals? I was under power lines, near a tall (20 ft) concrete wall and the direction finder on my etrex legeng kept bouncing around pointing in different directions. Not sure if it was the wall or the power lines. Any ideas?

---

The Legend doesn't have an electronic compass. When you slow down or stop moving, it's normal for the directional arrow to do what you mentioned. The closer you are to ground zero, the more erratic it may appear.

 

The arrow works when you're walking at a normal pace because the unit is doing two things:

• It makes a note of your position every second or so, and
• It assumes you are holding the unit so that the "top" is pointed in your current direction of travel.

By knowing where you were a second or two ago, and where you are right now, it can determine your direction of travel. If it can also assume that the unit is pointed in the manner noted above, then it can make an assumption about the current orientation of the display screen, and can then properly point the arrow in the correct direction.

 

When you slow down or stop, the unit can no longer accurately determine the unit's orientation. In a perfect world, the arrow should stay in the same place. But in the real world, the coordinates the GPS calculates will change slightly, for a variety of reasons. These random changes confuses the GPS's orientation calculations, causing the arrow to point in seemingly random directions.

 

The solution? Start walking again, if possible. If not, it's time to bring out a magnetic compass. While the arrow may not be pointing in the right direction, the bearing and distance listed should be correct (or, at least as correct as these things get).

 

"Don't mess with a geocacher. We know all the best places to hide a body."

[+RJFerret]

Since nobody else has jumped on the "signal bounce" reason, I'll voice it!

 

Although it's more common at cliffs, rock ledges, and where bedrock is exposed, I'm guessing the 20' concrete wall was more of an issue than the power lines. I'd think any interference from power lines would be relatively consistant and minimal, perhaps causing an error but not varying signals reaching your GPS. Signal bounce off the wall however would do just that.

 

The behaviour you describe I consistantly see near cliffs and whatnot. Foliage obstructions however usually cause the GPS to keep going onward, believing it's doing the right thing. I've never witness trouble from regular power lines or high-transmission lines (both of which I've passed under multiple times while caching).

 

If you search for "signal bounce" you'll find lots more info...

 

Hope this helps,

 

Randy

[+TresOkies]

I have had a situation recently where a highly charged electrical storm knocked three GPSRs out while I traveled. It went on for over 50 miles. The three were all Garmin--eMap, eTrex Vista, StreetPilot III.

 

Having said that, I'd still say it was the wall. I encounter problems with walls, overhangs, and rock ledges all the time. I rarely encounter problems with electrical fields.

 

-E

 

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N35°32.981 W98°34.631