Power Lines,

[+mikdeni]

I would like to hide a cache close to my home, under or near some large hydro transmission lines.

Will I get interference from the power lines when trying to get coords?

[+New England n00b]

I've found some like that, and it has never bothered by eTrex Legend. I think the frquency of the EMF coming off the lines is too far out of whack to mess with the signal the GPS uses.

[WH]

The power in the lines is 60Hz. GPS signals are up at 2.4GHz. Like noob said, they are too far apart to cause any problems.

[CoyoteRed]

IIRC, we've not ever had any problems with power lines.

 

That's not to say that it couldn't happen if it's an older unit and the EMI filters aren't working properly.

 

The best thing to do is actually get out there and experiment in your spot. If you are walking around the unit does some flaky things, then it might not be a good spot.

[+CharlieP]

I have found that power lines do cause some GPS reception problems, but it varies with the GPSR. I have an old Apelco marine GPS that will refuse to work at all under some very high voltage transmission lines (e.g., 500kV). My Garmin GPS76 does a lot better, but the lines still cause some problems.

[+orome]

It won't effect a GPS signal as those aren't transmitted over power lines. Nor are power lines like to affect GPS reception because the frequencies are so disparate.

[+StarBrand]

All logic and reasoning tells me it shouldn't interfere but the truth of the matter is that I have been to one cache in North Dakota see link where I had a hard time pinning down the signal - some report going to a museum area 120 feet to the east and some like me ended up about 150 foot west of the posted coords. There are a number of high voltage lines directly overhead.

 

Later a friend told me that the power company had come through and replaced old wire and insulators and now I see that virtually everybody is finding the cache with ease.

 

Seems to me that something in those lines was causing problems. Bad connection, loose wire, swaying tower - something.........

[+reveritt]

Why dont you post a question in the "GPS and Ham Radio" forum? Some of those guys may have some information on this.

[+Thot]

Why dont you post a question in the "GPS and Ham Radio" forum?  Some of those guys may have some information on this.

There's this thread in the Geocaching Topics fourm. But, I hadn't posted it since it wandered way off topic and didn't seem to reach an answer.

 

Then there's this short thread from when I posted the same question last summer.

Edited April 7, 2005 by Thot

[+Professor Screwloose]

Yes, it's true that the power in overhead lines runs at 60hz and normally should not interfere with your GPS but, in most urban areas there are a lot of transients from intermitant power surges and marginal connections at the pole, plus the RF interference from traffic signal switching circuitry etc. etc. I would imagine that, the more populated an area is, the more problems you will have.

[+mikdeni]

Thank you everyone. That gives me more insentive and I'm going to give it a try and hide one out there. Of course I will do a few tests first.

[+Greymane]

Even though the frequencies are so different, the problem with the EMI is that the field is so large around some of those lines and the interference wreaks havoc on the internals of the GPS, not just the incoming signal. If you measure the field, it seems fairly insignificant, but in such close proximity and with a sensitive device like a GPSr, it will have an impact.

 

I would just note in the cache description that the coordinates may be suspect due to this issue.

[+CENT5]

Electronically speaking the 60HZ power lines ARE a HARMONIC (albiet a distant one) of the 2.4Ghz GPS signal. Theoretically speaking it is so distant the energy at that harmonic is not measurable. (Typically a harmonic is not measurable or significant beyond the 63rd harmonic (In this case 3780hz.) Therefore the powerline cannot be affecting the signal as they are at the 400,000,000 th harmonic. In practicality, the powerlines outside my house (125kv) drive my GPSr absolutely NUTS. I can move 100 ft away and it's fine. Go figure.

[+Smitherington]

I remember one of my early cache finds in Kellog Forest west of Battle Creek. It was under some power lines and my numbers were all over. The clue nailed it for me but the numbers kept me moving all over.

[+EScout]

Graymane makes a good point. I have noticed problems around high voltage lines. It is probably RFI affecting the GPS electronics directly. I have seen radio transmissions affect many non-radio devices like phones, computer mice, computer monitors.

[George & Christina]

Another question: I am going to be looking for a cache near high voltage power lines. Most probably I will need to triangulate, and a GPSr's direction arrow is not much use there, this is best done using a magnetic compass. Will that have a problem with the lines overhead?

[+CharlieP]

Any device that emits an electromagnetic field may affect a compass. It depends on how strong the field is relative to the earth's magnetic field. I have found that my GPSR can affect my compass if I hold it too close. But I have used my compass in proximity to high voltage transmission lines and did not notice a problem ... but I was not directly under the lines. The lines seem to affect the GPSR more than the compass. I would suggest you set the compass then walk under the lines and see what happens. It would be really interesting to try this with a DC transmission line, but those are very rare, most are AC. I don't think you will see much deviation, if any. But a steel transmission tower could cause a large deviation.

Edited April 12, 2005 by CharlieP