Forum: Misc. GPS Equipment Information
Topic: GPS Interference ????
started by: PC Medic

Posted by Guest on Nov. 08 2001,7:11 pm
I am curious as to whether any of you have frequented a particular area that you "always" seem to have problems getting a good sat lock in, even though there is no real visible reason why this should happen?.

I ask because I have a cahe placed (Redwings Treasure) that is located in a park here in Va. Beach. This park is perfectly flat terrain (what isn't in Va. Beach!!) and just light pine tree cover in the area. Yet almost every one who has gone after it has reported strange readings from their GPS. Some to the point of not being able to locate the cache until after several attempts, and some never able to locate it.

Now I also had trouble the day I placed it but attributed t more to my jumping around trying to keep the squadrons of F-14 sized skeeters off of me while I got my readings.
Thing is I have returned to the site on 3 occasions at the request of others to confirm the cache was still there. Each time I noticed these same starnge behaviours from my GPS.
As you approach the cache area it will actually count down the feet to the single digits and point right towards the cache. Then it suddenly points in a totally different direction and the distance jumps by as much as 50'. Strange part is that if you go off in the new direction the distance agin starts to decrase to the single digits and then swings in a whole different direction and jumps up again. Now try hard enough and be persistant and eventually it will get you close enough to put the GPS away and start the normal hunt.

Now before you all jump in and say that is normal when you get within several feet of the cache, this is not the normal bouncing around I have seen. It is hard to really explain unless you have been there but an example is this past sunday. I took both my eTrex and 330X out. Both give same whacky reaction in the cache area. Both lock steady on Latitude when trying to get reading. Both have trouble locking longitude with big jumps while standing dead still. The most impressive reaction though (and first I have ever seen this) was while standing perfectly still the pointer on the eTrex and the waypoint icon on the 330X began spinning in circles at an impressive rate. Any faster and I dare say the LCD would not have been able to refresh quick enough to display the icon movement.

Now this park backs up to an area near U.S. Naval Communications Center at Dam Neck and about a mile the other direction is Oceana Naval Air Station. So it sits right between the two. I am wondering if it is possible (intentional or not) that something from the bases, perhaps radar, is screwing with the GPS reception.

Any thoughts on this from anyone?

Posted by mikechim on Nov. 09 2001,1:42 am
Hmmm... I can't say this has ever happened to me.  Did the problems start after 9/11....Could it be due to "selective deniability" ?  If so though, it would probably have to happen in the entire area around the bases..... hmm actually I'm stumped.    :(

Seeing the arrow freak out and go spinja crazy though would be kinda interesting.  :)
Posted by Quinn on Nov. 09 2001,10:14 am
You may wish to view the support pages within Magellan to see if this is something covered on the FAQ pages. You might have to go as far as resetting your GPS or reinitializing it (did I spell that right?) or maybe it was just the area you were in.
Posted by Guest on Nov. 09 2001,12:16 pm
Quote from Quinn, posted on Nov. 09 2001,12:14 am
You may wish to view the support pages within Magellan to see if this is something covered on the FAQ pages. You might have to go as far as resetting your GPS or reinitializing it (did I spell that right?) or maybe it was just the area you were in.


I doubt it is a issue with the Magellan as both the Mag and the eTrex have the same symptoms, as have others that have gone after the cache.

I am thinking something more in the way of local interference of some king in the same freq as the sat signals
Posted by Guest on Nov. 09 2001,12:24 pm
Quote from mikechim, posted on Nov. 09 2001,03:42 am
Hmmm... I can't say this has ever happened to me.  Did the problems start after 9/11....Could it be due to "selective deniability" ?  If so though, it would probably have to happen in the entire area around the bases..... hmm actually I'm stumped.    :(

Seeing the arrow freak out and go spinja crazy though would be kinda interesting.  :)


Started long before 9/11 though I had considered "Selective Deniability" and checked any way.  Base commander says no intentional interference from their side.

Wierd part is only happens in small area of park.
Probably radio-active waste with my luck  :D
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