2 Gps'r Causing Interference

[seemonkeys]

To do my first cache right, I borrowed another GPS'r to help find the proper coordinates. I held them both in the same hand and walked in from 2 directions over the corse of several days to get an average. It was almost exactly the same every time.

The first cacher to search reported I was off so I went back and again got the same coordinates.

I ran to the superstore and bought a new GPS'r which is giving me a new set of numbers that appear to be correct.

Using the first 2 GPS'rs alone now or with the new one I get the proper coord's but using them together they lock on to the original set of inncorrect numbers.

So my question is , can using 2 GPS'rs together affect their ability to receive or do I have some other problem I seem to be unaware of.

One is a Garmin 38 and the other a Magellan 300 (older style)

Thank you.

[+IVxIV]

Yes, I have heard that if you hold 2 GPSr's very close together (they're touching each other) then they can interfere with each other's signal. Not sure if quad or patch antenna's are both problematic this way..

 

But if you hold them at least a couple feet apart there shouldn't be any problem. You should be able to confirm this by placing each one apart (around 5 feet for good measure) and let them get a good signal lock. Now move them together & see if their co-ords fluctuate noticeably.

 

How far off was your reading as compared to the "correct" reading?

[+Team Cotati]

If both units were Garmin, you would have no problem. I've heard that Garmins are designed to cohabitate in a mutually cooperative manner. They also seem to perform well when continents apart. Life is good.

[+AuntieWeasel]

I've held a Legend in one hand and a Little Yellow in the other and they agreed within a few feet. There wasn't much point in doing this, of course. It was merely Ssssscience!

[+Glenn]

To do my first cache right, I borrowed another GPS'r to help find the proper coordinates. I held them both in the same hand and walked in from 2 directions over the corse of several days to get an average. It was almost exactly the same every time.

The first cacher to search reported I was off so I went back and again got the same coordinates.

I ran to the superstore and bought a new GPS'r which is giving me a new set of numbers that appear to be correct.

How are you determining who has the correct corrdinates?

 

Using the first 2 GPS'rs alone now or with the new one I get the proper coord's but using them together they lock on to the original set of inncorrect numbers.

  So my question is , can using 2 GPS'rs together affect their ability to receive or do I have some other problem I seem to be unaware of.

One is a Garmin 38 and the other a Magellan 300 (older style)

Thank you.

 

Not usually. A GRSr is a receive only unit and shouldn't interfere with one another. Unless one isn't properly shielded or the shielding was damaged.

 

You never said how far apart the two readings are. If it is only a couple of feet then there isn't any problem. If is a couple of yards, thats annoying but still not reason for consern. If it is more than that then there maybe a problem.

 

But, going on only what you have said I'd guess that the most likely problem is in the way your holding the units. You want to make sure your holding them both with the antennas up and not so close that one unit is blocking the other from "seeing" the satallites.

[Prof. Y. Lupardi]

Inside a GPS reciever many kinds of frequencies are generated.

An antenna is always two-ways physically speaking: because he can recieve he can also send. In whatever way you shield the GPSr components: the antenna will aways be able to leak frequencies to the outside world.

And when a nearby GPSr picks these up they might create interference inside the GPSr with the there used frequencies.

During an event when there were many GPSr available we found out that indeed some interfere on distances of <1 meters happens. As far as I remember it was a Magellan that disturbed some Garmin Etrex units but not all Etrex GPSr's that where there.

So I always advice: keep the GPSr's separated at least 2 armlenghts.

[+briansnat]

Yes according to GPS Info.Net

[+reveritt]

Not usually. A GRSr is a receive only unit and shouldn't interfere with one another.

 

All FM devices generate radio frequencies, even if they are just receivers. I would not be at all surprised if GPSrs in very close proximity interfered with each other.

[+Glenn]

Inside a GPS reciever many kinds of frequencies are generated.

An antenna is always two-ways physically speaking: because he can recieve he can also send. In whatever way you shield the GPSr components: the antenna will aways be able to leak frequencies to the outside world.

And when a nearby GPSr picks these up they might create interference inside the GPSr with the there used frequencies.

During an event when there were many GPSr available we found out that indeed some interfere on distances of <1 meters happens. As far as I remember it was a Magellan that disturbed some Garmin Etrex units but not all Etrex GPSr's that where there.

So I always advice: keep the GPSr's separated at least 2 armlenghts.

The amount of EMI given off from a properly working GPSr isn't enough to affect another GPSr. The EMI givin' off from a GPSr is usually wrong frequency and too low in power to affect anything. The receiving GPSr has at least one stage of filtering and shielding. An in properly shielded or in properly working GPSr is a different story.

[+Prime Suspect]

I've had both of my GPSrs operating at the same time, less than 2' apart. Didn't notice any degradation.

[+sbell111]

It seems unlikely that both units would both be affected in such a way that they both gave an identical incorrect reading.

Edited June 1, 2005 by sbell111

[+Team Shibby]

When I first purchased a Garmin V, I placed it side by side with a Garmin Venture and they interfered with each other. They worked fine when seperated, but whenever they were right next each other, they would both lose lock on satellites.

 

Kar

[+AtoZ]

No they will not interfer. Maybe it is the EMF you give off.

cheers

[+IVxIV]

Did you read the last guys note??

[+Team Perks]

No they will not interfer. Maybe it is the EMF you give off.

cheers

The tin foil hat will usually do the trick.

[+jimmyreno]

They may not interfer with each other, but put a compass near one and watch the needle spin.

The electrical circuits create a magnetic field around the gps.

[Prof. Y. Lupardi]

That asks for a home-experiment.

I have taken a small compass and my good old GPS12. Without switching the GPSr on the needle reacts to it from a distance of 7 cm. When switching the GPSr on: exactly the same.

Maybe there is some metal inside the plastic casing?

[+Glenn]

They may not interfer with each other, but put a compass near one and watch the needle spin.

The electrical circuits create a magnetic field around the gps.

Does your GPSr have an electronic compass?

[+Glenn]

That asks for a home-experiment.

I have taken a small compass and my good old GPS12. Without switching the GPSr on the needle reacts to it from a distance of 7 cm. When switching the GPSr on: exactly the same.

Maybe there is some metal inside the plastic casing?

Not just metal but magnetic too.

[+diverhank]

I geocache with a Garmin and a Magellan a few feet apart (one around my neck and the other on my wrist) and I've never got a problem with them interfering.

 

Keep in mind that two different GPSr will have different update rates and at an instant, don't give you the same solution necessarily. If you let them settle down (e.g. stop moving), both will come to the same solution more or less.

 

I use the differences to my advantages as sometimes the Garmin will get me within a few feet of the actual cache, others the Magellan will...it's almost as if depending on which brand was used to hide the cache...

[+skyraider]

This is kind of unrelated to Geocaching, BUT, If I have both my handheld GPS'rs turned on in the plane, (a Garmin 195 and a Garmin 295,) I have all kinds of problems. The heading needle on the 295 seems to lock up and I will fly right past an airport on a steady heading without the needle turning towards the airport. The antanaes are only about a foot apart.

 

Since that happened, I leave the 195 turned off, but ready to go if the 295 would quit for any reason. I have not had any problems using them this way and I still have the redundancy if I need it.

 

Skyraider

[+sbell111]

Have you considered sending your 195 into Garmin for a physical?

[JohnX]

This is off topic, but it really is not necessary to have two GPSrs and average multiple readings over several days to get the coordinates right. That is just fantastic overkill. Place your cache. Make 3 approaches and mark a waypoint. Discard one if it is way off from the other two, and average the results. There you go.

[seemonkeys]

Here are answers to most of the questions.

1. The coordinates were about a 1/4 mile to the SE but I didn't know that then.

2. How do you determine who has the right coordinates? This time it is obvious I was wrong.

3.The coordinates given by the 2 older GPS'rs were about 10 feet apart. (But a 1/4 mile off)

4.As far as my EMF affecting this I tried the tin foil hat.

5. There are electronic compasses on both units.

6. Even with the overkill I was still off. For some reason I never felt like they were right so I really tried to make sure I got it right.

With all the thoughts on the matter I decided to do some tests. We took all 3 units (the 3rd being a brand new Explorist) to the new agreeded upon as correct coordinates. The new one and the Garmin 38 both showed very close. Alone or seperate. The Magellan 300 shows the original wrong #'s. When placed with the new one it doesn't affect it. Placed with the Garmin 38, they both show the wrong coordinates give or take a little.

Placed by an RF audio device the 300 is making all kinds of noise. It is definitly transmitting. I am also starting to see other things that are wrong with it. I also found out it was opened up "to see how it works" before I got it.

Probably because of a lack of shielding in the older models, the 300 does seem to be affecting the 38. At least in this case.

Thanks for all the thoughs on the matter and I believe I'll be keeping the new one!!