Any experiences of testing multiple GPS receivers at once?

[Oregiano]

I plan to test 5 different units of MKT II, Venus and Sirf III Chipset.

 

To avoid disturbances, is there any experiences, how far from each other one should keep different units?

What is the safe distance between GPS receivers?

 

Thanks!

[+Walts Hunting]

Since they don't transmit just receive there is no reason to concern yourself with distance. When I used to do my class I had twenty in a group ganged up with no problems.

[+wmpastor]

Those of you who have tested gpsrs side-by-side, what is your conclusion about accuracy & performance? Are they pretty much the same, & the only real difference is in features, bells & whistles, etc.?

[robertlipe]

Walt's Hunting, they actually DO transmit trace elements of RF; that's a characteristic of Superheterodyne receivers even beyond the inevitable RF thrown off by the computer side of the house.

 

In practice, though, I've found no measurable interference. I ran some tests with about two dozen GPSes in a car and tried to quantify interference between 3-4 units either side by side or spaced two feet apart. I didn't keep the results, but I concluded thta it didn't really matter.

 

Wmpastor's question is too open-ended to really be answerable. Two makers can take the same chipset, load it with different antennas and firmware settings and get wildly different results from the exact same receiver. Certainly the better receivers these days are all "good enough" for geocaching and a new purchaser would do better evaluating ease of use, features, user interface, etc. than staring at charts of RF signal attenuation and dilution of precision vs. constellation charts.

 

Oh, and I have somewhere upward of a hundred GPSes....

Edited February 25, 2013 by robertlipe

[MtnHermit]

Oh, and I have somewhere upward of a hundred GPSes....

Oh, I thought I had too many at five.

[+BAMBOOZLE]

Walt's Hunting, they actually DO transmit trace elements of RF; that's a characteristic of Superheterodyne receivers even beyond the inevitable RF thrown off by the computer side of the house.

 

In practice, though, I've found no measurable interference. I ran some tests with about two dozen GPSes in a car and tried to quantify interference between 3-4 units either side by side or spaced two feet apart. I didn't keep the results, but I concluded thta it didn't really matter.

 

Wmpastor's question is too open-ended to really be answerable. Two makers can take the same chipset, load it with different antennas and firmware settings and get wildly different results from the exact same receiver. Certainly the better receivers these days are all "good enough" for geocaching and a new purchaser would do better evaluating ease of use, features, user interface, etc. than staring at charts of RF signal attenuation and dilution of precision vs. constellation charts.

 

Oh, and I have somewhere upward of a hundred GPSes....

 

My hero !!!

I have 30 or so ( never have done a count ).

By the way, I enjoyed reading your write up of the old Meridian line years ago. I no longer use them much but in many ways they are my all time favorite.....years ahead of their time with features new ones still lack.

[+StarBrand]

I once took 4 identical eTrex Venture HCx units out for testing once. They almost never had the same reading at the exact same spot or moment. Made finding caches even more frustrating - proved to me that once you get within 20 feet or so - put it away and use your eyes.

 

Another time I tested 4 different units at once (different brands). There seemed to be a slight amount of interference between 2 of them when held close together.

[+gelfling6]

I would tend to agree, side-by-side, it's dependent on the make/model of the GPSr to have any differences. (I've had magellan Vs. Garmin Vs. Lowrance off by as much as 20-30-feet each..) exact same make/models, should have absolute ZERO differences. (Umm.. yeah, +/- 5 feet.) As someone mentioned, these are strictly 'receive Only' devices, and thus should never generate interference to each-other, though, I will say they are also bound by FCC rules that say they (a) must never generate any interference, But ( MUST Accept any outside interference. But, (A) is not 100% golden rule.. You have to remember, there is a mini computer in the GPSr, which converts the received signal from the receiver, and displays it to the screen. CPU's require a frequency signal to operate (step from one command/function to the next,) This is usually a crystal controlled clock signal, and that, will generate a miniscule, but if you have something seriously sensitive to RFI, detectable RF signal. (which, is usually well out of the range of the GPS-Band signal range. (I.E. the satellites are at 1.2Ghz & 1.6 (actually 1.57)Ghz., most MPU's run at 700-800Mhz.)

[Oregiano]

On latest years I haven't been much engaged with radio waves.

But I believe there may be 2 possible problems, which I don't feel competent and therefore asked your experiences.

1. The GPS receiver RF oscillator radiance emission, which may disturb nearby devices

2. Loss of satellie transmitter field strength, if several GPS receiver antennas are too close to each other.

Edited February 26, 2013 by Oregiano

[+gelfling6]

Oh, and I have somewhere upward of a hundred GPSes....

Oh, I thought I had too many at five.

 

I'll see your five, and raise you 23.. Call! Yes, I am serious! (My brag list here on GC.com)

 

Minus from the list, Garmin eTrex Vista HCx & a Nuvi 40. ..

 

Robert's probably had the access to hundreds in the development of GPSBabel. (can't blame him!)

 

Stephen (gelfling6)

[+wmpastor]

 

Oh, and I have somewhere upward of a hundred GPSes....

 

Are you opening a museum?

 

If not, how can I get on your Christmas list?