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Antenna type, little difference.


EraSeek

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Joe's site says it is size, not type

 

Joe MeHaffey and Jack Yeazel say:

 

"Some people suggest that the Quad Helix antenna is "best" consumer GPS antenna under tree cover. This is not categorically true. There is little difference in performance between patch and quad helix antennas which have the same effective APERTURE. Aperture is directly proportional to antenna size and antenna gain is proportional to antenna aperture. Note that the Garmin G-12xl, G-12map, and eMap (among others) have a patch antenna while the G-76 series and the Magellan Meridian series use quad helix antennas. These models all have similar performance and sensitivity. All GARMIN models except the GPS 12 and eTrex series can be used with an external antenna. None of the of the recent Magellan models have external amplified antenna capability."

 

"The more recent units do have slightly more sensitivity but this is due more to improvements in semiconductor technology than anything else. The trend of improvements in effective sensitivity in newer technology units is likely to continue for the forseeable future and is not necessarily related to antenna type."

 

"Note also that the eTrex models are more compact units than the others listed. As a result, they have slightly less antenna gain (on the order of perhaps 2db

less) than the physically larger models and thus will have slightly less sensitivity which may be important under forest canopy."

 

"Thus, as a rule-of-thumb, physically larger GPS receivers are likely to have better forest canopy receive performance than more compact units regardless of

antenna type."

 

4497_300.jpg

 

"The liberty we prize is not America's gift to the world, it is God's gift to humanity" W.

 

[This message was edited by EraSeek on March 29, 2003 at 09:58 PM.]

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And again:

 

"Antenna patterns are another cause of wrong conclusions

about "which GPS has a more sensitive receiver. Many GPS

receivers use the patch antenna which has the antenna gain fall

off as you near the horizon. (Examples: G-12XL, EE, M-4000).

Others use the wrapped "helix" style antenna which has good

coverage almost all the way to the horizon. Outside in the open

spaces, both perform very well. The patch antenna is conceiv-

ably superior since it tends to reject signals very low on the

horizon and thus is somewhat less sensitive to multipath errors.

On the other hand, if you are indoors (or in a car), the lower

pattern coverage angles of the helix style antenna may pick up

SVs lower on the horizon (or multipath signals) through side

windows and stay locked where you might not with the patch. If

multipath signals are received and processed, you may see your

GPS position move hundreds and even thousands of meters away from

your actual position."

 

"In actual practice, I find little difference in "real world"

performance between the two antenna types under normal clear view

of the sky situations."

 

4497_300.jpg

 

"The liberty we prize is not America's gift to the world, it is God's gift to humanity" W.

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quote:
Originally posted by EraSeek:

_Joe's site says it is size, not type_

 

Joe MeHaffey and Jack Yeazel say:

 

"Some people suggest that the Quad Helix antenna is "best" consumer GPS antenna under tree cover. This is not categorically true. ...


 

All I know is that both my Rinos held a lock while my Vista was bouncing all over the place the last time I compared the them under tree cover.

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I bought an external "GPSGeek" antenna for an Emap. Chopped ends off an elastic cell phone case (Nokia 5190) leaving the clip for use on baseball cap brim. Cut a thin aluminum disc, placing it under antenna for a ground plane. Makes a huge and immediatley measurable difference under tree cover.

 

Had a another smaller green external antenna and had NO gain. Only advantage would be getting signal from outside, past signal blocking metal car skin. Or to a lesser extent away from head that would block signal.

 

"There's no need to be afraid of strange noises in the night. Anything that intends you harm... will stalk you silently."

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quote:
Originally posted by EraSeek:

_Joe's site says it is size, not type_

 

Joe MeHaffey and Jack Yeazel say:

 

"Note also that the eTrex models are more compact units than the others listed. As a result, they have slightly less antenna gain (on the order of perhaps 2db

less) than the physically larger models and thus will have slightly less sensitivity which may be important under forest canopy."

 

"Thus, as a rule-of-thumb, physically larger GPS receivers are likely to have better forest canopy receive performance than more compact units regardless of

antenna type."


 

Yes, I saw that on their website, but I'd also seen statements that the antennas used in the eTrex series are identical to those in the physically larger 12 series/eMap/etc.

So I sent an email to Garmin techsupport asking specifically if a smaller antenna was used for the eTrex models. Their reply was that they were all the same size and design. They also said there should be no performance difference between the eTrex models and the 12series/etc.

 

I have 4 GPS receivers - all Garmins with two having patch antennas and two quad-helix. If anything the sensitivity is generally slightly better with the patch units, but the difference is small and not enough for me to consider it a factor in making a purchase decision.

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I run my Street Pilot(helix antenna)and 12XL (patch antenna) next to one another near the center heat vent on the dashboard face, not on top. The 12XL mounted upright, signals "Poor GPS Coverage" about 10 times for each warning from the Street Pilot. Yet with my limited experience with the Street Piot in the woods, the 12XL seems to perform better.

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In my experience I seem to have noticed that a patch will lose signal under tree cover quicker than my Map76, but the Map76 will bounce around a lot more than a patch. No real tests involved.

 

4497_300.jpg

 

"See the wonderous works of Providence! The uncertainty of human things!" Geo.Washington

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quote:
Originally posted by EraSeek:

In my experience I seem to have noticed that a patch will lose signal under tree cover quicker than my Map76, but the Map76 will bounce around a lot more than a patch. No real tests involved.

 

http://img.Groundspeak.com/user/4497_300.jpg

 

_"See the wonderous works of Providence! The uncertainty of human things!" Geo.Washington_


 

This matches my experience. My solution is to use a GPS with a quad-helix antenna

(in my case, a GPS V) and carry an amplified patch antenna for those situation where

the quad-helix antenna is insufficient.

 

-Paul

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quote:
Peter said:

Yes, I saw that on their website, but I'd also seen statements that the antennas used in the eTrex series are identical to those in the physically larger 12 series/eMap/etc.

So I sent an email to Garmin techsupport asking specifically if a smaller antenna was used for the eTrex models. Their reply was that they were all the same size and design. They also said there should be no performance difference between the eTrex models and the 12series/etc.


 

Garmin responded to me in vitually the same way more than 3 years ago when I asked the same question prior to buying the yellow when it first came out. As for real world performance, I ran quite a few side by sides when I had an e-map, and couldn't find any difference in reception. In discussion on the newsgroup, Joe has insisted the eTrex tested out about 2db down in reception. This could be a result of the antenna being closer to the CPU, thus subject to more background noise. In practice, 2db isn't much, equates to about the same amount of change you'll get with a few degrees tilt. It doesn't explain the great differences people claim to see when using the different equipment. Having tried to compare through side by side tests, my own guess is part of the explanation is expectation, the rest differences in filtering, and software behavior. In most of my comparisions I found moving the receiver by just 6 inches or so generally made more of a difference in reception than which unit I used did.

 

As for comparing the Quad antenna receivers, and the eTrex, I still haven't noticed much of a difference. In fact, when I did my side by side stationary tests with a sportrak and Legend, 6 out of 10 times when One receiver wouldn't get a solution when the other would, it was the legend in the trees that actually got the lock. (More than 100 different locations involved) It's still remarkably easy to encouter conditions where non of my receivers work reliably, so there is still a lot of room for improvement.

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I would have started a new topic for this, but since the softwar change half the buttons don't seem to work for me, including "new topic".

 

Anyway, I'm on a garmin-rhino mailing list. Someone there tested a rhino against an etrex and says they got much better results with the rhino. From their test description, it sounds like they had both units oriented vertically against their body, which I figure is the worst possible position for the etrex.

 

Anyway, another theory was that by having the GPS units so close together (same pocket), they may have been interfering with each other due to leaking RF. It sounds like a theoretical possiblity, but I've never noticed such behavior.

 

Has anyone noticed problems operating two GPS recivers in close proximity?

 

George

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"Antenna Patterns and perceived "sensitivity" of GPS receivers

 

Sometimes people do side-by-side comparisons of GPS

receivers for sensitivity and come to incorrect conclusions.

This can happen for several reasons already discussed on the

newsgroup.

 

1) Some GPS receivers emit small amounts of Electro Magnetic

Interference (EMI) which can desense the receivers of other GPS

receivers a few feet away. One example of this is that the Eagle

Explorer EMI causes desense of the receiver in the Garmin G-12XL,

but not the other way around. Thus, if you put the two side by

side you will always find that the EE receives better. On the

other hand, if you separate them by 5 feet, things are pretty

equal."

 

4497_300.jpg

 

"See the wonderous works of Providence! The uncertainty of human things!" Geo.Washington

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The eTrex units without the click stick,should be a little better than the ones that have the click stick, and that is because of the placement of your thumb over the click stick(too close to the antenna).

 

Of all the Garmins and Magellans, my Vista was more likely to lose signal. Also other gps units other than the eTrex series, are more likely to be held up higher off the ground in front of you.

 

These thing effect signal reception:

*Your thumb over the click stick.

*How high you hold the GPS in relation to your body.

*The angle you hold the unit(flat vs Vertical)

*Low battery level

*WAAS may make the unit less responsive.(sluggish)

*How you hold the unit in relation to an opening in the tree canopy.

 

I have had many GPS units, both Garmin and Magellans since 1998, and learned alot about their antennas.

 

Always different...Hit refresh

maze?90+35+4+1+0+0+0+0+255+255+255

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There's a saying that

 

"They have the same basic parts and use the same signal. It is what they do with what they get that makes the difference"

 

Much is made about antenna's and certainly all antenna's are not the same and neither is the way they work or how the user is maybe expecting them to work especially with reference to Correct Orientation

 

Cheers, Kerry.

 

I never get lost icon_smile.gif everybody keeps telling me where to go icon_wink.gif

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I think we tend to overlook the unit-to-unit variations that exist due to manufacturing tolerances. Take any two units, exact same model, and you will see just as great a difference between those two "same type" units as you would see between two different brands or models.

I recently did some side-by-side comparisons of 4 units; 1 yellow e-trex, a Magellan Sportrak Map, and two Rino 120's. Didn't have heavy tree cover, so my "simulation" was to place the gps on my couch, indoors, and see how long it took to get a fix. The units were laid at about 30 to 45 degrees of incline; probably not perfect for either type of antenna. Once each unit got a fix, it was turned off and the next unit was rotated into the exact same spot and the process repeated. Trials were generally ended if 5 minutes went by with no fix. The e-Trex and one of the Rino's got a fix for each of five tries; the second Rino failed to lock once, and the Magellan failed to lock in under 5 minutes twice out of the five trials. The Rino's came in first and second for average time to fix; the e-trex was a close third, and the Magellan just consistently took longer for that fix under these conditions. (Could be my fault for antenna orientation.) Since the second place Rino didn't lock once, I would rate THIS BATCH of units like this:

#1 Rino "A"

#2 Yellow e-Trex

#3 Rino "B"

#4 Magellan Sportrak

The Magellan really wasn't all that bad, because this was a very difficult test condition.

 

So what did all this tell me? There was as much difference between the two Rino's as there was between the Better Rino and the e-Trex. Both brands were good, and both types of antenna from the same Manufacturer were good. Finally, those buying in a store should open three boxes, take the units outside, see which one seems to pick up the best, and pick themselves a "cherry"! icon_smile.gif

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