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Antenna Or Not?


bigbe

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I am just getting started in geocaching and have read alot about external antennas for gps units. I am getting a Garman 76 soon, and would like to know if it is worth getting an external antenna at the same time. Any input will be greatly appriciated

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The 76 series has the "quad helix" antenna, which is generally regarded as the best type as far as handhelds go.

 

The only time I've really used my external antenna is when flying on a commercial jet and travelling on Amtrak trains. Without the external, then I need to constantly hold the GPSr up to the window to get a lock. On a 5-hour flight, your arm gets tired. But with the external antenna and a window suction mount, I just pop the antenna on the window and set my GPSr on the tray table in front of me.

 

Unless you have a specific need for an external, I'd say wait and see if the GPSr's built-in antenna is good enough for you.

 

And if you do need an external, GPSGeek is a highly recommended seller by people in this forum. That is where I got mine. The 76 series GPSrs use the MCX connectors.

Edited by Neo_Geo
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It's reasonable for you to use an external antenna, if you use your GPS in City (poor satellite visibility) or, if your car has a heated windshield (the fine metalized mesh in the glass blocks the sattelite signals.

 

Othervise, it's not reasonable to pay extra money, IMHO

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I have a 76s which I use a lot in the car.

It does not have a heated windshield, but just being in the car knock down the reception quite a bit.

 

I got an enxternal (GPSGeek) and mounted it on the roof.

BANG, 9 sats at full bars.

Even when driving through all those nasty places that usually cut reception to 0.

 

IMHO .. if you have the coin and you spend a lot of time in the car, get the antenna. You will not be dissapointed.

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I am just getting started in geocaching and have read alot about external antennas for gps units. I am getting a Garman 76 soon, and would like to know if it is worth getting an external antenna at the same time. Any input will be greatly appriciated

In my opinion it's well worth having one handy - just in case. especially since you can pick one up on ebay for twenty bucks.

 

My 60CS works great on foot but in my van it often have trouble getting a signal lock. occasionally when heading certain directions on road trips (typically when travelling west to east) the signal would crap out on me -- usually at the worst possible time (for example when a complicated double turn is coming up on auto routing).

 

Now with the magentic attenae on the roof I don't have to worry about it and I have peace of mind.

 

It also came in handy last weekend when I was walking on foot through a patch of forest choked with pine trees.

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It's worth it if you know in advance that it will benifit you because you might save a little in shipping charges. However there is no harm done waiting to see if the GPS will give you good service right out of the box .

This is the best way to kow if you need one, I sold GPSr sense the early days of GPS (Pre first gulf war) I always told my customers to try the GPS without an antenna first, I had maybe 1 or 2 customers a year that ever needed one, and they were driving hummers (Hummers do not have see the sky well) We sold lots of GPSr over the years, maybe .05% of our customers needed and external antenna.

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I tried experiments with 2 GPS V's, one with an external antenna, and one without. Ther were fewer errors with the tracklogging with the GPS with the external antenna, and the tracklog looked better. Inside the car I had better reception when I had the external antenna magnetically stuck to the roof top of the car.

 

There is not much difference between one with an external antenna, and one without, except if when you are driving down a heavily wooded street.

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I second jollybgood's opinion. I used my eMap for over 3 years without an external antenna and never had any real issues with the reception. But then I got the $19 Glisson external and find that it frequently makes things better. My tracklogs are smoother and the elevation profiles recorded on bike rides are definitely more accurate with the external. It's also handy when driving to be able to have the GPS anywhere in the car without worrying about reception - even in areas with tall buildings like downtown SF.

 

If I had followed the advice to only get an external if 'necessary' I'd still be without it. But I found the improvement to be well worth the $21 (w/tax) cost.

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If you drive lots of rental cars, you know that each car is a little different in how the windshield and dashboard is set up. On some cars, the location to set up the GPS (to see the screen and to get reception) is ideal and worry free. On other cars, the flat area of the dashboard may be too far to view the screen, or so close that reception is not so good.

 

I have one of the antennas that can be used on dash or external (from Garmin), and it works great if I set the remote antenna almost all the way forward on not-so-ideal cars and the place the Garmin unit much closer to see the screen. I don't use it every time, but it has come in handy on several occassions. And even left inside the car, depending on the location, you can still get decent reception in a city with a bunch of skyscrapers.

 

Even better would be a the Japanese system for Positioning, which uses a triple combination of Cell triangulation, PHS triangulation, and GPS to show you exactly where you are all the time, even when you're underground, and is incredibly accurate. Then antennas wouldn't be an issue in cities, and in wilderness areas where Cell phones reach....

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Just to chime in again I was really surprised/amazed at just how LITTLE room the external antennae/cable really takes.

 

From the photos I saw on line I assumed they were HUGE with big thick cables attached to them.

 

When mine arrived in a small padded envelope I thought I was getting ripped off. You can literally cup the antennae and cable in one fist if you squeeze. At least the type that hooks up to the 60Cs.

 

So it's not like you're hauling around a big bulky mess of cables and hardware.

 

You could easily put the how thing in a ziplock bag and toss in your backpack until needed.

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Dumb question. For those of you running it on the outside of your car, are you using some sort of re-radiating antenna? Basically I'm just kinda wondering how you get the cable into the car to where the gps is if you aren't.

Cable is very thin....

I run mine thru the corner of the passenger front door and post at the window corner. No leaks or road noise.

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I'm trying to find a way to effectively mount one on my hat when hiking now.

I also have a Gilsson antenna. For hiking I sewed a little patch of cloth inside the top of my cap to serve as a pocket for the antenna. That way it's unobtrusive but still in the optimum position for good reception.

 

In the car I just run the cable out past the door weatherseal and put the antenna on the roof (it has a magnetic base) - the cable is thin enough not to cause any problems.

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Dumb question.  For those of you running it on the outside of your car, are you using some sort of re-radiating antenna?  Basically I'm just kinda wondering how you get the cable into the car to where the gps is if you aren't.

I have a van and the antenna came with a 16' cable so I ran the cable through my luggage rack down the side behind the glass of a pop-out side windown. Then I put the cable behind the trim on the roof lining and ran it all the way to the dash down along the bottom of the windshield and THEN to my GPS mount.

 

The cable is totally out of the way and invisible except for the six inches coming out from the windshield to the mount and where if comes down from the roof to the window.

 

Most folks aren't even aware I have an external antennae. You really have to look hard to notice it.

Edited by jollybgood
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I'm trying to find a way to effectively mount one on my hat when hiking now.

Groundspeak Forums -> Quoting a Post in Antenna Or Not?

I cut an old cellphone case in half and shoved the antenna inside. The clip then attaches to a hat brim. The cord is run out the back of my hat to the GPSr, held in a case attached to a backback shoulder strap. I used an old startac case.

 

Works pretty well, I keep it in the case most of the time.

 

I'm using an older style antenna.

I want a new and hopefully lighter antenna, so it doesn't add too much weight hanging out on the brim. Apparently GPS Geek was using, heavy magnets or a large chunk of metal as part of the design (for a ground plane?).

 

Suppose with a little sewing, velcro would work too.

 

-

Greenjeens

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Apparently GPS Geek was using, heavy magnets or a large chunk of metal as part of the design (for a ground plane?).

The magnets in the GPS Geek (Gilsson) antenna are removable, but they don't change the weight by much. I think the main reason to take them out would be for use near a magnetic compass. It does have a metal base presumably for a ground plane that adds some weight.

 

I put it in a little handsewn pocket inside the very top of my cap and the weight is not a problem in that location. But I could see it being noticeable if mounted on the brim and making the cap unbalanced.

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I found they produce the best reception all around. They are amplified.

 

I have one on the top of my day pack and it is fished down to the case hung in front. That way I can put the gps away out of sight and hands free and keep it running. Also the case keeps it warmer during sub freezing temps.

 

I have one one the very front part of the hood in center. The wire goes under the hood and fished though the fire wall. Even though it's angled abit because of the hood angle it recieve's 1st class still. When I have my slide in camper on the over the cab doesn't interfere with the signal.

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gps antenna should not need much of any ground plane its not a transmitter and the freq. used is not of a big wave length. When mounted on aircraft they come with gaskets wich makes no ground plane and on boats they mount to posts.

For trouble shooting GPS back in the day I Would hold antenna in hand out a window to get a signal.

 

Just put antenna on dash board of U haul you will get plenty of signal.

Edited by Sparkcha5er
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So where would you mount it on one of these?

 

truck_14.gif

 

The obvious spot is the very top of the truck - but it's aluminum so a magnet won't do. And it's a rental, so drilling and gluing is probably out of the question too :huh:

Put the antenna on the hood of the vehicle as far forward, the cable allows. The hood should be steel, and the magnetic antenna should work there. Of course the aluminum box on the truck may kill any signal, due to all the signals being reflected off the metal cargo box.

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The 76 series has the "quad helix" antenna, which is generally regarded as the best type as far as handhelds go.

 

Hmmm....I have an eMap and a GPSmap76s. And I tell ya' I'm not convinced the helical antenna pulls in the birds any better. I find also if you use the electronic compass you have to hold the receiver level and in so doing, you often lose sight of the satellites. :-(

 

I tried using my external antenna stuck to my hat, but the magnet on the Garmin antenna just isn't strong enough to stay put with a small piece of metal in the hat.

 

When used mobile, it works like a champ. All satellites measure full strength and I've never seen it lose lock. It does seem to chew through the batteries faster though.

 

Have a nice day!

C-A

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I tried using my external antenna stuck to my hat, but the magnet on the Garmin antenna just isn't strong enough to stay put with a small piece of metal in the hat.

 

That's easy to solve. Just get a bigger piece of metal. A 6"x6" square of 3/4" steel plate should hold the magnet quite well. Or if you don't like that, an old steel Army helmet should work, but that's for sissies. <_<

 

I find that a 1.5" steel washer from Home Depot does the trick for me. Taped to some foam rubber or plastic, it also doesn't hurt my head.

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So where would you mount it on one of these?

 

truck_14.gif

 

The obvious spot is the very top of the truck - but it's aluminum so a magnet won't do.  And it's a rental, so drilling and gluing is probably out of the question too :)

 

On top with HD Velcro from Wal Marts craft section. Run the wire down threw door gasket,etc.

 

That's like my camper combo. I mounted it out in the front at the very edge of the hood with HD Velcro fromWal Mart. It has survied all winter.

 

It recieves excellant and you can fish the wire under front of hood threw firewall.

Edited by capt caper
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So where would you mount it on one of these?

 

truck_14.gif

 

The obvious spot is the very top of the truck - but it's aluminum so a magnet won't do. And it's a rental, so drilling and gluing is probably out of the question too :blink:

I'd use some of that tacky-stuff that comes with the Garmin mounts (the temporary stuff) and stick it right on top of the box. B)

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Apparently GPS Geek was using, heavy magnets or a large chunk of metal as part of the design (for a ground plane?).

The magnets in the GPS Geek (Gilsson) antenna are removable, but they don't change the weight by much. I think the main reason to take them out would be for use near a magnetic compass. It does have a metal base presumably for a ground plane that adds some weight.

 

I put it in a little handsewn pocket inside the very top of my cap and the weight is not a problem in that location. But I could see it being noticeable if mounted on the brim and making the cap unbalanced.

The Gilsson model antenna SM-76, weighs about 2.5 oz. Not including the attached 40" cable.

The owner of the store said the (iron?) or a heavy mettalic base, was integral to the design and could not be removed.

 

I expected an incredible received sat signal, with the latest generation 60cs GPS chip, and the big quadralinear antenna... Not much of an improvement over the internal, Emap patch antenna, out in the real world of trees and canyons or even no obstructions:(

This amplified external antenna really delivers on the promise of noticable signal gain. I'm hoping the latest models are even better a lighter.

 

Haven't tested how much the battery life of the 60cs is effected by antenna drain. I'll usually only plug in the antenna connector, when needing a signal boost in tree cover, or when closing in on a waypoint.

 

I found an almost useful fact...The mimimum/optimum ground plane size, for cellular 800mhz frequencies, is 28" square, 28"x28". For PCS, 1900mhz the dimension is half or 14"x14". Although it seems a circle is a more appropriate shape?

Anyway, what is the correct size for GPS frequencies? What are the GPS frequencies?

 

-

Greenjeens

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I also have a GPS76 with the Gilson antenna and the difference with and without is significant in my trials. In heavy tree cover with 5 sats, connect the external antenna and get 9 or 10 with no other change. Worth every penny. I got mine to mount on the car while traveling and tried it in the woods. The only downside is the odd looks you get when you get set up to go into the woods and folks in the parking lot see you with an antenna on your hat. Not having to hold the GPS level all through the hike is also worth quite a bit. Any GPS I get to replace the 76 will have the capabilty to attach an external antenna.

 

Happy caching--

 

KYHilltopper --- Clint

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Not having to hold the GPS level all through the hike is also worth quite a bit.

Yep, it'll help this winter when it's below zero. I'll just pull it out for a quick read and won't have to wait for it to get a fresh loc. I don't like having anything out for too long when it's that cold. :D

Edited by Elf Danach
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I found an almost useful fact...The mimimum/optimum ground plane size, for cellular 800mhz frequencies, is 28" square, 28"x28". For PCS, 1900mhz the dimension is half or 14"x14". Although it seems a circle is a more appropriate shape?

Anyway, what is the correct size for GPS frequencies? What are the GPS frequencies?

The civilian GPS frequency is 1575 MHz or a wavelength of 19 cm (7.5"). The ground plane sizes you cite look rather large to me, corresponding to a square that's over two wavelengths long. Making it that big will work well but doesn't give you much improvement over smaller sizes (say a circle diameter of half a wavelength). Obviously the little antennas we're talking about here work fine without any additional ground plane, but there is some improvement when placed on a flat metal surface like a car roof.

 

My take on graldrich's comment above is that people who have units that accept an external antenna input are much more likely to experiment with and comment about such antennas. Garmin makes many such models (76 series, 60 series, eMap, II/III/III+/V, iQue, etc.) so it's natural that they're overrepresented here. The tests I did with an eMap vs. Meridian Gold & Plat. models under marginal reception conditions showed that they gave quite similar performance using their internal antennas (none could hold a lock when poorly oriented and all jumped between 2D and 3D lock at about the same rate when oriented optimally).

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I posted this on June 30th:

 

I just "tested my newly acquired 27C external antennae. Put it into the secret compartment of my Tilley hat, ran the cord to my 60cs, and headed into the thickest woods around. I put the GPSr into my pocket, which is about the worse scenario I could think of. The usual beeping of the signal being lost never occurred. Each time I pulled it out to check, there were 5 moderate to strong satellites showing. If I disconnected the external and held the unit as usual, it would immediately drop to 2 or 3 weak to moderate. Putting it into my pocket got the immediate lost signal. This is going to be fun when I go group caching!

 

I've since used it on both individual and group caching in heavy tree cover. The results are impressive compared to using just the Quad-helix...much more so than I had expected.

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How did the Garmin 27C compare with any other non-OEM antennas? I like Garmin stuff, but antenna design is not rocket science and could easily be built by any antenna producer.

Garmin premium prices may not reflect performance or build quality for this particular accessory.

 

Any other antennas to checkout? Gilsson still good? I've been out of the loop.

 

How much does the 27C weigh, lighter is better?

 

I once bought a really small antenna on ebay and there was no gain, it just got the signal out of a vehicle, with no amplification:(

 

Im not sure Garmin gets comparitively poor antenna performance, but [wildly speculating here] that would be one area to reduce battery drain on a color screen device powered by only 2 AA batteries.

 

It would be hard to say, how much an external could improve performance of other GPSr brands, unless an external antenna port was provided to compare.

 

Having the option to boost or not, and the option for an external antenna, makes for greater flexibility for GPSr placement and battery life. Wires are a hassle, but with some creativity, wiring tangles can reduced.

 

-

Greenjeens

Edited by Greenjeens
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The civilian GPS frequency is 1575 MHz or a wavelength of 19 cm (7.5"). The ground plane sizes you cite look rather large to me, corresponding to a square that's over two wavelengths long. Making it that big will work well but doesn't give you much improvement over smaller sizes (say a circle diameter of half a wavelength). Obviously the little antennas we're talking about here work fine without any additional ground plane, but there is some improvement when placed on a flat metal surface like a car roof.

 

Those dimensions seem large to me too, but article says they are minimum?

I don't know the formula or even basic theory why it works.

I'm beyond he limits of antenna knowledge here, but isn't the colinear, magmount "spring" design, two antennas stacked end on end?

Maybe the design has something to do with the 2 wavelength minimum dimension? Anyway the relationship is 4 times the antenna length 12"(1/2 wave) or 2x wavelength

 

Put my GPSr antenna on a large ~8" sheet metal square and was very surprised how big a difference it made, compared to not using anything. Usaully it's clipped alone on my hat brim. May try some smaller sizes (circles?), testing a usable size vs increased gain.

Walking around with a sheet metal circle on my head, is just a little too wierd, even for me:) Takes up too much time explaining the set up to the unintiated.

 

What is a Ground Plane?

http://www.criterioncellular.com/antennas/groundplane.html

 

"A Ground Plane is a flat surface of ferrous metal (galvanized, steel, etc) that a Magnet Mount or Body Mount antenna uses as an integrated part of it.

A Metal Car Body is a ground plane.

The metal top of a refrigerator is a ground plane.

A filing cabinet is a ground plane.

A tin roof is a Ground Plane.

A ground plane can be a cookie sheet!

A ground plane is NOT a metal roof gutter, a window frame, a downspout or any other piece of metal that is long and thin.

A ground plane MUST satisfy BOTH length and width dimensions outlined below.

Just as long as it is big enough:

for Dual Band/800 MHz/Nextel = 28" x 28" minimum

for 1900 MHz only = minimum 12" x 12"

A Ground Plane does not need to be electrically grounded. It simply needs to be a plane of metal.

Your local hardware store sells galvanized roof flashing for cheap that can be used as a ground plane.

Please note, the antenna should be mounted in the CENTER of the ground plane."

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Just because it's posted on the internet somewhere doesn't make it true. In the military we used ground-plane antennas, and 1/4 wave is sufficient, 1/2 wave more than enough. 2x wave is just not worth the effort at any wavelength.

 

You also don't need a solid 'plane' of metal to make a groundplane. Even a few metallic rods at the correct orientation will do the job. And it does not need to be ferrous metal. It just needs to be able to conduct electricity. Aluminum makes a better ground plane than iron, because aluminum conducts better than iron.

 

Any bozo with an extra $20/month can post anything he likes on the internet. Do not believe everything you read.

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