GPS Antenna confusion

[+BCollSuss]

Hi all, I need a big clue about GPS antennas!

 

I own a Garmin GPS III+, and I get frustrated at the reception when walking through dense woods. I have a simple fantasy -- "why not just get a better antenna?"

 

So I stupidly went to RadioShack and bought a telescoping scanner antenna for $12. When I plugged it into the BNC connector on my GPS, I got zero reception. I checked the manual, and -- doh -- the antenna only receives frequencies up to 1300Mhz. But looking on the web, it looks like the GPS satellites broadcast at 1575Mhz. Wow, that's pretty high frequency, higher than Ham radio, even.

 

Searching the web some more, it seems that all "GPS Antennas" for sale are coils of wire, meant to hang off your boat, or out your car window. And they all cost at least $100, yikes.

 

So my questions are:

 

1. is there something inherent about the 1575Mhz that implies all antennas must be coils, rather than rigid, telescoping ones? I assume not, since the antenna that came with my Garmin is a little stubby thing.

 

2. does anyone have a pointer to a telescoping antenna that *will* pick up a GPS signal? I want something that I can carry around in the woods. Or is my only option to buy an "official" Garmin antenna coil?

 

I wonder if I'm missing something here. :-)

[+Searching_ut]

I'm afraid a telescoping antenna isn't a good option. To begin with, the GPS signal is circularly polarized, while the design of antenna you're considering isn't. Secondly, since you want to try and increase gain, you need a design that is more directional. With GPS, at most you need a 180 degree beamwidth, anything else is wasted. A general rule of antenna design is that gain comes by compressing beamwidth, so in theory at least, when looking for maximum gain, the narrower the beamwith the better, provided you still can see enough of the sky to be effective. A good antenna designed for GPS should give you a boost of at least 3 to 6db over a dipole.

 

there are a lot of good external antennas on the market, many with built in amplifiers that can help out in the sort of conditions you're dealing with. You should be able to find them as cheap as the $20.00 range, or you can spend several thousand dollars on one designed for survey grade equipment.

 

A good place to start finding links to information on GPS is: http://gpsinformation.net/ If they don't have the information you're looking for on their site, they probably have a link to it, including a lot of equipment vendors.

[+EScout]

Everything Searching_ut says is right on.

The antenna on your GPS III+ is a pretty good one. If you are in your car, you can get the extension Coax cable with the suction cups and put it on the roof. Or, you can get an amplified patch antenna. Your GPSr supplies voltage through the coax connector to power it.

[+Tahoe Skier5000]

quote:

---

Originally posted by BCollSuss:

Hi all, I need a big clue about GPS antennas!

 

I own a Garmin GPS III+, and I get frustrated at the reception when walking through dense woods. I have a simple fantasy -- "why not just get a better antenna?"

 

So I stupidly went to RadioShack and bought a telescoping scanner antenna for $12. When I plugged it into the BNC connector on my GPS, I got zero reception. I checked the manual, and -- doh -- the antenna only receives frequencies up to 1300Mhz. But looking on the web, it looks like the GPS satellites broadcast at 1575Mhz. Wow, that's pretty high frequency, higher than Ham radio, even.

 

Searching the web some more, it seems that all "GPS Antennas" for sale are coils of wire, meant to hang off your boat, or out your car window. And they all cost at least $100, yikes.

 

So my questions are:

 

1. is there something inherent about the 1575Mhz that implies all antennas must be coils, rather than rigid, telescoping ones? I assume not, since the antenna that came with my Garmin is a little stubby thing.

 

2. does anyone have a pointer to a telescoping antenna that *will* pick up a GPS signal? I want something that I can carry around in the woods. Or is my only option to buy an "official" Garmin antenna coil?

 

I wonder if I'm missing something here. :-)

---

 

You must be treading through some REALLY thick forest, because my III+ gets excellent reception.

 

Using Opera 7.1

[+Lone Duck]

I don't know if a different antenna, or even an amplified antenna will improve the block the reception. The trouble with trees is that they block the signal. If there's no signal to be found, then no matter how good the antenna is it can't pick up what isn't there.

 

That Quack Cacher:

Lone Duck

 

When you don't know where you're going, every road will take you there.

[+Searching_ut]

Lone Duck said:

quote:

---

I don't know if a different antenna, or even an amplified antenna will improve the block the reception. The trouble with trees is that they block the signal. If there's no signal to be found, then no matter how good the antenna is it can't pick up what isn't there.

---

 

Probably just as importantly, once you start boosting gain way up there, you increase the odds of picking up a signal that came to you by means of other than direct line of sight. (Multipath) When this happens, all bets are off as to what sort of accuracy you're going to get. The frequency of the signal, polarization, and even the low power of the signal to an extent were all selected to try and reduce this problem. While boosting the gain may help in some areas, it can lead to significant problems in others.

[+RobAGD]

I wish I had my III+ back to be honest. I love my V it gets me every where and it is great for geocaching but I really think my 3 was way better under tree cover then my V has ever been.

 

As for Antennas, something I have been playing with is putting a stock antenna on a small fiberglass rod attached to my pack so that its clear of my body blocking its signal reception. All you need is a good shielded cable to make an extender from your GPS to the remote antenna.

 

-Robert

[+park2]

If you go for an external antenna, there is always this stylish & functional hat from another GPS manufacturer (I don't work for them, I just thought it was cool)

 

[+GeckoGeek]

quote:

---

Originally posted by RobAGD:

As for Antennas, something I have been playing with is putting a stock antenna on a small fiberglass rod attached to my pack so that its clear of my body blocking its signal reception. All you need is a good shielded cable to make an extender from your GPS to the remote antenna.

---

 

The signal loss even in good cable at GPS frequencies is very high. It won't take much cable to cancel out the extra gain in the antenna.

 

Since you don't want to get too directional with a GPS antenna, I think most of your gain is going to come from a larger collection area - translation: bigger antenna.

[+BCollSuss]

Thanks for the great replies, everyone. That gpsinformation.net site is fantastic... I have a lot of learning to do. Perhaps I'll ask my brother to help me understand some of the technology here... he's a physicist. I'm just a programmer. :-)

 

In general, it seems like I'm trying to solve a problem that no piece of hardware is really going to be able to fix. So I'll just live with it. On the other hand, this PDF article about building a homemade antenna seems like it would be really, really fun:

 

http://www.arrl.org/tis/info/pdf/0210036.pdf

 

:-)

[mingho]

quote:

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Originally posted by volks_ev71:

Originally posted by BCollSuss:

 

Searching the web some more, it seems that all "GPS Antennas" for sale are coils of wire, meant to hang off your boat, or out your car window. And they all cost at least $100, yikes.

 

---

 

Hi Opera.

 

A commercial amplified GPS patch antenna is comprised of linear amplifiers and filters inside a ceramic patch, RG174 cable and a GPS antenna connector (such as MCX, BNC, SMA, SMB and TNC). By the time one gathers up all those components, (not to mention small soldering iron and crimping tool), it may very well bring the cost above the commercially available amplified GPS antennas for roughly $19.49 + shipping. We manufacture and distribute a high performance GPS antenna (28dB) for Garmin GPS units.

 

You like to know more about the performance and specification of our antennas, please visit

http://store.yahoo.com/gilsson/ or

http://www.stores.ebay.com/id=32049213&ssPageName=L2

 

Thanks and good luck !

 

Kindest regards,

Ming Ho

Gilsson Technologies - GPSgeek

www.gilsson.com

[mingho]

quote:

---

Originally posted by volks_ev71:

quote:

---

Originally posted by BCollSuss:

Hi all, I need a big clue about GPS antennas!

 

I own a Garmin GPS III+, and I get frustrated at the reception when walking through dense woods. I have a simple fantasy -- "why not just get a better antenna?"

 

So I stupidly went to RadioShack and bought a telescoping scanner antenna for $12. When I plugged it into the BNC connector on my GPS, I got zero reception. I checked the manual, and -- doh -- the antenna only receives frequencies up to 1300Mhz. But looking on the web, it looks like the GPS satellites broadcast at 1575Mhz. Wow, that's pretty high frequency, higher than Ham radio, even.

 

Searching the web some more, it seems that all "GPS Antennas" for sale are coils of wire, meant to hang off your boat, or out your car window. And they all cost at least $100, yikes.

 

So my questions are:

 

1. is there something inherent about the 1575Mhz that implies all antennas must be coils, rather than rigid, telescoping ones? I assume not, since the antenna that came with my Garmin is a little stubby thing.

 

2. does anyone have a pointer to a telescoping antenna that *will* pick up a GPS signal? I want something that I can carry around in the woods. Or is my only option to buy an "official" Garmin antenna coil?

 

I wonder if I'm missing something here. :-)

---

 

You must be treading through some REALLY thick forest, because my III+ gets excellent reception.

 

Using http://www.opera.com/

---

[+Team Shibby]

Hey Ming Ho!

 

Nice to see you found our forums! I purchased my antenna from you and I have to tell you I love it! Of course I do not use it while I am hiking, my Garmin V performs flawlessly while hiking and caching with the factory quad.

 

I also purchased my +12v/serial combo cable from you which was another excellent deal! I hope you get some good recognition here in the forums, your products are top quality and the best prices around.

 

Anyone who needs a cable can be assured of the high quality of GpsGeek cables! Thanks again!

 

Kar

[mingho]

Hi Kar.

 

Thank you for your kind words. We do our very best in designing and manufacturing the best Garmin accessories at prices substantially below Garmin's OEM prices. We are glad you liked our products.

 

I am a geocacher myself, so I frequent here whenever time permits.

 

Kindest regards,

Ming Ho

Gilsson Technologies - GPSgeek

http://store.yahoo.com/gilsson

www.gpsgeek.com