OEM GPS Antenna

unixxx · 06-04-2006, 01:41 PM

I've decided I'm going to buy the Garmin GPS 15L OEM receiver but need an antenna to pair with it. I want something semi permanent (ie not magnetic, adhesive maybe) with good reception. Are there better performing higher gain GPS antennas or are they all pretty much the same? I've heard people mention that the Gilssons are cheaper and have better reception than the Garmins but is this true or just a marketing gimick. Even among the Garmins there is great price gap, why are the Garmin GA 25 antennas so much cheaper than the Garmin GA 26 antennas? Much of my driving is on tree covered roads if that affects the antenna type at all. I notice the my handheld Garmin 48 which has a "stick" antenna gets twice as many satellites as my roof mount Raytheon 120 which has a flat pancake antenna. Just want to buy the right antenna the first time. Thanks.

Change · 06-04-2006, 01:57 PM

If you get an active antenna, make sure you wire up the 15L so that you're giving a good clean 5v to the antenna bias line. I forgot that part and have to go back and add an LM7805. I'm using a Maxrad combination GPS antenna/NMO mount, it's designed to be active but it seems to work fine running passive.

The stick antenna is a quad helix, the flat pancake is a patch antenna. Patch has higher gain straight above, quad helix has higher gain towards the horizon. It looks like most vehicle antennas are patch antennas. See http://www.tessco.com/products/displ...h=false&page=1

unixxx · 06-04-2006, 02:50 PM

The antenna's going to be more than three feet from the receiver so I think I'll go with an active antenna. Will a high gain GPS antenna be more directional and decrease my ability to receive certain satellites? Thanks.

Change · 06-04-2006, 03:43 PM

Hm. Not really sure how much the gain will affect your horizon reception. Here's a little bit of info, but it's light on details: http://www.gpsinformation.org/joe/gpsantennaspecs.htm

unixxx · 06-04-2006, 04:04 PM

Thanks for the link, I've read in a few different places that helix is better for under the trees. I noticed that a lot of the patch antennas say they need a ground plane. Is placing the antenna on the roof of my car a sufficient ground plane or is something else needed?

Change · 06-04-2006, 04:30 PM

Roof/trunk lid are just fine as long as they're metal.

unixxx · 06-05-2006, 11:54 AM

Ok, I just decided to go with the Garmin GA27C. It's the active antenna that's recommended by the receiver's datasheet. Thanks for the help.