Most gps units are effected by vegetation, terrain, and tall buildings that interferer with the signal from the satellites. You did not mention the brand of your unit because each manufactures software process the signal in a different manner.
My Garmin Legend which is a few years old is a better gps unit then the day I bought it. The reason is that gps units that come with the ability to connect to a pc can be upgraded. Over the years Garmin has offered free upgrades for the Legend. These upgrades have improved how the unit processes information. It also upgrades the unit from 500 waypoints to a 1000 waypoints.
The next up grade does not require a pc cable. When I first purchased my gps units I took them outside, turned them on and let them initialize. This allows the gps to search for the satellite signal so that it knows where it is. Your gps will also receive updated Almanac information from the satellite. You need to leave the unit in place for about 30 minutes for it to receive a full updated Almanac. This will allow your unit to find and lock on to satellites faster. Because of new satellite launches by the United States and Europe I redo this process every few months. This has improved the reception of my units. The older Garmin Legend is now receiving 12 Satellites in good locations with WAAS turned on. When I am kicking around in the woods I have the WAAS option turned off because of poor WAAS reception. It causes the unit to search for the WAAS signal and runs the battery down. When new WAAS satellites are launched this will improve.
When I am walking around in the woods I am not always looking at my gps. I will have it on, and secured in a pocket. I will stop and look at the screen. Normally you will receive more satellites in a stationary position. You can determine the direction you were walking by the compass dial. If you swing around your non-electronic compass will be fixed in the direction you had been moving.
When you are in very heavy cover you might have to pull out your old fashion compass. While hunting I dropped into an area that had two hundred foot tall fir trees. My gps unit would not receive any signal. Once I got into a more open area, I set down, pulled the gps out, and let it re-acquire the signal.
For those who want to spend more for a new gps unit the Garmin 60Cx and the Garmin 76Cx are very good options. The units come with the highly sensative SiRF III chip. There are other manufactures who are using the SiRF II chip. There are a number of different chips being used by the manufactures. Again their software and how they handle the signal varies. But the SiRF chip offers higher-sensitivity along with good battery life. I should note the Garmin Legend Cx and Vista Cx do not offer the SiRF chip. What all the new x units offer in the upgradeable micro SD card memory. A worthwhile feature.
Currently Garmin is offering a $100 rebate on a couple of units that have the SiRF chip.
http://www.garmin.com/whatsNew/currentpromotions/Yesterday my Garmin Legend landed in Hawaii along with my grandchildren. I had loaded it with the Topo maps for two of the islands. Showed them how to find the beaches using the POI feature. (Points of Information). My advice was to let the unit re- initialize itself. This has to be done when a gps is turned off an moved a long distance. I also sent my FRS/GMRS radios with the family.
I have an external antenna for my Garmin 76C, but I do not recommended it when out bucking brush. Just another item to get hung up.
Copied from website:
With its rapid time-to-first-fix and high sensitivity, the SiRFstarIII architecture is designed to meet the rigorous demands of wireless and handheld LBS applications, and provides superior location performance, both indoors and out, for 2G, 2.5G, 3G asynchronous networks.
The SiRFstarIII architecture packs a performance punch, achieving time-to-first-fix of one second for aided starts in outdoor GSM environments and acquiring signals down to -159 dBm. This makes real-time navigation practical, including in many indoor environments, through urban canyons, and under dense foliage. Unlike the lengthy sequential search process of traditional GPS architectures, the SiRFstarIII architecture, with the equivalent of more than 200,000 correlators, enables fast and deep GPS signal search capabilities, resulting in significant improvement over todays architectures that contain a few hundred to a few thousand correlators.
The SiRFstarIII family is comprised of the GRF3w RF IC, the GSP3f digital section, and the GSW3 software that is API c
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