MI VHNTR: I have been going to that link for years. A very good source.
Victor Charlie: I believe we are on the same page for gps criteria. I believe that the criteria for field GIS work is a minimum of 4 satellites. I have been creating a number of track maps from my hunting trips. I have been plotting water sources and critter tracks. On the ridge top yesterday I was receiving up to eight satellites, but down in the steep gullys I was lucky to get four while standing still. Those super sized Sugar Pine take up a lot of sky. Part of yesterdays hunt crossed paths from two days ago. Found a bear track on top of my tracks for a short distance.
You hit upon receiver sensitivity. I understand that Magellan, Garmin, and Lowrance do a good job for the conditions in this area. The new generation of satellites should improve coverage under canopy. I review a lot of data put out by State and Federal land management agencies. BIA, FS, BLM, and others. There is a real value in an external antenna for their work. I have and still considering the purchase of an external antenna for my Garmin 76C. (It has a plug for an external antenna, the Legend does not.) The unit normally has more then adequate reception. But I noticed that when was busting Tan Oak Brush under a Pine stand, in a deep gulley. the number of tracking points dropped off. This was notable on the maps I printed out. The drop off was only for a few hundred feet in the thickest cover.
The down side would be how to manage the external antenna. I am thinking of creating a inside pocket in the top of my day pack. Some outdoors men hare created a pocket in their hat. To close to the brain pan for me, I cannot afford additional damage.
Is it required for better coverage for a few hundred feet. I think not! But I might justify it. I carried the gps in a cupholder in the old pickup and it worked great. The cup holders are lower in the new pickup. Coverage is not as great, but it still works a great deal of the time. Even the XM satellite radio blanks out at times.
For a little bit of research info.
www.fs.fed.us/database/gps I have found some good BIA info, the Parks Service tells you what you cannot do. At times you will find articles regarding testing of recreation grade gps by agency employees. I find these of interest.
I strongly recommend a mapping gps unit. If the price hurts take a look on the Internet. There is one location that sells factory refurbished Garmin units at a reduced price. They come with a factory warranty°°