The basic Etrex is not map capable. It is a basic GPS. The canopy problem is horse hockey...
Actually it is not. The satellites use microwave transmitters, around 1.2276 GHz, which is close to the radio frequency of hydrogen as defined by radio astronomers.
Microwave propagation is affected by several factors. One major inhibitor to propagation is absorbed by water. So in very heavy canopy during spring and summer there can be problems. Leaves after all have a heavy concentration of water. In fall and winter the reception will improve.
It is not much different than when some one using a satellite dish to view television losses signal during a heavy rain or snow storm. The microwaves are absorbed to the point the signal to noise ratio becomes unusable. With older gps units in the past I have experienced this both in Manitoba and northern Wisconsin. The angle of reception through the canopy is maximized. I assumed at the time that the signal loss was exceeding 20 db or greater in comparision to more southern locations lacking such heavy canopy and a higher angle of reception.
The systems Raimey uses are ultra accurate and capable of accuracy to within an inch or better, no were near the more gross consumer grade handheld accuracy. There has been improvement in recent years with the chip set, increased sensitivity. However, even the best commercial system can be impacted by absorption. I believe, but am not certain that only the military units can overcome this.
I have in the past done work in microwave frequencies up to and including 10 GHz. For a time, this was being considered for ultra wide band data transmission, fiber won the battle due in part to path loss issues.
Many handheld units use dual-conversion with a low-IF architecture. While this is conducive to preventing microchip architecture induced noise, it does restrict gain to about 95 dB and internal noise figures near 8 db. With low signal densities per mm^2 that 8 db does make a difference if path loss is increased by absorption.
Which to buy? The best you can afford. Your use will grow as you become familiar with the benefits.
Pete
