Antennas

I found the attached to provide a useful summary of the location and description of the common antennas on small planes

http://flighttraining.aopa.org/students/presolo/special/antenna.html

While watching another student pre-flight a plane early on I found he would clean the antennas underneath the plane. I found this useful to do since it really forces you to look at the surface underneath the plane. In addition the article mentions the following as another good reason to do that. It is common to hear the tower state "transponder appears to be inoperative, recycle" to a plane departing and this may simply be that the xpdr didn't get set to the right mode but it also might be because of the reasons mentioned below.

The spikes are prone to caking up with oil, reducing the transmitting range. Often, just cleaning a spike antenna doubles your transponder range and gets rid of those intermittent Mode C problems. The reason is that the ground secondary radars need only one sweep to determine your squawk code (Mode A), but they need two good sweeps to determine altitude information (Mode C). Hence, a dirty antenna may not conduct a good signal reliably. This goes for all antennas; a dirty antenna does not perform up to its potential.