Why do VHF signal strengths sometimes vary greatly when the antenna is moved only a few feet?
Why At VHF a signal usually arrives at your antenna by several paths at once: the direct path plus reflections off buildings, hills, towers and vehicles. Those copies arrive with different phase, so they add up in some spots and cancel in others, creating a standing pattern of strong and weak spots. Since a wavelength at 146 MHz is only about 2 meters, moving the antenna a few feet can shift you from a null to a peak. That is why mobile stations hear rapid flutter, or picket fencing, while driving.
Watch out Ionospheric propagation is rarely a factor at VHF for local contacts, and a few feet of path length would be utterly insignificant to skip anyway; Doppler shift changes frequency, not strength, and requires real motion between stations.
Short waves, short nulls: at 2 meters a peak and a null can be a few feet apart. Move the antenna, change the multipath mix.