The NOAA MST (mesosphere-stratosphere-troposphere) VHF radar at Poker Flat, Alaska, provides nearly continuous high time resolution measurements of the velocity of 3-m scale plasma density irregularities at altitudes ~85 km during the summer and less continuous but lower (~65 km) altitude observations during the winter. However, incomplete knowledge of the origin and behavior of the VHF scatteres limits the applications of these data. Observations from the nearby Chatanika incoherent scatter radar are used to investigate the effects of electron precipitation and magnetospheric convection electric fields on the VHF observations. It is shown that the backscattered VHF signal is usually enhanced when auroral particles increase the D region ionization. The magnetospheric convection electric fields do not generally affect the interpretation of the measured velocities of the 3-m plasma irregularities as mesospheric winds. Combined neutral wind measurements from the two radars show some evidence for a continuous tide from the mesosphere through the thermosphere.