Ive actually doen this kind of setup before...no and yes-depending on your antennas if you have an vhf antenna and you hook up an uhf antenna make sure you have an low noise antenna(if amplified)because the noise can destroy an weak signal.if you could please tell what kind of antennas you want to use
You cannot directly connect a UHF and a VHF antenna together without significant signal loss from both antennas. Antenna #1 will try to 'rebroadcast' the signals #2 collects, and #2 will also 'rebroadcast the signals #1 collects. However, there is an inexpensive device called a UVSJ (UHF-VHF-Signal-Joiner) that makes it possible. Really cheap.
If you want to combine two same-band antennas, they must be identical and (theoretically) spaced at least a quarter wavelength apart for a given channel. As an example, you need to seperate them by three feet for Channel 35. This applies to both vertically stacked and horizontally paired antennas: smaller distances for higher channels and greater distances for lower channels.
If the pair of matched antennas (UHF or VHF) are pointing exactly in the same direction, there can be a small signal strength gain: if they are pointed in different directions, there will be a small signal loss from both antennas, but signals may be able to be received from two (or more) signal sources. Also, the antennas must be correctly phased to work in tandem rather than cancelling each other out. It gets complicated.