DTV Antennae ?

[pallophotophone]

Hi,

Has anyone ever tried to use 2 powered indoor DTV antannae with their outputs combined ?
I had a thought, but it might have a problem w/ phase cancellation.
If I installed 2 antennae aprox. 5 feet apart, and combined their outputs w/ a tap or a splitter - using it in reverse- would the signals cancel out if one antenna received a signal that was out of phase, if that is a consideration in the digital realm ? What I wanted to do was position each antenna in the best possible location for a particular group of stations, but use only one piece of coax (CAC-6) to distribute it.
A rooftop installation for me isn't a reality. But 2 antennae on the enclosed back sun porch is!
Presently the signal just is too erratic on the S meter.

I'll bet someone know the real answer to this.
MANY THANKS !!!

Pallophotophone