Hi Old Stuff,
I've tried a few antennas in Manassas & the
7694 is a great choice for all the DC channels. You will likely need an amp like Tigerbangs suggested as channel 50's signal does not get out as well as TV FOOL predicts.
Unless Maryland Public Television is important to you, a rotator will likely not be necessary. As John Candle suggested, channel 30 is so close, it should come in well with the antenna pointed towards DC. I get 30 well here in Arlington through the back of the antenna.
If you want Baltimore as well, I suggest separate antennas like in my photo. (around $125.00) I personally haven't had much luck with Baltimore in Manassas, but have only experimented at locations near the fairgrounds.