Hi Ivan,
One of the downfalls of this type of "extreme" antenna is that first is an indoor design that is amplified. This means it receives signals through walls and interference from household appliances and amplifies them, meaning there is more "noise" in the recieved dtv signals because those appliances. The end result of this can be strangely unreliable reception.
Second, this design is UHF. If you want VHF you need to graduate to an antenna that supports high-VHF. UHF and high-VHF operate in completely different areas of the electromagnetic spectrum. Just like with tires you have to buy 18 inch tires to fit an 18 inch rim, if an antenna is designed for 174 mhz (high-VHF, real channel 7) vs 500mhz (UHF, real channel 19) you have very different characteristic of wavelength. Thus trying to put 20 inch tires on a 13 inch rims becomes an analogy. It doesn't work. Some get lucky and receive high-VHF signals with UHF systems, but that is normally when VHF signals are very close and very powerful. Those systems are also mounted outside.
Your high-VHF signals are good, but not very strong. This leaves you the best choice:
Install on your roof a
HBU11k.
http://www.solidsignal.com/pview.asp?p=HBU11K&ss=29217. Orientate to about magnetic 220.
Cheers.