Help in Getting OTA in Centreville, VA

Hi everyone,
I need help in getting full signal of OTA digital signal in Centreville, VA 20121. I've tried a lot of things, but either I'm missing something or it just isn't possible in my area.

Here's what I have tried with 5 different antennas:
1.) DB4 Antenna I've had this antenna for years when I first tried to go OTA a few years back. I first tried it in the attic. My goal in all of this is to get the main 4 networks (NBC, Fox, ABC, and CBS). In the attic I was able to get ABC and CBS, but no NBC or Fox. I mounted it outside on the roof and was able to get NBC and Fox, but not ABC or CBS. The run from the attic begins with a 20 feet RG59 run and then probably 50 feet of RG6 into the house and then another 20 feet to the TV. The run from the roof begins with 50 feet of RG6 and then 20 feet of RG59 to the TV.

2.) Mohu Leaf Antenna I tried both Mohu Leaf antennas amplified and not amplified. Both antennas only received NBC and Fox and NOT ABC and CBS. These I tried indoors so I didn't need a cable run and plugged them directly to the TV on my second floor

3.) AntennaCraft HBU33 I figured since I wasn't getting all of the signals maybe I needed a bigger antenna. So I picked this one from Radio Shack. It states the range is 70 miles and I'm only 20 something miles from the tower, so this should be overkill right. I didn't want to get on the roof again, so I tested this one first indoors pointing it through my second floor window. I figured it should do at least better than the Leaf and DB4 antenna, but no luck it still only picked up NBC and Fox and not the other two stations. I checked signal strength on my TiVo box and it ABC still never got over 33 and on average stayed in the 20s. I forgot to mention I tried this amp (Motorola Signal Booster 484095-001-00 Bi-Directional RF Amplifier) with the HBU33 and was able to pick up CBS, but no ABC. Oh one more thing cable run from the second floor window is 50 feet RG6 and 20 feet of RG59 to the TV

4.) AntennaCraft HBU55 I decided to go even bigger and got the HBU55 with a range of 100 miles. Still no dice. Same two channels NBC and Fox and the signal strength either remained the same or weaker. When I tried the Motorola amp with the bigger HBU55, I did get CBS again, but the signal was weaker and the picture kept going in and out. Again this is 50 feet of RG6 and 20 feet to the TV.

I'm not really sure what to make of all this. Any suggestions or ideas I can try. I'm willing to move the Antennas to the roof and try my tests again. It's just a lot of work to get those big antennas up there and I want to make sure I have a reasonable chance of success.

Other ideas I had was to get a real antenna amplifier like this an AntennaCraft DG201 pre-amplifier.

I also thought maybe my signal is too strong and perhaps a variable attenuator would help

Lastly here's my information when I ran my address on AntennaWeb.org and as you can see I'm less than 25 miles from the antenna.

Thanks in advance for your help!!!

Stations Antenna
WNVT-DT 30.6 IND
RF Channel: 30
13 miles at 176°Yellow
WFDC-DT 14.1 UNI
RF Channel: 15
22 miles at 67° Blue
WJLA-DT 7.1 ABC
RF Channel: 7
22 miles at 66° Blue
WNVC-DT 30.1 IND
RF Channel: 24
13 miles at 73° Blue
WUSA-DT 9.1 CBS
RF Channel: 9
22 miles at 66° Blue
WDCA-DT 20.1 MNT
RF Channel: 35
22 miles at 65° Violet
WRC-DT 4.1 NBC
RF Channel: 48
22 miles at 67° Violet
WTTG-DT 5.1 FOX
RF Channel: 36
22 miles at 65° Violet

Here's the report: http://www.tvfool.com/?option=com_wrapper&Itemid=29&q=id%3d2df9e3f28c112e

I have some regular street power lines 2 houses down that cross my path. And there's some huge power line towers about 1/2 mile down the road that also cross my antenna's path. If it is electrical interference is there anything I can do about that or am I just out of luck? I have two tuners one built into the television and my TiVo tuner. I tried them both, but just not with every combination of antennas and placement. I just thought this should have been easier. I'll keep trying different scenarios.

Please keep the ideas coming.

By the way what did you mean by low spot. Are you referring to elevation?

I took the antenna apart b/c it wouldn't fit through the door. I'll put it back together and test it again tonight or tomorrow and will let you know about DC 50, but I think that channel came in fine. It's just those two pesky VHF channels. Would an FM trap help with the electrical interference?

Weirdest thing. I just put that monster antenna in the attic and it gets ABC and CBS, but now no FOX or CBS. I just don't get it. I'll try it on the roof tomorrow, but I wonder if I need to combine two antenna signals now.

Any issue with me using a combiner with two antennas and calling it a day?

It's a bit lower b/c I used the existing DirecTV J-Mount

The weather has not cooperated the last few days. I'll let you know how my testing goes in a few days.