According to your TVF Report, you are almost next door to the transmitting towers. It's possible you are experiencing overloading due to the extremely high power levels.
Another possibility is that despite the extreme signal levels, the antenna is not receiving much of the available channel 5 signal.
A quick look at the Hauppauge web site reveals a very small antenna... I would be hard pressed to believe it is designed to cover any TV channels in the VHF band (2 through 13). Given it's apparent size, I suspect it is basically a UHF (Channel 14 through 69) design.
VHF antennas are physically larger than UHF antennas, because the wave length of the VHF signals is longer. (High frequencies = short wave lengths. Low frequencies = long wave lengths.)
I presume you are using the HVR-850 as a portable device, so packing around a large antenna is going to be impractical. (An example of an antenna designed to receive Channel 2 through 6 is the
Antennacraft Y526.)
I am inclined to think 'receiver overload'. To test, simply take the laptop to a location about 10 to 40 KM distant from the transmitting antennas and try there.
Absolutely, the last thing you need is an amplifier.
As Canada transitions away from analog broadcasting, you may find your situation improving, especially if the broadcasters move to UHF frequencies.