Bad Reception with Plextor ConvertX

Archived from groups: rec.video.desktop (More info?)

OK, I took the plunge and bought a Plextor ConvertX USB2 Video Encoder.

Using S-Video, or Composite Video everything works fine, but I really
bought it to use with the included EyeTV software.

Using the exact same cable I use to get crystal clear reception on any
of my TV's, when I plug it directly into the plextor I get a few
channels that are clear, but the rest are either extremely noisy or
unviewable.

This was using a roof top antenna, so I also tried it at a friend's
house. He has plain old ordinary analog cable. I verifed he had great
reception using his TV, and took the RF Coax cable directly off of the
TV and plugged it into the Plextor. What happened once again, was that
some of the regular channels like Fox and CBS came up, but many of the
other channels like HBO appear with noise for the sound, and others the
video was completely broken up. I mean, a plain old TV is picking up
these channels without a problem. Why wouldn't the plextor?

I thought an NTSC/Analog Cable Tuner is pretty standard? I tried
emailing plextor tech support but got no response. What I was hoping to
figure out is if there is something about tuners I don't know about
that would cause this, or if it is more likely I have a defective box.
If it's because of a cheap tuner being used that doesn't support all
the features a regular tuner would have, then I'll just return the box
rather than go through the process of getting a replacement and having
to go through the process a 2nd time for nothing.
Thanks in advance for any advice....