Brief explanation of my environment and what I'm trying to achieve below:

Environment
========
STB (set top box) is the piece of hardware/software that connects to
the VOD server via Ethernet, streaming IP while connecting the TV
using the RF input/output (RF modulator)build into the STB. Coax cable
comes from the cable company plugs into the "RF input" port of the STB
and the RF output connects to the TV.  Prior to this cable company
directly plugged coax into the TV.

Goal
===
Stream IP on one of the channels using a build in RF modulator from my
video server together with being able to view all the channels coming
from the cable company.
 
Issue
=====
I'll use channel "10" as our example to be the channel used for the IP
stream.  RF modulator is the device that allows you to strip off
channel 10 to be used for the IP stream.  Again, RF modulator is build
into the STB that allows me to use any channel to stream IP.

Streaming on channel 10 works fine, but it does not display any other
cable channels correctly.  If I change the channel to say 2, or 5 or
36, I see distortion.  In fact I see distortion across all the
channels at this point.  Channel 10 works fine that is used for IP
stream.  Now, If I shut the STB (goes into stand-by) then all channels
work ok.  Combination of stream and cable channel together does not
work properly.  It almost seems as signals are overlapping each other,
not sure.

Is there a way to watch all the channels while streaming IP on channel
10?  What is the solution to achieve this?  Do I need audio/video
modulator, tuner etc? Not sure.

Your expertise is greatly appreciated.

Thanks,
DP

the issue of distortion occurs because the inbuilt RF modulator has
some issue in separating the feed from your video server and your
cable companies feed. to aquire a feed with more fidelity try using an
external RF modulator to plug in both your video server feed and your
normal cable feed. now the solution will work only if u can get a
customised RF moderator for your specific purpose. this will however
require a thorough understanding of the frequencies of your normal
cable feed and the frequencies of your video server transmission. the
details regarding the transmission frequecies of your video feed can
be found out from the manual if you are using a COTS video server. the
cable feed part requires some R&D.revert to me regarding the approach
for any clarification/

Hi,

Thank you for your help.  I've tried about 5 differernt RF modulators
and using the same frequencies as my VOD server.  It did not work. 
I'm not clear about cable feed part and requiring R&D work.  Please
explain what type of R&D work.

Thanks,
Deny

Further if you don't know the frequencies of the two, how do you go
about getting the info.