On Thu, 19 Feb 2015 15:19:26 -0500, wrote:

I know the frequency, which by the way is between 200 and 300Mhz.

Do you know the bandwidth needed? If it's fairly wide band, you'll
probably end up with a hipass and lopass filters in series.

If I have this correct, the "stub" is a 1/4 wave length of the offending
frequency. The 75 ohm coax is cut to that length and is shorted on the far
end. The other end is connected via a "T" connector.

Stubs will work, but I prefer LC. Here's an FM band (100 MHz) notch
filter I threw together to keep the FM junk out of a local VHF ham
repeater.
http://802.11junk.com/jeffl/SCCARC-talk-2013-09-20/LTspice-FM-Notch/

Also, I don't know if the notch will be "deep" (high Q) enough to make
the digital data "un-usable" (can't decode).

What digital data? Make my life easy and supply:
1. What are you trying to accomplish? What problem are you trying to
solve?
2. What have you got to work with? Ability, test equipment,
materials, etc.

Does anyone have any suggestions, or can you recommend a place
where I can order a good CATV NF (I am willing to pay)?

There are plenty of custom filters around. Google. I gotta run
immediately....

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558