I've looked into PAR filters, but I need to know the offending frequency. The

problems is that PBS broadcasts the same shows on TV channels 13 and 16,
therefore I don't know the exact frequency.

Hiya-
The three different Par models offer rejection in the 152, 158 and 462 MHz
ranges... and if I'm not completely off, over-the-air TV channels 13 and 16
fall outside that range (13 is in the range of 211-216 MHz, and 16 is in the
482-488 MHz range)... so Par may not be able to help you in your case.
You could try building your own stub-type filter, attaching a 'T' connector
inline with your antenna lead-in, and attaching a specific frequency-cut,
open-ended stub of 50 ohm coax to the 'T' section (perpendicular to the antenna
lead-in)... the formula to find the stub length should be:
(75/Freq. MHz) x 0.67 = Stub Length in Meters... I couldn't find a formula that
finds the length in inches, but I'm sure it's out there!
The exact freq's you need to notch out (I just found a book that has them) a
Ch. 13 Pic-211.25, Audio-215.75
Ch. 16 Pic-483.25, Audio-487.75
So you can see the commercially available Par filters probably wouldn't
ultimately reject the freq's you need to kill.
Try a search for home-built stub and notch filters. There are some ideas out
there.
Good luck-
Linus