The purpose of the high-pass is to block (attenuate) low frequency RF from passing thru it, and the low pass blocks high freq's.
HI pass filters are typically for ingress control (for the return path), for noisy drops without two-way services. Some also have a "notch" that allow a certain frequency thru for 2-way settops.
A Low-pass might be used for modem-only drops where the tv channels are blocked, allowing only the return to pass thru, as well as the forward HSD channel...
Hows that?
