Surge Suppresors

Hello,

Could anyone help with a place I might find some schematics and or insight on surge suppressors (such as polyphasor), such as the type you attach to transmission lines for antennas or power supplies going to tower mounted radios and dishes, I am somwhat perplexed by the fact they pass both dc supplies and ac if and broadcast frequencies as well as squelching high powered lightning voltages without burning out the suppressor(most of the time),at the same time presenting very little resistance and inpedance to the intended frequencies and power supples going through them. Also, a while back there was a string on a site that had collections of different schematics that where available for viewing. If anyone remembers what that site is, it would be greatly appreciated.

thanks

J. Floyd