Dear spyguy, an analog scrambler isn't simple to made... First the technology of an analog scrambler is old and is cheap to use a digital link. like a wi-fi camera.
Because is necessary to convert, synchronize and transmit into the cable a signal for 750 foot!!!
I researched some schematic, but nothing...
If you want to buy a video analog scrambler see this link, and remember that the couple will be required.
(note for moderator, if isn't possible to report a commercial site, please delete the link...)