I know Sundays are lazy days, but I bet some of you are up to this challenge.
As a practical matter, we have a problem with 990KHz energy getting into out cameras and video inputs at the ATV Repeater site. We can't filter out the interference since it falls right in the middle of the video spectrum. We're quite sure the energy is coming in on the coax, functioning as an excellent antenna, and couples into the equipment. Everything is bypassed properly, but that's not good enough.
So here's the problem for you to solve. (We've tried torroids (even tuned to freq) and "hum" filters and they don't work!)
1. We want to loop the RG-59 (not RG-58) coax (look up the specs online) several times to provide 750 ohms of inductive reactance. Assuming we make several loops in the coax that are 4-inches in diameter (side-by-side), how many loops do we need? (Hints: The conductor diameter is the outside diameter of the shield and the spacing between turns is twice the thickness of the insulation on the coax.)
When you have that figured out, try this.
2. We want to loop CAT5 cable (look up the specs online) several times to provide 750 ohms of inductive reactance. Assuming we make several loops in the coax that are 4-inches in diameter (side-by-side), how many loops do we need? (Hints: The conductor diameter is different than for coax. The pairs are twisted. The spacing between turns is a little different than for coax.)
Have some fun with this and I wish you luck. Answers can be tested at the ATV Repeater site this afternoon.
Rod Fritz, WB9KMO
rod@sbatv.org
805-637-0985
P.S. Other ideas for solutions are welcome.