Electrical Interference???

[Dishman Dan]

How far away must electric wires (110V) be kept away from coax and ribbon cable with coax for satellite reception??? I dug a ditch about 2' deep to bury my cables running from my house to my satellite dishes. A freind has his just under the soil but I want mine deeper so I do not hit them with anything. The cables are in plastic conduit to protect from rocks and metal debris from a old barn that once stood. I want 110V power near my dishes for when I am working and testing out there without running extension cords. (It is well over 200' from my house!) I heard that if the power and coax cables run parallel of each other a certain distance should be maintained to avoid interference. Someone else I know has their coax for their Dish Network strapped to the main electric service wires on the house and they get no interference! It is a 2 story house and they run about 15' together! I want to make sure before I place the electric cable and bury them all that I will not get interference. The coax is already there in conduit as I mentioned before.

 

[wizard101]

What you are describing is electro-magnetic susceptibility and electrical-magnetic emissions.
Electro-magnetic susceptibility is how “well” a product (or cable) is shielded from outside EM interference.
Electrical-magnetic emissions is what is the flux density of the EM emitted from a product (or cable).
In you case the 110V line is the emitter into the coax. The field strength in the 110V is a function of Voltage/Current and frequency. In your case the field surrounding the 110V is very low. Coax by its nature is a very good high frequency conductor because it is completely encased in a ground shield. This shield in combination with the low EM produced by the 110V line means you will have no problem.

 

[sergei]

To get the greatest possible amount of protection you need to have two runs and install at least one in metal conduit and the other in gray electrical conduit. This way you can lay both in the same ditch, just make sure you ground every thing correctly, the last thing you want is to have a ground loop. This should help protect again lighting, and and rodent or any other damage down the road.
Also don't forget about a UPS and a Panamax surge protector for the feedhorn cables.

 

[wizard101]

Sergei, is correct about the gound loop. Forgot that part, Thanks

 

[Dishman Dan]

I guess it is not a lot to worry about but I thought that it could pose more of a problem! Many moons ago I had some electric education. There was talk about isolating the coax from the 110v lines. Perhaps older types of coax were more vulnerable?

 

[sergei]

It can cause problem and here's why....The biggest problem you could face is a cloud to ground lighting arc which can generate an intense magnetic field even a 1/4 mile from the lighting strike. When lighting strikes the earth, ground current radiates from the point of contact in all directions and generates a magnetic field, which in turn induces a transient on any buried conductor.
So run your dish cables in rigid steel conduit with give you the best shielding, the gray plastic conduit is best for rodent and water protection. DO NOT run them together because even as good as coax is a transient voltage could still be induced into either the coax or the other wires. You have good coax, really good coax and then the cheap stuff so be careful what you buy, be sure to get the best shielding.
Any damage to the coax which is not in conduit will allow water to enter and will then rust out the coax shielding. then you have basically no shielding and finally intermittent problems as the cable is rusted out.