We know that we can´t fly near cell tower and high voltage lines, but, what would be a safe distance? 100 meters? 200 meters? 500 meters?

Check out this link, specially the diagram that Markus provided.

Cheers

http://forum.dji.com/thread-4272-1-1.html

I was about 100 yards away from some high-powered lines and could not calibrate my compass because it said of electrical interference.  I moved another 50 yards away and it calibrated immediately.  Not sure about cell towers.

Like the other thread states, it depends on the power of the line and the shielding of the cable.
I flew about 50ft over a streetcar cable line and almost lost my P3.

If someone is interested, it´s a summary by what I googled and the link:
Big power line: a safe distance is 100 meters, but until 50 meters the interference is low, then I think that we can fly ( but not recommend 50 meters, it can interfere )
Low power line ( home line ): It should only interfere if it have many lines or if you are very close ( 10~20 meters )
Cell towers: It depends a little on where you live
Here in Brazil the frequency  for 4G is 2,5 Hz, too close Phantom RC ( 2,4 Hz ), I have already flew with a simple drone of another brand  ( RC 2,4 Hz ) very close of a cell tower ( 10 meters ) and no problems
I live 70 meters from a tower, I'll do some tests at this distance and after I´ll write here

•        there is no formula for this, this is just my opinion

I calibrate my compass and flew 70 meters of cell tower, no problens

I usually try and keep a 200 yrd minimum distance from transmission lines when I fly. I really don't think there an issue where I fly per se, I have flown my birds under them walking back to my truck and launched my birds within 50-100yrds with zero issue. I just  like to keep them at arms length.

Hey, all you people who have said 'I had no problems' were just lucky.  All lines with electricity can affect your Drone.  Powerlines, Cellphone towers and overhead lines of electric trains.  I worked at a company that had it's office next to a train line and we could not use (back then) normal CRT monitors and had to get the very very expensive first LCD Monitors that came out.
Do this easy test:  turn your car radio to AM mode and drive under a powerline - case proven!

Another good demonstration

Can ships marine radar affect our drones?

I presume it probably can.

helidan Posted at 2016-9-3 06:56
Can ships marine radar affect our drones?

I presume it probably can.

YES! Personal experience. Flying level in front or behind marine RADAR 50-200 meters away gets the brunt of the high energy RF from the RADAR. Flying directly above Marine RADAR has not caused any issues. This is due to the transmission pattern of the RADAR.

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Ive flown over a cell tower (without knowing) lost control but as it was a litchi mission it just carried on and i got control back after it came back over