To avoid ground loops I want to isolate several video channels (base-band). I have a video source with 4 channel, they all share the same ground.
I'm thinking about some transformer like used in audio application with an impedance of 75 ohm. Two issues: I can't find a suitable product, I will lost the DC offset.
Is there a better way?
For composite video you'd need a wideband transformer, as the signal has quite a bit of low frequency information.
Well, I simply googled "composite video transformer" and came up with this.
EDIT:
Composite video bandwidth seems limited to less than 10MHz so I can reuse the research I did to select a SPDIF transformer. So, Murata DA102.
Note transformers don't care about the 75R impedance. They do introcude a discontinuity though, so the length of transmission like from the transformer to the receiver should be kept short.
Unfortunately, composhite has a large low frequency component extending down at least as for as the field sync at 50 or ~60Hz, and really to DC. This makes classical transformers difficult, at least unless followed by a fairly clever DC restore circuit.
The standard solution in the broadcast game back in the day was a 'longitudinal stop coil' aka "Video humbucker" which was a common mode choke wound with small diameter coax on a standard iron transformer core, they were very effective, and are I believe still available.
