The common reason for it is really an earth loop, where a voltage difference has occurred at one end of your coax connection to the reverse of end, with respect to earth.
They'll be seen as different patterns on the screen or maybe cause a Digital video recorder to not record as a result of a distorted sync pulse. Below are a few visible problems you may notice.
There's no point in accusing anyone for these because they are erratic as to if they are likely to manifest but are more common if the security camera is installed in an area which has a different earthing point to the Digital video recorder or screen. For instance a surveillance camera pole isn't grounded to the same place as a structure in which the Digital video recorder is. The truth is you may get ground loops in numerous applications which include audio signals buzzing.
There are a few measuresthat shouldreduce thelikelihood ofhaving an earth loop but not one will prevent them.
- Isolate the camera from your bracket. This involves removing all electrical link between the security cameras housing and the mounting bracket but is only necessary if your mount will be on a conductive area such as a pole or tin.
- When ever putting in the coaxial , make certain there are no nicks in the insulating material due to pulling it around sharp surfaces .
- Wherever possible, connect the earth of both ends with one another. However this is expensive because you will have to install additional copper ground cable to every single camera.
- Install fiber optic connections for the distant surveillance cameras. This might be pricey but has many other merits. You've also eliminated lightning from travelling through your complete system, damaging almost everything. You can actually put multiple security cameras on a single fibre.
Doing a minimum of the first 2 above, should you get an ground loop you can put in a device called an earth loop isolator and the issue shall magically disappear.
The unit is available in various forms such as DIN rail or rack mounted but a good one to carry inside the tool kit is this in-line hum eliminator, which is installed in between your DVR channel and coax going to the camera.