pig 0 Posted May 10, 2015 Hi, I have a 4CH CCTV system installed. Whenever a high powered appliance is switched on (e.g. hair dryer, lawnmower), the picture goes very dark especially around the edges and large hum bars appear going across and down the monitors which are wired with RG59 coax. I have connected a 1M cable direct from the DVR to a monitor and the problem does not occur. Any suggestions? Regards. Share this post Link to post Share on other sites
the toss 0 Posted May 10, 2015 From the info you have supplied it would seem to be caused by EMI which would indicate poor shielding and /or earthing. You give very little info as to cable distances & types. So more info please Share this post Link to post Share on other sites
pig 0 Posted May 11, 2015 The DVR has a T-piece BNC splitter on it. From this splitter, one feed runs to one monitor (which is unaffected by this interference), and then a 15M run of RG59 runs to another T-piece in the second room. One feed then goes to a monitor and the other feed is then run by a 15M RCA cable to the final monitor (which is a TV). These two both suffer from the same interference. I have tried plugging the RG59 feed directly into the monitor in the second room which solves most of the intereference, but still some of the screen corners appear black. Any remedies? Thanks for your help. Share this post Link to post Share on other sites
the toss 0 Posted May 13, 2015 You have demonstrated the effect of multiple terminations while ignoring impedance matching. The first split (over a short run) to your first monitor is ok , the second split to the second monitor is useable and the third split to the TV ( over shielded audio cable) is the longest run & is terrible. To start with replace that thin audio cable terminated with RCA's with 75^ coax. If the monitors you are using are really monitors then they should have a switch to set the input impedance to either 75^ or high impedance ( may be labelled "term or bridgeing") All monitors should be set for high impedance except the last ( furtherest) which should be set for terminated (75^). This method is only good for 2 or three monitors at most and after that you will need to be using a VDA (video distribution amp) Share this post Link to post Share on other sites
