Stuartbe 0 Posted July 9, 2011 Hello all My name is stuart, Im new to the forum but have been in the security industry most of my life starting in the navy many years ago. Evryone seems helpfull from what I have read so far so im hoping for help with this issue that is driving me mad. Right... I line in a complex that has flats above and retail units bellow. I run my firm from downstairs and upstairs I have a prety standard pro type 8ch DVR. There are several cammera's all over the site. We have had a lot of crime arround the back recently and another bussiness and I decided to join forces. The other unit has a 4ch dvr system setup. What we want to do is send the output from my system to a monitor in his unit and an output from his sytem to mine so we can both keep an eye out and help each other, Simple enough but here is the problem. We are both of different phases in the complex. When connecting the units together we get heavy ghosting and distortion as expected. I checked and there is 1.3v floating between the cable from his unit to the ground on my unit. First try was to get some video ground loop isolators. These have hepled but not cured the problem. I am able to see his and he is able to see mine but if we do both at the same time the problem re-appears. I am allmost 100% sure this is some sort of ground loop issue and I am hoping you guys can help. This is the layout roughly bellow. My DVR bnc out......Ground loop isolator......twin coax cable core 1...........his monitor His dvr bnc out......second core of twin coax.... ground loop isolator.... into ch8 input on my dvr I can use one of the other but not both at the same time. I am thinking I need some way of sending video to him and visa versa with no ground potential between the two of us, IE fibre but thats a bit beyond the budget. When I say twin coax its actualy a cctv cable with a yellow and white phone and a power connection. I have made sure they dont have foil shield in common and grounded it one end only, Does anyone have any idea's or suggestions that may help me please. I would be very greatfull. Many Thanks for taking the time to read this. Stuart Share this post Link to post Share on other sites
SDM Group 0 Posted July 9, 2011 Why don't you do it via network log in to the DVR's Share this post Link to post Share on other sites
rory 0 Posted July 9, 2011 Also what kind of cable is that being used? It doesnt sound like CCTV Coax? Coax doesnt come with phone wire or yellow wire. Share this post Link to post Share on other sites
rory 0 Posted July 9, 2011 Why don't you do it via network log in to the DVR's This might be the best option. Get a couple cheap PCs and just have the network software auto login to the DVR and come up on OS startup. Share this post Link to post Share on other sites
Stuartbe 0 Posted July 10, 2011 Thanks for taking the time to reply all The cable in question is foiled cable with 4 internal conductors. The foil shielding is grounded at my and not the other. It is a cable that was allready there and is the diy type cctv link cable that comes with a BNC and DC power connector on each end. I was going to install new 75ohm dual coax such as the type sky uses but I dont think that will solve the ground issue. The trouble is I dont think Baluns will help as they down lift the ground unless I use active both ends and that can create problems. As there are several volts between the grounds I am thinking of running the monitor in the other shop/unit from my end so we both are connected to the same power supply. All that is at the other end from me is a single lcd tv/monitor with a composite video input. I am sure that the earth from the lcd at the other building is creating the loop and I am sure optical isolation will be the best solution. The monitor in the other unit runs from a switch mode PSU and I have noticed that the -ov on the psu is common with the outer ground of the phono. This is why I am thinking of having the PSU at my end running a 12v cable to the other end to power the monitor. Thanks very much for your help so far guys. Do you think it is an earth/loop issue that is creating this issue ? Many thanks again Stuart Share this post Link to post Share on other sites
tomcctv 187 Posted July 11, 2011 HI Stuartbe. it sounds like you are using alarm foil data cable. which is not a good cable to use. and if you are not using baluns at the moment. i would just pop one on each end. but before you do anything we need more info. how far are the DVRs apart from each other. are you using the monitor out on each unit ??? (you may also need to boost it) Share this post Link to post Share on other sites
Blake CCTV 3 Posted July 11, 2011 you are right it is a type of ground loop hum compounded by the different phase. running the reomte monitor from the local psu should help I had this problem once and found it was because of a different phase. If you're not that far apart have you thought of a using a good wireless link which will eliminate any phase/earth problem. I always steer clear of wireless links but this may be the best budget solution Share this post Link to post Share on other sites
Stuartbe 0 Posted July 12, 2011 (edited) Thanks all. You are correct about the cable type it is indeed foil wrapped TP cable. Blake TV get out my head. Last night I was thinking of running two propper coax cables sky shotgun type I think and a mains feed so three cables to the other unit. One coax from the call monitor out on my dvr to the monitor in the other unit and the mains feed would come from my end and my ups ect and would be wired into the monitor at the other end. The other coax would come from the other units monitor/call out and then connect into ch8 on my dvr by a ground loop isolator. I think this is going to be the best way to go. What is strange is that It works fine if the signal goes from me to him only and fine if it goes from him to me but not both at the same time... Very strange. The way I am trying to picture it is that allthough the call out monitor is in the other unit both its power and signal come from my end this should isolate it from any nuetral or earth loops. NB will keep the old FTP cable and use that for alarm signaling I think. I wont have to worry about ground loops there as it will all be relay switched. Wireless link is not something I want to use for security mainly but could be a last case use thought I think the idea above will work. Thoughts gents pls.... And thanks again for your assistance. PS.... Rough diagram attatched Edited July 12, 2011 by Guest Share this post Link to post Share on other sites
rory 0 Posted July 12, 2011 HI Stuartbe. it sounds like you are using alarm foil data cable. which is not a good cable to use. and if you are not using baluns at the moment. i would just pop one on each end. but before you do anything we need more info. how far are the DVRs apart from each other. are you using the monitor out on each unit ??? (you may also need to boost it) I just found this on a residential job I went to check, they had no picture on one camera and barely a picture on another .. but promised they saw the cable working at another job ... was like okay .. hooked it all up anyway since they were paying for the time ... less than 60' distances and full of lines .. switching it out for RG59 siamese. Share this post Link to post Share on other sites
