Guest rickster Posted February 25, 2005 Posted February 25, 2005 Hello, I'm a new member here and want to say thanks in advance for this forum. I have a fairly unique problem with a surveillance system. I'm getting RF interference from a nearby (300 yards) FM transmitter into my 4 camera video supply lines. Having several guy wired 400'-500' RG6 cable runs exposed on utility poles doesn't help matters any. Installing a wireless video tx/rx helped alleviate some RFI on a couple of cams and I actually got usable video with them. Not so lucky on the other two. When I inherited this system, it had AC powered cams. Switching to DC cams with metal housings helped reduce the RF substantually but not enough to be 100% stable. Chroma comes and goes and distortion happens frequently. It has been a royal pain to say the least! If anyone has any suggestions or would like more technical or equipment info to help with a response let me know. Otherwise, my next course of action is to run the cable in grounded metallic conduit and take the conduit right to the cam housing. Frankly, it's probably what I should've done to start with. But even this may not cure it being so close to the radio tower. If anyone else has run into a similar problem and cured it please take a few minutes to reply. My neck isn't on the line...just my pride! Many thanks again. TIA, Rick H
Brian c Posted February 25, 2005 Posted February 25, 2005 One word.......humbug! or a video loop isolation transformer. fit each input through one of these and bo should be your uncle. If you don't know......ask.
Monteey Posted February 25, 2005 Posted February 25, 2005 Hmm i guess another possible way of doing it would be running fibres then using convertors each end, probably not economically viable though Mark Hawks Ex BT Openreach Field Service Now Self employed telecom and data engineer www.mphtelecom.co.uk Also back doing sub contract work in the security industry. Retained firefighter Devon and Somerset Fire and Rescue
Doktor Jon Posted February 25, 2005 Posted February 25, 2005 ricksterI'm getting RF interference from a nearby (300 yards) FM transmitter into my 4 camera video supply lines. Having several guy wired 400'-500' RG6 cable runs exposed on utility poles doesn't help matters any. Installing a wireless video tx/rx helped alleviate some RFI on a couple of cams and I actually got usable video with them. Not so lucky on the other two. When I inherited this system, it had AC powered cams. Switching to DC cams with metal housings helped reduce the RF substantually but not enough to be 100% stable. Chroma comes and goes and distortion happens frequently. hi rickster, Just wanted to clarify one point; the guys have suggested you use a video isolation transformer which is the classic remedy for Earth Loop Hum (ELH). Now forgive me if I'm way off the mark, but you believe that the problem is RF being picked up by the cables, and yet the symptoms you describe sound like classic ELH. The slightly confusing issue is that changing from AC to DC cameras wouldn't ordinarily make any difference to a radiated pick up problem, unless the AC cameras were less well shielded against airborne interference. If you haven't already done so, it would be well worth testing the remaining two cabled cameras to see if earth loop isn't at least part of the problem (I'm guessing it possibly is). If you have a battery powered test monitor, check the signal quality by connecting directly to the BNC outlet on a problem camera. If you don't have a battery test monitor, use a mains powered monitor from the nearest mains feed to the camera itself. The chances of ELH in this situation would be virtually nil. If the picture is o.k., reconnect the main video cable and test again at the other end without connecting to anything else. If you have to use a mains powered monitor and the problem is present, remove the mains plug and just for testing purposes only , temporarily disconnect and insulate away the earth conductor. With a clear picture, the chances are it is ELH, in which case the suggestion of an Isolation Transformer on each camera cable is the simplest and cheapest way to go. If the problem still exists, then it is definitely air borne interference, and trying to filter it out will undoubtedly be problematic (an Isolation Transformer is unlikely to solve that problem). There would be a number of options to consider, but if you have already had some success with licence exempt microwave transmission, you could certainly consider changing over the two remaining cameras, using double screened co-ax or active UTP from camera to transmitter, and receiver to monitor. Let us know how you get on. D.J. P.S. Don't forget to reconnect the earth conductor in the monitor plug!
Guest IM_Alarms Posted February 25, 2005 Posted February 25, 2005 I had a similar problem with a redcare line, so I know what you are going through. Like Doktor Jon, I think you should try fibre. Do you know if the interference is picked up by the camera circuitry? or the transmission path?
ian.cant Posted February 26, 2005 Posted February 26, 2005 Excellent work Dr John, i would agree and suggest NVT baluns tho? Way cheaper than fibre and will do the job im sure. I wouldnt use the cheap versions though only NVT stuff. Check out theyre webby which is here.
Guest rickster Posted February 28, 2005 Posted February 28, 2005 Thanks for all the replies. I do indeed have a battery powered TFT monitor and get excellent video directly at all the cams. The vid quality is then lost to a different degree from each transmission line before plugging into the vid capture card(GV604). Each line is a solid run with no splices. The cabling (RG6 siamese) is attached to guy wire for stress relief between utility poles. The wireless setup unfortunately didn't work very well on the remaining two cams. The business has massive RFI in it's phone lines also. It is like having built-in MusicOnHold. They can't get the radio station or the phone company to take responsibility. I turned down another job close to this same radio tower as a result of this job. The vender doing it is having his own nightmares with it too. Yes - the AC powered cams were less shielded than the DC ones. The fiber sounds like it would work. I don't have much experience with fiber other than ADAT/Toslink from audio recording experience. These are analog cams with a PC based digital software recorder I'm using currently. Fiber sounds like a complete revamp? Please tell me more... I will look at the NVT baluns also. TIA, rick
Guest rickster Posted March 1, 2005 Posted March 1, 2005 Hello again, I ordered two of the NVT NV-214A-M passive baluns to try on the closest cam. It's about 50' away from the DVR. I will wired this up with cat5e using one of the twisted pairs within. I may have to go with an NV-214A-M and NV
Nova-Security Posted March 1, 2005 Posted March 1, 2005 Humbug wont clear RF interference and fibre would be too costly. Take Ian.Cant & Doktor Jon advice and use NVT cat 5 Tx Rx system we have used these on problem jobs work very well, and cat 5 cable is cheap. www.nova-security.co.uk www.nsiapproved.co.uk No PMs please unless i know you or you are using this board with your proper name.
Doktor Jon Posted March 1, 2005 Posted March 1, 2005 ian.cantExcellent work Dr John, i would agree and suggest NVT baluns tho? Way cheaper than fibre and will do the job im sure. I wouldnt use the cheap versions though only NVT stuff. Check out theyre webby I must be getting on, 'cos I don't even remember suggesting fibre Over what is a relative short distance, fibre would be a luxurious solution, but prohibitively expensive. I'd certainly agree that quality UTP would be the obvious way to go. Hope it works for you rickster.
Recommended Posts
Archived
This topic is now archived and is closed to further replies.