Hi Everyone, I have recently taken on a CCTV job and i was wondering if using RG6 Quad Shielded 18AWG cable is the best to use. Is there any disadvantages to using such a high quality cable. I was told RG59/U is the way to go, but i've also heard that it has losses over a 20 metre run. Anybody's help will be much appreciated.
Hi there Brite-Spark!. It really depends what's around the area where you are installing the coax and the length of the run. Personally I think that standard RG-6/U coax would be more than adequate for this application. That's all I've used in the past and never had any problems.
#144238 - 10/26/0508:41 PMRe: Whats a Better Coax For CCTV Applications
Given that you're dealing with baseband video with a bandwidth of 50Hz to about 5MHz, the losses of RG59 are very low in comparison to it's usual use at VHF and UHF. Even for VHF, a 20m run of RG59 does not cause concern. One of the instruments I work with is a video signal test rack where by means of a swtiching unit and pattern generator, baseband video can be fed through a number of different things to observe the effects. Such things include attenuators, filters, equalisers, and relevant to this topic, a 300m roll of military grade RG59 which would be about 25 years old. Compared to a straight through connection, there is a slight loss of contrast (ie. there's less than 1Vp-p of video at the end of the coax) when the 300m length of coax is placed in the signal path. Otherwise there doesn't appear to be any degradation. Winding up the contrast slightly on the monitor and you wouldn't even know. RG6 has lower loss than RG59 and is rapidly taking over with cable, satellite, and digital TV. The cost difference isn't as high as it once was, but beware of some really cheap nasty cable out there. To answer the question, it would be much more than 20m before worrying about the loss of RG59. There is certainly no disadvantage in using RG6.
#144239 - 10/27/0512:44 AMRe: Whats a Better Coax For CCTV Applications
What should I be looking for to check if its a bad quality cable?
The better quality co-axial cables have the foil sheilding bonded to the dielectric insulation over the centre conductor. Also, the shielding braid should be tinned copper and should be as thick as possible. I'd also go with a coax that has either a foam or an air-spaced dielectric covering on the centre conductor. I'd avoid any cables that have a stranded centre conductor, I've had nothing but problems with this sort of cable, especially when using it with F-type connectors. I have to agree with Aussie though, there are some really dodgy cables out there, worst place you can buy it from here in NZ is a DIY store.
#144241 - 10/27/0503:00 PMRe: Whats a Better Coax For CCTV Applications
I've got several 100 metre long RG59 cctv cables installed here, and they are all fine. For baseband video there is no problem with loss so long as you avoid the air-spaced cables. Moisture can get into any cable, but it's worst with the air-spaced types.
Do try to keep the terminations in the dry, as the cheaper nickel plated bnc connectors corrode to a high resistance or even a diode effect. This can be cured with silver plated bncs, as silver oxide is the only conductive oxide, but they are a good bit pricier than nickel plated.
#144242 - 10/27/0509:46 PMRe: Whats a Better Coax For CCTV Applications
Good on ya mate. Don't get me wrong, I have nothing against RG-59 cable at all, or Quad-shield for that matter. Up until a couple of years ago, I was using an entire system of RG-59 here at home and pumping UHF signals down it (Highest frequency 800MHz) with no noticeable picture degradation. I had pretty shortish runs though. Best of luck with your install B/Spark, let us know how it went.
#144245 - 10/28/0503:08 AMRe: Whats a Better Coax For CCTV Applications