Best was to lengthen RG59 cable?

[the toss 0]

Copy & paste from "transmission Engineering Principles"

 

Despite being shielded, interference can occur on coaxial cable lines. Susceptibility to interference has little relationship to broad cable type designations (e.g. RG-59, RG-6) but is strongly related to the composition and configuration of the cable's shielding. For cable television, with frequencies extending well into the UHF range, a foil shield is normally provided, and will provide total coverage as well as high effectiveness against high-frequency interference. Foil shielding is ordinarily accompanied by a tinned copper or aluminum braid shield, with anywhere from 60 to 95% coverage. The braid is important to shield effectiveness because (1) it is more effective than foil at absorbing low-frequency interference, (2) it provides higher conductivity to ground than foil, and (3) it makes attaching a connector easier and more reliable. "Quad-shield" cable, using two low-coverage aluminum braid shields and two layers of foil, is often used in situations involving troublesome interference, but is less effective than a single layer of foil and single high-coverage copper braid shield such as is found on broadcast-quality precision video cable.

 

You are distorting my words. I have not said that foil does not block interference. What I said was foil shielding was not particularly effective at CCTV baseband frequencies , it was designed for UHF.

Skin effect is irrelevant to the disscussion & only comes into effect (to any great extent) above a couple of hundred Mhz.

The whole purpose of the drain wire is to provide a "reliable" signal earth since aluminium foil is a totally unreliable conductor especially at the termination points. You talk about the foil needing enough copper to provide a "return" for the signal. You seem to be confusing your DC fundamentals with your transmission principles. We are talking negligable current for a 1Vpp composite video signal.

Why do you worry about DC resistance on a transmission line that is transporting a 5.5Mhz signal & where did you get the idea that CCTV operates at 25 - 30 Hz. All this cable is designed for a purpose & all have specific limitations. Work within the design parameters & you should have no problems. Use cable NOT designed for the job & it may work with varying degrees of success depending on the demands you place on it .

Now that you have informed me that braided shield RG6 is produced I'll go back & modify my original position. RG6 with foil shield is "not the best choice" for CCTV usage.

 

I'll not continue with this thread because any thread that narrows down to two participants with differing views inevitably become a slanging match.

The ccs cable you talk about is simply a con job pulled on the consumer probably by the same people that sell the 3" computer speakers that handle 500W each.

[survtech 0]

BCCS cable is quite valid for RF. Most homes are wired with it. In fact, CATV, MATV, Satellite ground stations and Cable companies use it, but what do they know? They've all fallen for the "con job".

 

Do you have any idea what the vertical sync signal frequency is? Try 25Hz (PAL) and 30Hz (actually 29.94Hz color) (NTSC).

 

OK. You're an "Installer and Trainer". I have an engineering degree with >45 years experience in electronics and ~20 years experience in CCTV system design, installation, troubleshooting and repair. But of course, you're correct.

[the toss 0]

BCCS cable is quite valid for RF. Most homes are wired with it. In fact, CATV, MATV, Satellite ground stations and Cable companies use it, but what do they know? They've all fallen for the "con job".

 

Do you have any idea what the vertical sync signal frequency is? Try 25Hz (PAL) and 30Hz (actually 29.94Hz color) (NTSC).

 

OK. You're an "Installer and Trainer". I have an engineering degree with >45 years experience in electronics and ~20 years experience in CCTV system design, installation, troubleshooting and repair. But of course, you're correct.

 

OK , I'll be sucked back in just once.

 

CCS cable will work on RF systems over short lengths but don't sit there wondering over problems you may get. Anyway cctv systems are not RF.

25Hz (30Hz) is not the vertical sync it is the frame rate.

I wouldn't waffle on about the DC & 30Hz characteristics of coax when you are ignoring the horizontal sync of 15.75 Khz & chroma signal of 3.58 Mhz.

If you want to talk qualifications - Electronics & Communications Deg (specialising in Transmission systems) 5 yrs of electronics design

11 yrs of Transmission systems (analogue & digital)

7 yrs of Microwave Radio transmission systems

17 yrs of security electronics (my own business)

 

See , I told you it would become a slanging match

 

Forgot to mention - the world didn't end so be happy & have a great Xmas.

[survtech 0]

Analog (baseband) video is not 5 or 6 MHz. It consists of a range of frequencies from around 25/30Hz to 5 or 6 MHz. 25/30Hz is also the frequency of the vertical sync pulse of analog video.

 

With analog video, there are two distinct loss factors: low frequency attenuation and high frequency attenuation. Both are affected by length and cable design.

 

Low frequencies (primarily sync signals) are attenuated by (the essentially DC) cable resistance. In order of highest resistance to lowest: "mini coax", RG59, RG6 and RG11.

 

Put an oscilloscope on a long piece of cable and compare sync pulse shape to the source. You will see that the longer the cable and the higher the resistance (a function of cable diameter and material) the poorer the sync pulse shape becomes. At a certain point, the receiving end will not be able to synchronize the frames. That will happen at a shorter distance with RG59 than with RG6. The low frequency losses will also affect the lower frequency video; causing smearing of the images.

 

Yes, high frequencies can also be attenuated by the cable. In particular, by cable capacitance. The longer the cable, the higher the overall capacitance, thus the larger attenuation of high frequencies. The color burst, at 3.58MHz (4.43MHz PAL) is among the high frequencies that get attenuated by cable capacitance. When the color burst gets sufficiently attenuated, colors become washed out and a monitor may only display black and white images.

 

In short RG6 (assuming all else is equal), with a larger diameter center conductor, will have lower attenuation per foot at low frequencies. Also note that each type (MiniMax, (which equals RG179), RG59, RG6 and RG11) has the same capacitance (16.2pf) per foot, so high frequency attenuation should be the same. Therefor, the only difference between types is the DC resistance.

 

Perhaps you could explain how the progressively larger cable sizes can carry video for longer distances without it depending on the DC resistance?

RG179 = 30Ω/k - 500 feet max distance

RG59 = 10.1Ω/k - 1,200 feet max distance

RG6 = 6.5Ω/k - 1,800 feet max distance

RG11 = 2.6Ω/k - 2,200 feet max distance

 

FYI, Here's a link to a nice CCTV cable reference. Note the maximum distances for each cable type.: West Penn Wire - Security - CCTV Product Line

Edited December 22, 2012 by Guest

[ak357 0]

Any of you The Toss or Survtech want to buy Leader NTSC generator ?

also I have Hitachi 60 meg scope with digital readout

[survtech 0]

Not terribly useful for IP.

[aibudo 0]

"This cable", "that cable". Use whatever cable that you've used in the past and are happy with. There are getting to be as many different different cable's and spec's as there are opinions. If it has worked for you, use it. If it has caused issues, don't. 55 years in the electronics industry and that is my "opinion"!

 

Engineers design a product and technicians make it work!

 

Dennis