Hi ,
We have a CCTV cam (Bosh WZ18) that is 1500 feet from the LCD display.
The cable that was used is a RG59 and having 2 splices (2 junctions).
The video signal is poor , we can see tha image but with lines and it's noisy.
Is there a way to improve or "rebuild" the signal ?
I tried a VID-AMP SPECO / PROVIDEO VID-AMP 1 IN / 1 OUT VIDEO AMPLIFIER but did not help.
A few questions to maybe lead you to the problem... Do you have a good picture when the display is connected close to the camera? If not, then either the camera or the display is bad. If yes, then the coax or the splices might be bad. Does the picture degrade when the amp is connected? Where do you have the video amp installed? It should be close to the camera; not the display. Are the camera and amp getting good power? Are the spliced connections clean and dry? Is the coax in good shape? Is it old?
-- David dgminala at mediacombb dot net
s, then
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Hi , it's a brand new cable. Splices are good. Signal at the CAM is good. I cannot connect the AMP to the CAM side , only at the Display side. That's an issue.
I thing the problem here is the lenght of the cable. Usually , RG6 would be better and less than 1000 feet. 1500 feet is very long.
Thanks
"benitos"
I cannot connect the AMP to the CAM side , only at the Display side. That's an issue.
** How are you getting power to the camera ?( runs on 12V DC or 24VAC at about 4 watts )
... Phil
I put 24VAC to the CAM now.
On DC12 , cable is too long ,was getting 6.5 volts to the CAM.
Much too long a cable.
Intersil makes a line of video equalizer chips that will correct the video signal for frequency dependent line losses:
There are different chips for different for different lengths.
The problem is that these chips were not really intended to operate as an external line driver/receiver pair, but rather to be designed into the camera. There may be such coax cable video equalizer driver/receiver pairs, but I couldn't find any. All I can find are video coax extender kits, such as:
-- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558
I forgot the data sheet. Note the photos of the video quality:
-- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558
Putting an amp at the dislay end just amplifies signal plus noise, it must be closer to the camera so that it only amplifies signal and not noise.....
"Phil Allison" :
Putting an amp at the dislay end just amplifies signal plus noise, it must be closer to the camera so that it only amplifies signal and not noise.....
** Where is this mysterious extra noise coming from ??The self noise of a 75 ohm source in a 5 MHz bandwidth ( circa 1uV ) is not relevant to a 1 volt video signal.
The antenna problem, where one is dealing with uV level signals, is another kettle of fish.
.... Phil
It's not a S/N problem. It's the change in group delay across the video frequency range that's distorting the parts of the NTSC video. Throw in a -6dB/octave loss to trash the amplitude. See the photos near the bottom of:
Instead of an adaptive equalizer, it can be done with a passive equalizer, followed by an amplifier to compensate for the losses. The adaptive equalizer adjusts itself, while the passive equalizer and amp design requires level adjustment. When something changes in the cabling, the levels need to be re-adjusted.
Typical video distribution amplifier:
Claims "3000 feet of Belden RG59U to within +/-0.05dB at 5MHz". Probably overkill for a security camera.
This design works to 250ft. More amplifier gain will be required for
1500ft.Here's another example. Claims 1000ft or more:
-- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558
"benitos"
** That sounds like you have a ground loop in the cabling passing noise into the shield of the RG59.Your 24VAC may well be the source.
Or possibly injection from AC power cables running along with the RG59.
Whatever, the pic should not contain noise or lines.
.... Phil
nto
Right , there is a 400VAC passing near in the ground.
Is it possible to remove noise at the Display end?
"benitos" "Phil Allison" "benitos"
Right , there is a 400VAC passing near in the ground.
Is it possible to remove noise at the Display end?
** Find the cause and fix that.If there is a common ground connection between the 24VAC and the RG59 - that is it.
Co-axial cables are good at rejecting external magnetic field interference - but may be subject to an AC electric field that runs alongside for 1500 feet.
.... Phil
e -
Perhaps a better 75 ohm cable like RG11 might help, but it will get quite expensive. Lenny
e -
No , I did not ground the RG to the 24VAC
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