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Topic Title: Closed Circuit Television Problem.
Topic Summary: C.C.T.V.
Created On: 27 October 2017 06:00 PM
Status: Read Only
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 27 October 2017 06:00 PM
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Zoomup

Posts: 3364
Joined: 20 February 2014

Hello All,
a customer of mine has a plug and play C.C.T.V. system. He recently suspected a camera as a failure. The camera was replaced and the cable also was replaced. The cable is very long, much too long in fact. But was connected up temporarily to test the new camera. The cable carries 12 Volt d.c. and a coax for the signal. Although the camera is a colour camera it only shows black and white on the monitor. Could the new long cable (partly coiled up with many turns of cable) be attenuating the camera's signal and only allowing a black and white image on the monitor?

Thanks Mike, I think that this is a question for you.

Bye,

Z.
 27 October 2017 06:14 PM
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mapj1

Posts: 9550
Joined: 22 July 2004

Is this a PAL video system? If so, perhaps possible , as the colour is transmitted as phase modulation on a sub-carrier at about 4MHz. You may not notice in the picture if there is a high frequency loss, the effect is to reduces the closeness of vertical lines per inch you can see, so that fine stripes fuzz together, but the monitor will know if the subcarrier is too low to detect.

wikki article on PAL and NTSC

However, it is a bit of long shot, not one I have seen before. Is it possible to bring the camera and monitor closer by a short bit of cable to see if suddenly it leaps into life ?
How long a cable and what type - I can look up the loss curves for you.

If not a lower loss cable or some kind of repeater may be in order. Or an IP camera.

-------------------------
regards Mike
 27 October 2017 07:15 PM
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AJJewsbury

Posts: 15990
Joined: 13 August 2003

Many colour CCTV cameras will switch into black and white mode at night (it's actually Infrared mode really) - any chance the camera has been fooled into thinking it's dark?
- Andy.
 27 October 2017 08:00 PM
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Zoomup

Posts: 3364
Joined: 20 February 2014

The maker is Swann. The system comes with plug and play pre-made ends on the cables. A 12 Volt plug and a B.N.C. signal plug and socket. I do not know what system the thing works on. The other cameras were working in colour whilst this one just displayed as black and white. It is positioned outdoors and the problem showed up during the daytime.

Interestingly I was quickly shown a power supply that had a plastic case which had burned a hole in the side and I could see what appeared to be part of a transformer. Near it was what appeared to be a coax cable which had singed and melted insulation. It appeared that the transformer power supply had got hot and had damaged the adjacent coax cable. The makers' service engineer when he attended said that this occurred due to a mutual "interference" between the coax cable and power supply unit. The cable had been in contact with the power supply's plastic case at the time of the incident. I condemned the power supply as being a fire risk, but the owner has kept it in service, despite having a charred hole in the case.

Z.
 27 October 2017 09:13 PM
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Fm

Posts: 1733
Joined: 24 August 2011

Hope you are using a colour monitor??
 28 October 2017 10:28 AM
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Zoomup

Posts: 3364
Joined: 20 February 2014

Originally posted by: Fm

Hope you are using a colour monitor??


Yes FM, the camera and monitor are colour types. The other colour cameras on the system work well.

Z.
 29 October 2017 03:27 PM
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kellyselectric

Posts: 185
Joined: 22 July 2016

Mutual interference? What a load of rubber that engineer was talking g a load of tosh most likely the coax developed a short in the PSU box and thats what caused the problem. The lack of color could be down to low voltage to that one camera or possibly the color information is being attenuated because the coax is in poor condition remember it doesn't need a hard short to muck up video signals just a poor connection can do it
 29 October 2017 04:05 PM
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Zoomup

Posts: 3364
Joined: 20 February 2014

Originally posted by: kellyselectric

Mutual interference? What a load of rubber that engineer was talking g a load of tosh most likely the coax developed a short in the PSU box and thats what caused the problem. The lack of color could be down to low voltage to that one camera or possibly the color information is being attenuated because the coax is in poor condition remember it doesn't need a hard short to muck up video signals just a poor connection can do it


Yes the engineer did not even bring a computer mouse to adjust the digital recorder box when required. The new camera cable is very long, so perhaps that is the problem. The customer just quickly connected it to check the camera. The cables are ready made in set lengths by the maker. It is a D.I.Y. plug and play system.

Some cables were run outside with no proper protection from the weather at joints, just tape wrapped, a real bodge. The householder is a retired crab fisherman so not really electrically qualified. Although I was impressed by some self amalgamating tape. It had done a good job in certain places at joints outside.

Z.
 29 October 2017 09:20 PM
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kellyselectric

Posts: 185
Joined: 22 July 2016

It could well be water in the coax this will increase losses at video frequently as well as causing a partial short at DC ide be tempted to just rip it all out and start afresh but I know thats probably not possibleso just get rid of the joints. Not sure how much you know about this sort of thing but a very important factor is to make sure the new coax is the same impedance as the rest of it
 29 October 2017 09:25 PM
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Fm

Posts: 1733
Joined: 24 August 2011

Replace with a cat 5 cable and a couple of baluns to see if its the cable
Or swap over some Of the known working cameras that show colour
 30 October 2017 12:54 AM
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kellyselectric

Posts: 185
Joined: 22 July 2016

I would say do a camera swap first that will prove whether it camera cable ive just had a thought that maybe one cam was damaged when the PSU went on fire so if thats the case all thats needed is repair or replacement of it which is a lot less pain than changing cables
 31 October 2017 08:21 AM
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Zoomup

Posts: 3364
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Thanks,

Z.
 31 October 2017 11:16 AM
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psychicwarrior

Posts: 555
Joined: 18 October 2010

bit late..but saw this on the web re:rg59 coax... is the one you saw longer than 100m...

"It loses only 2.5dB of signal per 100M length and as a rule of thumb, the maximum loss of video signal should be kept to 6dB or less. This equates to a maximum run, without the aid of an amplifier, of 240M. These runs can be extended even further up to 500M when using an amplifier. "
 31 October 2017 02:12 PM
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mapj1

Posts: 9550
Joined: 22 July 2004

I'd be a bit surprised if it is a real RG59, whih tends to be used at VHF/UHF, but it could be, or a well made clone, but note that in any case for all cables the losses are frequency dependant, so the higher frequencies get lost first.
Hence my comment that you may still get a low resolution picture, and lose the colour information.

Twisted pairs like in an ethernet cable are different in the detail but the trends are similar.

I'd not expect the balun dodge to be any better than a good coax. But, is it a good coax ?

I'd agree with others that a quick swap out test with the same camera and receiver and a shorter lead, or a camera that in known to work well on another cable will indicate where to addres the efforts

3dB is half your power lost to warming up the line.

-------------------------
regards Mike
 31 October 2017 02:31 PM
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psychicwarrior

Posts: 555
Joined: 18 October 2010

antihum.com rg59 I think the info came from that I quoted; recommended & supplied by some cctv gear wholesalers.
 31 October 2017 03:49 PM
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davezawadi

Posts: 3894
Joined: 26 June 2002

The problem sounds like excessive loss at higher frequencies, as has been suggested. The easiest way to check is to use a short cable and move the monitor close to the camera and see if all is well. The loss is a relative one, the colour frequencies (based around about 4.43 MHz) are attenuated more than the lower frequencies representing the syncs and large blocks of the video. The picture sharpness will be much reduced and there are two ways to correct the problem. The first is to use a bigger and better coax, or the signal may be corrected with an equalising amplifier, where the amplitude (and possibly phase (delay)) of the signal components may be adjusted with various controls. This adjustment is one of the main uses of the colour bar test signal which you may have seen accidentally broadcast. The adjustment is easy if you view the signal on an oscilloscope. The phase is adjusted using a modulated pulse and bar test signal , which is almost never seen outside a broadcast system. Such units are available from broadcast suppliers but are quite expensive. The horrible cables (power and video about 3mm diameter) supplied with these systems are very poor and really should only be used up to perhaps 10m for best results. Much better is RG59 proper copper cable with attached power twin, available from CPC. (Pt no CB17825).

-------------------------
David
BSc CEng MIET
david@ZawadiSoundAndLighting.co.uk
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