Problems CCTV

[Guest Ed raket]

I have put a camera with two monitors and a timelaps recorder in a factory.

The distance between cam and monitor 1 +/- 80 meters. Impedance switch on High

The distance between monitor 1 and monitor 2 , impendance switch on Low +/- 120 meters.

I have used RG 6 coax cables

When we check the monitors , theres alwast a fault on the picture , a wave going up and down over the screens , very slowly ?

Where that wave comming from , how can i fix it ,

Any idee's ?

[Guest Peter James]

Sounds like noise try a hum bug,

Does it go to the vcr then monitor 1 then 2? Or mon 1 then 2 then vcr?

Im not famliar with RG6 is this a low loss coax like RG11 ?

You may of been better off using a twisted pair and two balums for that sort of distance

Pete

[Guest Ed raket]

Hello Pete ,

Thanks for the replay ,

Some more information : The cable RG 6 it is indeed a low loss coax +/- 1 cm diam.

I have place the VCR near the end , between monitor 1 and 2 ,

the distance between the VCR and monitor 2 , its aprox 1,5m.

So a person in the room of monitor 2 can check the recorder tape on that monitor .

Whats a balum ? I think its a impedance transformer ?

( Used on home made transmit antenne when I was a radio amateur )

Already check my grossier for a twisted pair system until 1 Km :

costprice 510,00

[Guest Peter James]

Hi ED

A balum is a small transeiver that will let you send video down Cat 5 or a twisted pair. They come as passive (non powered) or powered passive will work upto 150m and trades at around £6.00 (6 GBP) powered transmit much further Ive seen them advertised to transmitt upto 2.4km trade around £22.00 (22 GBP).

You need two transievers one at each end.

I will PM you a web page to look at.

Pete

[Guest Ed raket]

Hello pete , again thanks for the reaply .

I have look to the site of SSAM , and sent already a mail to have some more info on that stuf to use twisted pair cables ( next time )

I also check some suppliers over here on that material : Gardiner Security , will send me some more details .

btw my country its Belgium.

I will keep You inform on the matter .

Greetings

Ed.

[Guest Andyp]

This problem looks like it is a cable problem or possible electrical interferance as Pete said. Check that the cable route isnt next to a mains cable or other high voltage cables.

Also check that the equipment isnt connected to the same fuse/ breaker as a high draw piece of kit such as air conditioning or similar.

Check the equipment is all on the same phase of the supply (not a electrician so cant help you with how to do that).

One final check is that you havent set the monitors up incorrectly with regards to termination.

Hopefully the above should help, these checks should solve 90% of problems.

Good Luck

[Guest Andyp]

Just an addition to the last post, try switching the impedence switches, ie high on monitor 2 and low on monitor 1. It might just be end of day brain drain but that sounds the wrong way round to me!

[JB_]

Cheap power supplies can also cause lines on your picture, you haven't said what voltage these cameras run on so far, but in the past a cheap and nasty plug in 12volt psu has caused probs for me, always best to use a high quality steel boxed psu. Not sure if it would work, but if it is a 12volt camera try running it on battery power alone with no connections to the mains see if it clears up. All a bit of a stab in the dark really.

[ian.cant]

I know its way too late but.........

There seems to be a few problems here. First of all the cable type is incorrect, RG6 is a satelite tv cable and while it will give you pictures at the other end they will more likely give a picture with problems, especially at distance.

Use RG59 preferably which should give good pictures up to 300mtrs max, or URM70.

The i mpedance or termination settings are correct, in other words the last device is terminated or set at 75ohms.

The humbars you are seeing is generally a ground loop. Ground loops occur when the earth potential at the camera is different from the potential at the monitor. This difference may only be a small voltage but it can cause large currents to flow through the shield of the coaxial cable.

However i suspect there is also a major problem with running the coax next to mains cables here. Mains pick up occurs when coaxial cable runs in parallel to a power cable. A sinusoidal voltage develops on both the shield and the video core. This is often seen as a "hum bar" passing down the screen.

The solution to both these faults is quite simple, fit a Humbug (as Peter mentioned earlier) which is a ground loop transformer, but you must fit the Humbug before the first monitor (at the monitor end not the camera end).

Provided there are no other installation faults such as proper connectors used, screen not touching earth etc then this should solve the problem.

[breff]

I have had this problem before and agree with Ian about ground loop. We changed the cameras to 12volt cameras(fitting psus at the cameras) and the problem disappeared. We had already tried a humbug but it didnt work.