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Thread: twisted pair & baluns

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    Cool twisted pair & baluns

    I had a job recently that involved joining two lengths of cat 5 to run video via baluns. I know it isn't the best way but it was unavoidable. Anyway the resultant picture had a broad vertical " ghost " bar slowly moving horizontally across the screen. I checked most things I could think of to no avail. Having said this I didnot see the original quality so it may always have been there. But it got me wondering what effect it would have if the twist direction was one way for the original piece of cable & reverse direction on the joined piece of cable . Any thoughts ?

    CCTV downunder or whoever you might be now ?
    Last edited by watchdog; 06-03-08 at 04:54 PM. Reason: last line



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    Premium Member mal's Avatar
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    When you say join what sort of join any join on cat 5 will cause reflection of signal

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    Is The Camera powered from a different mains supply to where the monitor is ie 2 different buildings? Have you checked picture at camera, tried a different monitor, i have found multiplexers with bad power supplies causing lines accross monitor or you may need to try a humbug at the monitor end.

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    mate, if you ever have to use baluns then my advise would be to use something decent like the NVT ones. I have used these before and never had a problem with them. The other cheapie ones that you can buy seem to cause people problems all the time.

    just my 2c

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    Quote Originally Posted by Chimp View Post
    mate, if you ever have to use baluns then my advise would be to use something decent like the NVT ones. I have used these before and never had a problem with them. The other cheapie ones that you can buy seem to cause people problems all the time.

    just my 2c
    I agree. Also, are the baluns used passive or powered?

    If they are powered you may be looking at a ground loop.

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    Quote Originally Posted by watchdog View Post
    I had a job recently that involved joining two lengths of cat 5 to run video via baluns. I know it isn't the best way but it was unavoidable. Anyway the resultant picture had a broad vertical " ghost " bar slowly moving horizontally across the screen. I checked most things I could think of to no avail. Having said this I didnot see the original quality so it may always have been there. But it got me wondering what effect it would have if the twist direction was one way for the original piece of cable & reverse direction on the joined piece of cable . Any thoughts ?

    CCTV downunder or whoever you might be now ?
    Put a test monitor at the camera and see if the noise is at the camera.

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    Quote Originally Posted by mal View Post
    When you say join what sort of join any join on cat 5 will cause reflection of signal
    No , this is not so. You can interrupt the twist for up to 10% of the wavelength of the carried signal without any major detriment. ( this info is direct from the Telstra Research Labs ) They are passive baluns and the power feed is from the same source as the recording equipment but run on the same cat 5 as the video signal. There is no significant voltage drop at the camera & total length of the cat 5 is about 30m. The interference is not readily visible at the camera but it would be hard to see as it is in direct sunlight & my test monitor is only a 3" screen. So what I'm really wondering is what is the effect of reversing the twist halfway along the cat 5 run ?

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    Agree it is low but with data it will resend the packet of corupt data but not so video BTW could you post a link to the Telsra artice would like to read

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    Just had a thought if it is not the camera you could try running coax to the join put the balum there this should help but try first
    Have been thinking about the reversal issue and can't think of any reason it would affect hope this helps

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    Quote Originally Posted by mal View Post
    Agree it is low but with data it will resend the packet of corupt data but not so video BTW could you post a link to the Telsra artice would like to read
    The original info is about 10yrs old from when I was working with them but there was a recent article about it in the last Home Automation magazine , I'm trying to find it but may have thrown it out.

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    Part of the standards for Cat5 cables is that the paiers have different twist rates to stop adjacent pairs cross talk levels going above a certain point. Sheilded cable might be another solution, I have one office in a demountable building at work that picks up a heap of mains hum for no reason that I can see and I want to redo it in Cat5 shielded and see if that works.

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    Quote Originally Posted by watchdog View Post
    The original info is about 10yrs old from when I was working with them but there was a recent article about it in the last Home Automation magazine , I'm trying to find it but may have thrown it out.
    I can't find the magazine. I'm now thinking it was an article that was worth keeping , so if anybody finds it I would like a copy

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    Watchdog, it the cat5 segregated along its run?

    Have you tried running a length of Cat5 between the camera and DVR on the floor to eliminate the cat5 from the equation?

    Have you tried a different camera from another location?

    I think the cat5 is inducing hum, maybe run along mains, as for the balun it is only there to balance the 75ohm on twisted pair so cross talk and twist ratios are not a problem as this is an analogue signal 1vp-p. i.e. not packet data getting kicked back or resent.

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    Quote Originally Posted by mal View Post
    Agree it is low but with data it will resend the packet of corupt data but not so video BTW could you post a link to the Telsra artice would like to read
    If you are still interested I have a new copy being sent & will post it when received

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    Just wondering if you sorted this one out? As a matter of interest how long is the cable run? I know from experience cat5e has a significantly shorter maximum cable distance than cat6, even when using powered baluns. Will post back when I get the actual specs. I have only used NVT ones, so different makes may have different specs perhaps?

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    Distance changes with baluns Disgruntled. They can go upto 2.4kms if the correct ones are used.

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    Hi disgruntled,

    Have a good look around, even the cheapy baluns work, have used quite a few..

    We have achieved 610m out of colour over cat5, 2 box's side by side,
    the specs says 300 m colour, 600m black and white.

    If you use amplified baluns (powered) you can reach 1200 + m's, I haven't tried 2.4kms) but it may work, I don't know that you'd want to send a signal that far, when you could just use a video servo and chuck and Ip in it and then view over lan/wan.. Id be more inclined to go that way as we have done for several companies who are reasonably closely located, but the video server could be accessed from anywhere in the world really.

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    digging up an old post here, but had the same problem today after installing a Pacom all in one camera on a shed, some 40 metres away from the main building which housed the DVR.

    On power up, found the same ghost bars described by watchdog.

    The outcome was there was a difference in the earth potential between the DVR and the metal pole we mounted the camera too.

    The Solution?

    The patented plastic bread cutting board camera isolation kit between the pole and the camera.

    Camera no longer earths itself through it's chassis to the pole.


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    Yeah the pacoms are bad for earth loops,

    Had some storage sheds that have 2 different potentials, I have used the bread board (plastic) ages ago on one site that had to have camera power at the cameras (12) so varied highly because of the soil.

    I always use the plastic flip top lid housings, never had an issue with them, also insulate bnc's at the dvr end.

    You can buy isolators (under $30 each) we got some recently, fixed an issue big time. about the size of a single channel balun.

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