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Diagonal lines on video
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vinnielo



Joined: 19 Feb 2008
Posts: 13
Location: hertbeat Country

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PostPosted: Thu Feb 21, 2008 12:06 am    Post subject: Reply with quote

I've plucked out the extension cable that was included in the kit, i.e. another cable of similar length, but not currently in use.
VERY strangely, I plugged the FTA satellite receiver upstairs to my TV downstairs. Bad hatching. There's probably something about the stairs.

Strange that those stairs also carry the RF from my Sky Digibox donwstairs to my TV card upstairs, and there's no real interference problem. Whatever this is only seems to affect analogue video and not RF.

Or perhaps the FTA->TV problem is ALSO caused by ground loops!
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fsphil



Joined: 09 Mar 2006
Posts: 1598
Location: Cookstown, N.Ireland

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PostPosted: Thu Feb 21, 2008 12:32 am    Post subject: Reply with quote

It sure sounds like a ground loop. Might explain why having the satellite cable plugged in (and grounded) reduces the pattern. It's proximity to the video cable may be helping to balance out any differences in ground. Maybe some kind of difference between your upstairs and downstairs mains. I have to admit I don't know much about grounds loops, and I'm not sure how you could test for that.

Is the nest box camera PSU and the computer on the same floor?

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https://webcam.sanslogic.co.uk/
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vinnielo



Joined: 19 Feb 2008
Posts: 13
Location: hertbeat Country

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PostPosted: Thu Feb 21, 2008 12:39 am    Post subject: Reply with quote

They are, yes. They're on different extension sockets at present, but I did try plugging them both into the same strip. No improvement.

When I was using the camera with the TV downstairs, the mains both came from the same double-socket on the wall, even if split off by different extension strips.
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vinnielo



Joined: 19 Feb 2008
Posts: 13
Location: hertbeat Country

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PostPosted: Thu Feb 21, 2008 12:45 am    Post subject: Reply with quote

Another observation which may be helpful is that before installing the nestbox, I tried testing with both my computer and my TV. The nestbox would have been located in the same room at the time. The cable would mostly have been coiled up. Now, I don't recall seeing any interference lines. Trust me, I would've spotted them if they were there. I'm the kind of guy who can notice if RGB video has been disabled on my TV Wink.
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fsphil



Joined: 09 Mar 2006
Posts: 1598
Location: Cookstown, N.Ireland

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PostPosted: Thu Feb 21, 2008 7:50 pm    Post subject: Reply with quote

If you have a multimeter, disconnect the video cable going into your computer and measure if there is a voltage difference or a current going between the shielding on the plug and the shielding on the socket on your PC. Try with and without the satellite cable connected.
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https://webcam.sanslogic.co.uk/
https://twitter.com/fsphil
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vinnielo



Joined: 19 Feb 2008
Posts: 13
Location: hertbeat Country

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PostPosted: Thu Feb 21, 2008 8:24 pm    Post subject: Reply with quote

I'm afraid I don't have such a tool, and I don't myself using it much should I purchase a kit. I might ask around to see if I can get one lent to me, but I don't think it's something I can easily get hold of.
I think we'd have to assume that there IS a voltage difference and to find a way of overcoming the problem.
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fsphil



Joined: 09 Mar 2006
Posts: 1598
Location: Cookstown, N.Ireland

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PostPosted: Thu Feb 21, 2008 9:02 pm    Post subject: Reply with quote

You could use a ground loop isolator. Genie have one, model GCB01 - CPC sell it for about 23. A fair bit for something that's not guaranteed to work!

Edit: You'd also need appropriate BNC -> Phono adapters if your camera only has a phono output.

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https://webcam.sanslogic.co.uk/
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vinnielo



Joined: 19 Feb 2008
Posts: 13
Location: hertbeat Country

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PostPosted: Thu Feb 21, 2008 9:08 pm    Post subject: Reply with quote

Heh, I was looking for ground loop isolators on eBay and found one for around 5. These were for car stereo systems so I asked the seller if the item was suitable for video. Unfortunately, I got a reply saying it wasn't. Is there any real difference?
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fsphil



Joined: 09 Mar 2006
Posts: 1598
Location: Cookstown, N.Ireland

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PostPosted: Thu Feb 21, 2008 9:12 pm    Post subject: Reply with quote

An audio one probably couldn't handle the high frequencies in video very well, if at all. (22KHz vs. over 5MHz).
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https://webcam.sanslogic.co.uk/
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fsphil



Joined: 09 Mar 2006
Posts: 1598
Location: Cookstown, N.Ireland

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PostPosted: Thu Feb 21, 2008 9:16 pm    Post subject: Reply with quote

You might just get away with connecting two video baluns together. I see someone selling pairs of them on ebay.
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https://webcam.sanslogic.co.uk/
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vinnielo



Joined: 19 Feb 2008
Posts: 13
Location: hertbeat Country

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PostPosted: Thu Feb 28, 2008 12:24 am    Post subject: Reply with quote

That's if I had easy access to the camera. I can't remember how the camera's connected to the cable, whether it's a plug/socket or if it's hard wired in. I'm a bit reluctant to touch the box again now that nesting season is drawing near.
The baluns I've seen on eBay have BNC ends on, which isn't ideal.
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