Av Output Measurement

[clipper]

Trying to troubleshoot a security camera setup. One of the cameras wasn't working although voltage to it was fine. When the AV output from other working cameras was looked at on the RF spectrum set at full bandwidth, activity noted across the range, particularly peaking at the lowest frequency. I'm assuming the 'real' activity is happening at 50hz which my meter doesn't cover. What's all the RF activity then? Noise? The faulty camera did show activity, though greatly reduced (from 30db to about 10db.)

[Theres Always Radio]

Clipper

Don't look at the video out with a spectrum analyser, use an oscilloscope with triggering set for negative and high frequency reject. You should end up with 1 volt pk-pk if using a feed through 75 ohm termination or around 2 volts pk-pk if unterminated.

James

[clipper]

Clipper

Don't look at the video out with a spectrum analyser, use an oscilloscope with triggering set for negative and high frequency reject. You should end up with 1 volt pk-pk if using a feed through 75 ohm termination or around 2 volts pk-pk if unterminated.

James

I don't have an oscilloscope. Just wondering what it is the spectrum on my meter is showing. Camera problem is sorted BTW.

[tonymy01]

The horizontal scan rate for PAL is 15.625kHz (or something near that). So this will be a peak. Then along a line depending on the pattern, you will have spectrum up to 5MHz. You will see spectrum up to this frequency only if you are looking at a high frequency image (e.g a striped pattern of vertical black/white stripes). So it varies depending on what is shown. I guess the low frequency repetition might be 50Hz and there may be spectrum at that low frequency, not sure.

Edited May 14, 2010 by tonymy01

[bellotv]

Trying to troubleshoot a security camera setup. One of the cameras wasn't working although voltage to it was fine. When the AV output from other working cameras was looked at on the RF spectrum set at full bandwidth, activity noted across the range, particularly peaking at the lowest frequency. I'm assuming the 'real' activity is happening at 50hz which my meter doesn't cover. What's all the RF activity then? Noise? The faulty camera did show activity, though greatly reduced (from 30db to about 10db.)

I'm curious what kind of spectrum analyzer you are using ?

Most types used in the TV antenna industry generally cover 45 MHz ~900 MHz.Ones that do Satellite as well go up to around 2GHz.

Many Pro installer Meters may have an optional coverage of 5 MHz -45 MHz for Reverse path analysis .

As the Video signal of a camera only has a bandwidth up to 5MHz,I doubt you would see anything much at all on the above type of analyzers unless you are lucky enough to own a truely proffessional one that does go down into the kHz area .

My only explanation on why you saw something was that it may have been harmonics.

If 1v p-p Video signal = 120 dBuV ,then its possible that harmonics are coming through at as you said around 30dBuV.

Ideally harmonics shouldn't be coming from the camera because if it was designed well,it should have some cut off filter above 5MHz,but who knows whats in ( or left out of) todays cheap electronics.

As was mentioned,an oscilloscope is the best way to observe a video signal.Dick Smith have a single channel one which would be ideal for this type of work and its about $120 from memory .It doesn't have all the fancy TV sync options that would be preferable but you would still be able to use it .

Edited May 13, 2010 by bellotv

[tonymy01]

edited my previous post, must have been drunk when I posted... line rate is 15kHz, but that is each line. Then along the line is oscilating image, up to 5-6MHz (PAL)...