oscilloscope, help please?

[ljarrald 0]

i know that to install cctv properly, i should test that the video signal at the DVR is 1V peak to peak.

i have an old 2 channel CRT type oscilloscope. it has BNC connectors that the 'probes' plug into.

can i plug the camera cable directly into the front, or does it have to go via the probe?

 

although i have had the oscilloscope for 3 years, i've only used it twice so am not too familiar with using it.

any help would be great, thanks

[ak357 0]

i know that to install cctv properly, i should test that the video signal at the DVR is 1V peak to peak.

i have an old 2 channel CRT type oscilloscope. it has BNC connectors that the 'probes' plug into.

can i plug the camera cable directly into the front, or does it have to go via the probe?

 

although i have had the oscilloscope for 3 years, i've only used it twice so am not too familiar with using it.

any help would be great, thanks

Yes u can plug camera direct but for proper reading u should have 75 Ohm load resistor across

and plz Google how to use scope

[survtech 0]

Yes, you can plug the camera directly into the scope's input but to determine the camera's output levels, you must use proper termination (75 ohms), as stated by ak357. The easiest way to do that is with a "T" connector and a 75 ohm terminator. See below.

 

 

I usually make my own terminators using a 1/4 watt 75 ohm resistor soldered to a connector. What I do is form loops out of the resistor's leads and solder the ends to a solder-type BNC connector.That way, I can attach the scope's clip lead to the loops but it's just as easy to use the "T".

 

If you adjust the display on the scope at its presets for H and V sync (most scopes have them), and your input attenuator to .2V per division, the signal should be 5 divisions from its highest to its lowest points - .1V per division should yield full CRT height on most scopes (that typically have a total of 10 vertical divisions). The image would look like this:

 

Shows Two Horizontal Lines

 

Shows Three Vertical Frames

 

Things to look for:

* The Sync signal (the square part that is the lowest point) should be relatively flat on the bottom and should be approximately 0.4V down from the bottom of the video signal. Losses caused by cable resistance will be more apparent in a "rounding" of the Vertical Sync signal when observing the vertical (V) frame signal. This rounding reveals low frequency cable losses typical of long runs or improper cable type (like "clad").

* The Color Burst signal (not normally there on black and white signals) should also be relatively square and be around 0.4V p-p. The color burst waveform can reveal a lot about a camera and the transport medium. It should be as close to "square" as possible. Heavy rounding on either side can be a symptom of high frequency signal loss in the cable (make certain it is loss-related by also "scoping" the camera with a short cable - some cameras don't put out perfectly square burst signals).

* The Active Video signal. Not a lot revealed here, especially on a standard oscilloscope. Look for a maximum peak of around 1V from the top of the video to the bottom of the sync. There may actually be some normal variation in this total level. Some manufacturers like to "push" a bit hotter signal and most DVR,s etc. can handle up to at least 1.5V p-p.

 

There's a pretty good basic explanation of the video signals HERE

[Soundy 1]

i know that to install cctv properly, i should test that the video signal at the DVR is 1V peak to peak.

You mean I've been doing it wrong all these years?

 

I don't know anyone in this business who 'scopes a camera signal except maybe as a last troubleshooting method.

[ljarrald 0]

Yes, you can plug the camera directly into the scope's input but to determine the camera's output levels, you must use proper termination (75 ohms), as stated by ak357. The easiest way to do that is with a "T" connector and a 75 ohm terminator. See below.

 

 

I usually make my own terminators using a 1/4 watt 75 ohm resistor soldered to a connector. What I do is form loops out of the resistor's leads and solder the ends to a solder-type BNC connector.That way, I can attach the scope's clip lead to the loops but it's just as easy to use the "T".

 

If you adjust the display on the scope at its presets for H and V sync (most scopes have them), and your input attenuator to .2V per division, the signal should be 5 divisions from its highest to its lowest points - .1V per division should yield full CRT height on most scopes (that typically have a total of 10 vertical divisions). The image would look like this:

 

Shows Two Horizontal Lines

 

Shows Three Vertical Frames

 

Things to look for:

* The Sync signal (the square part that is the lowest point) should be relatively flat on the bottom and should be approximately 0.4V down from the bottom of the video signal. Losses caused by cable resistance will be more apparent in a "rounding" of the Vertical Sync signal when observing the vertical (V) frame signal. This rounding reveals low frequency cable losses typical of long runs or improper cable type (like "clad").

* The Color Burst signal (not normally there on black and white signals) should also be relatively square and be around 0.4V p-p. The color burst waveform can reveal a lot about a camera and the transport medium. It should be as close to "square" as possible. Heavy rounding on either side can be a symptom of high frequency signal loss in the cable (make certain it is loss-related by also "scoping" the camera with a short cable - some cameras don't put out perfectly square burst signals).

* The Active Video signal. Not a lot revealed here, especially on a standard oscilloscope. Look for a maximum peak of around 1V from the top of the video to the bottom of the sync. There may actually be some normal variation in this total level. Some manufacturers like to "push" a bit hotter signal and most DVR,s etc. can handle up to at least 1.5V p-p.

 

There's a pretty good basic explanation of the video signals HERE

 

thank you!

my DVR has two BNC connections for each channel. they can be used to loop the video signal through the dvr to other things.

should i be putting a 75OHM terminator on each 'loop out'?

or will my DVR have one built in?

 

thanks.

[survtech 0]

If you don't attach anything to the looping output, the DVR probably terminates each input with 75 ohms. Some will have a switch that is opened when you attach a cable to the looping output while others have termination set in the software. In any case, once you attach a cable to the looping out, you should probably terminate the other end. Check the DVR's instructions to be sure.