Solved - On composite/CVBS cameras, Can I increase gain beyond factory limit?

[Logan]

Hi.

If someone have experience on this, have anyone ever try to turn up the max AGC limit on an analog CCTV camera?

Some old big cameras do have several internal adjustable trim resisters, but according to service manuals, the closest ones are for AGC reference @ 800mv, still cannot boost gain.

It seems most of them are using digital chips for processing, so maybe we cannot change it in a simple way?

Thanks.

[CaptDon]

I spent a lot of time trying to increase gain for low light level applications. The enemy is always noise. Shot noise in the vacuum tubes like vidicons, orthicons and the like. With CCD or CMOS it ends up being clock noise as well as a form of shot noise. The signal to noise ratio just goes to crap when you try to ramp up the gain. The signal to noise ratio of the detector is poor at low light levels and when you amplify trash you just get more trash PLUS the noise of the amplifier. Also when you ramp up the gain you find another problem that many detectors have a limited dynamic range. If you optomize for gain then the highlights overload. If you design to accommodate highlights then you need more scene lighting to eliminate objects in the shadows from disappearing. Logarithmic amplifiers can help and are used in radar video chains where echo strength varies by 100Db
or more, but they create a weird unusable look when processing an NTSC type signal and again you have a detector with small dynamic range between noise floor and overload.

[Logan]

Thank you for replying.
But many cameras are not going far enough to even show noise. When they meet lighting conditions they don't like, picture will just black out without giving me chance to consider SNR limit...

[NiHaoMike]

I suspect it's intentional so that cameras in poor lighting conditions don't trigger image based motion detection. If you can find the datasheets for the image processing chips, it might be possible to hack it to allow it to increase gain as much as needed to get an image even if it ends up noisy.

[Logan]

If you can find the datasheets for the image processing chips, it might be possible to hack it to allow it to increase gain as much as needed to get an image even if it ends up noisy.

Well, I couldn't believe this works, on multiple models.
It's unbelievable those manufactures don't set there devices to best performance with hardwares already inside.
I improved both sensitivity and dynamic range on them, with some jumper wires.

[Renate]

How about some IR illuminators?