security cams and video signals questions

[rezaf]

Hello,
I have some questions :
1- what kind of security cams have better quality in pictures, digital or analog?
2- Noise effect is less on what type?
2- how far I can send picture of security cam? with what kind of wire, coaxial or telephone wire)?
3- can I pass dc current with up to 10A from video cable of security cam together(external DC current and video signals)(with analog or digital cam)? It throws on the image noise or not?
4- if the current be AC how?
5- if the camera be analog, can I use 'DC Block' method for transmitting DC current and video signals together with one cable?
6- how far can I transmit or receive RS232 signals with copper wire? Is delayed or not?

Best Regards.
Thanks for Replies.

 

[rezaf]

any answer?
Please help me.

 

[karesz]

Hali Rezaf,
Im not a video specialist, but I believe, that the question is not Dig or An. Camera has higher picture quality, its better to ask for CCD or CMOS or even old tube cameras are better for an application?
In my opinion is generell on the first place CMOS, than CCD and on the last place Tube cameras.
CMOS Video cameras dont have light effect if some overlighting is active, and pixel failures makes no "line effects" as by CCDs, their are more sensitive too, what can be very important for security apps...
In all case, their are some better specialists on edabord as I...
K.

 

[IanP]

You asked several complex questions that would require complex answers;
I'll just touch some selected issues ..

First of all, majority of security cameras are CMOS with digital processing and then the signal is converted to analogue (if camera has component or composite video output(s)) ..

There are basically 4 types of transmission: [1]composite video over co-ax, [2]composite video over twisted pair, [3]IP network data streaming (These are web-like cameras with IP addresses, which send a continuous stream of pictures in the Motion JPEG format) over network cable and [4]wireless ..

Analogue transmission is not noise-resistant and therefore needs shielding, grounding, earthing etc. etc. techniques to prevent picture degradation ..

You have also asked about superimposing video signal and DC (or AC) ..
In theory it’s possible, but it’s impractical, so the video signal is FM-modulated and shifted from 0-6MHz to 6-12MHz and transmitted over coax together with DC, or wirelessly in, say 2.4GHz band ..

The RS-232 is not designed to operate over long distances and consequently the RS422 or the RS485 is used ..
See:
http://www.marcspages.co.uk/tech/long232.htm

IanP

 

[rezaf]

Very Thanks Friends.
Important things you mention, and the link was very careful. in the past I think that IP based cameras are digital and coax cameras are analog.
now I have other questions:
1- why the FM-modulated signal have DC voltage, Although have frequency?
2- can I pass DC current with free wires (transmission channels)of CAT5 (RJ45)standard cables(cable of IP cameras)? or I must use all wires of cable for camera data transmission?
3- how far can I send video of IP camera with RJ45 cable?

 

[IanP]

1- why the FM-modulated signal have DC voltage, Although have frequency?

The FM-modulated signal doesn't have a dc component, but if you need you can use the same coax for FM-signal from camera and dc supply for the camera ..

2- can I pass DC current with free wires (transmission channels)of CAT5 (RJ45)standard cables(cable of IP cameras)? or I must use all wires of cable for camera data transmission?

Power Over Ethernet devices: http://en.wikipedia.org/wiki/Power_over_Ethernet
Ethernet cable can carry up to 48VDC, 400mA ..

3- how far can I send video of IP camera with RJ45 cable?

http://www.foresight-cctv.com/IP Camera Cabling Solution.htm

IanP

 

[karesz]

...5- if the camera be analog, can I use 'DC Block' method for transmitting DC current and video signals together with one cable?

Hi Rezaf,
We have developed/installed CCTV networks [of course with analog (Vidicon) cameras] so good 30 years ago with such a solution ...
Greetings!
K.

 

[rezaf]

Thanks, Can I use analog out (Coax Cable) camera and use Video Balun, but connect stranded wire Instead of twisted pair wire and send video about 100 meter?

 

[IanP]

100m is no that long, it may work, but without test it's difficult to be sure ..
The main obstacle will be the unknown impedance and the difficulty in matching with that impedance, so there are no significant reflections – ghosting ..
In the worst case you may need to feed video signal via an amplifier with differential output and frequency compensation (line driver) ..

IanP

 

[karesz]

Hali,
Yes, the impedance of stranded wires is a big question & possibly an issue too...
In my opinion you will become not the best quality pictures because the stranded wires have not only some, "UNDEFINED(unknowed)" impedance, but more bad; their has overall more discontinuities as twisted pairs!
Otherwise: its reflexions after so 100m are at ca. 1-2 usec, these time is a picture on the monitor "over deflected", also not to see" ...
But not so in sharp contrasting picture-parts (black/white edges)!
Shorty said: you must check-verify it in life
K.

 

[rezaf]

ok, I go to test that I need Amplify or impedance matching or twisted stranded wire. May answer one of these ways.