Composite video over long distance RJ45

Thread Starter

yoannwyffels

Joined Mar 23, 2016
16
Hello,

I'm trying to accomplish sending a composite video signal over long RJ45 cable (> 100 meters).
For now, I succeed to run it over a 40m RJ45 cable with just a simple video buffer like this one:


VCC=+5V
C7=470uf

It gives me a better video quality this way.
But, if I increase cable distance (> 40m) I'm starting having some white strips over video :/
So I'm looking (and searching since 4 days) an IC or a circuit capable of repeating or amplifing video signal with just a +5V power supply.

MAX4030EESA
MAX4090

seems to fit the need, but I'm not sure.

What do you think about ? Does someone succeed transmit composite video over long RJ45 cable ?

Thank you
 

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AnalogKid

Joined Aug 1, 2013
8,259
Your circuit has an asymmetrical output impedance, and the effects of that increase as the cable capacitance increases with length.

Generally speaking, Maxim, Analog Devices, Linear Technology, and Intersil make excellent video driver chips. I remember reading about a single 5V video driver, but I don't remember who makes it.

ak
 

dl324

Joined Mar 30, 2015
9,617
I already saw this kind of thing. But I'm thinking they are just "passive" adaptater, nothing more (so they will not perform any amplification/correction/filtering...). Am I right ?
Do more research. They match the impedance of the video source to the cable. You need to use them at both ends of the CAT5 cable.
 

Thread Starter

yoannwyffels

Joined Mar 23, 2016
16
Your circuit has an asymmetrical output impedance, and the effects of that increase as the cable capacitance increases with length.

Generally speaking, Maxim, Analog Devices, Linear Technology, and Intersil make excellent video driver chips. I remember reading about a single 5V video driver, but I don't remember who makes it.

ak
MAX4030EESA seems acting as a video driver (If I well understand what's a "video driver" :p)
Since I started searching for analog video solutions...I have to say, this is over complicated !
 

Thread Starter

yoannwyffels

Joined Mar 23, 2016
16
Do more research. They match the impedance of the video source to the cable. You need to use them at both ends of the CAT5 cable.
Thanks dl324, I've just bought a pair of them on ebay...Will try this low cost and passive solution in parallel of others.
Thank you !
 

AnalogKid

Joined Aug 1, 2013
8,259
I have to say, this is over complicated !
No, it isn't, but composit video is a very complex signal. And, the vast majority of the standard components and circuit designs are for a cable system that is not yours. There is a very big difference between coax and UTP when dealing with high frequencies.

ak
 

Thread Starter

yoannwyffels

Joined Mar 23, 2016
16
No, it isn't, but composit video is a very complex signal. And, the vast majority of the standard components and circuit designs are for a cable system that is not yours. There is a very big difference between coax and UTP when dealing with high frequencies.

ak
So, does video baluns (as mentioned by dl324) will be a good solution for at least 100m cable ?
 

Thread Starter

yoannwyffels

Joined Mar 23, 2016
16
No, it isn't, but composit video is a very complex signal. And, the vast majority of the standard components and circuit designs are for a cable system that is not yours. There is a very big difference between coax and UTP when dealing with high frequencies.

ak
I think I've found what you were talking about "video driver":

driver MAX4447
https://www.maximintegrated.com/en/products/analog/amplifiers/MAX4447.html

receiver MAX4444
https://www.maximintegrated.com/en/products/analog/amplifiers/MAX4444.html

is that what you were talking about ?
 

crutschow

Joined Mar 14, 2008
24,121
Yes, those differential drivers and receivers should do what you want.
With those you don't need the baluns.
Note that you need to match the characteristic impedance of the line, which is 100Ω for Cat5 cable.
(So use 50Ω for the two resistors at the output of the MAX4447 driver and one 100Ω across the line at the receiving end, with a gain of 2V/V for the driver. That will give on overall signal gain of 1).

As a nit, the cable is Cat5 or Cat6 which typically use RJ45 connectors, so it's more correctly called Cat5/6 cable or ethernet cable , not RJ45 cable. ;)
 

Thread Starter

yoannwyffels

Joined Mar 23, 2016
16
You're right crutschow, we can also call them twisted pairs ! ;) I will send video signal over Cat5e cable (which is connected on RJ45 connector :p).
Thank you about resistors details, I ordered them with a MAX1044 to get an inverted voltage (+5 / -5v) as thoses IC needs -5V to run.

About the 100 ohm resistor at end of the line...There is 2 pins on MAX4444 (IN- and IN+). Where did you put that resistor ?
 
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