matrixgti

Here the nano balun viewed on 120x zoom.

Hi All, I'm Flavio from Italy ,this is my first post on this forum, hope to write in right place. I design and built sewer inspection system that basically are similar to CCTV system (camera -> cable -> DVR -> monitor ) , Usually camera are small CCD on CMOS with PAL or NTSC composite video output running directly through 75 ohm Coaxial cable. This is fine for cable lenght up to 90 mt with acceptable quality loss. Now I have to built a 150/200 mt system with no coax , I have a shielded twisted pair available inside the main cable , the idea is to build a passive balun inside the camera housing to drive the pair and a video buffer IC at the end of the cable to reconstruct and filter the signal again in a 75 omh unbalanced. I'm newbe to balun design and any help would be appreciated, i'm able to build SMD type PCB so no problem with small dimension IC or passive components as I have a small room on the camera side PCB to plece the balun. I find some balun in SMD like this http://it.rs-online.com/web/p/chip-baluns/8319305/ and the recustruction filter like this http://docs-europe.electrocomponents.com/webdocs/14bf/0900766b814bf87b.pdf But I need an help to be sure Im on the right way to archive the goal. Thanks in advanced for any help and sorry for language mistake.

UPDATE: I did some experiment with balun, I open a cheap commercial balun I rip off the coil and I test the system, It Works perfect over 200 mt of shielded twisted pair but coil was too big for my camera so I order a nano smd coil from RS components ( cod. 831-9318 from TDK ) it is very very very small like 2x2x1 mm , I was able to solder 4 wire directly on the component pad ( really a nightmare ) but just to see how it perform... and IT Work better than the bigger coil of the commercial balun in 1/30 of space ! This is the commercial balun opened This is the TDK nano balun size ! This is the video over 200 mt plus overlay and reconversion in 75 ohm unbalanced ( stripes are due to CRT monitor, image is very clear ) Now i have to design a proper PCB to handle the reflow soldering of that components , hope this experience will help someone that need to create his own nano balun ! Thanks Flavio

Thanks, as we are a very small company I did the project alone, from mechanics to electronics and assembly. I'm good with digital stuff but I'm very poor on analog signals like CVBS thats why I need help for the balun side.

Ok, at this point is better to explain more in detail the "camera" side: The "head" of the system is composed by a nano cmos camera , with stantard 1 Vp-p cvbs output, 75 ohm terminated, a stainless steel waterproof housing, a led ring, a self levelling mechanism (camera will stay orizontally if body rotate due to an eccentric weight, an RF locator system based on 640 Hz signal and a coil antenna, a slip ring 4 way contact (for endless rotation possibility ). External dimension are 42 mm diameter and 60 mm lenght Camera body and lens are 12x12 mm square and 20 mm lenght , fixed focus fixed zoom Electric circuit is slitted in 3 round PCB, front led PCB and locator PCB that rotate with the camera, and a back plate PCB that connect the head with the cable with a threaded system with 4 pogo-pin , +12v , GND, Video and LED supply variable voltage (to control led brightness ). The space available for balun is only on back PCB and of course I will loose the LED dimming against the second balanced line for the video, but this is OK for this mod. there is no way to go HD for different reason, light sensibility, space of the housing and also the "ground" side is already setted for cvbs signal type. I attach some picture of the prototype, the locator board is not yest pupulated in the picture but actually working.

Hi, this will be ok for a test but not for a series production, let say 20 pcs, I need to find a commercial component that not require disassembling, in camera PCB i have some square mm for the balun, thats why I was looking for smd solution over discrete coil that is what I espect to find opening an "inline" balun

Thanks for the reply tomcctv ,nice to read that i need only two balun, but i have no room to fit a commercial balun like the one you attach, does the smd balun on my link will do the same in small smd package ? like this