I building an interconnect board which will hold one side of the video balun pair (plus power and rs485). The other side will be a commercially available video balun which connects to the camera.

Right now I am having trouble matching the two sides.

I ordered three coils from coil craft - PWB3010LB, PWB-1.5-ALB, and WB1010-SMLB

All of them transfer the video, but the vertical sync is off by ~40%. the colour is slightly off (a little bit pink), but otherwise the video is fine! :)

What does the vertical sync problem indicate?


enter image description here

  • \$\begingroup\$ What do you mean by 'off by 40%'? What video format are you using? Can you post a schematic of how you have connected the transformer? \$\endgroup\$
    – MikeJ-UK
    Mar 27, 2012 at 9:25
  • \$\begingroup\$ Sorry, I mean the top of the video is located at just below the middle of the screen. I am transmitting NTSC. \$\endgroup\$
    – michael
    Mar 28, 2012 at 4:53
  • \$\begingroup\$ OK, I missed the NTSC tag! \$\endgroup\$
    – MikeJ-UK
    Mar 28, 2012 at 10:00

1 Answer 1


It looks like you are transformer-coupling the video. The problem is that in order to preserve the vertical sync pulse, you need a bandwidth extending down to well below 60Hz (the field rate), otherwise you will see excessive 'tilt'. The PWB3010-1LB is specified with a bandwidth down to 3.5kHz (presumably in a 50\$\Omega\$ system) and this is nowhere near low enough. The way commercial video baluns are connected is like this :-

Video balun schematic

This arrangement ensures that both sides of the twisted-pair have an approximately equal impedance to ground and has a bandwidth down to dc (so there is no galvanic isolation - which may be an issue for you). The symmetrical footprint of the Coilcraft transformer means that it can be rotated through 90° to configure it like this.

  • \$\begingroup\$ hmmm, do you know any sources for coils appropriate for this application? \$\endgroup\$
    – michael
    Mar 28, 2012 at 19:06
  • \$\begingroup\$ @michael - It looks from your layout that you could just rotate the transformer by 90 degrees and try it out - it might be OK. \$\endgroup\$
    – MikeJ-UK
    Mar 28, 2012 at 19:46

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