Noise and Hissing problem in audio and dotted line problem in video.

Discussion in 'General Electronics Chat' started by sadatan, Dec 29, 2010.

  1. sadatan

    Thread Starter New Member

    Feb 24, 2010
    15
    0
    I got my AV board assembled on new PCB with TL071 used for preamp,DRV134 as a Transmitter,INA137 as receiver and TPA6211 as amplifier .and for Video transmitter and receiver iam using LMH6733.
    I have some issues with the system:
    1.
    Now i am getting my video very clean on receive side as i am using video receive on one side and video transmit on other side on two similar cards,but i am getting the some moving dotted lines on my screen at times.

    2.

    Also i am getting some noisy sound along with home hiss on audio.the noisy sound is eliminated as soon as i remove video camera.

    Please help me in removing the problem.
     
  2. edgetrigger

    Member

    Dec 19, 2010
    133
    19
    I suspect it on EM interference. Visual dots may be emi noise. Conducted or radiated is what we have to analyse. Just a off the shelf line filter will reduce conducted noise into the system. Hope sufficient bypassing of the power supply close to the IC's are done. Use tantulum capcitors in place of ceramic disc. Also check on the return path on your PCB. You have to keep it short and multiple return paths for each IC withou looping will also reduce the noise and oscillations.

    If possible enclose the ckt with an aluminium foil without shorting the ckt. A good source of EM is a mobile phone. Just place the phone close to your ckt and you shouldn't get interference if EMI/EMC is take care of
     
    Last edited: Dec 29, 2010
  3. sadatan

    Thread Starter New Member

    Feb 24, 2010
    15
    0
    Thanks for the reply. I don't find any effect of mobile on the performance.
     
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