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Solving Digital TV Interference

Discussion in 'Hobby Electronics' started by David L. Jones, Sep 12, 2006.

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  1. Ok, I love my digital TV, but interference from other stuff in the
    house is really starting to bug me. Almost anything that switches on
    and off will usually interfer in some way (lights, dishwasher, fridge,
    appliances etc), and the roller door shuts the box down completely.

    Anyone got a good solution that has worked for them?

    I've heard about earthing the coax shield to a separate copper pipe,
    any success here?

    Dave :)
  2. atec 77

    atec 77 Guest

    borrow a cheap ups and isolate the digital gear with that , you may need
    to earth the gear and coax on a separate telecommunications style earth
    but a combination of both should kill the problems .
  3. Howdy Dave,

    are you using quad shield coax?

    If you are using a combo yagi antenna with band 1,2,3 and 4 tuning it will
    pick up great amounts of interference, such as cars ignitions, dirty power
    pole insulators, switching noise form around your house, etc.

    Here is a great resource for antenna selection

    As soon as I moved to a log periodic antenna , I solved my signal
    level/quality issues, and since cannot produce any picture/sound corruption
    from local switching, etc

    I'm deep in a gully up in the Dandenong Ranges of Melbourne, the
    transmitters are only ~5km away but my log periodic is aimed 120 degrees off
    the imagined line of sight to the transmitters, picking up a reflection off
    a gum tree covered hill. I'm the only person in my street with digital SBS!

  4. Hi Mark
    Yep, brand new quad shield (and F connectors) all the way through the
    house. Just standard coax from the wall to STBs though.
    Yes, I'm using a digital capable combi.
    Don't want to change it though as it's less than a year old. I choose a
    combi because at the time I had one STB and one analog TV, now I've got
    two STB's, but can't really justify a new antenna unless it is the only
    thing that will solve the problem (unlikely).
    In this case I would guess that it was the increase in signal strenth
    that did the trick.
    I suspect that I won't be able to fix my problem with an increase in
    signal strength, as my antenna is already a high gain "fringe" type and
    I'm getting >80% signal strength on all channels, so any improvement
    there would be marginal I suspect.

    I think I'll start with the earthed coax and work from there.

    Dave :)
  5. atec 77

    atec 77 Guest

    Also make sure your house ground is installed correctly , check the
    termination of the wire on the ground stake.
  6. eltan

    eltan Guest

    Have the similar if not the same problems as you and all I did is turn off
    everything TV, STB, VCR etc... at the main and turn it back on and retune
    STB again and it work fine.

    BTW I'll only using bunny ear antenna and its too troublesome for me to
    install outdoor antenna too.
  7. Wayne Reid

    Wayne Reid Guest

    I read the other posts. As you have a good antenna and cable, then the most
    likely source of the interference is through the AC wiring itself (switch
    noise etc.). The UPS example sounds like overkill. You could look for a STB
    with a better designed power circuit - but how would you know.

    I tried winding a few turns of the wiring from the plug-pack around one of
    those ferrite blocks (the hinged ones - you can get them at Jaycar). This
    almost eliminated the problem on my Kross STB. The Thompson STB was never
    really as vulnerable to switch noise, but it's plug-pack packed it in (as
    they are apparently prone to do).

    Try the ferrite thing - they only cost a few $$$. Tell the Jaycar dude what
    you intend to do and he'll tell you which one to buy.

    If there is still noise, it may be worthwhile cutting the DC plug-pack
    wiring and putting a serial inductor and a parallel capacitor as noise
    filters. Goole for a simple circuit.

    Lots of STBs have this problem by the way. My wife hates digital because of

    Hope that helps.

  8. Phil Allison

    Phil Allison Guest

    "David L. Jones"

    ** First thing to work out is the nature of the interference problem.

    If the picture is momentarily freezing or pixelating, then the data stream
    is being corrupted due to * in-band* electrical impulse noise ( in-band =
    in the same frequency range as the digital transmission). If s not, then
    the noise is not in-band at all.

    Which channels are most affected ??

    In order to seriously corrupt the digital signal, the impulse noise needs to
    be of comparable strength to the level being delivered by the antenna - so
    the signal strength at the particular reception location plus the relative
    gain and directivity of the antenna in use are important. A weak signal is
    vulnerable and a strong one is not.

    Since the energy spectrum of impulse noise falls with increasing frequency,
    the UHF band is far less vulnerable and so too are channels 11 and 12
    compared to channels 6 and 8 in the VHF band.

    Channels 7, 9, 10 & 2 transmit digitally on channels 6, 8, 11 & 12

    SBS transmits digitally on UHF 34 ( 571.5 MHz) in Sydney.

    In-band noise interference is likely to be picked up directly by the antenna
    itself, rather than the connecting cable, in the average house situation.
    Improving the cable shielding will not help if this is the case. A communal
    antenna system, cabled to many residents in a unit block, may be different
    matter since the co-ax cable may run in close parallel with installed AC
    power wiring.

    Probably, the thing most likely to work for those in average to weak signal
    area is a better antenna - one with more gain than the usual general
    purpose antenna and designed only for that part of the VHF band from
    channels 6 to 12 plus the UHF band.

    I note that WES finally have such an antenna on display at Ashfield, for
    not too many dollars.

    Looks like a strangely overgrown UHF type.

    ........ Phil
  9. I've had two Thomson STB plugpacks die.
    My Thomson DTI500 is just as vunerable as my new DigiCrystal PVR, and
    it seems to happen across all channels, although some channels are more
    susceptible than others even though they all have the same (very good)
    signal level. Not surprising really given the wide bandwidth we are
    talking about. The roller door is the only thing that blats out every
    channel completely.
    Was going to try that, just didn't have any ferrites to hand. That is
    the easiest solution if it works.
    Thanks for the input everyone. Looks like there are several plans of

    Dave :)
  10. Allan

    Allan Guest

    Another Idea Dave,
    if you can get hold of a different STB, and see if that does it as well.
    Maybe its a Box problem, like poor filtering in the pSu.
    DSE used to have a 7 day return policy, so you could buy one, try it and
    compare, then return for refund.
  11. Update:
    I have tried the following:
    1) Checked Mains earth - looks fine.
    2) Checked for close proximity between antenna cable and mains cabling
    - fine, at least 1m clearance, except for the short drops down the
    walls where it is much closer. But nothing I can do there anyway.
    3) Installed seperate mains earth stake to the coax shield - made no
    4) Changed coax from wall to STB to RG6, so my entire system from
    antenna to STB in is now quad shield RG6 with F connectors. Perhaps a
    minor improvement, no change in STB receive signal level though.
    5) Added ferrites to the power inputs and even coax as well. Perhaps a
    minor improvement again.

    Basically the result is no joy. Two different brands of STB are still
    showing the interence with mains device switching, but it is better
    than before, so I have a usable improvement at least.
    It really only leaves the antenna I guess, but I'm not changing that
    for now as it is fairly new. Guess I'll just have to live with the

    Thanks for the input everyone.
    Dave :)
  12. Phil Allison

    Phil Allison Guest

    "David L. Jones"

    ** The dishwasher, fridge and roller door need to be suppressed
    nternally - often just a class X cap in the right spot or X cap plus
    50-100 ohm carbon comp resistor in series to act as an arc snubber.

    Light switches are not much of a problem unless you INSIST on staring at the
    TV screen when you operate one - again X caps or snubbers across each would
    fix them too.

    ........ Phil
  13. Thanks Phil, have been meaning to do that for a while.
    It's not me who's switching the lights, it's the wife!
    And of course, due to murphy the interruption occurs just at the
    crucial point when Jamie or Adam are about to say something important!

    With the PVR I don't even have to be watching when Murphy strikes and
    annoys me several days later. Ahh technology....

    Dave :)
  14. atec77

    atec77 Guest

    Borrow a ups and see if it improves , I suspect the noise is mains borne
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