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Aligning aerial for freeview

Discussion in 'Audio Visual' started by DaveHerns, 8 Sep 2013.

  1. DaveHerns

    DaveHerns

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    Is alignment of the aerial as critical now we only have digital TV and not analogue ? Is it OK just to point the aerial in the direction of the transmitter? In the old days you knew it was OK when you had no ghosting, now it's hard to tell
    I have a satelite alignment meter but is it the same as an aerial alignment meter? I suppose it would need a power supply to replace the voltage in the cable to the dish
     
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  3. Sam Gangee

    Sam Gangee

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  4. northernchappy

    northernchappy

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    Read more: http://www.diynot.com/forums/audio-visual/aligning-aerial-for-freeview.375799/#ixzz2ea630ZEA

    It's of equal importance to align the aerial for analouge or the new digital signal.. especially if it's a high gain aerial it will have a more narrower "acceptence" angle as a trade off the higher gain it is.

    Don't know about the meter you describe.
    I used a website called wolfbane (I lost the url), where you enter your postcode and it gives you a compass direction, and used a compass to align ther aerial.
    Lastly there's no such thing as an analogue/digital aerial. some pepole i know are using 15 yeaer old aerials because they can still receive the same bandwith. the signal is still UHF which all telly aerials can receive, it;s just the language that your telly understands has changed.
     
  5. DaveHerns

    DaveHerns

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    Its's a 48 element loft aerial feeding a Samsung TV.We found the flylead/wall socket had been crushed by furniture so did a direct connection with F couplings which improved things.
    TV has a signal strength and bit rate error readout .We're getting about 60-70% signal strength and the error rate is nil on same channels and up to 150 odd on others .Picture is good on some channels and breaks up on others
    We'll try moving the aerial within the loft but I'm wondering if it's 4G interference that's causing the break up and if we need a filter
     
  6. Sam Gangee

    Sam Gangee

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    All I have to add to my previous reply is that, if it's 4G interference, you will already have received the offer of a free filter from the organisation dealing with this.
     
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  8. Lucid

    Lucid

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    I wouldn't put too much faith in the TV's built-in signal metering. At best they tend to be hopelessly optimistic.

    This last weekend I went to a house on an aerial call. They had a Samsung TV too. The guy explained how he would lose signal occasionally and showed me the TV's OSD metering. Bit Error was at zero during the time I viewed, Strength was at 100. I have a pro meter so can make some accurate signal strength and error ratio measurements. The TV's strength meter was maxing out at just 63dBuV. It shouldn't really do that until around 74dBuV. I dropped in some attenuation. 9dB of signal reduction showed up as 95 on the TV meter. 12dB as 90.

    It's a bit too convoluted to go in to explaining; but if you have 60-70% on a TV meter that is equally as optimistic then I'd say you haven't enough signal level on the weaker channel groups. That's partly why the error rate goes up such a lot. Digital will work fine with signal levels of 45dBuV~70dBuV at the TV so long as the TV tuner is sensitive enough and doesn't overload too easily.

    A low error rate is more important than loads of signal. Having said that, you still need enough signal to start with. In your case I think that the stronger signal groups are just on the right side of acceptable. The weaker muxes fall below that threshold.

    Incidentally, the fly-lead can have quite a big impact on signal level. I replaced the crappy thin supermarket one on this TV with some WF100 because it is far better shielded. In doing that I measured a 2dB signal increase at the TV. That's like another 60% of signal.
     
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  9. DaveHerns

    DaveHerns

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    Thanks, chaps
    We'll have a look at it on Sunday .Strange thing is that the previous owners of the house just used a set top aerial in the loft crudely connected to the downlead,However we never saw it working !
    I did use proper coax to make the new flylead Signal level was much lower before I did that plus replaced the damaged wall socket
     
  10. Sam Gangee

    Sam Gangee

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    It's not strange. As I stated above, and as stated on the linked page, the location of an aerial indoors can be critical. Indeed it may be extremely critical - especially if an inadequate aerial is used. You might find that moving it just 1cm from the optimum position causes the signal for some multiplexes to be lost.

    Some people have the patience to fiddle just to save a few pounds. Some people simply put up with missing channels.
     
  11. DaveHerns

    DaveHerns

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    Luckily it's not my house ! I've got the crappiest aerial in my loft installed in 1982 and it's currently running 3 TV's and gives Freeview HD on one
    In view of what you say I'll leave mine well alone
     
  12. SimonH2

    SimonH2

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    http://www.wolfbane.com/cgi-bin/tvd.exe

    Very useful it is as well. Just bear in mind that like most of the tools like this, the terrain database is fairly coarse and may not include small local details. For example, for me it shows completely clear LOS to Winter Hill - but in fact it's not quite LOS at my end as there is a bit of a ridge with some houses on it.

    When I put ours up, I used a compass for initial alignment, turned on the TV, and twirled the aerial both ways to see where the signal dropped off. I then set the aerial in the middle of these two positions. it's usually easier to work to "signal drop off on each side" than to try and find a peak value in the middle. IIRC, I refined it by inserting a lot of attenuation so the drop off would happen over a narrower angle.
    As it is, I could have made do with a smaller aerial, but I work on the basis that it's easier to throw away signal if you have too much. One Humax box works best (including not also tuning in Moel-Y-Parc) with a 9dB attenuator. The rest of my kit is happy without that.
     
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