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Digital TV transmitters


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I am impressed folks!! Thank you..

I was wondering if our aerial was facing the correct way because any time we get less than good weather out digital picture degrades badly, but our nearest transmitter is due North and that is where the aerial is pointing, domage!! It is pointing slightly downwards and the tx. is on the top of the Pic du Nore which is quite high, 1211 meters, and about 20 miles North.

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Generally,  and if you have clear line of sight to the Pic de Nore, twenty miles should be within range for an erp (effective radiated power) of 8 kW,  assuming a good working aerial.   

Had you told us you lived at Castres I would have been able sagely to utter an "ah",  because there is a sharply defined,  technically necessary,  deeply unpopular,  "notch" carved into the horizontal radiation pattern of the Pic de Nore aerial used for digital in a NNW direction,  but clearly that's not your problem.   (It's regularly covered in the local press in that direction!)

An aerial sloping downwards is not giving of its best,  I'd also look at the quality of the cabling,  connection plugs,  and the junciton box on the aerial itself,  assuming you can get at it safely.   Digital reception,  as I'm sure you know,  tends to degrade non-gracefully when there are adverse conditions,  whereas the effects on analogue quality are often minor.  

What's your analogue picture like?   The three main programmes should be on channels 58/61/64.   How many elements (rods) has your aerial got?

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Hi Martin, sorry about the delay, bin busy... For a change. The aerial has 9 elements with the one nearest the upright being the very flat oval.

I am not sure about the connections as the complete setup, wiring/aerial, must be over 20 years old. They were installed when we moved in. The analog signal is not bad, but no where near as good as the digital one I must admit. I will have a look tomorrow to se exactly what the situation is as far as being able to see the Pic, bit dark now!!

Thank you for the info [:D]..

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The very flat oval sounds like the actual dipole (the bit connected to the TV);  there should be 7 or so directors in front (ie north in your case) of the oval,  and a reflector behind (which may be a single rod like a director,  or a panel of rods,  or a mesh shield or similar)

The connections are very simple,  but if water has got in over the years they may have deteriorated,  either at the aerial itself,  or water could have got into the coax lead.

At the powers currently in use for digital (which will be considerably increased when analogue closes and when there are no restrictions caused by the two systems having to exist side by side) you really need a cracking analogue picture if the digital is to work reliably.    In addition most of the Pic de Nore channels are high up the band (ie high frequencies) which tend to suffer first if you've got say trees in the way.    (I attempted to help some friends near Leominster,  their transmitter uses similar high channels for digital,   and whilst their analogue picture was excellent,  the digital channels quite literally got worse in frequency order,   with the one they really wanted (BBC 4) simply not triggering the box at all -  when it got light the cuprits turned out to be a fine line of oak trees).

As you've found,  digital (when it's working) hides the progressive deterioration as signal decreases that you would see on the analogue picture;   but when the signal drops sufficiently the digital picture suddenly freezes and disappears,   whereas you can still watch the analogue through a haze of snow and red (in the case of SECAM) flashes.

It does sound as though you need to review the aerial,   if you can get up there the digital box no doubt has an on screen signal meter which would allow you to play about with the position until you get an improvement......

Bonne chance and be careful.

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