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TV Aerial orientated question

Discussion in 'Cables & Switches' started by J80FAB, Jul 15, 2005.

  1. J80FAB

    J80FAB
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    I’m looking for some advice regarding the installation of a loft aerial to replace the existing outside basic ‘contract’ style aerial & 30 year old coax cable. :eek:

    I am situated approximately 16 miles away from Emley Moor as the crow flies in the BD15 area of Bradford. The property is on a fair elevation & there is a ‘valley’ and then a slight hill in the distance in the path of the transmitter to the extent that the transmitter is not visible. Apart from this there is really nothing else ‘blocking’ the path from at least the mid-point of the property upwards.

    The current basic aerial set-up receives all analogue transmissions but the picture on some of the channels is really poor to say the least. Also the complete bouquet of digital terrestrial channels is available through the current set-up although blocking/pixelation is an issue but this may also be down to a sub-standard electronics make-up of the Nokia Mediamaster 9850T as this was never an issue with the Pioneer STB I used to have which On-Digital supplied.

    I have purchased HF109 double-screened cable & a Triax Unix 52 element aerial. I have also read-up on information concerning an array of aerial-orientated issues including the cons of a loft installation.

    I want to install in the loft for two main reasons (1) I am not willing to go onto the roof, (2) I would prefer the aerial in the loft as the property is elevated & therefore gets its fair share of battering from high winds and (3) I would like to take the aerial away with me if I were to move.

    Unfortunately one area that I did not research very well until after buying the aerial was aerial ‘banding’ & gain. The Emley Moor transmitter caters for Band B ( channels 35 to 53 ). However the aerial which I bought is designated as being ‘wideband’ therefore attaining its manufacturer’s claimed gain of 14.5 dB in the 48 to 68 channel range (band C/D) & a lower gain for the remaining channels.

    The main question I want to ask is after I have installed the aerial & I am not satisfied with the result on analogue and/or digital I do not know if I should change it for a :

    i) 52 element Band B aerial

    or

    ii) 100 element Band B aerial

    or

    iii) 100 element wideband aerial


    I am now aware of the fact that a wideband aerial is basically regarded as ‘a jack of all trades and a master of none’, however a 100 element wideband aerial would nevertheless at least exhibit a higher gain over a greater range of UHF channels & would also be useful if digital bouquets were to appear outside of this Band B range in the future. It would also be more adaptable if it was ever to be taken to an area outside of the Band B range of UHF channels.

    Taking into consideration that the aerial is going to be loft-mounted, if the performance of a 52 element aerial is not up to scratch would the installation of a 100 element aerial due to its reported higher gain be more desirable regardless of whether it is wideband or not ?

    Having assembled the Triax Unix 52 I have done a sort of quick DIY test with a run of low grade coax cable by holding it up several centimetres from the ceiling which borders the roof & pointing it towards the transmitter in the direction of the bedroom window. The aerial connected to a portable tv has managed to give a ‘clear’ picture for BBC 1, BBC 2 and ITV. The picture for Channel 4 ( UHF channel 41 & at a lower gain of about 12dB for this wideband aerial ) is more ‘grainy’ though Channel 5 being even further down the scale on UHF channel 37 is clearer that Channel 4, but this quality in picture could be down to the low grade run of coax cable.

    Sorry to have gone on but I wanted to make everything clear & would really very much appreciate anyone’s comments about the aerial as I will be at a loss as to what I should do if the Triax 52 does not perform very well.
     
  2. vex

    vex
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    J80FAB

    A quick hit set of answers for you.

    1, Being that close to the transmitter really should give you a perfect picture, however it will depend on how 'big' the valley and hill is that is blocking your lineo of site.

    2, You have the right aerial, wideband is what you should be supplied for Freeview because in order to get all the multiplexes the other bands are used. A 'grouped' aerial will actually restrict your reception.

    3, I would say gues-timate that most of your receiption problems are down to the age and quality of the current system rather than actual signal strength. Especially as the original coax cables and aerial used were as good as a bit of wet string for receiption. This is one of the reason for 'grouping' is to reject the 'out of band' signals from other transmitters near by. Contractor aerials also had a poor (relatively) front to back and sidelobe rejection allowing them to pick up additional interferance.

    4, The H109F cable is a great cable to start with, the sheilding is good alround and therefore it will also be good at rejecting signal interferance and therefore improve you picture quality.

    Hope this answers some of your questions.

    Out of interest, why did you get ride of the original On Digital STB? I am still running mine prefectly well.

    Chris
     
  3. J80FAB

    J80FAB
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    :hiya: vex

    Thanks for your reply

    I mounted the aerial yesterday in the loft with a short run of the H109F cable to a TV just below on the landing & spent most of the day ‘playing’ with it to see what sort of results I could get.

    My main reason for wanting to install a new aerial set-up is to improve analogue reception. For receiving Freeview whether I have a wideband or a Band B aerial at this particular location is not an issue as all the digital multiplexes transmitted by Emley Moor fall into the Band B channel range in any case.

    After installing the aerial the analogue picture is not 100% perfect on all channels but this could be down to a number of things such as the aerial being in the loft and the valley & hill which sit in the line of site & which I would class as ‘medium’ in size. There is also the fact that it is a wideband aerial. A friend lives in the same area but much further up than myself. He has a basic style contract-type loft installed aerial & all analogue channels are picture-perfect. His portable TV in the kitchen has just a ‘loop’ aerial perched on top of the set & the picture quality is so good you would think it was coming from a roof-top aerial.

    Anyway from what I understand a ‘banded’ aerial not only blocks out interference from local transmitters as you stated but is also optimized to perform at its best for analogue channels in that particular band. With this in mind would I not have a better picture for Channel 5 for example using a Band B aerial than with this wideband one ? A wideband aerial has its highest gain between around UHF channels 49 and 67. With this in mind I can confirm that the best picture quality I am currently getting with the Triax 52 is on BBC 2 which is UHF 51. The remaining channels are below UHF channel 49 and are not as good.

    After installing the Triax 52 I also tested the Nokia Mediamaster 9850T which still suffers from ‘blocking’ when there are fluctuations/interference within the electricity supply caused light switches and appliances turned on & off. This does not happen with our digital satellite receiver ( thank God !) & was never an issue with the Pioneer. A sign of cheap & inferior electrical components/design in the Nokia ???

    The Pioneer was given by ITV Digital with their channel subscription & returned to them when the subscription was cancelled. Pity as they would have probably let me have it because they went bust a few months later !

    I will probably attempt some more tweaking with the aerial & perhaps put it in a different place in the loft to see if reception can be improved any further. Though I must also begin with running a new length of H109F cable from the loft area to the main TV downstairs :(
     

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