Digital Aerial Question

Having read a fair bit from the archives via Google Groups I've got *another* aerial question.
I live 2 miles from the transmitter (CO10 0NH) and need a better loft aerial for Freeview. BBC channels are Ok but ITV/C4 are poor. The questions are: 1/ Is it possible to sucessfully intall a new loft aerial yourself and get good results? I'd hate to have to call someone out through failure! 2/ Which aerial would suit best? 3/ Is getting it right really trial and error or is there a specific sequence to follow? 4/ How can I efficiency of the current cables?
Thanks
Charles
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Charles Ping wrote:

it's possible, and if it didn't work the failure is not too public, being confined to your own loft ;-)

according to http://www.wolfbane.com/cgi-bin/tvd.exe?DX=L&HT=7&OS=CO10+0NH you need a group E aerial for digital reception from sudbury
whereas according to http://tx.mb21.co.uk/info/tvtxlist.shtml sudbury uses group B for analogue reception
if you want the best digital *only* reception get a group E aerial, if you want analog and digital you'll need to compromise on a wideband group W, the lower frequency channels (analogue ones in this case) will suffer most, but even the higher frequencies will give lower signal with a group W than a group E.
You sure you can't have an external aerial? even if professionally fitted rather than diy? would really be best

if you do plump for a group W (and maybe even if you don't) do the initial positioning while viewing an analogue channel, to get strongest signal, which is easiest to tell with out proper equipment, then see what you get with digital, but more difficult to tell, depending what IDTV/STB you have it may show the signal level and/or quality, look at them over a longer period, perhaps in different weather conditions, and with passing mopeds in mind, you might spend a lot of time in the loft twiddling ...

if it's got a copper foil as well as copper braid it it a good double screened cable, otherwise you'd be better off replacing it, if it has aluminium foil, or braid only replace it.
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Charles Ping wrote:

Yes, with provisos. I happen to watch freeview via a computer running linux. So my procedure was:
1) Get in loft with laptop with WIFI enabled. 2) Point aerial in about the right direction with compass. 3) Log into computer with tuner card over SSH. 4) Attempt to tune card. 5) Watch continuous signal strength and bit-error-rate numbers while fiddling with aerial.
In my case I had a choice of 3 transmitters so part of the exercise was finding out which one was best.
I'm not sure how I'd do it without such a setup, other than borrow a signal meter of the type the installers use. It is much fussier than analogue TV, which a compass bearing would often be good enough.

I used a Televes DAT45. Very directional, optional masthead amplifier (Try it without, use it later if needs be). Bigger version available with massive gain: Televes DAT75. In theory, the instructions say you should be several miles from the transmitter to use one of these, but my local transmitter 2 miles away is the mostly feebly powered relay in the country ;-<
Have some attenuators handy and plug them in when trying your equipment, then remove attenuation piecewise.
Externally mounted would be better, but I couldn't be bothered, especially as I rent and want the aerial back when I leave. You will get much better results with a soffit or chimney mount though.

If you have some way to measure the signal, it's incremental trial an error. You might manage if you decoder has some sort of signal strenght display and you can position the TV where you can see it from the loft hatch.
This will be painful if you have you use another person. Took me 4 hours (probably less than an hour if I only had one transmitter to choose from).

Don't know. I worked on the premise of stuffing the biggest signal I could down them and attenuating at the TV end if needed.
HTH
Tim
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Charles Ping wrote

ISTM you are damn close to the transmitter, so I would think the chances for a loft aerial are good; saving intervening mountains, skyscrapers etc

Point it in the same direction as the neighbours, and twiddle. most set top boxes will evaluate signal quality and strength. Try to avoid connectors - a run of good cable from aerial straight to the set is nice,
Ask on uk.tech.digital-tv;
mike
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Not to mention the wrong kind of roof-tiling or local high objects (eg chimneys) in the way. I'd take a small TV into the loft and test it with a short length of cable before spending lots of time fitting the cable. Once it's seen to work (and read recent discussions in uk.tech.digital-tv for reasons why it might not) then the rest is simple diy.
--
John Cartmell john@ followed by finnybank.com 0845 006 8822
Qercus magazine FAX +44 (0)8700-519-527 www.finnybank.com
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On Sun, 15 Jan 2006 08:51:15 +0000, Charles Ping wrote:

Definitely.
I 'll expand on others advice. When I first installed a loft aerial, I went up there wiotha portable wotha loop on it. That quickly showed me where the best place was - under the thatch with chicken wire all over it was a nono.
But there is a tiled extesnion, and signal seemed perrty good there.
So off to the local aerial shoppe, and I got the longest yagi that would physically fit.
Amd a ploe and clamp to bolt to te wooden floor I had up there.
Final alignment was done with the portable telly.
I wasn't intending to go digital, so I got a narrow band aerial.
However, when I did, it worked well enough to stay there.
I am 12 miles from sudbury, but up a hill.

wideband is better provbably than what I got.
BUT if you get decent analog reception up there with the portable, chances are you will get decent digital too.

WEll you can take a compass bearing to get it pointed at Sudbury...after that the analogue telly is the best way to go. Its pretty obvious to find points where signal degrares - espcially on CH5 which is lower power - and 'biset the angle)
After that try a little tiwsitng and a little up and down to see if it makes any difference. If you have multuipath sometimes this helps find a multipath null.

IF you are intending to run more than one telly, I strongly suggest you make up a DECENT new downlead to a distribution amplifier, or put one in the loft, and connect the old cables to that. With a nice 10-15dB boost at 2 miles range, you could probably use a bit of telephone cable and get a good signal after boosting ;-)
Re running cables inside teh house is a vile experience. To be avoided at all costs IMHO. Distribution amps are not expensive.

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That close to the transmitter you should buy a log-periodic type of aerial. These are nowhere near as common as the typical Yagi variations you get. You will need to find a specialist aerial supplier.
The main advantage of the log periodic in this situation is that it has excellent side and rear rejection, with no troublesome side lobes. This makes it far easier to eliminate the ghosting and reflection that often occurs both due to loft installation and proximity to the transmitter. However, depending on the loft construction and the path to the transmitter, it might not be possible to obtain good reception from within the loft.
Log periodic aerials also have the benefit of being a fundamentally wideband type, so is ideal for digital reception where the frequency spread is large. It has lower gain than an equivalent Yagi (but a much more constant one over the full spectrum which can help with some problem transmitters), but proximity to the transmitter helps allieviate the lower gain.
An example log-periodic aerial:
http://www.blake-uk.com/downloads/UHF%20TV%20Aerials/Digilog%20UHF%20Leaflet.pdf

Without test equipment, it is easiest to adjust it on an analogue signal, as you can see signal strength and reflections directly. Hurry though, before analogue disappears.

If they're no good, replace with CT100 or equivalent.
Christian.
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Following up to Christian McArdle

so are you saying I can "tune" an aerial for the analogue, then buy a freeview box and digital should work as the source is the same place? I certainly didnt have to move my ML's aerial for Freeview. Or buy a digital aerial.
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as
before
Certainly with a log periodic which can typically cope with 3 octaves and so don't really care about frequency. It may be more difficult with a Yagi, with bad side lobes and frequency dependent response where the analogue signal may be at completely the other end from the digital signal.
Buy an attenuator at the same time to make the signal worse, so you can get it pointed exactly right. Then remove the attenuator afterwards.
Christian.
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Following up to Christian McArdle

there are a lot of words there I've never seen before, at least in those combinations.

but I think I can repeat it back sufficiently well to get the job done! Thanks!
--
Mike Reid
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It may be true. It may not. It depends on your local transmitter(s) and the type and quality of your aerial (and the direction the aerial is pointing).
But don't give up and pay a cowboy aerial fitter as that may leave you worse off - and with less money.
--
John Cartmell john@ followed by finnybank.com 0845 006 8822
Qercus magazine FAX +44 (0)8700-519-527 www.finnybank.com
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Following up to John Cartmell

at least not without trying first! My current setup is an aerial I found in the loft when we moved in lashed to a rafter, so it can only get better.
Don't try this at home. Using PC and listening to radio so didnt switch off mains to pull lighting fuse to do some work, some pillock had left a thread of fusewire sticking out from the fuse. Ouch!!! Now what idiot wired that fuse? :-S
--
Mike Reid
Walk-eat-photos UK "http://www.fellwalk.co.uk " <-- you can email us@ this site
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We recently had a freeview aerial fitted and it was around 60 including aerial

I wonder who?:)
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Following up to Ophelia

you cant get the staff nowadays.
--
Mike Reid
Walk-eat-photos UK "http://www.fellwalk.co.uk " <-- you can email us@ this site
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The Reid wrote

When you've fixed the aerial I'm sure some of the chaps will tell you how to install a new distribution box with contact breakers.
;-)
--

mike

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Following up to mike

they already did when I asked about cooker points :-)
--
Mike Reid
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The Reid wrote:

Heh. Hope I'll remember that next time I wander into someones house to work on their electrics.
Think this topic/warning deserves it's own thread(opps pun!)!
--
Adrian C

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the
pointing).
Oh and always buy a wideband these days. Who knows what will happen to the frequencies transmitted when they switch off analogue. They haven't even decided if they're going to nick half the spectrum yet.
Christian.
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Christian McArdle wrote

Wanna bet?
--

mike

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My understanding was that they wanted to, but couldn't get a good enough price for it, so it will probably be used for HDTV in the future. If this rumour is true, it is very good news.
Christian.
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