My outside aerial was pointing to Winterhill, but when it fell off, I
mounted a loft aerial pointing to the Storeton repeater. The orientation
must be vertical. I get a perfect analogue picture, channel 5 is superb,
digital is fine too.
Take a good look at the picture in the link you posted. They claim 43
ele's but I count 10 directors (each apparently counted 4 times!) the
dipole and reflector.
That's not strictly Kosher!
The ele's might well be compound elements, but being co-located I
can't see them being "just as good as" a "Bona- Fide" 43 element beam
if such a thing existed, (beyond a certain limit diminishing returns
sets in anyway). Better IMO to use 2 x proper 18 ele. beams and a
But, I'm not an expert, (I'm an old radio amateur), so take a look
FWIW I've had a good experience with loft aerials I'm in an an
elevated position in Leeds LS27 and at one time I was getting good
results from Bilsdale West Moor 40 miles away directly North over flat
countryside, but an aerial for Emley Moor 10 miles away needed to be
higher up since I was looking straight into the hill behind me.
I'm in Leeds LS16 one of the highest bits of Leeds, we have a direct
line of sight to Emley Moor- maybe 15-20 miles as the crow flies?
When we moved in the aerial was a settop aerial blanched in the loft on
a box. The picture was ok really, but not brilliant. I replaced it with
larger but fairly cheap aerial mounted on the internal wall in the loft-
nothing but a few roof timbers ad the felt and tiles in the way.
Get a decent picture now.
In theory, more elements increases the gain on-axis and reduces
it off-axis, so it should be better if you can accurately perform
the more critical alignment it requires.
However, I'm sceptical that many aerials are really designed that
accurately, at least as far as the physics goes. I suspect much of
the design is to 'look' higher quality so they can charge more;-)
IIRC the number of elements increases teh gain slightly, but the real
gain is in drectionality and freedom from ghosting.
If the transmitter is behind hills/houses you do need LOT of height,
but its easy to check yoiurloft with a set top aerial and a small TV up
there. If you can get reaosnable quality from that, and move around to
find teh best spot, a decent aerial in the same spot will do about 4-10
times better than the set top aerial. 4 stomes stronger and maybe 10
times better on ghosting.
Final alignment is done by ot looking at signal strength, but picture
quality. You want to make sure your main ghosts are coming into the
antenna best rejection lobes, this is usually a few degrees off maxiumum
In the end you fiddle around with te antenna and a TV in the loft, til
you are pretty sure its as good as you are going to get, then bolt it
down and enjoy whatever you can get.
Frankly it will be better than a quick external installation by a cowboy
rigger in 99 cases out of 100.
Doing it this way also allows you to assess the best place within the
loft. Metal tanks and metal in the house will make big differences, so
its not always obvious where the best place actually is till you try em
I was thinking about changing tactics and fitting a loft aerial that I
can fit / adjust myself, but i`m not sure whether I might need to
consider a higher spec aerial than might normally be required if it was
Take a look at the TLC aerials, they have one high gain version, just make
sure you buy the correct band .... check the IBA site to find out what your
transmitter is - and whether you need to set for horizontal or vertical
That means whether it stands up or lies flat, and where it points.
Hint - check the neighbours.
Also if you're buying from a reasonable dealer, he'll be able to tell you.
There are web sites that will, or you could ring bbc information
information, but I've got a suspicion thats gone down the tubes like the
rest of the Beeb.
I can't find a site, but this being the ng that it is, I very much doubt if
we'll wallow in ignorant bliss for long.
At the moment my aerial gets a reasonable analogue picture, but with
some ghosting. Would I be right in thinking that if I got a digital
set-top box this setup would be more forgiving of ghosting? I think
the signal itself is fairly strong, but there's just a bit of
reflection off nearby trees and things.
On 7 Dec 2003 14:32:09 -0800, martin firstname.lastname@example.org (Martin
Ghosting is the result of signals being reflected from some other
object between the transmitter and your receiving antenna. Because
the signal takes a longer time to reach you (think of it as corners of
a triangle, you get a ghosted image offset to the right on an analogue
You can roughly work out the extra distance by measuring the offset as
a percentage of the total screen width. On a standard 625line/50Hz
TV (which is what you have, one line takes just under 64 microseconds
in total, but thre is about 53 microseconds worth visible because of
synchronisation time. So your extra delay is roughly the proportion
of the screen for the ghosted image multiplied by 53 uS.
The TV signals travel at approx. the speed of light (299,792,458
metres/sec); so from this you can work out the extra distance.
Generally the transmitter is a lot further from you than the
reflecting object, so to a good approximation, the distance you
calculate is the distance the object is from you.
Sometimes, if the objects are very close, e.g. surrounding walls and
other objects, the ghosted image will be so close that it just appears
to be a fuzziness of the verticals of the picture.
With digital TV, you would not see ghosting directly, since the
digital information is placed on an analogue signal and the decoder
uses that. The decoder is taking the signal and making decisions
millions of times per second (the data bit rate) about whether the
signal is 1 or 0 and uses that. However it is doing that by
sampling the level of the signal at that rate. This works well in
principle, but there are problems with it. Interference to the
signal or poor signal will mislead the decoder about whether given
bits should be 0 or 1. Currently digital TV transmissions use a
very low power in comparison with the analogue TV, which is one of the
reasons why people are having to use better antennas for digital TV.
If you factor in an additional delayed signal (which is what ghosting
on analogue is), the decoder will see it as interference to the wanted
signal. Depending on how strong the delayed signal is relative to
the wanted one, the decoder may make mistakes as it will with
Up to a point, the decoder can take care of this because the
transmitted digital signal has extra data added that is used to help
the decoder detect and correct such errors.
Beyond a certain rate of errors, these mechanisms fail and the result
is the the picture and sound will freeze or the picture breaks into
small blocks (called macroblocks). Obviously you don't want this.
Therefore, when an antenna is set up for digital reception, it is not
a case of pointing and hoping or looking on the screen for best
picture or minimum ghosting. A proper installer will have a piece
of test gear which measures the rate of errors coming in the signal.
This takes account of all the interference and multiple reception
paths, and generally the objective is to minimise the error rate.
You could try with your existing antenna, but don't be surprised if
you have to get a new, more directional one which will give a stronger
signal and because it is more directional, reject unwanted reflected
To email, substitute .nospam with .gl
<snip long treatise on ghosting to summarise the relevant bits>
(i) All digital transmission methids have one theing in common. They
work better at high signals, and tend to stop working altogether on low
ones. They do not, for the most part, degrade gradually and gracefully.
(ii) Andy sez, and I have no reason to douvbt it, that digital signals
are at lower signal strength..
There are two points here. The first is that if the signals are weaker
so are the ghosts. So unless you have almost double images now - in
which case a better antenna pointing in a different direction slightly,
is called for, that ought to work OK.
But the second point is I don't know what the modulation method is. I do
know that it invloves digital compression to get teh data rate down, but
how that data is encoded is not somethig I am aware of - however it
would seem strange indeed if it were done in such a way as to make te
signal peculiarly sensitive to low apmlitude time delayed analogues.
Ghosts. Given the amount of computing power and the bitrate, it would
alos seem that adaptive filtering to detect static ghposts and eliminate
them would in fact be pretty simple. So my guess is that digital signal
qre bothe encoded to elminintae ghost effects, and probably filtered to
remove even more - at leats in better designed sets.
The technology of all this gubbins has come on very fast with mobile
phones - fast and stable chips to do FFT stuff etc exist, and
de-ghosting is pretty much basic algorithims for DSP's.
There is compression anyway (MPEG-2 for the video) and forward error
correction. Modulation is Coded Orthogonal Frequency Division
More that you ever wanted to know can be found by Google searching
using 'DVB-T' as a keyword.
On 9 Dec 2003 04:53:48 -0800, martin email@example.com (Martin
It is, unless you want to get a professional in.
Try it over a week or two and also on different channels. The
behaviour can vary according to which frequency is used and with the
To email, substitute .nospam with .gl
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