TV aerial?

On 15/06/13 01:48, John Rumm wrote:

not so sure about that. there are 'how many errors before correction' and 'how many errors after correction' collected somewhere. errors before correction can be quite high and yet still give a usable stream.
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On 15/06/2013 07:49, The Natural Philosopher wrote:

You may get that level of detail on some of the PC based decoders, but its rare to see anything that detailed on your average STB.
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On 15/06/2013 01:48, John Rumm wrote:

Any idea why it is like that? Did the marketing department get to specify what diagnostics to display and choose the number that looks most favourable to the set and is minimally informative. The decoder must know how hard it is having to work and have these other numbers!
It would be much more useful to be able to see the raw BER - you can basically see the results of uncorrected errors in the output bitstream as glitches in the MPEG decoder long before "Quality" gets to 0.
IME anything with Q<4 is totally unwatchable and Q>8 is needed for decent quality picture. I expect these Q numbers vary with maker (in my case Panasonic). I use FreeSat most of the time these days...
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On 15/06/2013 09:29, Martin Brown wrote:

Not having studied the low level frame format used over the air in DVBT, I don't know what level of error identification is actually visible in the coded stream. However, with many FEC systems the small errors in the source stream simply get fixed in the process of decoding such that you are not even aware what they were or where they were. Its only once the stream is decoded and you can attempt to makes sense of the data, and have access to framing information, and checksums etc that you can tell what sort of quality of data you actually have.

The difficulty here is there is there not being a standard way of presenting this information - each box maker does their own thing, so you never know if you are comparing like with like.
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On Thu, 13 Jun 2013 16:40:32 +0100, John Rumm wrote:

Oooh, you're going to make me go and do something to help myself, aren't you?
Right... <heads out with binoculars and camera> There IS a small, seemingly-unlabelled box at the base of the aerial mast.
<pries covers off Vision boxes> Aha. One of them - the aerial-side one - is a V23-100 Power Supply. The other - the inner one - is a V52-100 2-way Amplifier.
The aerial points the same basic direction as neighbours, which does appear to be the right basic direction for the Ridge Hill transmitter.

I thought I'd tried both, but you know what it's like when you're shouting instructions upstairs to SWMBO...
<wanders off to DIY> OK, so both on - 65-75% PSU for external on, internal off - 15-20% PSU for external on, internal disconnected from coax - 55-65% PSU for external off, internal on - 20-25% PSU for external disconnected from coax, internal on - 30% Both off - 10% Coax out of internal, to living room disconnected - 10%...
So it seems as if both are doing _something_, but the interesting thing is what happens with the internal one disconnected - it's almost as good as with it powered up, much better than connected but off. There's still no usable signal, though.
That's with the TV & STB downstairs. The STB's aerial socket won't connect to the co-ax before the Vision boxes, unless I start fannying with connectors. The co-ax comes out of the second box, and straight downstairs to the socket in the living room. I can't easily totally bypass both boxes, either.
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On 13/06/2013 17:35, Adrian wrote:

This ought to be enough to get a signal that might break up but should work after a fashion. All other permutations could be suffering from overload (as could this if there is a strong local signal inside the wide band of UHF & VHF that the mast head amplifier handles).

My instinct is that your mast head amplifier is already overloaded or defective and so the digital signal has in effect been scrambled.

You will probably need an adapter something like:
(Amazon.com product link shortened)71142737&sr=1-4&keywords=coaxial+f+connector+male+to+male
Maplins should have them too but higher price.
The other thing to try is a cheap and cheerful set top aerial
(Amazon.com product link shortened)71142991&sr=1-1&keywords=tv+aerial#productDescription
Ugly but seems to review OK and cheap. I just use a conventional external aerial and a pole when I need a portable TV aerial. YMMV.
Much easier than going up the chimney.
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On Thu, 13 Jun 2013 18:10:40 +0100, Martin Brown wrote:

Same results as with everything, though - it can search and find channels, but no actual usable signal. "Signal quality" still shows as 0%.

Less than a quid and a half, delivered...? Ordered!
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Could I suggest that you either take some pix of other aerials locally and your own aerial and post them somewhere. If you are not that happy with them being public about that mail them over.. discretion guaranteed..
And/or ask your nearest neighbours what their reception is like and have they had any troubles and as best they know is it now better or worse since DSO..?
It might be that something is overloading this setup or picking up something it didn't ought to and or its unstable and generating spurious signals over the TV spectrum..
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Tony Sayer


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On Thu, 13 Jun 2013 23:31:40 +0100, tony sayer wrote:

Here we go... Wide view of whole aerial pole
http://farm8.staticflickr.com/7441/9040084135_6453983f46_o.jpg
(The house is low two-storey, to give you an indication of overall height above ground)
Aerial itself
http://farm8.staticflickr.com/7397/9042309740_ecb2a208d4_o.jpg
The thingy at the bottom of the pole
http://farm3.staticflickr.com/2812/9040085409_db05ae1da7_o.jpg
Next door have a weeny little bent-tin cheapo crappy thing mounted at ground floor gutter level. The few other houses in this little enclave have aerials very similar to ours in both altitude and style.
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On 14/06/2013 14:09, Adrian wrote:

If next door can get a decent picture on their TV set with that "weeny little bent-tin cheapo crappy thing" low down on the gutter then you should talk to them about it and get a similar device yourself.
It isn't compulsory to install your TV aerial as high as possible although usually it does help if there is a hill in the way.
Unless you are a really massive fan of "Dave" Freesat is the obvious choice in a remote location where TDTV is so difficult to obtain.
I remain curious as to how it is possible for the system to recognise the channels and channel IDs in setup without being able to at least partially decode some of them into jumpy video and broken sound.
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On 14/06/13 15:03, Martin Brown wrote:

+1.
That's why I thought getting a tv dongle for the puter might be worth doing.
I've never had a case where the scan detected a station that something didn't appear on screen and in the channels list.
Except one of my sony ST boxes which did similar and is now sitting behind me for the usual 3 year period before I sigh, realise it wont fix itself and throw it in the bin/.
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On Fri, 14 Jun 2013 15:03:17 +0100, Martin Brown

Quest and Yesterday are also missing on Freesat but present on Freeview
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Adrian wrote:

Despite the fact that my previous good professional advice was lost to you because of the mellée of uninformed speculation and sheer bollocks that surrounded it, I will say this: The aerial is a Vision V11-441 44. Google it. It is the right way up so the box won't be full of water. It appears to have been properly installed, so will most likely be correctly aligned. The grey box on the mast is a Vision brand amplifier. It's odd that the aerial cable goes into the right side. I know some old Vision products were like that, so maybe it's one of them. That housing is used for other things, but I should think it's an amplifier. The cables are not well secured so one of them might have pulled back in the f plug and thus not be making contact. The whole installation is quite old, by the looks of it. The amp could easily have been trashed by nearby lightning. If not you will definitely need a PSU to feed 12V to the amp. As I suggested before the first box inside will most likely be a PSU. Note that this could be faulty even if a simple meter says otherwise. If you have a telly with the option of putting 5V on the aerial feeder you could enable that and connect direct to the aerial. 5V will power the amp.
Bill
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On Sat, 15 Jun 2013 01:39:55 +0100, Bill Wright wrote:

A perennial risk...

Umm, OK. So that's a decent aerial, the right one for the transmitter, and shouldn't be my problem, right?

Always a good start. <grin>

OK, great. Certainly the rough direction appears to be both consistent with neighbours and fits the map.

It's going to be ladder o'clock, isn't it?

Not sure that's a great risk - it's a long way from being the highest thing in the immediate vicinity. But, again, I'm quite happy to be wrong.
Basic relevant history - the house was bought in the mid '90s, and a lot of work done to it - including new roof and a big kitchen extension (other end of the house to the aerial and all of the coax) - before they died in the mid-late '00s. Since then, the work to the place was finished off by their son and the house only used occasionally, but remained (very) fully furnished. The only TV here was a weeny ancient portable, no STB. Hence the likelihood that there's never been any Freeview watched here.

OK, I think you might have missed a post or three, too. Yes, the first box inside did turn out to be a Vision V23-100 PSU.
Turning that off and/or on makes a fairly big difference to the reported signal strength. Removing it from the line makes little difference. The other box is definitely an internal amp (Vision V52-100), which gives similar results disconnected to on, but a big (downward) difference connected-but-off.
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[Snip]

To get the amplifier working you need to have the PSU switched on. Any results you get without it being on are meaningless.
In a previous post you said:

Is the "weeny little bent-tin cheapo crappy thing" pointing the same way as yours? or does it have the roads vertical and is pointing to the Clyro mast. If so, perhaps you should do the same.
One possibility is that the amplifier is being overloaded . If it was originally installed in the analogue days, the extra muxes, plus Clyro might well cause the "hundred or so channels" that you see. Or lighting damage might be the problem. The aerial doesn't need to be the highest point in the area, a lighting strike in the vicinity is all that is needed.
I don't think it's a DIY job, you need someone with suitable test equipment.
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From KT24

Using a RISC OS computer running v5.18
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On 15/06/13 10:02, charles wrote:

There are generally 105 or so channels on a full freeview installation.
The Ridge Hill transmitter is now using LESS power than it was when it transmitted analogue. Down from 100KW to 20KW per mux. So its doubtful that its overloading. Clyro miht be overloading it, if its actually pointing that way, but even so, I'd expect to see clyro stations available when the mast head and other amp are off. .
The really salient issue is that the 105 channels are detected reliably, but not displayed.
That suggest to me a fault in the STB, which is why I suggested buying a cheap PC TV adapter to eliminate that as a problem.
The fact that the fault developed at the exact time the box was shunted around in a removal van may or may not be coincidental.

I think its perfectly possible to DIY it, but it has to be done methodically.
The first thing to do is try a different STB. Because its easy and its cheap. And requires no ladder climbing.
Then move further up towards the mast head itself, to see where if anywhere the signal degrades.
BUT I have to say, degraded signal in my experience of half a dozen installations, ALWAYS results in 'channels not found' Not in 'channels found, but not displayed correctly'.
That combinations sounds too much like corrupted software in the STB itself. And its happened to one of my boxes here. I had the channels list, but didnt get any stations. Swapping the STB resulted in normality restored,. so that STB is for the bin.
I dunno how much a cheap STB costs these days - most seem to have recorders built in and are expensive, hence recommending a sub £30 PC dongle instead.
Oh. some STBS still available in that price range it seems. (Amazon.com product link shortened)
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On 15/06/2013 10:40, The Natural Philosopher wrote:

Some (typically older) STB boxes have a habit of sticking the first channels they find into the allocated "slots" and then moving duplicates found later to the high numbers. Annoying where the later ones are the better quality ones you are after.

Which IIRC due to the way the DTV system works amounts to the same level in practice...

Overloads can come from signals other than the ones you are attempting to capture though. I used to find it was a delicate balancing operation here prior to DSO to get enough gain to lift the DTV channels to a usable level, without over driving the amp with the analogue signals that were at the time 30 - 40dB stronger.
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On Sat, 15 Jun 2013 10:02:58 +0100, charles wrote:

I was thinking that having the PSU off would show the signal without the amp boosting it, but bypassing the PSU would show if the PSU was somehow interfering with the signal.

It is.
I haven't managed to speak to 'em yet to find out if they're using that aerial or not. I'm going to pop round to next-door-but-one and see if I can try my STB on their aerial to rule that out.

I'm starting to come to that conclusion, but it's as well to rule everything DIYable out first.
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On 15/06/2013 16:34, Adrian wrote:

The problem is that an unpowered amp does not just become a straight through connection with no gain. Without power, it will act as an attenuator, and actually reduce the signal available, and in addition possibly distort it as well.
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On 15/06/2013 08:44, Adrian wrote:

Ridge Hill has all its muxes in group A (on channels 21, 22, 24, 25, 27, 28), so yes the aerial is correct for the area.

Sadly, its not just a direct strike that can fry it...
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